WO2008092212A1

WO2008092212A1 - Bovicola ovis ecdysone receptor

Info

Publication number: WO2008092212A1
Application number: PCT/AU2008/000119
Authority: WO
Inventors: Matthew Pollard; Garry Noel Hannan; Lloyd Douglas Graham; Ronald Johnston Hill
Original assignee: Commonwealth Scientific And Industrial Research Organisation; Australian Wool Innovation Limited
Priority date: 2007-02-01
Filing date: 2008-02-01
Publication date: 2008-08-07

Abstract

The present invention provides polynucleotide which encodes an EcR or USP polypeptide of a B. ovis ecdysone receptor. The present invention contemplates the use of such polynucleotides in the generation of transgenic constructs, cells, animals, microorganisms, plants or acquatic organisms. The present invention further contemplates the use of such polynucleotides to confer resistance or immunity to B. ovis and to treat an animal having B. ovis infestation.

Description

Bovicola ovis Ecdysone Receptor

FIELD OF THE INVENTION

The present invention relates to the identification and characterisation of the ecdysone receptor from Bovicolα ovis (the Sheep Body Louse), and the nucleic acid encoding therefor. The present invention also relates to the use of such receptors, and such nucleic acids in screening methods, particularly in identifying modulating agents of such receptors.

The present invention also relates to a method for selective destruction of RNA encoding an ecdysone receptor EcR protein employing RNA interference technology.

BACKGROUND TO THE INVENTION

The order Phthirαpterα are wingless parasites of mammals and birds and comprises some five thousand species of lice worldwide. Typically lice exhibit a narrow host range and are often limited to a single species. Lice may be divided into sucking lice and biting lice primarily on the basis of the nature of their mouthparts. Sucking lice can act as vectors of disease such as human epidemic typhus or cattle rickettsial anaplasmosis. Biting lice are usually not disease vectors but heavy infestations of either biting or sucking lice can cause skin irritation associated with an immune reaction.

It is estimated that there are 6-12 million infestations of the human head louse, Pediculus humαnus capitis, annually in the United States alone (Frankowski and

Weiner, 2002). In the early 1990's the associated direct and indirect costs were estimated at $367 million (Clore and Longyear, 1990) and more recent estimates revise this figure to a value closer to $1 billion Hansen and OΗaver (2004). Sheep are also subject to infestation, but in this case there are three species of lice that are at issue: the foot louse, Linognathus pedalis, the face louse, Linognathus ovillus, and the sheep body louse, Bovicola ovis. Of these lice, B. ovis presents by far the most serious problem (NSW Department of Agriculture, Agfact A3.9.31 October 2001). The total annual cost to the sheep industry in Australia has been recently estimated at $123 million (Sackett et al 2006). All lice species are currently developing resistance to a number of commonly used control agents including lindane, pyrethroids and permethrin (Frankowski and Weiner, 2002).

Novel compounds developed to overcome this resistance seek to mimick insect hormones and act by complexing with insect members of the steroid receptor superfamily to control insect development and are likely candidates for pesticides with desirable properties. In recent years the characterisation of insect steroid receptors, that play a critical role in insect development, has provided targets and molecular tools for the discovery of novel chemistries for use in the constant fight against insect pests. Most of the initial research carried out on the molecular biology of the insect steroid receptor superfamily has been on Drosophila melanogaster (Diptera).

Growth, molting, and development in insects are generally regulated by the ecdysteroid hormone, 20-hydroxyecdysone (2β, 3β, 14α, 2OR, 22R, 25-hexahydroxy-5β-cholest-7- ene-6-one), hereafter referred to as "ecdysone" (molting hormone) and the juvenile hormones (Dhadialla et al 1998). The molecular target for ecdysone in insects, the ecdysone receptor, consists of at least the ecdysone receptor protein (EcR) and the ultraspiracle protein (USP). EcR and USP are members of the nuclear steroid receptor super family that is characterized by signature DNA and ligand binding domains, and a transcription activation domain (Koelle et al 1991). Ecdysone receptors are responsive to a number of steroidal compounds such as ecdysone, ponasterone A and muristerone A. It has been found that synthetic ecdysteroids are too costly for general use as insecticides. Recently, non-steroidal compounds with ecdysteroid agonist activity have been described, including the commercially available insecticides tebufenozide and methoxyfenozide (see International Patent Application No. PCT/EP96/00686 and US Patent 5,530,028). Both analogs have exceptional safety profiles for non-target organisms. The commercial synthetic insecticides targeting ecdysone receptors exhibit activity that is largely selective for the insect orders Lepidoptera and Coleoptera. There is a requirement for safe insecticides targeting the ecdysone receptors of pests in other orders.

Polynucleotides encoding EcR proteins have been cloned from a variety of insect species, including Dipterans (see US patents 5,514,578 and 6,245,531 Bl), Lepidopterans, Orthopterans, Hemipterans, and one Homopteran aphid, all from the class Arthropoda including the following examples, a fruit fly Drosophila melanogaster EcR ("DmEcR"; Koelle et al (1991), a yellow fever mosquito Aedes aegypti EcR ("AaEcR"; Cho et al 1995), a sheep blowfly Lucilia cuprina EcR ("LcEcR"; Hannan and Hill, 1997), a blowfly Calliphora vicinia EcR ("CvEcR"), a Mediterranean fruit fly Ceratitis capitata EcR ("CcEcR"; Verras et al 1999), a locust Locusta migratoria EcR ("LmEcR"; Saleh et al 1998), an aphid Myzus persicae EcR ("MpEcR" see International Patent Application Publication W099/36520). The nucleotide and/or amino acid sequences of these ecdysone receptors have been determined and are publicly available.

The ecdysone receptor complex typically includes proteins that are members of the nuclear receptor superfamily wherein all members are generally characterized by the presence of an amino-terminal transactivation domain, a DNA binding domain, and a ligand binding domain separated from the DNA binding domain by a hinge region. The DNA binding domain is characterized by the presence of two cysteine zinc fingers between which are two amino acid motifs, the P-box and the D-box, which confer specificity for ecdysone response elements. These domains may be either native, modified, or chimeras of different domains of heterologous receptor proteins. The EcR and USP proteins, as subsets of the steroid receptor family, also possesses less well- defined regions responsible for heterodimerization properties. Because the domains of nuclear receptors are modular in nature, the ligand binding domain, DNA binding domain, and transactivation domain may be interchanged between receptors to produce functional chimeric receptors with new properties.

The insect ecdysone receptor protein (EcR) heterodimerizes with the ultraspiracle protein (USP), the insect homologue of the mammalian RXR, to form the ecdysone receptor which binds ecdysteroids and ecdysone receptor response elements and activates transcription of ecdysone responsive genes (Riddiford et al 2000).

The EcR/USP/ligand complexes play important roles during insect development and reproduction. The EcR and USP proteins are members of the steroid hormone receptor superfamily and as such exhibit the five modular domains characteristic of the superfamily: A/B (transactivation), C (DNA binding, heterodimerization), D (hinge, heterodimerization), E (ligand binding, heterodimerization and transactivation and in some cases, F (transactivation), domains. Domains such as A/B, C and E retain their function when they are fused to other proteins.

The present inventors have now cloned, isolated and characterised a novel EcR protein and three novel USP proteins from B. ovis. These novel polypeptides and the polynucleotides encoding these proteins are provided. In targeting such ecdysone receptors of B. ovis the present inventors have identified useful methods for identifying new modulating agents of these receptors that would serve as effective agents to control sheep body lice and, almost certainly, other lice from within the order Phthiraptera. To the best of their knowledge, the B. ovis ecdysone receptor is the first example of the molecular cloning of a Phthirapteran ecdysone receptor.

Furthermore, the present inventors have demonstrated a method employing RNA interference technology to selectively inactivate the RNA encoding an EcR protein in vivo. RNA interference (RNAi) is an evolutionarily conserved mechanism that responds to double-stranded RNA (dsRNA) and brings about the sequence-specific silencing of homologous genes (Fire et al 1998). Hairpin loop RNAs can be stably expressed in insect cells from introduced expression plamids (Tavernarakis et al, 2000). Here, new expression plasmids have been constructed using RNAi to suppress the endogenous expression of the ecdysone receptor protein (EcR) in cultures of cells derived from the lepidopteran insect, Spodoptera frugiperda. The inventors have then demonstrated that this suppression is selective for the endogenous S. frugiperda EcR permiting the expression of RNA introduced into the cells encoding an EcR from the sheep blowfly Lucilia cuprina. This provides the basis for a method to express ecdysone receptors from pest insects in established S. frugiperda tissue culture cell lines with no significant background from endogenous S. frugiperda EcR to permit screening of chemical libraries against different pest EcRs in vivo for new ligands as potential insecticides. It also provides a basis for arming host animals and plants with an RNAi to selectively inactivate an insect pest's EcR encoding RNA thereby providing resistance to the pest.

SUMMARY OF THE INVENTION

The present inventors have successfully characterised one novel EcR and three novel ultraspiracle (USP) isoforms of the ecdysone receptor from B. ovis. The novel EcR, BoEcRCl, has the polynucleotide sequence of SEQ ID NO:1 and the amino acid sequence of SEQ ID NO:5. The present results indicate the isolation of two major BoUSP isoforms differing in their A/B domains. The first novel USP isoform, BoUSP5, has the polynucleotide sequence of SEQ ID NO:2 and the amino acid sequence of SEQ ID NO:6. The second novel USP, BoUSPl 5, has the polynucleotide sequence SEQ ID NO:3 and the amino acid sequence of SEQ ID NO:7. A third USP isoform, BoUSPl 1, has the polynucleotide sequence SEQ ID N0:4 and the amino acid sequence SEQ ID N0:8.

In addition, the present invention provides the means for identifying and developing specific modulating agents, such as ligands which bind and either agonise or antagonise the ecdysone receptors, thereby functioning as highly-specific pesticides against B. ovis, offering significant commercial and environmental benefits.

Furthermore, the present inventors have demonstrated a method for the in vivo selective suppression of endogenous expression of RNA encoding an EcR in cells of an animal. Accordingly, in a first aspect, the present invention provides an isolated polynucleotide comprising a nucleotide sequence which encodes, or is complementary to a sequence which encodes an EcR polypeptide of a B. ovis ecdysone receptor, wherein the polynucleotide comprises a nucleic acid sequence that is at least 60% identical, preferably at least 70% identical, more preferably at least 80% identical, even more preferably at least 90%, 95%, 96%, 97%, 98% or 99% identical to the sequence set forth in SEQ ID NO: 1 and most preferably, the sequence set forth in SEQ ID NO: 1.

In a second aspect, the present invention provides an isolated polynucleotide comprising a nucleotide sequence which encodes, or is complementary to a sequence which encodes a USP polypeptide of a B. ovis ecdysone receptor, wherein the polynucleotide comprises a nucleic acid sequence that is at least 60% identical, preferably at least 70% identical, more preferably at least 80% identical, even more preferably at least 90%, 95%, 96%, 97%, 98% or 99% identical to the sequence set forth in any one of SEQ ID NO:2, SEQ ID NO:3 or SEQ ID NO:4, and most preferably, the sequence set forth in SEQ ID NO:2, SEQ ID NO:3 or SEQ ID NO:4.

In a third aspect, the present invention provides an isolated polynucleotide comprising a nucleotide sequence which encodes or is complementary to a sequence which encodes a B. ovis EcR polypeptide, the polypeptide comprising an amino acid sequence at least 60%, preferably at least 70% identical, more preferably at least 80% identical, even more preferably at least 90%, 95%, 96%, 97%, 98% or 99% identical to the sequence set forth in SEQ ID NO: 5 and most preferably, the amino acid sequence set forth in SEQ ID NO:5.

In a fourth aspect, the present invention provides an isolated polynucleotide comprising a nucleotide sequence which encodes or is complementary to a sequence which encodes a USP polypeptide of a B. ovis ecdysone receptor, the polypeptide consisting of an amino acid sequence at least 60%, preferably at least 70% identical, more preferably at least 80% identical, even more preferably at least 90%, 95%, 96%, 97%, 98% or 99% identical to the sequence set forth in any one of SEQ ID NO:6 or SEQ ID NO:7 or SEQ ID NO: 8 and most preferably, the amino acid sequence set forth in any one of SEQ ID NO:6 or SEQ ID NO:7 or SEQ ID NO:8.

In a fifth aspect, the present invention provides an isolated polynucleotide which encodes an EcR polypeptide wherein the polynucleotide has a sequence that hybridises under high stringency conditions to the nucleotide sequence set forth in SEQ ID NO:1; or a sequence fully complementary thereto, wherein high stringency conditions are a hybridisation and/or wash carried out in less than the ionic strength of 5xSSC, 0.05 M sodium phosphate, 42% formamide, 0.1% SDS at a temperature of at least 38⁰C and a washing step of at least 38⁰C in 2xSSC.

In a sixth aspect the present invention provides an isolated polynucleotide which encodes a USP polypeptide wherein the polynucleotide has a sequence that hybridises under high stringency conditions to the nucleotide sequence set forth in any one of SEQ

ID NO:2, SEQ ID NO:3 or SEQ ID NO:4; or a sequence fully complementary thereto, wherein high stringency conditions are a hybridisation and/or wash carried out in less than the ionic strength of 5xSSC, 0.05 M sodium phosphate, 42% formamide, 0.1% SDS at a temperature of at least 38°C and a washing step of at least 38⁰C in 2xSSC.

In a seventh aspect, the present invention provides an isolated EcR polypeptide of a B. ovis ecdysone receptor comprising the amino acid sequence set forth in SEQ ID NO:5, or a sequence at least 60% identical, preferably at least 70% identical, more preferably at least 80% identical, even more preferably at least 90%, 95%, 96%, 97%, 98% or 99% identical to the sequence set forth in SEQ ID NO:5.

In an eighth aspect, the present invention provides an isolated USP polypeptide of a B. ovis ecdysone receptor comprising an amino acid sequence set forth in any one of SEQ ID NO:6, SEQ ID NO:7 or SEQ ID NO:8; or a sequence at least 60% identical, preferably at least 70% identical, more preferably at least 80% identical, even more preferably at least 90%, 95%, 96%, 97%, 98% or 99% identical to the sequence set forth in any one of SEQ ID NO:6, SEQ ID NO:7 or SEQ ID NO:8.

In a ninth aspect, the present invention provides a genetic construct comprising an isolated polynucleotide as hereinbefore described, operably linked to a promoter sequence.

In a tenth aspect, the present invention provides a recombinant cell comprising an isolated polynucleotide according to the invention hereinbefore described, or the genetic construct according to the ninth aspect of the invention. In an eleventh aspect of this invention, there is provided a transgenic animal (such as a mammal or insect), microorganism, plant or aquatic organism, containing one or more cells as mentioned above.

In a twelfth aspect, the present invention provides an isolated fragment of the B. ovis EcR or USP polypeptide as hereinbefore described, preferably an isolated fragment comprising one or more functional domain regions.

In a thirteenth aspect, the present invention extends to the use of the B. ovis ecdysone receptor or fragment thereof as described herein as a gene switch.

In a fourteenth aspect, the present invention provides a method of identifying a modulator of a B. ovis ecdysone receptor comprising:

(a) assaying the binding of a reporter ligand to a B. ovis ecdysone receptor polypeptide of the present invention in the presence of a potential modulator; and

(b) assaying the binding of a reporter ligand to the ecdysone receptor polypeptide of the present invention without said potential modulator; and

(c) comparing the binding of the reporter ligand in the presence of the potential modulator to the binding of the reporter ligand in the absence of the potential modulator, wherein a difference in the level of binding indicates that said potential modulator is a modulator of B. ovis ecdysone receptor.

In a fifteenth aspect, the present invention provides a method for screening a candidate compound for its ability to interact with a B. ovis ecdysone receptor of the present invention or ligand binding domain (LBD) thereof, the method comprising the steps of: (a) incubating a B. ovis ecdysone receptor or LBD thereof with a candidate compound; and (b) measuring the level of binding of the candidate compound to the ecdysone receptor or LBD thereof. The ecdysone receptor or LBD thereof and candidate compound may be further incubated with a fluorescent compound as described in WO2005/005427. In a sixteenth aspect, the present invention provides a method of modulating the expression of a B. ovis EcR target gene in a cell, tissue or organ, the method comprising the step of introducing into said cell, tissue or organ, a double stranded nucleic acid molecule in which one of the strands is substantially identical to the nucleotide sequence of the EcR target gene or region thereof of B. ovis.

In a seventeenth aspect, the present invention provides a method of conferring resistance or immunity to B. ovis in an animal, the method comprising the step of introducing into said animal, a double stranded nucleic acid molecule in which one of the strands is substantially identical to the nucleotide sequence of the EcR target gene or region thereof of B. ovis.

In an eighteenth aspect, the present invention provides a method of treating an animal having a B. ovis infection, comprising the step of administering to the animal a double stranded nucleic acid molecule in which one of the strands is substantially identical to the nucleotide sequence of the EcR gene or region thereof of B. ovis.

In a nineteenth aspect, the present invention provides a method of silencing the expression of an endogenous B. ovis ecdysone receptor protein (EcR) in a cell, tissue or organ, the method comprising the step of introducing into said cell, tissue or organ, a double stranded nucleic acid molecule in which one of the strands is substantially identical to the nucleotide sequence of the EcR target gene or region thereof of B. ovis.

In a twentieth aspect, the present invention provides an animal, wherein the genome of the animal comprises a heterologous nucleic acid, wherein one of the nucleic acid strands is substantially identical to the nucleotide sequence of the EcR gene or region thereof of B. ovis, the nucleic acid encoding both sense and antisense RNA strands which when the nucleic acid is transcribed, the sense and antisense RNA strands associate to form a hairpin structure.

In a twenty-first aspect, the present invention provides a method of modulating the expression of a B. ovis EcR in an insect cell, said method at least comprising the steps of: (a) selecting a nucleotide sequence which is substantially identical to the sense and antisense strands of a B. ovis EcR target gene or a region thereof;

(b) producing a synthetic gene comprising nucleotide sequence; (c) introducing said synthetic gene to said cell;

(d) expressing said synthetic gene in said cell for a time and under conditions sufficient for translation of the mRNA product of said target gene to be modified.

The synthetic gene may encode both sense and antisense RNA strands which when the nucleic acid is transcribed, the sense and antisense strands associate to form a hairpin structure.

The hairpin structure may comprise 19 to 30 nucleotides.

In a twenty-second aspect, the present invention provides a double-stranded RNA molecule comprising at least 19 nucleotides and having at least 90% sequence identity to the sequence shown in one or more of SEQ ID NO:1, SEQ ID NO:2, SEQ ID NO:3 or SEQ ID NO:4. In some embodiments the RNA molecule has 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% identity to the sequence shown in one or more of SEQ ID NO:1, SEQ ID NO:2, SEQ ID NO:3 or SEQ ID NO:4.

SUMMARY OF SEQUENCE LISTING

SEQ ID NO:1: The nucleotide sequence of the open reading frame of a cDNA molecule which encodes the EcR polypeptide subunit of the B. ovis ecdysone receptor and amino acid sequence therefor contained in the plasmid pBK-CMV.

SEQ ID NO:2: The nucleotide sequence of the open reading frame of a cDNA molecule which encodes the EcR protein partner (USP polypeptide) subunit of the B. ovis ecdysone receptor and amino acid sequence therefor contained in plasmid pBK-CMV- BoUSP5. BoUSP5 encodes the longer USP polypeptide isolated.

SEQ ID NO:3: The nucleotide sequence of the open reading frame of a cDNA molecule which encodes the EcR protein partner (USP polypeptide) subunit of the B. ovis ecdysone receptor and amino acid sequence therefor contained in plasmid pBK-CMV- BoUSP 15. BoUSP 15 encodes the shorter USP polypeptide isolated.

SEQ ID NO:4: The nucleotide sequence of the open reading frame of a cDNA molecule which encodes the EcR protein partner (USP polypeptide) subunit of the B. ovis ecdysone receptor and amino acid sequence therefor contained in plasmid pBK-CMV- BoUSPI l. BoUSPI l encodes the longer BoUSP polypeptide isolated but incorporates the silent nucleotide change A 104 IG.

SEQ ID NO:5: The amino acid sequence of the EcR polypeptide subunit of the

B. ovis ecdysone receptor encoded by SEQ ID NO:1.

SEQ ID NO:6: The amino acid sequence of the USP polypeptide subunit of the B. ovis ecdysone receptor encoded by SEQ ID NO:2.

SEQ ID NO:7: The amino acid sequence of the USP polypeptide subunit of the B. ovis ecdysone receptor encoded by SEQ ID NO:3.

SEQ ID NO:8: The amino acid sequence of the USP polypeptide subunit of the B. ovis ecdysone receptor encoded by SEQ ID NO:4.

SEQ ID NO:9: Nucleotide sequence of the degenerate sense PCR primer used to construct the BoEcR cDNA screening probe nucleotide sequence SEQ ID NO:11. SEQ ID NO: 10: Nucleotide sequence of the degenerate antisense PCR primer used to construct the BoEcR cDNA screening probe nucleotide sequence SEQ ID NO:11.

SEQ ID NO:11: Nucleotide sequence of the BoEcR cDNA screening probe.

SEQ ID NO:12: Conceptually translated amino acid sequence of the BoEcR screening probe given in SEQ ID NO: 11.

SEQ ID NO: 13: Nucleotide sequence of the degenerate sense PCR primer used to construct the 108bp BoUSP cDNA screening probe nucleotide sequence SEQ ID NO: 15.

SEQ ID NO: 14: Nucleotide sequence of the degenerate antisense PCR primer used to construct the 108bp BoUSP cDNA screening probe nucleotide sequence SEQ ID NO: 15.

SEQ ID NO: 15: Nucleotide sequence of the 108bp BoUSP cDNA screening probe.

SEQ ID NO: 16: Conceptually translated amino acid sequence of the 108bp

BoUSP screening probe.

SEQ ID NO: 17: Nucleotide sequence of the degenerate antisense PCR primer designed to the BoUSP C domain nucleotide sequence to amplify more of BoUSP C domain and the BoUSP A/B domain.

SEQ ID NO:18: Nucleotide sequence of vector-specific T3 primer T3PCR.

SEQ ID NO: 19: Nucleotide sequence of BoUSP obtained using PCR primers

SEQ ID NO: 17 and SEQ ID NO: 18.

SEQ ID NO:20: Nucleotide sequence of 213bp BoUSP screening probe. SEQ ID NO:21: Nucleotide sequence of sense PCR primer used with antisense primer SEQ ID NO: 10 to generate 213bp BoUSP screening probe SEQ ID NO:20.

SEQ ID NO:22: Nucleotide sequence of sense PCR primer containing 5'-SpeI site used to clone BOECR_DEF domain into a modified version of the shuttle plasmid pFastBac Dual.

SEQ ID NO:23: Nucleotide sequence of antisense PCR primer containing 5'-NotI site used to clone BOECR_DEF domain into a modified version of the shuttle plasmid pFastBac Dual.

SEQ ID NO:24: Nucleotide sequence of BOECR_DEF construct including Spel/Notl cloning sites.

SEQ ID NO:25: Nucleotide sequence of sense PCR primer containing 5'-PstI site used to clone BOUSP_DEF into a modified version of the shuttle plasmid pFastBac Dual.

SEQ ID NO:26: Nucleotide sequence of antisense PCR primer containing 5'-

Kpnl site used to clone BOUSP_DEF into a modified version of the shuttle plasmid pFastBac Dual.

SEQ ID NO:27: Nucleotide sequence of BOUSP_DEF construct including Pstl/Kpnl cloning sites.

SEQ ID NO:28: Nucleotide sequence of reDBDf PCR primer.

SEQ ID NO:29: Nucleotide sequence of reLBDr partially degenerate PCR primer.

SEQ ID NO:30: Nucleotide sequence of fragment SfgDNAlF insert in plasmid pTOP08.

SEQ ID NO:31: Nucleotide sequence of fragment SEB160.

SEQ ID NO:32: Nucleotide sequence of fragment SENl 60. SEQ ID NO:33 : Nucleotide sequence of fragment 34ATCTA.

SEQ ID NO:34: Nucleotide sequence of fragment 36TAGAT.

SEQ ID NO:35: Nucleotide sequence of fragment 123B3.

SEQ ID NO:36: Nucleotide sequence of fragment 567N8

SEQ ID NO:37: Nucleotide sequence of 71 δduplex insert in plasmid pIR 1

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows western blots of crude cell lysates from cells expressing the BOECR_DEF- BOUSP_DEF heterodimer probed with antibodies to detect the N-terminal protein tag fused to each subunit. Thus the hexa-His tagged BOECR_DEF subunit is detected using an anti-hexa-His antibody whilst the FLAG-tagged BOUSP_DEF subunit is detected using an anti-FLAG antibody.

Figure 2 depicts the purified BOECR_DEF-BOUSP_DEF upon analysis by SDS-PAGE and coomassie staining after sequential purification by immobilised metal affinity column chromatography via the hexa-His tag fused to the N-terminus of the BOECR_DEF subunit followed by size fractionation on a Superdex 200 column. The DEF domains of the BoEcR (37.1 kD) and BoUSP (33.6 kD) subunits are defined in tables 1 and 2 respectively.

Figure 3 shows binding of [³H]-ponasterone A as a function of free ligand concentration employing the recombinant heterodimer BOECR_DEF-BOUSP_DEF in a crude cell lysate - data used for Kd value determination.

Figure 4 shows the competitive inhibition curve for ecdysteroid 20-hydroxyecdysone, RH5992 and Halofenozide. DETAILED DESCRIPTION OF THE INVENTION

The present invention advantageously provides isolated polynucleotide and polypeptide sequences of a novel ecdysone receptor protein (EcR) and three novel isoforms of ultraspiracle (USPs) from the B. ovis ecdysone receptor. The polynucleotides and polypeptides of the present invention are useful in screening methods, particularly in identifying modulating agents of such receptors.

Accordingly, in a first aspect, the present invention provides an isolated polynucleotide comprising a nucleotide sequence which encodes, or is complementary to a sequence which encodes an EcR polypeptide of a B. ovis ecdysone receptor, wherein the polynucleotide comprises a nucleic acid sequence that is at least 60% identical, preferably at least 70% identical, more preferably at least 80% identical, even more preferably at least 90%, 95%, 96%, 97%, 98% or 99% identical to the sequence set forth in SEQ ID NO:1 and most preferably, the sequence set forth in SEQ ID NO:1.

In a third aspect, the present invention provides an isolated polynucleotide comprising a nucleotide sequence which encodes or is complementary to a sequence which encodes a B. ovis EcR polypeptide, the polypeptide comprising an amino acid sequence at least 60%, preferably at least 70% identical, more preferably at least 80% identical, even more preferably at least 90%, 95%, 96%, 97%, 98% or 99% identical to the sequence set forth in SEQ ID NO: 5 and most preferably, the amino acid sequence set forth in SEQ ID NO:5. In a fourth aspect, the present invention provides an isolated polynucleotide comprising a nucleotide sequence which encodes or is complementary to a sequence which encodes a USP polypeptide of a B. ovis ecdysone receptor, the polypeptide consisting of an amino acid sequence at least 60%, preferably at least 70% identical, more preferably at least 80% identical, even more preferably at least 90%, 95%, 96%, 97%, 98% or 99% identical to the sequence set forth in any one of SEQ ID NO:6 or SEQ ID NO:7 or SEQ ID NO: 8 and most preferably, the amino acid sequence set forth in any one of SEQ ID NO:6 or SEQ ID NO:7 or SEQ ID NO:8.

The first novel USP isoform, BoUSP5 has the polynucleotide sequence set forth in SEQ ID NO:2 and the polypeptide sequence set forth in SEQ ID NO:6. The second novel

USP isoform, BoUSP 15, has the polynucleotide sequence set forth in SEQ ID NO:3 and polypeptide sequence set forth in SEQ ID NO:7. The third novel USP isoform,

BoUSPI l, has the polynucleotide sequence set forth in SEQ ID NO:4 and polypeptide sequence set forth in SEQ ID NO: 8. The present results indicate the three isoforms are probably the result of differential splicing. Whilst all three isoforms possess identical polypeptide sequences, the initiation of translation of BoUSP 15 occurs downstream compared to that of BoUSP5 and BoUSPI l. BoUSP 15 is an N-terminal truncated isoform of BoUSP5 and BoUSPl 1. BoUSPl 1 contains a silent nucleotide change from adenosine (A) to guanosine (G) at position 1041 compared to BoUSP5 and BoUSP 15 with no resulting change in polypeptide sequence. This is possibly an artifact of splicing.

Those skilled in the art will be aware that variants of the polynucleotide sequences set forth in any one of SEQ ID NO:1 to SEQ ID NO:4 or fragments thereof may be isolated by hybridisation under suitable stringency conditions as exemplified herein. Such variants include any genomic sequences, cDNA sequences, mRNA or other isolated polynucleotide molecules derived from the polynucleotides exemplified herein by the Sequence Listing. Additional variants from those described above are not excluded. Accordingly, the isolated polynucleotide molecule according to the first, second, third or fourth aspects of the invention may comprise a fragment of a polynucleotide sequence encoding a full-length novel EcR or a novel ultraspiracle (USP) isoform from B. ovis. It is to be understood that a 'fragment' of a polynucleotide sequence encoding a B. ovis EcR polypeptide or a USP polypeptide of a B. ovis ecdysone receptor refers to a nucleotide sequence encoding a part or fragment of such a receptor which is capable of binding or associating with an insect steroid or an analogue thereof, or a modulator of the receptor, such as a candidate insecticidally active compound. Fragments of a polynucleotide sequence would generally comprise in excess of ten contiguous nucleotides, for example fifteen contiguous nucleotides. In some embodiments the fragments contain twenty contiguous nucleotides and may contain thirty consecutive nucleotides, derived from the base sequence and may encode one or more domains of a B. ovis EcR or a USP polypeptide of a B. ovis ecdysone receptor.

The novel EcR, BoEcRCl, has the polypeptide sequence set forth in SEQ ID NO:5. The USP polypeptide of a B. ovis ecdysone receptor has the polypeptide sequence set forth in any one of SEQ ID NO: 6 to SEQ ID NO: 8. The polynucleotide sequences SEQ ID NO:2 and SEQ ID NO:4 encode the identical polypeptide sequences, SEQ ID NO:6 and SEQ ID NO:8; therefore two ecdysone receptor heterodimers, BoEcR- BoUSP5 and BoEcR-BoUSP15 can form from the aforementioned polypeptides.

In determining whether or not two polypeptide sequences fall within percentage identity limits, those skilled in the art will be aware that it is necessary to conduct a side-by-side comparison or multiple alignment of sequences. In such comparisons or alignments, differences will arise in the positioning of non-identical residues, depending upon the algorithm used to perform the alignment. In the present context, reference to a 'percentage identity' or 'similarity' between two or more amino acid sequences shall be taken to refer to the number of identical and similar residues respectively, between said sequences as determined using any standard algorithm known to those skilled in the art. For example, amino acid sequence identities or similarities may be calculated using the GAP programme and/or aligned using the PILEUP programme of the Computer Genetics Group, Inc., University Research Park, Madison, Wisconsin, United States of America (Devereaux et al, 1984). The GAP programme utilizes the algorithm of Needleman and Wunsch (1970) to maximise the number of identical/similar residues and to minimise the number and length of sequence gaps in the alignment. Alternatively or in addition, wherein more than two amino acid sequences are being compared, the Clustal W programme of Thompson et al, (1994) is used.

In determining whether or not two polynucleotide sequences fall within percentage identity limits, those skilled in the art will be aware that it is necessary to conduct a side-by-side comparison or multiple alignment of sequences. In such comparisons or alignments, differences may arise in the positioning of non-identical residues, depending upon the algorithm used to perform the alignment. In the present context, reference to a 'percentage identity' between two or more nucleotide sequences shall be taken to refer to the number of identical residues between said sequences as determined using any standard algorithm known to those skilled in the art. For example, nucleotide sequences may be aligned and their identity calculated using the BESTFIT programme or other appropriate programme of the Computer Genetics Group, Inc., University Research Park, Madison, Wisconsin, United States of America (Devereaux et al, Nucl. Acids Res., 12:387-395, 1984).

In some embodiments, fragments of the polypeptides of the present invention include one or more regions or domains which are involved in the interaction or association between the monomeric polypeptide subunits of a multimeric receptor and/or which are involved in the interaction or association between (i) a cognate steroid or receptor ligand or cis-acting DNA sequence; and (ii) said monomeric polypeptide subunits or the receptor per se. In other embodiments, the fragments comprise the DNA-binding domain, linker domain or a part thereof, or ligand-binding domain (eg. hormone- binding domain) of an EcR polypeptide or novel EcR from B. ovis ecdysone receptor polypeptide. The polypeptide may retain the biological activity of the novel ecdysone receptor and a novel ultraspiracle (USP) isoform from B. ovis, it is then required to include at least a ligand-binding region comprising the ligand-binding domain and at least a part of the linker domain of the EcR polypeptide subunit, optionally in association with a ligand-binding region comprising at least the ligand-binding domain and at least a part of the linker domain of the EcR partner protein (USP polypeptide) subunit of said receptor. Additional fragments are not excluded.

In a fifth aspect, the present invention provides an isolated polynucleotide which encodes an EcR polypeptide wherein the polynucleotide has a sequence that hybridises under high stringency conditions to the nucleotide sequence set forth in SEQ ID NO:1; or a sequence fully complementary thereto, wherein high stringency conditions are a hybridisation and/or wash carried out in less than the ionic strength of 5xSSC, 0.05 M sodium phosphate, 42% formamide, 0.1% SDS at a temperature of at least 38°C and a washing step of at least 38⁰C in 2xSSC.

In a sixth aspect the present invention provides an isolated polynucleotide which encodes a USP polypeptide wherein the polynucleotide has a sequence that hybridises under high stringency conditions to the nucleotide sequence set forth in any one of SEQ ID NO:2, SEQ ID NO:3 or SEQ ID NO:4; or a sequence fully complementary thereto, wherein high stringency conditions are a hybridisation and/or wash carried out in less than the ionic strength of 5xSSC, 0.05 M sodium phosphate, 42% formamide, 0.1% SDS at a temperature of at least 38⁰C and a washing step of at least 38⁰C in 2xSSC.

A nucleic acid molecule is 'hybridisable' to another nucleic acid molecule, such as a cDNA, genomic DNA, or RNA, when a single stranded form of the nucleic acid molecule can anneal to the other nucleic acid molecule under the appropriate conditions of temperature and solution ionic strength (see Sambrook et al, 1989). Hybridisation and washing conditions are well known to persons skilled in the art and exemplified in Sambrook, J., Fritsch, E. F. and Maniatis, T. Molecular Cloning: A Laboratory Manual, Second Edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor (1989), particularly Chapter 11 and Table 11.1 therein (entirely incorporated herein by reference). The conditions of temperature and ionic strength determine the 'stringency' of the hybridization.

Stringency conditions can be adjusted to screen for moderately similar fragments, such as homologous sequences from distantly related organisms, to highly similar fragments, such as genes that duplicate functional enzymes from closely related organisms. For preliminary screening for homologous nucleic acids, low stringency hybridisation conditions, corresponding to a hybridisation temperature of 55°C, can be used, e.g., 5x SSC, 0.1% SDS, 0.25% milk, and no formamide; or 30% formamide, 5x SSC, 0.5% SDS). Moderate stringency hybridisation conditions correspond to a higher Tm, e.g., 40% formamide, with 5x or 6x SCC. High stringency hybridisation conditions correspond to the highest Tm, e. g., 50% formamide, 5x or 6x SSC.

Hybridisation requires that the two nucleic acids contain complementary sequences, although depending on the stringency of the hybridisation, mismatches between bases are possible. The term 'complementary¹ is used to describe the relationship between nucleotide bases that are capable of hybridising to one another. For example, with respect to DNA, adenosine is complementary to thymine and cytosine is complementary to guanine. Accordingly, the instant invention also includes isolated full length and fragment nucleic acid sequences that are complementary to the complete sequences as disclosed or used herein as well as sequences which are substantially similar to the nucleic acid sequences of the invention.

In a specific embodiment of the invention, polynucleotides are detected by employing hybridisation conditions comprising a hybridisation step of 38°C, and utilizing conditions as set forth above. In one embodiment, the hybridisation temperature is 40°C; in another embodiment, the hybridisation temperature is 42°C; in still another embodiment, the hybridisation temperature is 44°C.

Post-hybridisation washes also determine stringency conditions. One set of preferred conditions uses a series of washes starting with 2X SSC, 0.1% SDS at room temperature for 30 minutes (min), then repeated with 2X SSC, 0.1% SDS at 37°C for 30 minutes.

The appropriate stringency for hybridising nucleic acids depends on the length of the nucleic acids and the degree of complementation, variables well known in the art. The greater the degree of similarity or homology between two nucleotide sequences, the greater the value of the Tm for hybrids of nucleic acids having those sequences. The relative stability (corresponding to higher Tm) of nucleic acid hybridisations decreases in the following order: RNA: RNA, DNA: RNA, DNA: DNA. For hybrids of greater than 100 nucleotides in length, equations for calculating Tm have been derived (see Sambrook et al, supra, 9.50-0. 51). For hybridisation with shorter nucleic acids, i.e., oligonucleotides, the position of mismatches becomes more important, and the length of the oligonucleotide becomes an important factor in determining specificity (see Sambrook et al, supra, 11.7-11. 8). As other factors may significantly affect the stringency of hybridisation, including base composition and length of the complementary strands, presence of organic solvents and extent of base mismatching, the combination of parameters is more important than the absolute measure of any one.

The length for a hybridisable nucleic acid is at least about 10 nucleotides. In one embodiment, the length for a hybridizable nucleic acid is at least about 15 nucleotides, such as at least about 20 nucleotides; and may be at least 30 nucleotides.

Furthermore, the skilled artisan will recognize that the temperature and wash solution salt concentration may be adjusted as necessary according to factors such as length of the probe.

In a seventh aspect, the present invention provides an isolated EcR polypeptide of a B. ovis ecdysone receptor comprising the amino acid sequence set forth in SEQ ID NO: 5, or a sequence at least 60% identical, preferably at least 70% identical, more preferably at least 80% identical, even more preferably at least 90%, 95%, 96%, 97%, 98% or 99% identical to the sequence set forth in SEQ ID NO:5.

In an eighth aspect, the present invention provides an isolated USP polypeptide of a B. ovis ecdysone receptor comprising an amino acid sequence set forth in any one of SEQ ID NO:6, SEQ ID NO:7 or SEQ ID NO:8; or a sequence at least 60% identical, and may be at least 70% identical. In one embodiment the sequence is at least 80% identical and in another embodiment the sequence is at least 90%, 95%, 96%, 97%, 98% or 99% identical to the sequence set forth in any one of SEQ ID NO:6, SEQ ID NO:7 or SEQ ID NO:8. The polynucleotides of the present invention are also useful for developing genetic constructs which comprise, and preferably express, the novel ecdysone receptor EcR polynucleotide or novel isoforms of the EcR partner protein, ultraspiracle (USP) from B. ovis, thereby providing for the production of the recombinant polypeptides in isolated cells or transformed tissues.

Accordingly, in a ninth aspect, the present invention provides a genetic construct comprising an isolated polynucleotide as hereinbefore described, operably linked to a promoter sequence.

The polynucleotide may be in an expressible format, such that it is possible to produce a recombinant polypeptide therefrom. Reference herein to a 'promoter' is to be taken in its broadest context and includes the transcriptional regulatory sequences of a classical genomic gene, including the TATA box which is required for accurate transcription initiation in a eukaryotic cell, with or without a CCAAT box sequence. Promoters may be cell, tissue, organ or system specific, or may be non-specific. Using specific promoters, the expression of a bioactive agent or other polypeptide encoded by a structural gene to which the promoter is operably connected may be targeted to a desired cellular type.

In the present context, the term 'promoter' is also used to describe a synthetic or fusion molecule, or derivative which confers, activates or enhances expression in a cell in response to an external stimulus. Accordingly, the promoter may include further regulatory elements (i.e. upstream activating sequences, enhancers and silencers) which alter gene expression in response to developmental and/or external stimuli, or in a tissue-specific manner. Preferred promoters may contain copies of one or more specific regulatory elements, in particular steroid responsive elements (SREs) or hormone-responsive elements (HREs), to further enhance expression and/or to alter the spatial expression and/or temporal expression pattern.

Placing an isolated nucleic acid molecule of the present invention operably under the control of a promoter sequence means positioning said gene or isolated polynucleotide such that its expression is controlled by the promoter sequence. Promoters are generally positioned 5' (upstream) to the genes that they control. In the construction of heterologous promoter/structural gene combinations it is generally preferred to position the promoter at a distance from the gene transcription start site that is approximately the same as the distance between that promoter and the gene it controls in its natural setting, i. e., the gene from which the promoter is derived. As is known in the art, some variation in this distance can be accommodated without loss of promoter function. Similarly, the preferred positioning of a regulatory sequence element with respect to a heterologous gene to be placed under its control is defined by the positioning of the element in its natural setting, i.e., the genes from which it is derived. Again, as is known in the art, some variation in this distance can also occur.

Those skilled in the art will recognise that the choice of promoter will depend upon the nature of the cell being transformed and when expression is required. Furthermore, it is well-known in the art that the promoter sequence used in the expression vector will also vary depending upon the level of expression required and whether expression is intended to be constitutive or regulated.

For expression in eukaryotic cells, the genetic construct generally comprises, in addition to the polynucleotide molecule of the invention, a promoter and optionally other regulatory sequences designed to facilitate expression of said polynucleotide molecule. The promoter may be derived from a genomic clone which normally encodes the expressed protein or alternatively, it may be a heterologous promoter derived from another genetic source. Promoter sequences suitable for expression of genes in eukaryotic cells are well-known in the art.

Suitable promoters for use in eukaryotic expression vectors include those capable of regulating expression in mammalian cells, insect cells such as Sf9, Sf21 {Spodoptera frugiperdά) or Hi-5 (Trichoplusia ni), yeast cells and plant cells. Preferred promoters for expression in eukaryotic cells include the plO promoter, MMTV promoter, polyhedron promoter, the SV40 early promoter and the cytomegalovirus (CMV-IE) promoter, promoters derived from immunoglobulin-producing cells (see, United States Patent No 4,663,281), polyoma virus promoters, and the LTR from various retroviruses (such as murine leukaemia virus, murine or Rous sarcoma virus and HIV), amongst others (See, Enhancers and Eukaryotic Gene Expression, Cold Spring Harbor Press, New York, 1983, which is incorporated herein by reference). Examples of other expression control sequences are enhancers or promoters derived from viruses, such as SV40, Adenovirus, Bovine Papilloma Virus, and the like.

Wherein the expression vector is intended for the production of recombinant protein, the promoter is further selected such that it is capable of regulating expression in a cell which is capable of performing any post-translational modification to the polypeptide which may be required for the subject recombinant polypeptide to be functional, such as N-linked glycosylation. Cells suitable for such purposes may be readily determined by those skilled in the art. By way of exemplification, baculovirus may be used to express recombinant polypeptides using standard protocols in Sf9, Sf21 or Hi-5 insect cells.

Numerous expression vectors suitable for the present purpose have been described and are readily available. The expression vector may be based upon pFastBac Dual, pCR- TOPO2.1, piRES, and pDual.

Examples of eukaryotic cells contemplated herein to be suitable for expression include mammalian, yeast, insect, plant cells or cell lines such as COS, VERO, HeLa, mouse C 127, Chinese hamster ovary (CHO), WI-38, baby hamster kidney (BHK), MDCK, 3T3, HEK, Sf21 (insect) Sf9 (insect) or Hi-5 (insect) cell lines. Such cell lines are readily available to those skilled in the art.

The prerequisite for expression in prokaryotic cells such as Escherichia coli is the use of a strong promoter with an effective ribosome binding site. Typical promoters suitable for expression in bacterial cells such as E. coli include, but are not limited to, the lacz promoter, temperature-sensitive A, or AR promoters, T7 promoter or the IPTG-inducible tac promoter. A number of vector systems for expressing the nucleic acid molecule of the invention in E. coli are well-known in the art and include pETDuet-1 (Novagen), pRSETb (Invitrogen), pET-based vectors or pGEX-4T, and pACYC are others described for example in Ausubel et al (1992). Suitable prokaryotic cells include strains of Corynebacterium, Salmonella, Escherichia coli, for example, but not limited to, BL21(DE3), Bacillus sp. and Pseudomonas sp, amongst others. Bacterial strains which are suitable for the present purpose are well- known in the relevant art (Ausubel et al, 1992).

The genetic constructs described herein may further comprise genetic sequences corresponding to a bacterial origin of replication and/or a selectable marker gene such as an antibiotic-resistance gene, suitable for the maintenance and replication of said genetic construct in a prokaryotic or eukaryotic cell, tissue or organism. Such sequences are well-known in the art.

Selectable marker genes include genes which when expressed are capable of conferring resistance on a cell to a compound which would, upon absent expression of said selectable marker gene prevent or slow cell proliferation or result in cell death. Preferred selectable marker genes contemplated herein include, but are not limited to antibiotic-resistance genes such as those conferring resistance to ampicillin, Claforan, gentamycin, G-418, hygromycin, rifampicin, kanamycin, neomycin, spectinomycin, tetracycline or a derivative or related compound thereof or any other compound which may be toxic to a cell. The origin of replication or a selectable marker gene will be spatially-separated from those genetic sequences which encode the recombinant receptor polypeptide or fusion polypeptide comprising same.

Preferably, the genetic constructs of the invention, including any expression vectors, may be capable of introduction into, and expression in, an in vitro cell culture, or for introduction into, with or without integration into the genome of a cultured cell, cell line or transgenic animal.

In a particularly preferred embodiment, the expression vector is selected from the group consisting of pFastBacDual, piRES, pDual, pETDuet-1 (Novagen), pRSETb (Invitrogen), pET-based vectors or pGEX-4T, and pACYC. In a tenth aspect, the present invention provides a recombinant cell comprising an isolated polynucleotide according to the invention hereinbefore described, or the genetic construct according to the ninth aspect of the invention.

As used herein, the term 'recombinant cell' shall be taken to refer to a single cell, or a cell lysate, or a tissue, organ or whole organism comprising same, including a tissue, organ or whole organism comprising a clonal group of cells or a heterogenous mixture of cell types, which may be a prokaryotic or eukaryotic cell that comprises a polynucleotide of the present invention or a fragment thereof that has been incorporated artificially into the cell, preferably the polynucleotide is incorporated in the cell with a suitable vector so that it can replicate and express itself many times.

As used herein, the term 'recombinant cell' is meant to also include the progeny of a transformed cell.

In one embodiment, the recombinant cell of the present invention expresses the polypeptide encoded by the polynucleotide molecules of the present invention.

In another embodiment, the cell expresses the EcR or a novel ultraspiracle (USP) isoform from Bovicola ovis, or a fragment thereof and comprises a nucleic acid sequence encoding a bioactive molecule or a reporter molecule.

To produce the recombinant cells of the invention, host cells are transfected or co- transfected or transformed with nucleotide sequences containing the DNA segments of interest (for example, the novel EcR or an ultraspiracle (USP) isoform from Bovicola ovis,) by well-known methods, which vary depending on the type of cellular host. For example, calcium chloride transfection is commonly utilized for prokaryotic cells, whereas lipofection, CellFectin or calcium phosphate treatments are often used for other cellular hosts. See, generally, Sambrook et al, (1989); Ausubel et al, (1992); and Potrykus (1990). Other transformation techniques include electroporation, DEAE- dextran, microprojectile bombardment, lipofection, microinjection, and others. In an eleventh aspect of this invention, there is provided a transgenic animal (such as a mammal or insect), microorganism, plant or aquatic organism, containing one or more cells as mentioned above. Reference to plants, microorganisms and aquatic organisms includes any such organisms.

Insect steroid receptors, such as the B. ovis EcR and USP polypeptide subunits of the B. ovis ecdysone receptor, are characterized by functional ligand-binding domains, and DNA-binding domains. The B. ovis ecdysone receptor contains a DNA-binding domain (Domain C), and a ligand-binding domain (Domain E), separated and flanked by additional domains (see Tables 1 and 2). The C domain preferably comprises a zinc-finger DNA-binding domain which is usually hydrophilic, having high cysteine, lysine and arginine content. The E domain is a globular domain that binds ligands, coactivator proteins and corepressor proteins. Amino acid residues proximal to the C domain comprise a region initially defined as separate A and B domains. Region D separates the more conserved domains C and E. Region D typically has a hydrophilic region whose predicted secondary structure is rich in turns and coils.

In a twelfth aspect, the present invention provides an isolated fragment of the B. ovis EcR or USP polypeptide as hereinbefore described, preferably an isolated fragment comprising one or more functional domain regions. Any of the functional domains may be used to construct chimeric nuclear receptors by functionally linking them to components of other nuclear receptors for use, e.g. in ecdysone switches. Fragments of the B. ovis EcRs and USP e.g. encompassing the D and E or just the E domains may be expressed to produce functional ligand binding protein for use in binding assays and screens for ligands exhibiting new chemistries.

As is known in the field, ecdysone receptors and their functional domains are employed as components of ecdysone switches for the control of therapeutic genes in mammalian cells (Lafont & Dinan, 2003; Yang et al, 1986) and for control of transgenes more generally in agriculturally important species, both animal and plant (Lafont & Dinan, 2003; Padidam ef α/, 2003). Accordingly, in a thirteenth aspect, the present invention extends to the use of the B. ovis ecdysone receptor as described herein in gene switching. A gene switch is generally a system in which a gene of interest is turned off or is partly inactivated, or alternatively is turned on or partially activated, in one state but may be for example switched on, or off, by some alteration in a cell containing the gene. For the purpose of this aspect, the terms "gene switch" or "gene switching" refer to the combination of a response element associated with a promoter and an ecdysone receptor based system which, in the presence of one or more ligands, modulates the expression of a gene into which the response element and promoter are incorporated.

The recombinant or isolated B. ovis ecdysone receptor polypeptides as described herein may be thermostable. By 'thermostable' is meant that the polypeptide does not exhibit reduced activity at bacterial, plant or animal physiological temperatures above about 28°C or above about 30°C. The thermostability of insect steroid hormone receptors also refers to the capacity of such receptors to bind to ligand-binding domains or regions or to transactivate genes linked to insect steroid hormone response elements at bacterial, plant or animal physiological temperatures above about 28°C or above about 30°C.

The present invention clearly extends to variants of the polypeptides of the present invention. The polypeptide may be substantially free of naturally associated insect cell components, or may be in combination with a partner protein which associates with the insect steroid receptor so as to confer enhanced affinity for insect steroid response elements, enhanced affinity for insect steroids or analogues thereof. For example, the polypeptide sequences (eg SEQ ID NOs:5 to 8) described herein may be varied by the deletion, substitution or insertion of one or more amino acids.

In one embodiment, amino acids of the polypeptides described herein may be replaced by other amino acids having similar properties, for example hydrophobicity, hydrophilicity, hydrophobic moment, charge or antigenicity, and so on.

Substitutions encompass amino acid alterations in which an amino acid of the base polypeptide is replaced with a different naturally-occurring or a non-conventional amino acid residue. Such substitutions may be classified as 'conservative', in which case an amino acid residue contained in the base polypeptide is replaced with another naturally-occurring amino acid of similar character, for example GIy- Ala, Lys~Arg or Phe-Trp-Tyr.

Substitutions encompassed by the present invention may also be 'non-conservative', in which an amino acid residue which is present in the base polypeptide is substituted with an amino acid having different properties, such as a naturally-occurring amino acid from a different group (eg. substituted a charged or hydrophobic amino acid with alanine), or alternatively, in which a naturally-occurring amino acid is substituted with a non-conventional amino acid.

Those skilled in the art will be aware that several means are available for producing variants of the described polypeptide sequences, when provided with the nucleotide sequence of the nucleic acid molecule which encodes said polypeptide, for example site-directed mutagenesis of DNA and polymerase chain reaction utilising mutagenised oligonucleotide primers, amongst others.

Such polypeptide variants which are capable of binding insect steroids or receptor modulators and ligands clearly form part of the present invention. Assays to determine such binding may be carried out according to procedures well known in the art.

The polypeptides of the present invention can include fusion polypeptides, such as but not limited to, fusion between different regions of different insect receptor polypeptides. Different domains of the polypeptides of the invention may be replaced with foreign polypeptide fragments. Fusion polypeptides of the present invention can include fusion with a second polypeptide, for example a detectable reporter polypeptide such as - β-galactosidase, β-glucuronidase, luciferase or other enzyme, or a FLAG peptide, hapten peptide such as a poly-lysine or poly-histidine or other polypeptide molecule.

In order to produce a fusion polypeptide, the nucleic acid molecule which encodes the polypeptide of the invention, or an analogue or derivative thereof, is cloned adjacent to a second nucleic acid molecule encoding the second polypeptide, optionally separated by a spacer nucleic acid molecule which encodes one or more amino acids (eg: poly- lysine or poly-histidine, amongst others), such that the first coding region and the second coding region are in the same open reading frame, with no intervening stop codons between the two coding regions. When translated, the polypeptide thus produced comprises a fusion between the polypeptide products of the first and second coding regions. Wherein a spacer nucleic acid molecule is utilised in the genetic construct, it may be desirable for said spacer to at least encode an amino acid sequence which is cleavable to assist in separation of the fused polypeptide products of the first and second coding regions, for example a thrombin cleavage site.

A genetic construct which encodes a fusion polypeptide further comprises at least one start codon and one stop codon, capable of being recognised by the cell's translational machinery in which expression is intended.

In some embodiments a genetic construct which encodes a fusion polypeptide may be further modified to include a genetic sequence which encodes a targeting signal placed in-frame with the coding region of the nucleotide sequence encoding the fusion polypeptide, to target the expressed recombinant polypeptide to the extracellular matrix or other cell compartment. The genetic sequence encoding a targeting signal may be placed in-frame at the 5'-terminus or the 3'-terminus, particularly at the 5'-terminus, of the coding region of the nucleotide sequence which encodes the fusion polypeptide.

Methods for the production of a fusion polypeptide are well-known to those skilled in the art.

In a further embodiment the biological function of the polypeptides as herein described can be modulated by making specific changes (e. g. addition, substitution or deletion) to only those amino-acids within each domain that are critical for determining the relevant function (eg. ligand-binding activity, DNA binding site affinity, etc), such as by site-directed mutagenesis. Accordingly, the polypeptides of the present invention can differ in amino acid sequence and/or exhibit different biological properties to a naturally-occurring B. ovis ecdysone receptor. Accordingly, the present invention extends to any variants of B. ovis ecdysone receptor polypeptides referred to herein (including species variants for example, the Human Body Louse) and nucleic acid sequences encoding same, wherein said variants are derived from a receptor polypeptide as described herein and exhibit demonstrable ligand-binding activity, and either comprises an amino acid sequence which differs from a naturally-occurring receptor polypeptide, or exhibit biological activity.

As with other aspects of the invention, the variants described herein may be produced as recombinant polypeptides or in transgenic organisms, once the defined recombinant polynucleotides are introduced into a suitable host cell and expressed therein.

The B. ovis ecdysone receptor polypeptides described herein may be purified by standard techniques, such as column chromatography (using various matrices which interact with the protein products, such as ion exchange matrices, hydrophobic matrices and the like), affinity chromatography utilizing antibodies specific for the protein or other ligands such as dyes or insect steroids which bind to the protein. Wherein the recombinant polypeptide is expressed as a fusion polypeptide, it is also possible to purify the fusion polypeptide based upon its properties (eg size, solubility, charge etc).

Alternatively, the fusion polypeptide may be purified based upon the properties of the non-receptor moiety of said fusion polypeptide, for example substrate affinity. Once purified, the fusion polypeptide may be cleaved to release the intact polypeptide of the invention.

Alternatively, polypeptides may be synthesized by standard protein synthetic techniques as are well known in the art.

In a preferred embodiment, the isolated polypeptides of the invention are provided as a precipitate or crystallized by standard techniques, preferably for X-ray crystal structure determination.

The B. ovis ecdysone receptor polypeptides of the invention or ligand binding domains thereof, or their complexes with EcR partner proteins, such as USP polypeptide of B. ovis ecdysone receptor, or ligand binding domains thereof, which confer enhanced affinity for insect steroid response elements or partner proteins (USP polypeptides) or ligands, are particularly useful to model three-dimensional structure of the receptor ligand-binding region. In this embodiment of the invention, modulators of a B. ovis ecdysone receptor, such as but not limited to, insecticidal agents may be produced which bind to, or otherwise interact with, the ligand-binding region of the receptor, and preferably interfere with ligand binding. In the same way, agents may be developed which have a potentiated interaction with the insect steroid receptor over and above that of the physiological insect steroid which binds to the receptor.

Accordingly in a fourteenth aspect, the present invention provides a method of identifying a modulator of a B. ovis ecdysone receptor comprising:

(a) assaying the binding of a reporter ligand to a B. ovis ecdysone receptor polypeptide of the present invention in the presence of a potential modulator; and (b) assaying the binding of a reporter ligand to the ecdysone receptor polypeptide of the present invention without said potential modulator; and

The B. ovis ecdysone receptor polypeptide of the present invention may comprise a complex of an EcR and a USP polypeptide. In some embodiments, the reporter ligand is [ H]-ponasterone A or a fluorescent conjugate, such as any one of the fluorescent conjugates as described in WO 2005/054271 titled "Assay for ligands of the Ecdysone receptors" the entire contents of which are incorporated herein. WO 2005/054271 describes suitable fluorescent conjugates that are useful as ligands in in vitro ligand binding assays, including fluorescence polarization (FP) assays for ecdysone receptor ligands. The FP format is homogenous, ie. , the binding reaction and FP measurement of each assay is performed in the same compartment (e.g. a single well in a multiwell plate).

The assay is therefore ideally suited to the miniaturisation and automation that underpins industrial high throughput screening programs. The fluorescent compounds can, for example, be prepared by reacting a reactive group in the fluorescent moiety with a nucleophilic group in the compound that binds to the B. ovis ecdysone receptor of the present invention. The fluorescent moiety may be selected from the group consisting of unsubstituted and substituted fluorescein moieties, unsubstituted and substituted dansyl moities, and unsubstituted and substituted coumarin moieties. The fluorescent moiety may be attached by derivatisation of a hydroxyl group on the alkyl side chain of an ecdysteroid moiety that is capable of binding to an ecdysone receptor or ligand binding domain thereof. For example, the fluorescent moiety may be attached to the ecdysteroid by derivatisation of a reactive primary hydroxyl group on C-26 such as occurs in inokosterone, 26-hydroxyecdysone, 20,26-dihydroxyecdysone, makisterone B, amarasterone A, amarasterone B, ajugasterone B, sidasterone A, sidasterone B and 26-hydroxy-polypodine B. In an alternative embodiment the fluorescent moiety is attached by derivatisation of a hydroxyl group at C-25 of an ecdysteroid selected from the group consisting of 20- hydroxyecdysone, makisterone A, polypodine B and rapisteronc D.

WO 2005/05427 also provides assays for screening compounds for their ability to interact with ecdysone receptors. The assays described in WO 2005/054271 are also useful for screening and identifying modulating agents, including insecticidally-active compounds such as ligands which bind and either agonise or antagonise the B. ovis ecdysone receptors of the present invention.

Accordingly, in a fifteenth aspect, the present invention provides a method for screening a candidate compound for its ability to interact with a B. ovis ecdysone receptor of the present invention or ligand binding domain (LBD) thereof in a competitive inhibition format, the method comprising the steps of: (a) incubating a B. ovis ecdysone receptor or LBD thereof with a candidate compound; and (b) measuring the level of binding of the candidate compound to the ecdysone receptor or LBD thereof.

As used herein a 'modulator' is a compound or molecule that agonises or antagonises the binding properties and/or biological activity of a B. ovis ecdysone receptor. Preferred potential modulators according to this embodiment include by way of example ecdysteroids such as 20-hydroxyecdysone, muristerone A, ponasterone A, ajugasterone C and polypodine B. The reporter ligand may be any ligand that is known to bind to B. ovis ecdysone receptor, which binding may be monitored or assayed readily. For example, the reporter ligand may be [³H] -ponasterone A or fluorescent ecdysteroid conjugates such as MB4628, MB4592, MB4603 or MB4622 as described in WO 2005/054271. Standard methods can be used to assay the binding of the reporter ligand.

This embodiment of the invention may be applied directly to the identification of potential insecticidally-active compounds or alliteratively, modified for such purposes by assaying for the binding (direct or indirect) of the B. ovis ecdysone receptor polypeptide of the invention to a steroid response element (SRE). According to this alternative embodiment, the binding assayed in the presence or absence of a potential insecticidally-active compound is compared, wherein a difference in the level of binding indicates that the candidate compound possesses potential insecticidal activity.

Accordingly, substances may be screened for insecticidal activity by assessing their ability to bind, in vivo or in vitro, to the intact B. ovis ecdysone receptor or alternatively, the ligand-binding regions of the B. ovis ecdysone receptor polypeptide (eg. domain D linked to domain E or domains C, D and E of BoEcR linked with BoUSP to form a heterodimer or ligand binding domains (E) of B. ovis EcR and B. ovis USP. An example of this embodiment may, for instance, involve binding the B. ovis ecdysone receptor polypeptide to a support such as a plurality of polymeric pins, whereafter the polypeptide resident on the plurality of pins is brought into contact with candidate insecticidal molecules for screening. The molecules being screened may be isotopically labelled so as to permit ready detection of binding. Alternatively, reporter molecules may be utilized which bind to the insect steroid receptor candidate molecule complex. Alternatively, compounds for screening may be bound to a solid support, such as a plurality of pins which are then reacted with the thermostable insect steroid receptor or complex with a partner protein. Binding may, for example, be determined again by isotopic-labelling of the receptor, or by antibody detection or use of another reporting agent.

In an alternative embodiment, insecticidally-active agents are identified using rational drug design, by expressing a USP polypeptide of a B. ovis ecdysone receptor or a fragment thereof which includes the ligand-binding region, optionally in association with a B. ovis EcR or ligand binding domain thereof, and optionally in association with a B. ovis steroid or analogue thereof, so as to form a complex, determining the three- dimensional structure of the ligand binding domain of the complex, and identifying compounds which bind to or associate with the three-dimensional structure of the ligand binding domain, wherein said compounds represent candidate insecticidally- active agents.

The methods described herein for identifying modulators of B. ovis ecdysone receptor and insecticidal compounds, may be performed using prokaryotic or eukaryotic cells, cell lysates or aqueous solutions.

The present inventors have demonstrated a method employing RNA interference technology to selectively inactivate the RNA encoding an EcR protein in vivo. In particular, the inventors have successfully constructed an RNAi expression plasmid to suppress the endogenous expression of the ecdysone receptor protein (EcR) in cultures of cells derived from the lepidopteran insect, Spodoptera frugiperda. Accordingly, in a sixteenth aspect, the present invention provides a method of modulating the expression of a B. ovis EcR target gene in a cell, tissue or organ, the method comprising the step of introducing into said cell, tissue or organ, a double stranded nucleic acid molecule in which one of the strands is substantially identical to the nucleotide sequence of the EcR target gene or region thereof of B. ovis.

By 'introduced' it is meant that the double stranded nucleic acid molecule is exogenously added or created in vivo by expression of an exogenous nucleic acid which has been introduced into the cell, tissue or organ.

The double stranded nucleic acid molecule may be at least 21 nucleotides in length, for example at least 25 nucleotides in length. In some embodiments the nucleic acid molecule is at least 30 nucleotides in length and is typically at least 90%, 95%, 96%, 97%, 98% or 99% identical to the sequence set forth in SEQ ID NO:1.

It would be appreciated by persons skilled in the art of the present invention, that the double stranded nucleic acid molecule may be introduced into animal cells which are vulnerable to being preyed upon by specific pest insects but as yet have not been infected. Alternatively, the double stranded nucleic acid molecule may be introduced after an animal has been infected with the B. ovis pest insect.

It would further be appreciated by persons skilled in the art of the present invention, that where it is desired to introduce the double stranded nucleic acid molecule into an invertebrate cell, the length of the double stranded nucleic acid can be considerably longer compared with that for mammalian cells, typically around 0.5kb and greater.

In one embodiment, the cell, tissue or organ is that of a sheep.

Standard methods may be used to introduce the double stranded nucleic acid molecule into the cell, tissue or organ for the purposes of modulating the expression of the target gene. For example, the nucleic acid molecule may be introduced as naked DNA or

RNA, optionally encapsulated in a liposome, in a virus particle as attenuated virus or associated with a virus coat or a transport protein or inert carrier such as gold or as a recombinant viral vector or bacterial vector or as a genetic construct amongst others.

Administration means in the case of animals, include injection and oral ingestion (e.g. in medicated food material), amongst others.

The double stranded nucleic acid molecule may also be delivered by a live delivery system such as using a bacterial expression system optimised for their expression in bacteria which can be incorporated into gut flora. Alternatively, a viral expression system can be employed. In this regard, one form of viral expression is the administration of a live vector generally by spray, feed or water where an infecting effective amount of the live vector (e.g. virus or bacterium ) is provided to the animal.

The carriers, excipients and/or diluents utilised in delivering the double stranded nucleic acid molecule to a host cell, tissue or organ should be acceptable for veterinary applications. Such carriers, excipients and/or diluents are well-known to those skilled in the art. Carriers and/or diluents suitable for veterinary use include any and all solvents, dispersion media, aqueous solutions, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents, and the like. Supplementary active ingredients can also be incorporated into the compositions.

As used herein the term 'modulating' is taken to mean that expression of the target gene is reduced in amplitude and/or the timing of gene expression is delayed, compared to the expression of said gene in the absence of the inventive method as described herein.

Accordingly, whilst not limiting the scope of the invention as described herein, the present invention is directed to modulation of gene expression which comprises the repression, delay or reduction in amplitude of target gene expression in a specified cell, tissue or organ of a eukaryotic organism, in particular a vertebrate or invertebrate animal, such as an insect or other animal vulnerable to being preyed upon by B. ovis.

In one embodiment, the double stranded nucleic acid molecule is at least 21 nucleotides in length, and may be at least 25 nucleotides in length. In some embodiments the nucleic acid molecule is at least 30 nucleotides in length and may be at least 90%, 95%, 96%, 97%, 98% or 99% identical to the sequence set forth in SEQ ID NO:1.

The introduced nucleic acid molecule according to the invention may be in an expressible form.

In one embodiment, the animal is a sheep.

By 'expressible form¹ is meant that the nucleic acid molecule is presented in an arrangement such that it may be expressed in the cell, tissue, organ or whole organism, at least at the transcriptional level (i.e. it is expressed in the animal cell to yield at least an mRNA product which is optionally translatable or translated to produce a recombinant peptide, oligopeptide or polypeptide molecule).

In order to obtain expression of the double stranded nucleic acid molecule in the cell, tissue, or organ of interest, a synthetic gene or a genetic construct comprising said synthetic gene is produced, wherein said synthetic gene comprises a nucleotide sequence at least 90%, more preferably at least 95%, 96%, 97%, 98% or 99% identical to the sequence of SEQ ID NO:1, in operable connection with a promoter sequence which is capable of regulating expression therein. Thus, the double stranded nucleic acid molecule will be operably connected to one or more regulatory elements sufficient for transcription in eukaryotes to occur.

In an eighteenth aspect, the present invention provides a method of treating an animal having a B. ovis infection, the method comprising the step of administering to the animal a double stranded nucleic acid molecule in which one of the strands is substantially identical to the nucleotide sequence or region thereof of B. ovis. The double stranded nucleic acid molecule may be administered by any means known in the art. For example, the nucleic acid molecule may be administered topically or systemically.

The heterologous nucleic acid according to this aspect of the invention may be DNA or cDNA.

In one embodiment, the animal is a sheep.

The nucleic acid molecule may be at least 21 nucleotides in length, for example at least 25 nucleotides in length, In some embodiments the nucleic acid molecule is at least 30 nucleotides in length and may be at least 90%, 95%, 96%, 97%, 98% or 99% identical to the sequence set forth in SEQ ID NO: 1.

In one embodiment, the heterologous nucleic acid is operably linked to a promoter sequence as hereinbefore described.

Accordingly, in a twenty-first aspect, the present invention provides a method of modulating the expression of a B. ovis EcR in an insect cell, said method at least comprising the steps of: (a) selecting a nucleotide sequence which is substantially identical to the sense and antisense strands of a B. ovis EcR target gene or a region thereof;

(b) producing a synthetic gene comprising nucleotide sequence;

(c) introducing said synthetic gene to said cell;

The term 'synthetic gene¹ refers to a non-naturally occurring gene which preferably comprises at least one or more transcriptional and/or translational regulatory sequences operably linked to a structural gene sequence. The synthetic gene may encode both the sense and antisense RNA strands which, when the nucleic acid is transcribed, the sense and antisense strands associate to form a hairpin structure. In some embodiments the hairpin structure comprises 19 to 30 nucleotides.

In a twenty-second aspect, the present invention provides a double stranded RNA molecule comprising at least 19 nucleotides and having at least 90% sequence identity to the sequence shown in one or more of SEQ ID NO:1, SEQ ID NO:2, SEQ ID NO:3 or SEQ ID NO:4. In some embodiments the RNA molecule has 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% identity to the sequence shown in one or more of SEQ ID NO: 1 , SEQ ID NO:2, SEQ ID NO:3 or SEQ ID NO:4.EQ ID

In order that the nature of the present invention may be more clearly understood, preferred forms thereof will now be described with reference to the following non- limiting examples. EXAMPLE 1

1. Experimental animals and RNA Isolation

B. ovis were harvested from an infested sheep using a pipette attached to a vacuum collection box. Live third instar lice were subjected to total RNA isolation using the guanidine isothiocynate-CsTFA method (Okayama et al, 1987). mRNA was purified from total RNA using the PolyATtract mRNA isolation kit (Promega) and quantitated by spectrophotometry.

2. Preparation of a homologous BoEcR C domain screening probe by PCR

Initial attempts to generate a PCR product using the degenerate primers and procedure described in Hannan and Hill (1997) failed despite modifications to parameters such as the thermocycling conditions. A further four degenerate primers were designed to a multiple polynucleotide sequence alignment of EcR cDNAs from other species. Using various combinations of the available degenerate primers and the B. ovis cDNA library as a template (refer to section 4 below) yielded a 141 bp which was cloned into the vector pGEM-T Easy (Promega) and sequenced on one strand (NBF). The polynucleotide sequence obtained indicated the product encoded a steroid nuclear receptor binding domain, and a BLAST search of conceptually translated sequences indicated highest identity to Locusta migratoria (migratory locust) EcR. The nucleotide sequences of the degenerate primer combination used to amplify the novel fragment of BoEcR are given in SEQ ID NO:9 and SEQ ID NO: 10. The resulting novel BoEcR polynucleotide and polypeptide sequences are shown in SEQ ID NO: 11 and SEQ ID NO: 12 respectively in the Sequence Listing.

3. Preparation of a homologous BoUSP C domain screening probe by PCR

PCR was attempted using the degenerate primers which have been used in the past to produce USP probes from other organisms (Hannan & Hill, 2001; Tzertzini et al, 1994) and the B. ovis cDNA library as a template. However, the PCR failed to generate any products even upon testing different thermocycling and reaction conditions. As with the BoEcR probe, two further pairs of degenerate primers were designed and tested in various combinations with those previously used. One combination of these degenerate primers (as given by SEQ ID NO: 13 and SEQ ID NO: 14 respectively) produced a 108 bp product which was subsequently cloned into the vector pGEM-T Easy. Sequencing of this product and BLAST searches revealed its similarity to other USP and RXR molecules, the most closely related protein being that of Bombyx mori (domestic silkworm). The polynucleotide and conceptually translated amino acid sequences of this novel BoUSP fragment are given in SEQ ID NO: 15 and SEQ ID NO: 16 respectively.

4. cDNA library construction and screening

A B. ovis cDNA library was constructed from 5 μg of oligo-dT primed mRNA using a Lambda Zap Express bacteriophage libray construction system from Stratagene. The primary library consisting of 2.2 x 10⁶ plaque forming units (pfu) per mL was amplified once to yield a final titre of 1.47 x 10⁹ pfu/mL.

EcR screening:

5 5 x 10 pfu of this library were cultivated on a lawn of E. coli XLl Blue (Stratagene) bacteria and screened for the presence of EcR-containing inserts using the BoEcR cDNA probe. Briefly, plaques were immobilised on Hybond N (Amersham) membranes, denatured and fixed according to manufacturer's directions. Membranes were subsequently dried and nucleic acids crosslinked to them using UV light (Stratalinker, Stratagene) prior to prehybridisation in a buffer containing 4x SSC or 4x SSPE, 5x Denhardt's solution, 45% formamide, 0.1% SDS, 5%-10% (w/v) dextran sulphate. Prehybridisation was performed for a minimum of four hours at 42⁰C after the addition of a final concentration of 20μg/ml sonicated salmon sperm DNA that had been boiled for 3 minutes and snap-cooled on ice.

Radiolabelling of the BoEcR probe was performed using the Decaprime system (Ambion) and [α P]-dATP (Amersham) using 5ng of each sequence-specific primer used to isolate the screening probe, 25ng of BoEcR screening probe as the template and following the manufacturers directions. Unincorporated nucleotides were removed by size-exclusion on a Sephadex NAP5 column (Pharmacia) prior to boiling the probe for 3 minutes, snap-cooling on ice and addition to the pre-hybridisation reaction. The resulting hybridisation reactions were left to proceed overnight at 42⁰C. Membranes were then washed twice in either 2x SSPE/0.1% SDS or 2x SSC/0.1% SDS at 37⁰C for 45 minutes per wash prior to visualisation by autoradiography.

This process resulted in the isolation of over 30 plaques potentially containing BoEcR DNA. These BoEcR clones were subsequently plaque-purified by two further rounds of screening resulting in a total of sixteen potential clones. These were excised from the bacteriophage to form pBK-CMV phagemids according to the manufacturers protocol (Stratagene). Six of the clones were chosen for DNA sequencing; five of which shared the polynucleotide open-reading frame of pBK-CMVBoEcRCl (BoEcRCl) given in SEQ ID NO:1 and amino acid sequence of SEQ ID NO:5. The remaining clone appears to contain a premature stop codon in the E-domain of the protein and is unlikely to be functional. Presumably this has arisen as an artefact of cloning.

USP screening:

The isolation of BoUSP encoding cDNAs proved more difficult than for BoEcR. Initially 5 x 10⁶ pfu from the library were screened using the 108 bp BoUSP cDNA probe resulting in the detection of no positive plaques. This experiment was repeated using a further 5 x 10⁶ pfu and lower-stringency membrane washing conditions to no avail. Since the C domain BoUSP probe had itself been amplified from the library, it may be safely inferred that BoUSP encoding cDNA is present. This suggested that the BoUSP cDNA fragment being used as a probe was not exhibiting sufficient affinity for recognition of phage containing the target DNA sequence. To counter this problem a strategy was introduced to develop a longer probe fragment exhibiting higher affinity.

Producing a higher affinity BoUSP probe

Using the DNA sequence information shown in SEQ ID NO: 15, an antisense C domain PCR primer (SEQ ID NO: 17) was designed for use with the vector-specific primer T3PCR (SEQ ID NO: 18) and a sense C domain primer was designed for use with the vector-specific primer T7PCR. These were used in an attempt to isolate the 5'- and 3'- cDNA ends of BoUSP respectively by PCR amplification from the cDNA library. Experiments to isolate the 5'-cDNA end of BoUSP resulted in the cloning of a 500 bp product, SEQ ID NO.19. Unfortunately, attempts to amplify the 3'-cDNA end of BoUSP failed.

Using the DNA sequence information in SEQ ID NO: 19, a new probe of 213 bp was PCR amplified (SEQ ID NO:20) using the primer given in SEQ ID NO:21. In addition to the C domain fragment included by the original 108 bp screening probe, this new 213 bp screening probe included the polynucleotide sequence that encodes the last few amino acids of the predicted A/B domain.

A total of 900,000 pfu from the B. ovis library were screened using the longer 213 bp probe as described above, except the Hybond N membrane was substituted with Biobond Plus nylon membrane (Sigma). This resulted in the isolation of 18 plaques potentially containing BoUSP encoding cDNAs. After further rounds of plaque purification these were subsequently excised from the bacteriophage. Of the ten clones sequenced, six were the longer BoUSP isoform; four of which have the polynucleotide sequence BoUSP5 (SEQ ID NO: 2) and amino acid sequence SEQ ID NO:6, the remaining two possessing the polynucleotide sequence BoUSPI l (SEQ ID NO:4) and the amino acid sequence SEQ ID NO: 8. Of the six longer isoforms two possessed an A1041G substitution as highlighted in polynucleotide sequence SEQ ID NO:4. This, however, was a silent nucleotide change probably caused by splicing with no resultant amino acid sequence change, SEQ ID NO: 8. A further clone was a premature truncation of this longer isoform and probably arose as a result of the cloning procedure. The remaining three BoUSP clones were a shorter version of the longer six clones and are given by polynucleotide sequence BoUSP 15 (SEQ ID NO:3) and amino acid sequence SEQ ID NO:7. The sequences are shown below (refer also to the Sequence Listing). Sequence ID NO: 1

ATGTATCGGGGAAACTCTTCTACCACAAAACCTATAGGCAGCGGAGAAGACGATCTTATTTTAACACAAG TTAAATCGGAACCTCAAGTTCACAGCCCCTGCGAAAAAGACATGACTTCTTCAGGCAGCAGTCAATCAAG TTTCCTTTTCAATACAATTTCTATTAATAACAAGAGATGTAAAACTGATGAATGTTCGGGAAATCCTTCA AGTCCTGGACCTCCTATGGGAAGTGCACCTTTAACACCATCACCTGGGCCCCATAATCAATATACAGTTA TAAATAATGGATATTCATCGCCGATGTCTTCAGGAAGCTACGACCCTTACAGCCCTAACGGAAAATTGGG AAGAGACGATCTTTCACCCCCTGGAAGTTTAAACGGATATAGCGTCGATAGTAGTGATGCTAAGAAGAAG AAAGGTCCAACACCGAGACAACAAGAAGAACTTTGCCTTGTGTGTGGAGATAGGGCTTCAGGATATCATT ATAATGCTCTCACTTGCGAAGGTTGTAAAGGTTTTTTTCGTAGAAGCATCACAAAAAATGCGGTTTATCA GTGTAAATATGGAGATAGCTGTGAAATAGATATGTATATGAGGAGAAAGTGTCAAGAATGTAGATTAAAA AAGTGCCTTAGCGTGGGCATGAGACCTGAGTGCGTAGTACCAGAAATTCAATGCGAAGTTAAAAGGAGAG AAAAAAAAGCACAACGGGAAAAGGGCAAGCCAACGTCGACAACAAACGGTACGCCCGATTTAATAATGGC TGATGCACCTGTGATTAAAACGGAGCCTAATACTACTCAGTCACATATTGAGAAAACAGCGACTAACGGA GTTAAACCTATTAGTCCTGAACAAGAAGAACTTATTCATAGGCTTGTGTATTTTCAAAATGAATATGAAC AGCCCTCTGATGAAGATCTTAAAAGAATATCGAACACGCCTTCGGAAGGGGAGGATCAAAGCGATCTCAA TTTTAGACATATAACTGAAATAACAATACTAACTGTTCAGTTAATAGTAGAATTCGCCAAAAGATTGCCT GGGTTTGATAAATTATTAAGGGAAGACCAGATTGCCTTACTCAAAGCTTGCTCAAGCGAGGTTATGATGT

GGATAGTTATAGTTTAGCCGGAATGGGAGAAACTGTTGATGACTTATTAAGGTTCTGTCGACAGATGTAT GGCATGAAAGTAGACAATGCGGAGTATGCTTTGCTTACTGCCATTGTCATATTTTCAGAGAGACCATCTC TTATTGAAGGCTGGAAAGTGGAAAAAATTCAAGAAATATATTTAGAAGCTCTTAAGGTATATGTGGATAA TAGGCGGAAACCTCGATCGGGAACGATATTTGCAAAATTACTCTCCGTTTTGACGGAACTAAGAACTCTC GGAAATCTCAATTCCGAAATGTGCTTTTCTCTAAAACTTAAAAACAAAAAGCTGCCGCCATTCCTGGCCG AAATATGGGACGTGATTCCT

Sequence ID NO: 2

ATGGACGGCGGAGAAAGAGTGCTAAGTGTGGAGCTTGGAGGCCCTCAGTCACCGCTTGACATGAAACCAG ATACAGCAACTTTACTCGGAGGAAATTTCTCTCCAAACGGCGCTCCTAATAGTCCCAACTCCTTCAATAT GGGTCACAGTAGTTTACTTGGAAATAGTTCCAGTAATAAAATGACGTCCTACCCTCCAAATCATCCTCTT AGTGGTTCCAAGCATTTATGTTCCATTTGTGGCGATAGAGCTAGTGGCAAACATTATGGAGTTTATAGTT GTGAGGGATGCAAAGGTTTTTTTAAAAGAACAGTTCGAAAAGATCTCACTTATGCATGTCGAGAGGAAAG AAACTGTATTATTGATAAGAGGCAAAGAAATCGTTGTCAGTTTTGTCGTTACAATAAATGCCTGGCCATG GGAATGAAAAGAGAAGCAGTACAGGAAGAACGCCAGCGAACAAAAGAACGAGAACAAGGCGAAGTTGAAT CCTCGGGGACTATGCAAGCCGATATGCCTGTAGAAAGGATATTAGAAGCCGAAAAAAGGGTAGAATGTAA AGTTGAAAATCAAAATGAGTATGAAAATGCAGTTGCAAATATTTGCCAAGCCACAAATACTCAGTTATAT CAATTAGTGGAATGGGCTAAACACATTCCTCATTTTTCTTCGCTTCCAATTGAGGATCAAGTTTTGCTTC TTCGAGCAGGATGGAATGAACTACTAATAGCTGCATTTTCCCATAGGTCAGTAGAGGTTAGGGATGGAAT TGTTCTTGGAGCTGGAATTACAGTGCATCGGAATTCAGCTCATCAAGCGGGAGTAGGAACTATTTTTGAT AGAGTTTTGACTGAGCTAGTTGCTAAAATGAGAGACATGAACATGGACAGAACCGAATTGGGTTGTTTGC GGTCTATTATTTTATTTAATCCAGAAGTTCGAGGTTTAAAATCAGGTCAAGAAGTCGAACTTTTAAGGGA AAAGGTATATGCCGCCTTGGAAGAGTATACTCGCGTAACAAGACCCGAAGAACCAGGTCGATTTGCAAAA CTTCTTTTGAGACTTCCAGCTCTCAGATCCATTGGACTTAAATGTCTCGAACACCTTTTCTTTTTTCGAT TAATTGGTGACATACCGATTGACACATTTCTTATGGACATGCTGGGCTCTACCTCTGACTCA

Sequence ID NO: 3

ATGGGTCACAGTAGTTTACTTGGAAATAGTTCCAGTAATAAAATGACGTCCTACCCTCCAAATCATCCTC TTAGTGGTTCCAAGCATTTATGTTCCATTTGTGGCGATAGAGCTAGTGGCAAACATTATGGAGTTTATAG TTGTGAGGGATGCAAAGGTTTTTTTAAAAGAACAGTTCGAAAAGATCTCACTTATGCATGTCGAGAGGAA AGAAACTGTATTATTGATAAGAGGCAAAGAAATCGTTGTCAGTTTTGTCGTTACAATAAATGCCTGGCCA TGGGAATGAAAAGAGAAGCAGTACAGGAAGAACGCCAGCGAACAAAAGAACGAGAACAAGGCGAAGTTGA ATCCTCGGGGACTATGCAAGCCGATATGCCTGTAGAAAGGATATTAGAAGCCGAAAAAAGGGTAGAATGT AAAGTTGAAAATCAAAATGAGTATGAAAATGCAGTTGCAAATATTTGCCAAGCCACAAATACTCAGTTAT ATCAATTAGTGGAATGGGCTAAACACATTCCTCATTTTTCTTCGCTTCCAATTGAGGATCAAGTTTTGCT TCTTCGAGCAGGATGGAATGAACTACTAATAGCTGCATTTTCCCATAGGTCAGTAGAGGTTAGGGATGGA ATTGTTCTTGGAGCTGGAATTACAGTGCATCGGAATTCAGCTCATCAAGCGGGAGTAGGAACTATTTTTG ATAGAGTTTTGACTGAGCTAGTTGCTAAAATGAGAGACATGAACATGGACAGAACCGAATTGGGTTGTTT GCGGTCTATTATTTTATTTAATCCAGAAGTTCGAGGTTTAAAATCAGGTCAAGAAGTCGAACTTTTAAGG GAAAAGGTATATGCCGCCTTGGAAGAGTATACTCGCGTAACAAGACCCGAAGAACCAGGTCGATTTGCAA AACTTCTTTTGAGACTTCCAGCTCTCAGATCCATTGGACTTAAATGTCTCGAACACCTTTTCTTTTTTCG ATTAATTGGTGACATACCGATTGACACATTTCTTATGGACATGCTGGGCTCTACCTCTGACTCA

Sequence ID NO: 4

ATGGACGGCGGAGAAAG ATACAGCAACTTTACTCGGAGGAAATTTCTCTCCAAACGGCGCTCCTAATAGTCCCAACTCCTTCAATAT AGTGGTTCCAAGCATTTATGTTCCATTTGTGGCGATAGAGCTAGTGGCAAACATTATGGAGTTTATAGTT AAACTGTATTATTGATAAGAGGCAAAGAAATCGTTGTCAGTTTTGTCGTTACAATAAATGCCTGGCCATG

CCTCGGGGACTATGCAAGCCGATATGCCTGTAGAAAGGATATTAGAAGCCGAAAAAAGGGTAGAATGTAA AGTTGAAAATCAAAATGAGTATGAAAATGCAGTTGCAAATATTTGCCAAGCCACAAATACTCAGTTATAT CAATTAGTGGAATGGGCTAAACACATTCCTCATTTTTCTTCGCTTCCAATTGAGGATCAAGTTTTGCTTC TTCGAGCAGGATGGAATGAACTACTAATAGCTGCATTTTCCCATAGGTCAGTAGAGGTTAGGGATGGAAT TGTTCTTGGAGCTGGAATTACAGTGCATCGGAATTCAGCTCATCAAGCGGGAGTAGGAACTATTTTTGAT AGAGTTTTGACTGAGCTAGTTGCTAAAATGAGAGACATGAACATGGACAGAACCGAATTGGGTTGTTTGC GGTCTATTATTTTATTTAATCCAGAAGTTCGAGGTTTAAAATCAGGTCAAGAAGTCGAACTTTTAAGGGA AAAGGTATATGCCGCCTTGGAAGAGTATACTCGCGTAACAAGACCCGAAGAACCAGGTCGGTTTGCAAAA CTTCTTTTGAGACTTCCAGCTCTCAGATCCATTGGACTTAAATGTCTCGAACACCTTTTCTTTTTTCGAT TAATTGGTGACATACCGATTGACACATTTCTTATGGACATGCTGGGCTCTACCTCTGACTCA

5. Conceptually-translated amino acid sequences of BoEcRCl, BoUSP5, BoUSPIl and BoUSP15

The conceptually-translated amino acid sequence of BoEcRCl is 520 residues long as detailed in Sequence ID NO:5. BoUSP5, BoUSPIl and BoUSP15 are 394, 394 and 348 amino acids in length respectively as detailed in Sequence ID NOs: 6, 8 and 7 respectively. In each case the amino acid sequence displays all domains typical of a nuclear receptor. The sequences are shown below (refer also to the Sequence Listing).

Sequence ID NO: 5

M Y R G N S S T T K I G S G E D D L I L T Q V K S E P Q V H S P C K D M T S S G S S Q S S F

L F N T I S I N N K : C K T D E C S G N P S S P

G P P M G S A P L T S P G P H N Q Y T V I N N

G Y S S P M S S G S D P Y S P N G K L G R D D

L S P P G S L N G Y V D S S D A K K K K G P T P R Q Q E E L C L V C G D R A S G Y H Y N A L

C E G C K G F F R R S I T K N A V Y Q C K Y G S C E I D M Y M R R K C Q E C R L K K C L S V G

M R P E C V V P E I Q C E V K R R E K K A Q R E

K G K P T S T T N G T P D L I M A D A P V I K T

E P N T T Q S H I E K T A T N G V K P I S P E Q

E E L I H R L V Y F Q N E Y E Q P S D E D L K R

I S N T P S E G E D Q S D L N F R H I T E I T I

L T V Q L I V E F A K R L P G F D K L L R E D Q

I A L L K A C S S E V M M L R M A R R Y D V G S

D S I L F A N N Q P Y T R D S Y S L A G M G E T

V D D L L R F C R Q M Y G M K V D N A E Y A L L

T A I V I F S E R P S L I E G W K V E K I Q E I

Y L E A L K V Y V D N R R K P R S G T I F A K L

L S V L T E L R T L G N L N S E M C F S L K L

K N K K L P P F L A E I W D V I P

Sequence ID NO: 6

M D G G E R V L S V E L G G P Q S P L D M K P D

T A T L L G G N F S P N G A P N S P N S F N M G

H S S L L G N S S S N K M T S Y P P N H P L S G

S K H L C S I C G D R A S G K H Y G V Y S C E G

C K G F F K R T V R K D L T Y A C R E E R N C I

I D K R Q R N R C Q F C R Y N K C L A M G M K R

E A V Q E E R Q R T K E R E Q G E V E S S G T M

Q A D M P V E R I L E A E K R V E C K V E N Q N

E Y E N A V A N I C Q A T N T Q L Y Q L V E W

A K H I P H F S S L P I E D Q V L L L R A G W N

E L L I A A F S H R S V E V R D G I V L G A G I

T V H R N S A H Q A G V G T I F D R V L T E L V

A K M R D M N M D R T E L G C L R S I I L F N P

E V R G L K S G Q E V E L L R E K V Y A A L E E

Y T R V T R P E E P G R F A K L L L R L P A L R

S I G L K C L E H L F F F R L I G D I P I D T F

L M D M L G S T S D S

Sequence ID NO: 7

M G H S S L L G N S S S N K M T S Y P P N H P L

S G S K H L C S I C G D R A S G K H Y G V Y S C

E G C K G F F K R T V R K D L T Y A C R E E R N

C I I D K R Q R N R C Q F C R Y N K C L A M G M

K R E A V Q E E R Q R T K E R E Q G E V E S S G

T M Q A D M P V E R I L E A E K R V E C K V E N

Q N E Y E N A V A N I C Q A T N T Q L Y Q L V E

W A K H I P H F S S L P I E D Q V L L L R A G W

N E L L I A A F S H R S V E V R D G I V L G A G

I T V H R N S A H Q A G V G T I F D R V L T E L

V A K M R D M N M D R T E L G C L R S I I L F N

P E V R G L K S G Q E V E L L R E K V Y A A L E

E Y T R V T R P E E P G R F A K L L L R L P A L

R S I G L K C L E H L F F F R L I G D I P I D T

F L M D M L G S T S D S Sequence ID NO: 8

M D G G E R V L S V E L G G P Q S P L D M K P D

T A T L L G G N F S P N G A P N S P N S F N M G

H S S L L G N S S S N K M T S Y P P N H P L S G

S K H L C S I C G D R A S G K H Y G V Y S C E G

C K G F F K R T V R K D L T Y A C R E E R N C I

I D K R Q R N R C Q F C R Y N K C L A M G M K R

E A V Q E E R Q R T K E R E Q G E V E S S G T M

Q A D M P V E R I L E A E K R V E C K V E N Q N

E Y E N A V A N I C Q A T N T Q L Y Q L V E W

A K H I P H F S S L P I E D Q V L L L R A G W N

E L L I A A F S H R S V E V R D G I V L G A G I

T V H R N S A H Q A G V G T I F D R V L T E L V

A K M R D M N M D R T E L G C L R S I I L F N P

E V R G L K S G Q E V E L L R E K V Y A A L E E

Y T R V T R P E E P G R F A K L L L R L P A L R

S I G L K C L E H L F F F R L I G D I P I D T F

L M D M L G S T S D S

6. Characterization of various domains and helices of BoEcRCl, BoUSP5, BoUSPIl and BoUSP15 proteins

Based on the full length nucleotide and amino acid sequences of B. ovis BoEcRC 1 , BoUSP5, BoUSPI l and BoUSP 15 at sections 4 and 5, various domains and helices of the proteins have been defined in Tables 1 and 2.

Table 1 Positions in nucleotide and amino acid sequences corresponding to various domains and helices of B. ovis clone BoEcRCl.

Table 2 Nucleotide and amino acid sequences corresponding to various domains and helices of B. ovis USP clones BoUSP5, BoUSPl 1 and BoUSP15.

EXAMPLE 2 Construction of a baculovirus for co-expression of the ligand binding regions of BoEcR and BoUSP

Step Ia: Preparing the plasmid pBK-CMV-BoEcRnFF

A pair of primers, SEQ ID NO:22 and SEQ ID NO:23, were designed to permit the PCR amplification and subsequent cloning of the BOECR_DEF domain into the plasmid pBK-CMV. This plasmid was used for sequencing the amplified construct prior to subcloning into pFastBac Dual using the added 5'-SpeI/3'-NotI sites. Amplification of the construct was performed using the proofreading polymerase Ultrapfu II (Stratagene) in a Mastercycler gradient S PCR machine (Eppendorf) using the following cycling parameters: (94⁰C 2 mins) x 1; (94⁰C 30s, 6O⁰C 30s, 72⁰C 30s) x 25; (72⁰C 3 mins) xl. The polynucleotide sequence of the BOECR_DEF domain is presented in SEQ ID NO:24.

Step Ib: Preparing the plasmid pBK-CMV-BoUSPDEF

An identical protocol to that used in step Ia was employed to clone the BoUSPDEF domain into pBK-CMV using the primers detailed in SEQ ID NO:25 and SEQ ID NO:26 respectively. Here the added 5'-PstI/3'-KpnI sites were employed for cloning purposes. The polynucleotide sequence of the BoUSPDEF domain is presented in SEQ ID NO:27.

Step 2: Sub-cloning BOECRΠFF and BOUSPDFF into pFastBacDual

Firstly the pFastBac Dual shuttle vector was engineered to contain a 5'-hexa-His tag followed immediately by a Spel site under the control of the PH promoter. Secondly a 5'-FLAG tag was inserted upstream of a Pstl restriction site under the control of the PlO promoter. This engineered vector was then used for the sequential insertion of BoEcRDEF via the Spel/Notl sites followed by BoUSPDEF using the Pstl/Kpnl sites to yield a hexa-His-BoEcRDEF and FLAG-BoUSPDEF coexpression shuttle plasmid.

Step 3. Transposition of the pFastBacDual hexa-His-BoEcRPEF/FLAG-

BOUSPDEF expression cassette into the baculovirus chromosome.

Infective baculovirus was produced from the pFastBac Dual shuttle vector described above by transformation into DHlOBac competent E. coli. DHlOBac E. coli contain a helper plasmid expressing a Tn7 transposase and a Tn7 target site within the baculovirus chromosome. As the hexa-His-BoEcRoEF/FLAG-BoUSPoEF expression cassette is flanked by Tn7 donor sites in the pFastBac Dual shuttle plasmid, transposition of the complete expression cassette into the receptor site of the baculovirus chromosome is subsequently facilitated by the transposase-expressing helper plasmid. Selection of bacteria containing the recombinant baculovirus chromosome (bacmid) was performed by adding a chromagenic substrate to agar plates used to plate the DHlOBac cells post-transformation. Colonies devoid of the expression cassette express the lacZ gene that turns this substrate blue, whilst this enzyme is inactivated (by insertional mutagenesis) in colonies possessing the hexa-His- BOECRDEF/FLAG-BOUSPDEF expression cassette.

White colonies were subjected to multiple rounds of plating to ensure their purity prior to growth in liquid culture. Bacmid DNA was prepared using an alkaline lysis procedure in which attention was payed to minimisation of shear forces.

Mid-log phase Sf9 cells were transfected with bacmid DNA using standard protocols. The transfected cells were cultured at 26-28⁰C until signs of late-phase baculovirus infection were apparent, i.e. cessation of cell growth, increase in cell diameter and detachment. Primary virus was isolated from cultures by low speed centrifugation and harvesting the resulting supernatant. The primary virus stock was typically amplified once by infecting a further 50 ml shaker culture of mid-log phase Sf9 cells to yield a high titre viral culture form use in subsequent expression studies.

EXAMPLE 3

Production and purification of recombinant heterodimeric BOECRD_EF/BOUSPDEF ligand binding regions

Small scale production of recombinant heterodimeric BOECR_DEF-BOUSP_DEF ligand binding regions was performed by infection of 50 ml mid-log phase suspension cultures of Sf9 insect cells in Schott bottles using the amplified virus stock and maintenance in a 26-28⁰C shaker platform incubator. Insect cells infected with the virus engineered to express BOECR_DEF-BOUSP_DEF ligand binding regions were shown by western blotting to contain the expressed BOECR_DEF and BOUSP_DEF polypeptides tagged by N-terminal hexa-His and FLAG epitopes respectively (Figure 1).

A 5.1L culture of sf9 cells infected with the recombinant BOECR_DEF-BOUSP_DEF ligand binding domain bacmid yielded approximately 23 g cell paste. The heterodimer was affinity-purified from crude cell extracts using a nickel chelate resin (IMAC, immobilized metal affinity chromatograpy) to capture the hexa-His-tag of the recombinant EcR ligand binding region, followed by elution with an imidazole- containing buffer. The recovered fraction was subjected to further purification by size fractionation using a Superdex 200 (GE Healthcare) column. Final yields were estimated from measurements of protein concentration. Approximately 1 mg purified recombinant protein was obtained per gram of cells. Identity, integrity and purity of the receptor complex were monitored by SDS-polyacrylamide gel electrophoresis (Figure 2).

Ligand binding studies

Ligand binding was measured using a [³H]-ponasterone A binding assay. This involved trapping the heterodimeric receptor-[³H]-ponasterone A complex on glass fibre discs and washing away unbound steroid before solublizing the filters in scintillant and scintillation counting in a Packard Tri-carb scintillation analyser.

Prior to determining the Kd value of the B. ovis receptor heterodimer experiments were conducted to determine the fraction of the radiolabeled ponasterone A that could never be bound to the receptor heterodimer. This data enabled Kd value determination using a defined quantity of the crude cell receptor extract (0.00075mg/ml protein) and varying the concentration of [³H] -ponasterone A in the reaction (Figure 3).

These results demonstrated that the recombinant virus was expressing functional ligand binding regions that were able to heterodimerise and form a recombinant B. ovis ecdysone receptor complex that bound ecdysteroids with high affinity. Equilibrium binding studies using the model ecdysteoid radioligand [ H] -ponasterone A gave a Kd value of 0.76 ± 0.05 nM for BOECR_DEF-BOUSPD_EF (Figure 3). Comparing these data with purified preparations of other receptor ligand binding domain heterodimers cloned from other insects previously studied by this group suggests the B. ovis heterodimer has a low Kd value as determined by equilibrium binding studies that is comparable to that previously observed in Myzus persicae (Table 3). Overall these results suggest that the B. ovis recombinant proteins have a relatively high affinity for ponasterone A. Table 3: Comparison of specific activitiy and Kd values for recombinant ligand binding heterodimers (DEF regions) across ecdysone receptors from five different insect species.

EXAMPLE 4

Use of recombinant heterodimeric BOECR_DEF/BOUSP_DEF ligand binding region protein in a fluorescence polarisation competitive binding assay to screen a chemical library and characterise candidate insecticides

Titration of BOECR_DEF/BOUSP_DEF protein

Recombinant ligand binding heterodimeric BOECR_DEF/BOUSP_DEF protein was expressed and purified as described in Example 3 above and titrated against the fluorescent ecdysteroid conjugate employing fluorescence polarisation monitoring as follows.

Titrations involved mixing diluted recombinant sheep body louse heterodimeric BOECR_DEF/BOUSP_DEF protein stock with fluorescence polarisation (FP) assay buffer (5OmM sodium phosphate pH 7.4, 10OmM NaCl, and 0.5mg/ml of BSA) with 36nM fluorescent conjugate as described in WO 2005/05427. At the commencement of each experimental session the PHERAstar was adjusted to give a reading of lOOmP for a 200μl sample of 36nM fluorescent conjugate in FP assay buffer. Receptor dilutions covered the range 0.2 to 600μg/ml. For the BOECRDEF/BOUSPDEF receptor the optimal concentration was determined to be lOOμg/ml.

Assay mixtures were allowed to reach equilibrium by incubating overnight at 4°C and then equilibrating at room temperature for 3 hours before reading the polarisation values at 25°C.

Competitive Inhibition Assays

Competitive inhibition assays involved mixing diluted competitive inhibitor stock with a fixed concentration of receptor (lOOμg/ml) and fixed concentration of fluorescent conjugate (36nM) in FP assay buffer. Competitive inhibitor concentrations covered the range 3 to 300,00OnM. As noted above, at the commencement of each experimental session the PHERAstar was adjusted to give a reading of lOOmP for a 200μl sample of 36nM fluorescent conjugate in FP assay buffer.

Figure 4 shows the competitive inhibition curve for the ecdysteroid 20- hydroxyecdysone and two small molecules RH5992 and Halofenozide. At low competitor concentrations (~370mP) all of the fluorescent conjugate is bound to the receptor. At high competitor concentrations none of the fluorescent conjugate is bound to the receptor. Note: high competitor concentrations may depress the polarisation value to below that of the free fluorescent conjugate.

The data can be used to determine the concentration of competitor at which 50% of the fluorescent conjugate is not bound to the receptor (IC₅₀).

Screens

The purified BOECR_DEF/USP_DEF protein was used to test three thousand compounds from the CSIRO compound library for binding to the BOECRDEF/USPDEF protein.

Significant hits included a family of methylene lactams (shown in Tables 4, 5 and 6) that were characterised further using the fluorescence polarisation competitive binding assay determined above to determine IC₅₀ values against the recombinant sheep body louse B. ovis ECRDEF/USPD_EF protein and the corresponding protein from the sheep blowfly Lucilia cuprina as recorded in Table 7.

Table 4

Table 5

Table 6

Table 7 IC₅₀ values for binding of exemplified compounds to the ecdysone ligand binding domain of Bovicola ovis and Lucilia cuprina

Bovicola ovis insecticidal testing

Method 1

The mortality testing was performed using the method of Levot & Hughes (1990). Lice were removed from donor sheep using a vacuum pump. Two 60 x 60mm cloth squares were prepared for each insecticide dilution. Starting at the centre of the cloth, 1 mL of each dilution was pipetted onto each cloth rectangle and allowed to dry at room temperature for 24 h. Control cloths were prepared with solvent only. Cloths were placed into labelled glass tubes and live lice were placed into the tubes. Tubes were sealed and incubated at 34⁰C for 16 h. Lice were then removed from the tubes and their condition tabulated.

Method 2

A modification of the method of Gough et al (2002) was used to assess the action of the compounds of the invention on B. ovis. Lice were collected from infested sheep. Bioassays were performed in multi-welled tissue culture plates. Test compound was added to a diet of epidermal scrapings from sheepskin and that was added to the wells. The nymphal lice were added to the wells. Wool treated with the test compounds was then added to the well and the plates incubated in sealed humidity jars containing saturated ammonium chloride (70% RH) and maintained at 36⁰C. Control wells have the wool treated with the solvent only. Mortality of the louse population was assessed at 72 h and again after 9 days. Insecticidal activity was determined for compounds selected on the basis of low IC₅₀ values for binding to the recombinant heterodimeric BOECRDEF/BOUSPDEF ligand binding region protein of B. ovis and is recorded in Table 8.

Table 8. Activity of exemplified compounds in whole insect Bovicola ovis screening, expressed as LD₅Q (ppm) or % kill @ ppm

EXAMPLE 5

Engineering and utilisation an RNAi specific for the Spodoptera frugiperda ecdysteroid receptor (EcR) gene: the basis for a new bioassay to estimate specific induction of insect pest EcRs by ecdysteroids and other ligands

The present inventors have developed a method of suppressing the expression of the endogenous ecdysone receptor in cultures of cells derived from the lepidopteran insect Spodoptera frugiperda (SfEcR). The inventors further demonstrate that such cells are suitable for the development of an assay to estimate the specific induction of an introduced EcR from the dipteran insect Lucilia cuprina by the ecdysteroid, ponasterone A.

The inventors chose to target the least conserved of the EcR from Spodoptera frugiperda, the D-domain, in order to minimise any unwanted interaction with the D- domains of other insect species in the assays. A novel fragment of the EcR D-domain from Spodoptera frugiperda was cloned and its sequence shows good agreement with that reported later by Chen et al (2002). Both the sense and antisense arms of the EcR D-domain were cloned by PCR as described below and inserted into an RNAi expression plasmid. Sf9 cells were subsequently co-transfected with the RNAi expression plasmid and a Lucilia cuprina EcR expression plasmid as described below.

Experimental PCR cloning of the EcR D-domain

A 631 bp fragment containing the D domain of the Spodoptera frugiperda ecdysteroid receptor (EcR) gene was reverse transcribed and PCR amplified from Sf9 cell RNA using forward primer reDBDf 5^I-GCCTCGGGGTACCATTATAAC-3^I (SEQ ID NO:28), and a partially degenerate reverse primer, reLBDr 5¹- GGNAGNCC(C/T)TTNGCGAA(C/T)TC -3' (SEQ ID NO:29), and blunt-end cloned into pCR2.1-TOPO (Invitrogen) to construct pTOPO8 DNA SEQUENCE SfgDNAlF (SEQ ID NO:30): for the insert in new plasmid pTOPO8

AAAGCTTCTCCAAATGACNTTGAAATTGAACGGTAATTGGTATGACCAAGGGTACGAAGC CTTGTACAANNTTTTTTTTTTTTTTTAACATTTTAATGGGTCGACGGTTTTGCCCCGCTA TCTCNCCACATAGGCAGATTACGGTCGCATTCGAGTTTTATTCAGTGATCTGAATTAAAT GGGCATATTTATTCTCGGGTCGACAGTGAAGGTTGGCGGAGACGTACGGAGATGTCCGAT AGGCGACTGTGACTTGTGAAGCAGACGCCCTGCAGACAGCTATTGTGACGACTAACTGTC TGTTCATGCACGCGCAGCTCATAACAACCTCGGCACAATGCGCCAATTTAAAGCTGAATT GGCACATTCGTGGGCGAGCCACACAAGGGCTGTGTATGTGTAGATCGTGTAGTAATATCT AGGTTAGCTACGCACGTGACCTAGTTGCACTAAAAGTCTTAAGAGAACATTTTTGCTGCT GCATTAGTTAGGATTTGTAACCGTCTGGTGGGCGTGAATTCGGTATTTATCGTGCTTTAA ATATATTGAGTACAGAGTCCTGTTTCGCATGAAACAATGGATTTCAGAGTTATAAGATAT TTATCACACTTTGCTGTCACACCAACGGTATCGTACCTTTACACCCTTCACATGTGAGCG CATTGTAATGGTACCCCGAGGCAGAATTCCGAAGGGCGAAANCTGCAGATATCCATCANA CTGNCGGCCGCTCGAGCATGCNGCTAGAGGGCCAAATTCGAGGAAGNNNANTCTNNAGAN

TTNCNTGNTATTCNTNNNAGANNNCN (SEQ ID NO:30)

PCR cloning of sense and anti-sense arms of the SfEcR D-domain

Two fragments were synthesised and and used as primers in PCR reaction 1. The fragments were as follows:

(a) Fragment SEB 160, comprising the sequence 5'-

CGCGGATCCGAGGCCCGAGTGTGTGGTG-3' (SEQ ID NO:31) was synthesised with a BamHl tail; (b) Fragment 36TAGAT, comprising the sequence 5'-

GGAAGCCCTAGATGGCCGTCTTCATCCGACTGCCAG-3' (SEQ ID NO:34) was synthesised with an Sβl tail.

Two fragments were synthesised and and used as primers in PCR reaction 2. The fragements were as follows: (c) Fragment SEN 160, comprising the sequence 5'- GAATGCGGCCGCTAGGCCCGAGTGTGTGGTG-3' (SEQ ID NO:32) was synthesised with a Notl tail;

(d) Fragment 34ATCTA, comprising the sequence 5'- GGAAGGCCATCTAGGCCGTCTTCATCCGACTGCCAG-S' (SEQ ID NO:33) was synthesised with an Sβl tail;

1) PCR: SEB 160 vs 36TAGAT using SfEcR gDNA plasmid pT0P08 as template to produce fragment 123B3 (SEQ ID NO:35).

2) PCR: SEN 160 vs 34ATCTA using SfEcR gDNA plasmid pTOPO8 as template to produce fragment 567N8 (SEQ ID NO:36).

Fragments 123B3 (SEQ ID NO.35) and 567N8 (SEQ ID NO:36) were then cloned into the TOPO plasmid. This resulted in the production of two new plasmids, pTOPO- 123B3 and pTOPO-567N8, each containing a sense-oriented 635-bp DNA fragment derived from the D domain of the Spodoptera frugiperda ecdysteroid receptor (SfEcR) gene but with a Sβl tail at the 5' end of the insert in pTOPO-123B3 and with a Sβl tail at the 3' end of the insert in pTOPO-567N8.

DNA SEQUENCE 123B3

NAANNGGNCAAGTGAGCGCAACGCAATNAATGTAAGTTAGCTCACTCATTAGGCACCCCAGGCTTTTACA CTTTATGCTTCCGGCTCGGTATGTTGTGTGGAATTGTGAGCGGATAACAATTTCACACAGGAACCAGCTA TGACCATGATTACGCCAAGCTTGGACCGAGCTCGGATCCACTAGTAACGNCCGCCAGTGTGCTGGAATTC GCCCTTGNAAGGCCTAGATGGCCGTCTTCATCCGACTGCCAGGTCTGTGTGACTCTTTTTAGGTCCTCCT CTGACGGCTGTTCGTAGCCTTCTTGGTACCAGACCAGCCTCGCTATTAGGGACTTCTGGTTGGCGGTGAG GGGGGGCACATTCTTCAGCCTGTTCTGTTCCATTAGCTTCTCATTCAGGAACCGCGGCACCACCTCGTGA ATTCTTGCAGCCTCTGGGGGCGGTGGATCACATTGCATAATGGGAGGCATGTGATCATCTACTGTCGTTG

CGAGC (SEQIDNO:35) DNA SEQUENCE 567N8

GNNGAGCGCNAACGNAATTAATGTGAGTTTAGGCTCACCTCATTNAGGCACCCCCAGNCTTTNACACTTT

TATGNTTCNGGGCTTNGTATGTTTGTGTGNAAATTGTAAGCGGATAACAATTTCACNCAGGAAACAGTTA

TGNCCATGATTACGCCAAGCTTGGTACCGAGTNGGATCCACTAGTAACGGCCGCCAGTGTGCTGGAATTC GCCCTTGAATGCGGCCGCTAGGCCCNAGTGTGTGGTGCCAGAAAACCAGTGTGCAATNAAACGGAAANAG

AAAAAGGCNCAAAGGGAAAAAGACAAGTTGCCCGTCAGTACAACGACAGTAGATGATCACATGCCTCCCA

TTATGCAATGTGATCCACCGCCCCCAGAGGCTGCAAGAATTCACGAGGTGGTGCCGCGGTTCCTGAATGA

GAAGCTAATGGAACAGAACAGGCTGAAGAATGTGCCCCCCCTCACCGCCAACCAGAAGTCCCTAATAGCG

AGGCTGGTCTGGTACCAANAAGGCTACGAACAGCCGTCAGAGGAGGACCTAAAAAGAGTCACACAGACCT GGCAGTCGGATGAAGACGGCCTAGATGGCCTTCCAAGGGCGAATTCTGCAGATATCCATCACACTGGCGG

CCGCTCGAGCATGCATCTAGAGGGCCCAATTCGCCCTATAG (SEQ ID NO:36)

Construction of the RNAi expression plasmid containing the forward and reverse arms of the EcR D-domain

Expression plasmid pIEl-3 (Novagen) was subjected to restriction enzyme digestion with BgHl + Notl and treated with calf intestinal phosphatase (CIP). Plasmid pTOPO-

123B3 was subjected to restriction digestion with BamHI [37⁰C; Promega Buffer B;

75-100%] + Sfil [5O⁰C; Promega Buffer B; 100%] to release fragment 123B3 and plasmid pTOPO-567N8 was subjected to restriction digestion with Sfil [5O⁰C; Promega

Buffer B; 100%] to release fragment 567N8. Fragment 567N8 was then subjected to further restriction enzyme digestion with Notl [37⁰C; Promega Buffer D; 100%].

Promega Buffer B [50% NaCl] was adjusted to Promega Buffer D [100% NaCl] by adding 5M NaCl. pIEl-3 (Novagen) that had been treated with BgHl and Notl as described above, fragment 123B3 flanked by BamHI + Sfil restriction sites and fragment 567N8 flanked by Notl +Sfil sites were subjected to a three-way ligation. This resulted in a construct containing a sense-oriented 718-bp head-to-tail concatenation of the DNA fragment derived from the D domain of the Spodoptera frugiperda ecdysteroid receptor (SfEcR) gene in new plasmid pIRl. DNA SEQUENCE 718duplex (SEQ ID NO:37): for the insert in new plasmid pIRl.

GATCTGCGGCCGCTAGGCCCNAGTGTGTGGTGCCAGAAAACCAGTGTGCAATNAAACGGAAANAGAAAAA GGCNCAAAGGGAAAAAGACAAGTTGCCCGTCAGTACAACGACAGTAGATGATCACATGCCTCCCATTATG CAATGTGATCCACCGCCCCCAGAGGCTGCAAGAATTCACGAGGTGGTGCCGCGGTTCCTGAATGAGAAGC TAATGGAACAGAACAGGCTGAAGAATGTGCCCCCCCTCACCGCCAACCAGAAGTCCCTAATAGCGAGGCT GGTCTGGTACCAANAAGGCTACGAACAGCCGTCAGAGGAGGACCTAAAAAGAGTCACACAGACCTGGCAG TCGGATGAAGACGGCCTAGATGGCCGTCTTCATCCGACTGCCAGGTCTGTGTGACTCTTTTTAGGTCCTC CTCTGACGGCTGTTCGTAGCCTTCTTGGTACCAGACCAGCCTCGCTATTAGGGACTTCTGGTTGGCGGTG AGGGGGGGCACATTCTTCAGCCTGTTCTGTTCCATTAGCTTTTCATTCAGGAACCGCGGCACCACCTCGT GAATTCTTGCAGCCTCTGGGGGCGGCGGATCACATTGCATAATGGGAGGCATGTGATCATCTACTGTCGT TGTACTGACGGGCAACTTGTCTTTTTCCCTTTGTGCCTTTTTCTCTTTCCGTTTCATTGCACACTGGTTT TCTGGCACCACACACTNGGGCCTTGGATC

Co-transfection of Sf9 cells with the RNAi expression plasmid and Lucilia cuprina EcR expression plasmid

Transient assay of RNAi activity

Sf9 (Spodoptera frugiperda) insect cells were maintained as described in Graham et al, (2007). Transient transfections were conducted using DOTAP (Boehringer- Mannheim) at 15 μg/ml, essentially as described previously (Hannan and Hill, 1997). Replicate 96 well dishes of subconfluent Sf9 cells were cotransfected with (1) pIRl or unmodified pUC18 at 0.1 μg/ml, (2) pIVLM (a pIEl-3 derived plasmid for expression of the modified Lucilia cuprina EcR gene, VPLcEcR Plasmid pVPLcEcR (Hannan and Hill, 2001) was subjected to restriction digestion with Kpn 1+ Xbal. The excised VPLcEcR fragment was filled with Klenow and ligated into pIEl-3 (Novagen) which had been subjected to restriction enzyme digestion with Pmel and treated with calf intestinal phosphatase (CIP).) or unmodified pUC18 at 0.1 μg/ml and (3) pMK (an expression plasmid for the reporter gene β-galactosidase) at 1 μg/ml. For induction experiments, the ecdysone analogue ponasterone A (a gift from Dr Denis Horn) was added to cells at 1 μM, 6 h after transfection. For control experiments, cells were treated only with carrier ethanol. β-galactosidase in extracts of cells were measured 72 h after transfection as described previously (Hannan and Hill, 1997). RESULTS:

Table 9 Selective silencing of SfEcR in tissue culture cells.

All wells contain reporter gene plasmid pMK (1000 ng/ml).

The results show that in the absence of the ecdysteroid, ponasterone A (experiments 1 , 3, 5 and 7) there was no induction by either the endogenous SfEcR or of the introduced LcEcR of β-galactosidase expression.

In the presence of the RNAi specific for SfEcR (experiments 3, 4, 7 and 8) there was specific inhibition of induction by the endogenous SfEcR of β-galactosidase expression.

In the presence of the RNAi specific for SfEcR there was no specific inhibition of induction by the introduced LcEcR (experiments 5, 6, 7 and 8) of β-galactosidase expression. Generation of stably transfected cell lines.

For generation of stably transfected Sf9 cells, pIRl plasmid was transfected with pIEl- 3-neo (plasmid with neomycin (geneticin) resistant marker). Transfected cells were selected with geneticin (500 mg/ml).

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

All publications mentioned in this specification are herein incorporated by reference. Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia before the priority date of each claim of this application.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

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Claims

1. An isolated polynucleotide, comprising a nucleotide sequence which encodes, or is complementary to a sequence which encodes, an EcR polypeptide of a B. ovis ecdysone receptor, wherein the polynucleotide comprises a nucleic acid sequence that is at least 70% identical to the sequence set forth in SEQ ID NO: 1.

2. An isolated polynucleotide, comprising a nucleotide sequence which encodes, or is complementary to a sequence which encodes a USP polypeptide of a B. ovis ecdysone receptor, wherein the polynucleotide comprises a nucleic acid sequence that is at least 70% identical to the sequence set forth in any of SEQ ID NOs:2, 3, or 4.

3. An isolated polynucleotide comprising a nucleotide sequence which encodes, or is complementary to a sequence which encodes, a B. ovis EcR polypeptide, wherein the polypeptide comprises an amino acid sequence that is at least 70% identical to the sequence set forth in SEQ ID NO:5.

4. An isolated polynucleotide, comprising a nucleotide sequence which encodes or is complementary to a sequence which encodes a USP polypeptide of a B. ovis ecdysone receptor, the polypeptide comprising an amino acid sequence at least 70% identical to the sequence set forth in any of SEQ ID NOs: 6, 7, or 8.

5. An isolated polynucleotide which encodes an EcR polypeptide, wherein the polynucleotide has a sequence that hybridises under high stringency conditions to the sequence set forth in SEQ ID NO:1, or a sequence fully complementary thereto, wherein high stringency conditions are a hybridisation and/or wash carried out in less than the ionic strength of 5 x SSC, 0.05M sodium phosphate, 42% formamide, 0.1% SDS at a temperature of at least 38⁰C and a washing step of at least 38⁰C in 2 x SSC.

6. An isolated polynucleotide which encodes a USP polypeptide, wherein the polynucleotide has a sequence that hybridises under high stringency conditions to the nucleotide sequence set forth in any of SEQ ID NOs: 2, 3, or 4, or a sequence fully complementary thereto, wherein high stringency conditions are a hybridisation and/or wash carried out in less than the ionic strength of 5 x SSC, 0.05M sodium phosphate, 42% formamide, 0.1% SDS at a temperature of at least 38⁰C and a washing step of at least 38⁰C in 2 x SSC.

7. An isolated EcR polypeptide of a B. ovis ecdysone receptor, comprising the amino acid sequence set forth in SEQ ID NO: 5 or a sequence at least 70% identical to the sequence set forth in SEQ ID NO:5.

8. An isolated USP polypeptide of a B. ovis ecdysone receptor, comprising an amino acid sequence set forth in any of SEQ ID NOs:6, 7, or 8 or a sequence at least 70% identical to the sequence set forth in SEQ ID NOs:6, 7, or 8.

9. A genetic construct comprising a polynucleotide of any one of Claims 1 to 6, operably linked to a promoter sequence.

10. A recombinant cell comprising a polynucleotide of any one of Claims 1 to 6 and/or the genetic construct of Claim 9.

11. A transgenic animal, microorganism, plant or aquatic organism containing one or more cells of Claim 10.

12. An isolated fragment of the B. ovis EcR or USP polypeptide of Claims 7 or 8.

13. A fragment of Claim 12, which comprises one or more functional domain regions.

14. Use of a molecule selected from one or more of the group consisting of:

(a) a polynucleotide of any one of Claims 1 to 4;

(b) a polypeptide of Claim 7;

(c) a polypeptide of Claim 8;

(d) a polynucleotide encoding a polypeptide of Claim 7;

(e) a polynucleotide encoding a polypeptide of Claim 8;

(f) a fragment of Claim 12;

(g) a fragment of Claim 13 ; and

(h) a polynucleotide encoding a fragment of Claim 12 or Claim 13, as a gene switch.

15. A method of identifying a modulator of a B. ovis ecdysone receptor, the method comprising the steps of:

(a) assaying the binding of a reporter ligand to a B. ovis ecdysone receptor polypeptide of Claim 7 and/or Claim 8 in the presence of a potential modulator;

(b) assaying the binding of a reporter ligand to the ecdysone polypeptide without said potential modulator; and

(c) comparing the binding of the reporter ligand in the presence of the potential modulator to the binding of the reporter ligand in the absence of the potential modulator,

wherein a difference in the level of binding indicates that the potential modulator is a modulator of B. ovis ecdysone receptor.

16. A method of screening for a candidate compound for its ability to interact with a B. ovis ecdysone receptor of Claim 7 and/or Claim 8, or ligand binding domain (LBD) thereof, the method comprising the steps of:

(a) incubating with a B. ovis ecdysone receptor or LBD thereof with a candidate compound; and

(b) measuring the level of binding of the candidate compound to the ecdysone receptor or LBD thereof.

17. A method of Claim 16, which is in a competitive inhibition format.

18. A method of Claim 16 or Claim 17, wherein the B. ovis ecdysone receptor or LBD thereof and candidate compound are further incubated with a fluorescent compound as described in WO2005/005427.

19. A method of modulating the expression of a B. ovis EcR and/or USP target gene in a cell, tissue or organ, the method comprising the step of introducing into the cell, tissue or organ a double stranded nucleic acid molecule in which one of the strands is substantially identical to the nucleotide sequence of the EcR and/or USP target gene or region thereof of B. ovis.

20. A method of conferring resistance or immunity to B. ovis in an animal, the method comprising the step of introducing into said animal a double stranded nucleic acid molecule in which one of the nucleic acid strands is substantially identical to the nucleotide sequence of the EcR and/or USP target gene or region thereof of B. ovis.

21. A method of treating an animal having a B. ovis infestation, comprising the step of administering to the animal a double stranded nucleic acid molecule in which one of the strands is substantially identical to the nucleotide sequence of the EcR and/or USP gene or region therein of B. ovis.

22. A method of silencing the expression of an endogenous B. ovis ecdysone receptor protein (EcR) and/or USP in a cell, tissue or organ, the method comprising the step of introducing into said cell, tissue or organ a double stranded nucleic acid molecule in which one of the strands is substantially identical to the nucleotide sequence of the EcR and/or USP target gene or region thereof of B. ovis.

23. An animal having a genome which comprises a heterologous nucleic acid, wherein one of the nucleic acid strands is substantially identical to the nucleotide sequence of the EcR and/or USP gene or region thereof of B. ovis, the nucleic acid molecule encoding both sense and antisense RNA strands which when the nucleic acid is transcribed, the sense and antisense strands associate to form a hairpin structure.

24. A method of modulating the expression of a B. ovis EcR and/or USP in an insect cell, the method comprising the steps of:

(a) selecting a nucleotide sequence which is substantially identical to the sense and antisense strands of a B. ovis EcR and/or USP target gene or a region thereof;

(b) producing a synthetic gene comprising the nucleotide sequence;

(c) introducing said synthetic gene to the cell; and

(d) expressing the synthetic gene in the cell for a time and under conditions sufficient for translation of the mRNA product of the target gene to be modified.

25. A method of Claim 24, wherein the synthetic gene encodes both sense and antisense RNA strands which when the nucleic acid is transcribed, the sense and antisense strands associate to form a hairpin structure.

26. An animal of Claim 23 or method of Claim 25, wherein the hairpin structure comprises at least 19 nucleotides.

27. An animal of Claim 23 or method of Claim 25, wherein the hairpin structure comprises 19 to 30 nucleotides.

28. A double stranded RNA molecule comprising at least 19 nucleotides and having at least 90% sequence identity to the sequence shown in one or more of SEQ ID NO: 1 , SEQ ID NO:2, SEQ ID NO:3 or SEQ ID NO:4.