WO1999063052A2 - Bigenic mouse models and assays to identify proliferation and differentiation regulators - Google Patents

Bigenic mouse models and assays to identify proliferation and differentiation regulators Download PDF

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Publication number
WO1999063052A2
WO1999063052A2 PCT/US1999/012417 US9912417W WO9963052A2 WO 1999063052 A2 WO1999063052 A2 WO 1999063052A2 US 9912417 W US9912417 W US 9912417W WO 9963052 A2 WO9963052 A2 WO 9963052A2
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bigenic
gene
human mammal
hedgehog
animal
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PCT/US1999/012417
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French (fr)
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WO1999063052A3 (en
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David H. Rowitch
Andrew P. Mcmahon
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The President And Fellows Of Harvard College
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Publication of WO1999063052A3 publication Critical patent/WO1999063052A3/en

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    • AHUMAN NECESSITIES
    • A01AGRICULTURE; FORESTRY; ANIMAL HUSBANDRY; HUNTING; TRAPPING; FISHING
    • A01KANIMAL HUSBANDRY; AVICULTURE; APICULTURE; PISCICULTURE; FISHING; REARING OR BREEDING ANIMALS, NOT OTHERWISE PROVIDED FOR; NEW BREEDS OF ANIMALS
    • A01K67/00Rearing or breeding animals, not otherwise provided for; New or modified breeds of animals
    • A01K67/027New or modified breeds of vertebrates
    • A01K67/0271Chimeric vertebrates, e.g. comprising exogenous cells

Definitions

  • the present invention relates to bigenic mouse lines, cells of the mouse lines, and methods of use to identify agents that modulate the activity of cell proteins involved in tissue proliferation and differentiation.
  • Improved animal model systems would be desirable for studying the developmental consequences of a lethal phenotypes in the embryo in utero and for providing a screening system for identifying novel therapeutic agents that may be used to correct the resultant abnormalities in the adult animal.
  • hedgehog proteins that play an important role in development are the class of regulatory molecules identified as hedgehog proteins.
  • the hedgehog family of proteins which was first identified in Drosophila and subsequently observed in mammals, is expressed in different organizing centers which can initiate signals that pattern neighboring tissues.
  • hedgehog proteins play an important role in the development of the central nervous system including forebrain development.
  • hedgehog genes and hedgehog receptor genes have been correlated with several human diseases (Hammerschmidt et al.. 1997). These include cancers such as brain tumors including medulloblastoma and memngioma; skin cancers such as basal cell carcinoma: and breast cancer.
  • a transgenic non-human mammal substantially all of whose cells contain a non- viral regulatory DNA sequence linked to a recombinant hedgehog gene introduced into the mammal or an ancestor of the mammal at an embryonic stage.
  • a transgenic non-human mammal can be the mammal having an endogenous coding sequence substantially the same as a coding sequence of the recombinant hedgehog gene
  • the mammal is a rodent, for example, a mouse
  • the regulatory sequence comprises a UAS sequence (SEQ LD NO:l).
  • the invention provides a bigenic non-human mammal, substantially all of whose cells contain a non- viral regulatory DNA sequence linked to a recombinant hedgehog gene sequence: and a transcriptional activator sequence, introduced into the mammal or an ancestor of the mammal at an embryonic stage.
  • the embodiment can be a bigenic mammal having an overexpressed vascular system in the central nervous system, for example, the mammal is an embryo, and is capable of a fespan, for example, ot 9 dpc, of 12.5 dpc. of 18.5 dpc, of parturition, of one month post- partu ⁇ tion, of three months post-partu ⁇ tion. or of one year post partuntion.
  • a further embodiment of the invention is the bigenic non-human mammal wherein the transcriptional activator gene is GAL4 Further, the transcriptional activator gene is regulated by a tissue specific promoter, for example, the tissue specific promoter is a wnt promoter or a col II promoter In a further embodiment of the bigenic non-human mammal, the transcnptional activator gene is regulated by an inducible promoter, for example, the inducible promoter is regulated by a fusion of GAL4 protein and a second protein, for example, the second protein is activated by binding an RU486 mitepnstone molecule
  • a further embodiment ot the invention is a bigenic non-human mammal for use as a model for disease, for example, the disease is cancer, for example, a cancer of the breast, skin, prostate, kidney, lung, and central nervous system
  • the cancer is a primitive neuroectodermal tumor, or the cancer is a medulloblastoma
  • a further embodiment of the invention provides an isolated cell of a bigenic non- human mammal obtained from the above bigenic mammal The isolated cell of the bigenic non-human mammal is selected from the group consisting of an embryonic-stem cell, a tumor cell, a nerve cell, and a vascular cell
  • Another embodiment of the invention is a transgenic non-human mammal having an insertion mutation of an Ihh gene, for example, the insertion can comprise a selectible marker, and the insertion can comprise a deletion of the Ihh gene
  • an embodiment of the invention provides an isolated population of cells selected from the group consisting of a transgenic non-human mammal, and its bigenic progeny
  • an embodiment of the invention is a method ot identifying the effect of misexpression of a target transgene in a signal transduction pathway that includes a hedgehog protein, in a progeny animal, comprising, (a) forming a first transgenic animal having a first transgene encoding a transcnptional activator of a eukaryotic species different from the animal; (b) forming a second transgenic animal having a second transgene comprising the target gene and having a recognition sequence for the transcnptional activator that is located upstream of the target gene, (c) mating the first and the second transgenic animals to form a bigenic animal, and (d) causing the target gene to be misexpressed in the animal
  • a further aspect of this method of identifying the effect of misexpression of a target transgene provides the transgenic animals formed from an animal
  • a further embodiment of the invention is a method of assaying for a temporal requirement for the presence of a hedgehog protein on progression of a disease, comprising:
  • Another embodiment of the invention is method of assaying for a temporal requirement for the presence of a hedgehog protein during progression of the disease in the bigenic animal in the disease model line, wherein the treatment comprises administration of an agent selected from the group consisting of an inhibitor of cholesteroid biosynthesis, an anti-hedgehog antibody, and a sterol analog.
  • An embodiment of the invention further provides a method for determining therapeutic efficacy of an agent, comprising: (a) forming a bigenic mouse according to the method above, wherein the misexpressed target gene is a hedgehog gene; (b) administering the agent to the mouse; and (c) determining therapeutic efficacy of the agent.
  • Another method provides that (b) further comprises administering the agent to the mouse in a pharmaceutical carrier at an effective dose.
  • (c) further comprises comparing lifespans of the bigenic mouse of (b) with the bigenic mouse of (a), for example where the bigenic mouse in (a) is an embryo.
  • a further embodiment of the invention is a method of obtaining an expanded population of neural stem cells from a subject, comprising: treating a neural stem cell from the subject with a hedgehog protein, so that proliferation of the stem cell provides an expanded population of neural stem cells.
  • the hedgehog protein is sonic hedgehog protein.
  • the subject has a condition selected from the group consisting of Parkinson's disease, Alzheimer's disease, and spinal cord injury. Thus the condition can be treated by administration to the subject of a sample of the expanded cell population.
  • An embodiment of the invention provides a method for inactivating an Ihh gene in a non-human mammal, comprising: (a) constructing a recombinant vector carrying an Ihh insertion mutation; (b) injecting an embryonic stem cell with the vector; and (c) implanting the stem cell into an adult mammal.
  • the vector in (a) carries a deletion of exon 1 of the Ihh gene.
  • FIG. 1 is a schematic representation of a signaling pathway of which exogenously supplied hedgehog functions to effect changes in nuclear gene transcription.
  • HH hedgehog protein is shown as an extracellular protein that binds a receptor composed of the products of genes indicated PTC (iox patched), and SMO (smoothened).
  • PTC iox patched
  • SMO smoothened
  • a cytoplasmic protein complex comprising microtubule protein and Cos-2 (costal-2) and Fu (Fused)
  • FIG. 2 shows a schematic drawing of transgenes WEXP-GAL4, UAS-/ ⁇ cZ and
  • Plasmid pWEXP-GA 4 is a driver vector that comprises full-length GALA, which was cloned into the WEXP2 expression vector under control of the Wnt-1 promoter.
  • the reporter transgenic construct a vehicle vector carrying a UAS-ZACZ, was constructed to utilize the Wnt-1 promoter and 5 copies of the UAS.
  • Plasmid pUAS-S was constructed with full-length mouse Shh cDNA target gene cloned into expression vector WEXP3C. Wnt-1 regulatory sequences were then replaced by 5 copies of the UAS.
  • the arrows indicate sites of hybridization for each of the oligonucleotide primers used in genotyping the various transgenic lines and progeny as described in the Examples.
  • Figure 3 is a diagrammatic representation of the strategy for forming mouse
  • FIG. 4 shows the GAL4/U AS bigenic system for misexpression of proteins in transgenic (Tg) mice, wherein (a) shows structure of the WEXP-GA 4 transgene; (b) shows structure of the UAS-lacZ transgene and expression of ⁇ -galactosidase in the Wnt- 1 pattern in a GAL4II S-lacZ 10.5 dpc (days post coitum) embryo with black arrows indicating expression observed in the midbrain-hindbrain junction and dorsal spinal cord as a blue color; and (c) shows structure of the UAS-Shh (sonic hedgehog) transgene and phenotype of a GAL4/UAS-Shh 10.5 dpc embryo.
  • Ectopic expression of the neural tube floorplate marker, HNF3 ⁇ is indicated by arrows and occurs in analogous positions to lacZ expression under wnt-1 in the brain (b).
  • Figure 5 shows data obtained from the GAL4IU AS system for providing ectopic gene expression in the developing CNS.
  • Panels A-D show whole mount histochemical analysis of target reporter ⁇ -galactosidase activity in transgenic mouse embryos.
  • A Lateral view showing pattern of lacZ expression under control of Wnt-1 regulatory sequences.
  • B, C Lateral views of 10.5 dpc and 12.5 dpc bigenic Wnt-1-Gal4 X UAS-lacZ embryos showing expression pattern of lacZ (arrow indicates roofplate expression in the spinal cord).
  • D Transverse (top) and bisected (bottom) views of lacZ expression in the rostral spinal cord of a bigenic embryo at 18.5 dpc.
  • Panels E-J show morphological analysis of wild-type (left) and Wnt-1 -GAL4 X UAS-Shh bigenic (right) litter mates at: E: 10.5 dpc (arrow indicates anterior neural tube defect); F: 12.5 dpc. Panels G-J show analysis at 18.5 dpc. Lateral views are shown of (G) wild-type and (H) bigenic embryos. Note tissue mass protruding from midbrain which covers cerebral hemispheres (arrow). Panel I: Dorsal view of bigenic embryo showing hyperplastic spinal cord which protrudes from the back covered by a thin epithelial membrane.
  • UAS-Shh Tg Wnt-1 -GAL4 X UAS-Shh bigenic mice, wherein (a) shows a dorsal view of a 18.5 dpc UAS-Shh Tg embryo demonstrating overgrowth of the brain and spinal cord, and increased vasculature in the dorsal CNS where Shh is ectopically expressed: and (b) shows a transverse section at the level of the forelimb of an 18.5 dpc UAS-Shh Tg embryo. The region dorsal tissue in the spinal cord was observed to be hyperplastic. with hydromyelia (gross enlargement and distension) of the spinal cord central canal.
  • FIG 7 shows the result of misexpression of Shh in the dorsal CNS. Ectopic expression of Shh in the midbrain ventralizes the midbrain. inducing ectopic expression of Shh target gene Hnf-3 ⁇ in the dorsal CNS. The whole mount was analyzed by Hnf-3 ⁇ immunostaining.
  • Figure 8 shows the targeting strategy used to generate Ihh mouse knock-out mutants by homologous recombination with a vector in which the first exon at the Ihh locus is deleted, thereby generating a null allele.
  • Hedgehog A hedgehog protein includes a member of a family of cell proteins found in invertebrates such as Drosophila and in vertebrate eukaryotes. including humans, which are essential to tissue pattern formation that distinguish the variety of tissues formed during embryonic development.
  • a hedgehog protein molecule is post-translationally modified by addition of a cholesterol molecule.
  • Figure 1 shows the hedgehog signal transduction pathway and the concomitant effects on nuclear transcription of binding of a hedgehog molecule to a cell receptor.
  • Hedgehog proteins are secreted factors and determinants of dorsal- ventral polarity in the central nervous system (CNS), being essential for induction and subsequent differentiation of ventral cell types. Hedgehog proteins act via signal transduction. Sonic hedgehog appears to induce hypervascularization, hyperplasia and in some situations, neoplasia, a property that is shared with Indian hedgehog protein which appears however to reduce vascularization. Neoplasia is linked not only to hedgehog gene expression but also in humans to the loss of the patched protein receptor ( Figure 1). Patched is a membrane protein which down regulates transcription of the genes encoding transforming growth factor (TGF) ⁇ and Wnt families, and transcription of its own gene.
  • TGF transforming growth factor
  • Patched has been implicated in oncogenesis, including development of basal cell carcinoma and of syndrome (Gorlin. (1987) Medicine 66:98-113), which includes f ibromas of the ova ⁇ es and heart, cysts of skin and jaw and mesentery, meningiomas and medulloblastomas.
  • the present invention provides a binary transgenic (bigenic) system in which protein expression exemplified by expression of hedgehog is regulated by a promoter that is not normally recognized in a mammalian cell (described herein by the term "extra- mammalian" promoter; Figures 2,3).
  • the promoter is in turn activated by a transcnptional activator protein, expression of which is under the control of a tissue specific enhancer.
  • a binary transgenic system provides the opportunity to activate otherwise silent transgenes in progeny obtained from a simple genetic cross, because the transcnptional activator is maintained in one line of mouse, while the silent target gene under control of an extra-mammalian promoter is maintained in a second mouse line. Only when the two lines are crossed does abnormal expression of the target gene occur (A. Brand et al. (1993) Development 118:401-415: Ornitz et al. (1991) Proc Natl Acad Sci. USA 88:698-702). Ormtz et al.
  • MMTV mouse mammary tumor virus
  • hedgehog as used here and in the claims shall include the hedgehog protein from any organism, for example from an invertebrate or a vertebrate organism, and shall include any polypmo ⁇ hic vanant or mutation, including a substitution mutation, a deletion, or an insertion mutation that retains the developmental and differentiation functions of dorsoventral patterning and prohferative function of the wild type hedgehog protein.
  • the term shall further include hedgehog proteins of all members of the hedgehog family, for example, Some hedgehog. Indian hedgehog, desert hedgehog, zebra hedgehog, tiggywinkle. and other members ot the hedgehog family.
  • the hedgehog protein of the invention shall include a hedgehog protein synthesized from a hedgehog-encoding DNA sequence that is at least 70% homologous, at least 807c homologous, at least 90% homologous, at least 95% homologous, and at least 98% homologous to the sonic hedgehog protein which retains the functions of the hedgehog protein.
  • the hdegehog protein includes a protein encoded by a nucleic acid that hybridizes under stringent conditions as defined herein with a portion of a gene encoding a hedgehog protein.
  • the term shall further include any chemical analog or derivative composition of a hedgehog protein, including a peptidomimetic which maintains the hedgehog functions as described in the examples herein.
  • Hedgehog is a secreted protein that functions as modified by addition of a cholesterol moiety as an intercellular signalling system.
  • Hedgehog signalling can be interrupted by one of several chemical treatments of an animal or a cell in culture, for example, by addition of an anti-hedgehog monoclonal or polyclonal antibody, by addition of an inhibitor of cholesterol biosynthesis such as lovastatin, pravastatin and simvastatin (Merck, Rahway, NJ), or by addition of the steroidal alkaloid cyclopamine (Incardona, J. et al.(1998) Devel. 125:3553-3562).
  • Cyclopamine has been shown to exert teratogenic effects (for example, cyclopia) due to direct antagonism of sonic hedgehog signal transduction.
  • Administration of these agents to a bigenic animal that is an embodiment of the invention, particularly bigenic animals that are formed in an animal line that is an animal model of a disease, at times during embryonic development, can provide a method of assaying for a temporal requirement for hedgehog protein during the progression of a disease.
  • the term “protein” includes the terms “polypeptide,” and “peptide.”
  • a "regulatory DNA sequence” is used herein to describe a sequence of DNA to which one or more proteins can bind, so that transcription of a DNA sequence can be initiated or increased or decreased.
  • the regulatory DNA sequence can be a promoter, an operator, or an enhancer site.
  • a regulatory DNA sequence can also be a terminator site, for example, a tract of several adenyl residues at the end of a gene (polyA).
  • a UAS is an upstream activating sequence that can bind a GAL4 protein, such binding resulting in an increase in transcription of DNA downstream from that site.
  • An enhancer site can also increase transcription from downstream DNA.
  • the UAS of the invention (SEQ ID NO 1) is known to function from a location that is upstream of the target gene
  • a "promoter is a DNA sequence with ability to bind to an RNA polymerase molecule to initiate transcnption Extent of binding is influenced by promoter strength, and by protein tactors that interact with an enhancer site at or adjacent to the promoter
  • a regulatory DNA sequence can be located within a protein coding region of a gene, however, the protein coding region of all or a part ot a gene shall be referred to herein as a gene
  • the engineered vectors used herein generally select a site upstream of a gene for regulation of transcription of the gene, however it is within the scope of the invention to locate a regulatory sequence within the protein coding region of a gene
  • a "recombinant protein' is a protein that is synthesized in vivo from a transgene or a recombinant gene, so that it can be distinct both in cell location and in regulation of expression from a naturally occurnng homologous gene, if any, within the cell
  • the recombinant proteins that are used in embodiments of the present invention can carry mutations, including without limitation, substitutions, chain terminations, deletions and insertions
  • a recombinant protein can be encoded by DNA that is homologous to the gene encoding the protein, providing that the function of the protein is retained
  • a "bigenic ' animal is the result of a cross between two different transgenic animals, such that a 1 1 1 1 Mendehan progeny ratio is observed, the ratio describing progeny which consist of one wild type, one ot each of the single hemizygous transgenic animals, both of which may have phenotypes identical to the wild type, and one bigenic progeny animal
  • Figure 2 shows
  • an "embryo" of an animal is the term used to describe the progeny trom the zygote stage until partuntion
  • An "inducible” gene is capable of being expressed in response to addition to cells or administration to an animal of an exogenous chemical or drug Transcription mediated by a steroid-receptor like protein to which the chemical RU486 (metipnstone; Roussel- Uclaf , Hoechst) has been bound is inducible by administration to an animal or addition to cells in culture of this chemical
  • a "fusion" protein is a non-naturally occurnng protein obtained from genetic manipulation of two or more genes encoding respectively amino acid sequences derived from two or more different proteins, to create a fusion gene having the two or more proteins tranlated in the same reading frame
  • the GALA protein can be fused to all or a portion of another protein, for example to confer inducibility. such that mitepnstone (RU486) can be added to cell medium or administered to a transgenic or bi
  • Homology' refers to sequence similanty between two peptides or between two nucleic acid molecules Homology can be determined by companng a position in each sequence which may be aligned for pu ⁇ oses of companson When a position in the compared sequence is occupied by the same base or amino acid, then the molecules are homologous or identical at that position A degree of homology between sequences is a function of the number of matching or identical positions shared by the sequences
  • a "gene" encoding for a hedgehog protein for example a sonic hedgehog or an Indian hedgehog protein within the scope of an embodiment of the invention if it encodes a protein that has substantially the same function of the wild-type hedgehog protein.
  • a hedgehog gene that is within the scope of the present invention may have a mutation, for example without limitation, a point mutation resulting in an amino acid substitution or chain termination, a deletion, an insertion, it the encoded protein retains hedgehog function
  • a gene that is homologous to a hedgehog gene that encodes a protein capable of confernng a normal hedgehog phenotype is within the scope of the embodiment of the invention
  • Preferred regulatory sequences encode a UAS sequence which is at least 764% homologous (having 13 homologous and 4 nonhomologous nucleotide residues), more preferably at least 82 3% homologous (having 14 homologous and 3 nonhomologous nucleotide residues), more preferably at least 88 3% homologous (having 15 homologous and 2 nonhomologous nucleotide residues), and even more preferably at least 94 1% homologous (having 16 homologous and 1 nonhomologous nucleotide residues).
  • a GAL4 protein which is an embodiment of the invention is one compnsing an amino acid sequence which retains the functions of binding to a UAS and activating transcription, and has an amino sequence which is at least 60% homologous, more preferably 70% homologous and most preferably 80%. 90%, or 95% homologous with the wild type GALA amino acid sequence (Brand, A et al , 1993)
  • nucleic acid which hybndizes under high stnngency conditions to a ' probe '.
  • a ' probe ' which is a nucleic acid which encodes a portion of an inserted transgene sequence as shown in SEQ ID Nos 2, 3, and 4
  • a suitable probe is at least 12 nucleotides in length, is single-stranded, and is labeled, for example, radiolabeled or fluorescently labeled
  • Appropnate moderate conditions of stringency of conditions of formation of double-strandedness which promote DNA hybridization for example, 6 0 x sodium chlonde/sodium citrate (SSC) at about 45°C.
  • SSC sodium chlonde/sodium citrate
  • suitable stringency conditions include selecting the salt concentration in the wash step trom a low stringency of about 2 0 x SSC at 50°C, and then using a wash of a high stringency condition, of about 0 2 x SSC at 50°C
  • the temperature in the wash step can be increased from low stringency conditions at room temperature, about 22°C, to high stnngency conditions at about 65°C
  • a GAL4 protein which is an embodiment of the invention is encoded by a gene which hybndizes to the wild type GAL4 gene under stnngent conditions
  • Tm can be calculated in degrees C as 2(number of A+T residues) + 4(number of C+G residues)
  • Hybndization or annealing of the probe to the nucleic acid being probed should be conducted at a temperature lower than the Tm, e g . 15 °C. 2 ⁇ °C. 25 °C or 30°C lower than the Tm.
  • the effect of salt concentration (in M of NaCl) can also be calculated, see for example. Brown. A., "Hybndization” pp. 503-506, in The Encyclopedia of Molec. Biol, J. Kendrew. Ed., Blackwell, Oxford (1994).
  • an "animal model" for a disease is an animal treated with a chemical composition, or a mutant animal, that displays symptoms identical or similar to a human subject having the disease.
  • the mouse mutant Patched for example, is an animal model of cancer.
  • Animal models for human cancers can be formed using the bigenic animals that are embodiments of the present invention, for example, misexpression of a hedgehog protein causing ectopic proliferation of nerve stem cells in the CNS can be an animal model of a brain tumor
  • a "therapeutic effect ' resulting from addition to a cell culture or administration to an animal of a chemical or a protein agent can be observed as a prevention or a remediation of symptoms of disease, in companson to cells or animals not receiving the chemical.
  • a therapeutic effect is a demonstration of effectiveness of an agent to cause a phenotype which is more normal than a phenotype observed from ectopic expression of a hedgehog protein, for example, in the bigenic animals of the invention
  • an "effective dose” is that amoung of exogenously added or administered, or in vivo generated Shh protein or other hedgehog protein, or other chemical entity, capable of achieving a successful endpoint of a therapeutic effect
  • Bigenic transgenic systems may be formed as follows: a first or "carrier" vector is made having a regulatory sequence placed adjacent to and upstream of a target gene of interest.
  • the regulatory sequence is recognized by an extra-mammalian regulatory protein, for example the extra-mammalian upstream sequence may be a regulatory sequence from yeast (for example, UAS) or from he ⁇ es virus (for example, LPE).
  • a second or "dnver" vector contains DNA encoding a gene for a transcnptional activator wherein the expression of this gene is capable of tnggenng the regulatory sequence in front of the target gene on the first earner vector, for example yeast transcriptional activator (GAL4). or he ⁇ es transcnptional activator (VP16)
  • GAL4 yeast transcriptional activator
  • VP16 he ⁇ es transcnptional activator
  • a tissue specific regulatory sequence may be used to promote the expression of the transcriptional activator such as wnt-1 enhancer and promoter which target gene expression to cells of the nervous system ( Figures 2, 4).
  • the Wnt-1 enhancer is ideally suited for directing gene expression in the roofplate of the CNS (Echelard et al., Development (1994) 120:2213-2224), and it has been used to misexpress chicken Shh in transgenic mice (Echelard et al., Cell (1993) 75: 1417-1430); however in studies by Echelard et al. (1993, 1994) the CNS malformation resulting from Wnt-1 control of Shh expression was lethal, and no transgenic embryos survived to birth.
  • tissue specific regulatory sequences may be used, including those that target bone (for example collagen type ⁇ enhancer), skin (keratin- 14 enhancer), kidney (pax-2 enhancer), and CNS (nestin, neuron specific enolase. transerythrin). These tissue specific promoters may in turn be regulated by inducible enhancer sequences.
  • An example of an inducible system utilizes RU486 which binds to a membrane receptor protein and is translocated to the nucleus (Wang et al., Nature Biotechnology (1997) 15:239-243) and therefore has particular utility for regulating expression of hedgehog protein.
  • an inducible system having utility in this invention is a tetracycline regulated system in which the tet repressor from Escherichia coli is fused to the He ⁇ es simplex virus viral protein 16 (VP16) transcriptional activation domain (Schockett et al. Nature Biology (1997) 15:217) such that addition of tetracycline induces VP16-promoter regulated expression.
  • VP16 He ⁇ es simplex virus viral protein 16
  • the present invention uses a regulated gene expression system to cause selective expression of hedgehog proteins, for example Sonic hedgehog protein (Shh), and also to express lacZ as a convenient marker ("reporter”) system, well known in the art, to monitor the activity of enhancers, promoters and transcriptional activator sequences.
  • lacZ reporter is used as a control in parallel with studies on hedgehog gene expression ( Figures 2-4).
  • Each of two types of vectors is introduced into a mouse to yield two types of lines of novel transgenic mice, each having a normal phenotype.
  • the target gene is not expressed until the two mouse strains are cross bred and progeny embryos are obtained.
  • the progeny of the cross can express the target gene, and therefore the phenotype observed in the progeny of the cross is different from that of each of the two parental lines.
  • the extra-mammalian transcriptional activator exemplified by GALA is not normally present in mouse cells, genes with lethal effects on the embryo can be stably maintained in transgenic mice under control of the extra-mammalian promoter (exemplified by UAS).
  • An embodiment of the invention uses this novel system to determine the effects of synthesis of abnormal amounts of regulatory proteins during embryogenesis
  • the bigenic mouse provides a system for analyzing in vivo vasculanzation of the brain, and an assay system to identify novel factors to enhance or diminish such vasculanzation.
  • an embodiment of the invention provides explant cultures of the hypervasculanzed tissue, which when cultured in vitro, provide a system for analysis of translocation of drugs across the blood brain barrier, tor identifying agents that affect translocation, for analyzing hyperplastic including neoplastic properties of the cells, and for analyzing agents that modulate or reverse the hype ⁇ lasia.
  • An embodiment of the invention provides a system in which for the first time abnormal activation of hedgehog signal transduction in specific neural cells can be associated with generation of neoplasia.
  • over-expression of Shh in the brain unexpectedly caused the surface of the mouse brain, usually smooth, to become wrinkled, an appearance normally associated with higher animals such as cats and humans. Consequently, the bigenic mouse models of the invention can be used to study regulation of brain size and density as well as cellular composition and thereby provide a system for testing therapeutic agents that can reverse the neuronal deficit seen in patients with neurodegenerative diseases.
  • the expanded zone of neural growth have cell precursors may also be a useful tissue for obtaining neural stem cells tor therapeutic purposes.
  • the bigenic animal system of the present invention is further suited for analysis of medulloblastoma.
  • an inducible RU486-GAL4 transcriptional activator that relies on Pax-2 enhancer to target hedgehog protein expression to the cerebellum ensures that over-expression occurs after early brain development. This system avoids the abnormal development of the early brain that is observed in response to over-expression of hedgehog, and consequently enables formation of a cerebellum prior to activation of the regulatory protein.
  • the bigenic mouse model of the invention provides a means for modulating hedgehog gene expression for analyzing the effect of varied amounts of hedgehog, and an assay system for testing chemicals and cells as agents for therapeutic benefit for patients having abnormal hedgehog protein or suffering from the effect of abnormal levels of hedgehog.
  • An object of an embodiment of the present invention is the use of methods of assay with the bigenic animal and cell lines, mutants, vector constructs, and methods of the present invention, to identify, for example, the effect of misexpression of a target transgene.
  • the misexpression of the transgene can be that of a reporter transgene, for example, a reporter gene on a vector that causes a color development such as lacZ as described in the examples herein.
  • Methods of screening including synthesis of chemical libraries and culture and assay of screen organisms in sterile multi-well plastic dishes containing for example 96 or 354 wells per dish, robots for delivery of samples to each well using devices such as automated multi-pipeters, and for processive manipulation of each dish, and for computerized reading of growth as optical density or production of light absorbant material at a given wavelength in each well, are well known to those of ordinary skill in the art of design of screens of chemical agents.
  • Such methods can be used to monitor potential inhibition of proliferation of tissues or cells of a bigenic animal in the presence and absence of a vanety of chemical entity agents, and to record the extent of proliferation ot cells and/or tissue differentiation in the presence and absence of the candidate chemical, and of control animal or cells under these conditions.
  • an agent for example a hedgehog composition or analog or peptidomimetic, identified by an embodiment of the invention that is a method ot assay can be subjected to a pre-clinical trial in an animal or a subject.
  • a "pharmaceutically acceptable carrier” includes any and all solvents, dispersion media, e.g , human albumin or cross-linked gelatin polypeptides, coatings, antibactenal and antifungal agents, lsotonic, e.g., sodium chloride or sodium glutamate, and abso ⁇ tion delaying agents, and the like that are physiologically compatible.
  • the carrier is suitable for oral, topical, intravenous, intramuscular, subcutaneous, parenteral, spinal or epidermal administration (e.g., by injection or infusion)
  • the active compound can be coated in a material to protect the compound from the action of acids and other natural conditions that can inactivate the compound.
  • Routes of administration also include, without limitation, lntraute ⁇ ne, intraartal, intrathecal. intracapsular, intraorbital, intracardiac, mtradermal, intrapentoneal, transtracheal, subcutaneous, subcuticular, intraarticular, subcapsular, subarachnoid, intraspinal. epidural and intrastemal injection and infusion.
  • Administration of an agent to a maternal parent of an embryo progeny animal is within the scope of the invention.
  • Dosage regimens are adjusted to provide the optimum desired response, e.g., a therapeutic response, such as restoration of a normal CNS prohferative response.
  • a therapeutic response such as restoration of a normal CNS prohferative response.
  • a single bolus can be administered, several divided doses can be administered over time or the dose can be proportionally reduced and administered over a time period by infusion, or increased, as indicated by the exigencies of the therapeutic situation
  • a suitable daily dose of a composition of the invention will be that amount of the composition which is the lowest dose effective to produce a therapeutic effect. Such an effective dose will generally depend upon the factors described above.
  • Examples 1-3 describe materials and methods used in preparation of a bigenic mouse system which is capable of expressing a lethal mutation in the hedgehog protein.
  • Example 1 describes construction of the vectors used in producing the parental transgenic mice, the genotype characterizations of which are described in Example 2. Procedures for analysis of mouse tissues by in situ hybridization and immunostaining are given in
  • Example 3 Methods of measuring cell proliferation and apoptosis are given in Example 4, and the results observed show that misexpression of sonic hedgehog from 9.5 to 18.5 dpc caused hyperplasia of the embryonic CNS when Shh was under GAL4IU AS control.
  • a lethal phenotype was observed in Example 5 to result from micro-injection of the Wnt-1 enhancer-mouse Shh transgene into mouse embryos.
  • Example 6 the phenotypes of progeny from a cross of parental lines was examined, and 25% (the bigenic progeny) were found to have a lethal phenotype characterized by the presence of an open neural tube in the midbrain region.
  • Example 7 describes construction of a knock-out mutation of Indian hedgehog is constructed.
  • the lethal phenotype of mouse embryos carrying an Indian hegehog null mutation was found to be due to a defect in formation of blood or blood supply.
  • Example 1 Construction of vectors for forming transgenic parents of bigenic animals An overall strategy of the embodiment of the invention comprising bigenic animals is first constructing each of the two transgenic parents, then crossing them as shown in Figures 2-3 to obtain bigenic animals in the Mendelian proportion of one- quarter of the progeny. Vectors were constructed so that one transgenic parent contains a driver vector which expresses an extra-mammalian transcnptional activator, and the other parent contains a vehicle vector capable of expressing a target gene in the presence of the transcnptional activator.
  • the Wnt-1 expression vector pWEXP-2 (Echelard et al., 1993) was digested with Nrul and treated with calf intestine alkaline phosphatase (CLAP).
  • the plasmid pGaTB was digested with HindUI and Fspl to release a DNA fragment encoding GAL4; this was end-filled with the Klenow fragment of DNA polymerase I and cloned into the pWEXP-2 vector.
  • the transgene was purified from vector sequences by digestion with A tll. (b) Constructing a vector carrying a hedgehog gene regulated by an extra- mammalian promoter.
  • pUAS Shuttle was constructed as follows. A Kpnl and BglTL fragment of plasmid XB3 was replaced with an ohgonucleotide polylinker encoding an Xhol site. This construct was digested with Notl and Kpnl, and was treated with CLAP. To this vector a Notl-Kpnl fragment of pUAS-/ ⁇ cZ, compnsing five copies of UAS, was added, generating plasmid pUAS-Shuttle. Finally, pUAS-Shuttle was digested with Xhol and BgJR and was treated with CIAP.
  • a Sall-BgRl fragment of pWEXP-3C was isolated and cloned into the vector, creating plasmid pUAS-S z z.
  • the transgene was punfied from vector D ⁇ A by digestion with Sail and BglU prior to micro-iniection.
  • D ⁇ A sequencing of these constructs was carried out using both the ABI dye terminator and the di-deoxy chain termination methodologies.
  • the genotyping determinations for pWEXP2-GAL4, pWEXP3C-5/z/z. and UAS-Shh mice and embryos employed an upstream oligonucleotide primer from exon 1 of untranslated sequence of Wnt-1 pner (5 -TAA GAG GCC TAT AAG AGG CGG-3'. SEQ ID NO: 2), which primes approx 60 bp upstream of the Wnt-1 translational initiation site: a downstream primer from within GALA (5'-ATC AGT CTC CAC TGA AGC-3', product size ca.
  • the plasmid XB3 (Echelard et al.. 1994) was digested with Notl and treated with CLAP
  • the pentamer array of UAS sequences from plasmid pUAST was amplified by PCR using primers that inco ⁇ orated Notl and Eagl recognition sequences.
  • the PCR products were digested and cloned into the XB3 vector to produce pUAS-/ ⁇ cZ.
  • the transgene was punfied from vector D ⁇ A by digestion with Sail, and was micro-injected into control mouse embryos to confirm the specificity of gene expression under the tissue specific enhancer.
  • transgene pWEXP3C-S/z/ ⁇ was punfied from vector D ⁇ A by digestion with Sail, and was micro-injected into control mouse embryos to determine that the Shh gene encoded the correct functional protein and caused the lethal phenotype.
  • Example 2 Production and genotyping of transgenic mice
  • Transgenic mice were generated by micro-injection of linear D ⁇ A fragments obtained from vector D ⁇ A into pronuclei of B6CBAF1/J (C57BL/6J x CBA J) zygotes as descnbed (Echelard et al., 1994).
  • the transgenic mouse line Wnt-1/GALA was produced by injection of transgene pWEXP2-GA 4. All transgenic mice were made following standard protocols as descnbed in "Manipulating the Mouse Embryo " B Hogan, 2nd Ed Cold Spring Harbor Press, Cold Spring Harbor, NY (1994).
  • G 0 Founder (G 0 ) transgenic mice were identified by Southern blot of E ?/?I-digested genomic DNA using probes for GAL4 (line W ⁇ XP2-GAL4) or lacZ (lines UAS-/ ⁇ cZ and UAS-Shh; probes described in Rowitch et al.. 1999, Devel Neurosci., in press, inco ⁇ orated herein by reference). Subsequent genotyping of UAS-/ ⁇ cZ transgenic embryos or mice by PCR was carried out as described in Echelard, et al. (1994).
  • Genotyping of WEXP2-GA 4 and UAS-Shh transgenic embryos or mice was performed using the upstream primer described supra (SEQ LD NO:2) from exon 1 of the untranslated sequence of Wnt-1 and the downstream primer described supra (SEQ LD NO:3) from within GALA or mouse Shh (SEQ ID NO:4) , respectively.
  • PCR conditions were as described in Echelard et al. (1994).
  • transgenic mice carrying any one of the vectors that are embodiments of the invention exhibited normal wild-type phenotypes in comparison to parental mice which had not received a transgene.
  • Example 3 Whole mount and section histology, in situ hybridization and immunohistochemistry for assay of misexpression
  • embryos were harvested between 9.5-18.5 dpc, dissected in phosphate buffered saline (PBS) and fixed overnight in 4% paraformaldehyde.
  • PBS phosphate buffered saline
  • Whole mount in situ hybridization was carried out per standard lab protocols.
  • Embryos for histologic analysis, BrDU incorporation, and in situ hybridization were fixed in either Bouin's or 4% paraformaldehyde overnight or up to 24 hrs, embedded in paraffin wax and sectioned at 6-7 ⁇ m. Sections were stained with hematoxylin-eosin or toluidine blue.
  • BrDU (Sigma. St. Louis, MO) inco ⁇ oration was measured using a dose of 50 ⁇ g/kg injected intraperitoneally into pregnant mice exactly 3 hrs before sacrifice at 12.5 and 18.5 dpc. Embryos were fixed either in Bouin ' s or 4% paraformaldehyde and sectioned as described above. Dividing cells that had incorporated BrDU were identified using monoclonal IgG (Becton-Dickenson) and immunoperoxidase staining (Vector Labs; Burlingame, CA) employing FTTC-tyramide (NEN; Boston, MA).
  • Apoptotic death was measured by techniques established in the art, for example, the TUNEL procedure (Gavrieli. Y. et al.(1992) J.Cell Biol. 119:493-501) on adjacent sections, and electron microscopy. Reagents TdT and biotinylated-16dUTP were obtained from (Boehringer-Mannheim).
  • Shh was placed under GAL4IU AS regulation which gives consistent expression of Shh at ectopic locations such as the roofplate of transgenic mouse embryos.
  • the phenotype observed to result from Shh misexpression included hype ⁇ lasia of the dorsal CNS, and activation of Hedgehog transcriptional targets, e.g., Patched and Gli, and was observed in embryos from 9.5-18.5 dpc ( Figures 4-6).
  • Hedgehog transcriptional targets e.g., Patched and Gli
  • Hype ⁇ lastic tissues were predominantly nestin-positive, however, dispersion of tissue samples into cell culture medium yielded differentiation of cells into neurons, astrocytes and oligodendrocytes. Markers of ventral progenitor populations in the spinal cord were expressed with an altered pattern as a consequence of ectopic Shh expression.
  • Example 5 The effect of a lethal mutation in hedgehog protein
  • the yeast transcription factor GALA was expressed in the dorsal CNS under the control of the Wnt- 1 enhancer (WEXP-GA 4: Figure 3).
  • a second transgenic line (UAS-lacZ) directed expression of reporter gene ⁇ -galactosidase (lacZ), under control of UAS ( Figure 3).
  • UAS-lacZ heterozygous animals were mated with WEXP-GAL heterozygotes, 25% of progeny embryos showed ⁇ -galactosidase expression in the Wnt-1 pattern of tissues and cells.
  • the progeny capable of expressing ⁇ -galactosidase in the Wnt-1 pattern were otherwise normal in phenotype.
  • Example 5 The effects of sonic hedgehog misexpression in the embryonic CNS in bigenic mouse progeny
  • Shh-Tg the gross phenotype of progeny of the UAS-Shh x WEXP-GAL4 cross
  • Fig.5 hydromyelia
  • the phenotype was consistent among the progeny observed, indicating 100% penetrance of the Shh gene, i.e., that the phenotype and the genotype of animals coincided in every case, and was observed in at least 50 Shh-Tg progeny embryos.
  • Example 6 Construction of an Indian hedgehog loss of function mutation
  • the Indian hedgehog gene Lhh has been thought to be expressed in the yolk sac of visceral endoderm from 8 dpc (Farrington, S., et al. (1997) Mech.Dev. 62:197-211), in the gut epithelium lining mid-and hindgut from 10.5 dpc and in the hindstomach and columnar epithelium of inestine and rectum (Bitgood, M. et al. (1995) Dev. Biol. 172:126-138), in tooth dental lamina from 9.5 dpc (Kronmiller, J. et al.
  • Lhh is an essential gene, i.e., whether a potential lethal phenotype is demonstrated by an Lhhllhh homozygotes
  • a targeting vector ( Figure 8) based on the structure and restriction sites of the Lhh gene was constructed.
  • the targeting vector carries a DNA with a deletion of the El of Lhh replaced by neo. and having DNA encoding TK following E2 and E3 of the Lhh gene.
  • mice carrying the markers of the targeting vector Following successful isolation of mice carrying the markers of the targeting vector, probes for distinguishing the wild type and insertion knock-out mutant Lhh genes by digestion and analysis of Xhol and Ncol fragments were used, and the predicted sizes of Xhol and Ncol fragments that hybridized with the probes and that were used to identify each genotype, are also shown in Figure 8. Mice carrying the Lhh knockout gene, and heterozygous for the normal Lhh gene were thus constructed.
  • Example 7 Crossing knock-out heterozygotes to determine the effects of an Indian hedgehog loss of function mutation among homozygous progeny
  • mice carrying the knockout mutation constructed in the previous example were bred, and embryos having each of a homozygous wild type genotype, a heterozygous genotype, and a homozygous mutant Ihh genotype were harvested from among all embryos as a function of time after the matings.
  • Embryonic death of Ihh homozygotes was determined to be due to a defect in formation of the blood or the blood supply.
  • a further aspect of the phenotype was a reduction in the size of the main blood vessels observed in the null double Ihh mutant embryos compared with normal embryos (homozygotes and heterozygotes) at 11 5 dpc.
  • Bigenic mice were formed by crossing a first parental mouse line having a driver vector with the collagen II enhancer (col II: Metsarante. M. et al. (1995) Dev. Dyn. 204:202-210) used to express GAL4, with a second mouse line having a earner vector with UAS upstream of Ihh. Expression in the embryonic progeny of this cross was compared to that of progeny from crossing the first parent with each of UAS-/ ⁇ cZ and UAS-Shh. The data show that expression of GALA under control of the collagen LI enhancer restricts expression to chondrocytes, and further that Lhh expression can be specifically activated in chondrocytes.

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Abstract

Transgenic stable animal lines having genes essential for development under regulation of extra-mammalian transcription signals, such that bigenic combinations cause ectopic expression of the transgene in one or more specific tissues, and methods of use of bigenic animals and cells, are provided.

Description

USE OF BIGENIC MOUSE MODELS AND ASSAY SYSTEMS TO IDENTIFY AGENTS THAT REGULATE PROLIFERATION AND DIFFERENTIATION
Technical Field
The present invention relates to bigenic mouse lines, cells of the mouse lines, and methods of use to identify agents that modulate the activity of cell proteins involved in tissue proliferation and differentiation.
Background In developmental biology, a dominant lethal mutation that occurs in germ cells or is introduced into the fertilized egg using transgenic methodology can result in death of the embryo early in gestation. The death of the embryo is problematic with regard to analysis of the defect because it is not possible to form breeding colonies of these mutants. A similar problem can arise when a transgenic mouse is made in which a protein is expressed in abnormal amounts or in unusual tissues so as to give rise to a lethal phenotype. Consequently, a new transgenic manipulation is required each time such effect in the protein is to be studied which adds to the cost, the time and the variability of the experimental system.
Improved animal model systems would be desirable for studying the developmental consequences of a lethal phenotypes in the embryo in utero and for providing a screening system for identifying novel therapeutic agents that may be used to correct the resultant abnormalities in the adult animal.
Among proteins that play an important role in development are the class of regulatory molecules identified as hedgehog proteins. The hedgehog family of proteins, which was first identified in Drosophila and subsequently observed in mammals, is expressed in different organizing centers which can initiate signals that pattern neighboring tissues. In particular, hedgehog proteins play an important role in the development of the central nervous system including forebrain development. There are at least eight cloned hedgehog proteins having a broad spectrum of biological activity (WO 95/18856). The biological activities ol the hedgehog proteins have been descπbed in Hammerschmidt et al Trends in Genetics (1997) 13:14-21 and in Tabin C. et al. Trends in Cell Biology (1997) 7.442-446, both references hereby incorporated by reference herein. Defects in hedgehog genes and hedgehog receptor genes have been correlated with several human diseases (Hammerschmidt et al.. 1997). These include cancers such as brain tumors including medulloblastoma and memngioma; skin cancers such as basal cell carcinoma: and breast cancer.
There is a current lack of animal models for analyzing the effects of defective regulatory genes during development and for providing screening assays to identify therapeutic agents that might regulate the function of these regulatory proteins.
Summary of the Invention In a preferred embodiment of the invention, a transgenic non-human mammal is provided, substantially all of whose cells contain a non- viral regulatory DNA sequence linked to a recombinant hedgehog gene introduced into the mammal or an ancestor of the mammal at an embryonic stage. For example, a transgenic non-human mammal can be the mammal having an endogenous coding sequence substantially the same as a coding sequence of the recombinant hedgehog gene In one embodiment of the invention, the mammal is a rodent, for example, a mouse In a preferred embodiment of the transgenic non-human mammal, the regulatory sequence comprises a UAS sequence (SEQ LD NO:l).
In a further embodiment the invention provides a bigenic non-human mammal, substantially all of whose cells contain a non- viral regulatory DNA sequence linked to a recombinant hedgehog gene sequence: and a transcriptional activator sequence, introduced into the mammal or an ancestor of the mammal at an embryonic stage. Thus the embodiment can be a bigenic mammal having an overexpressed vascular system in the central nervous system, for example, the mammal is an embryo, and is capable of a fespan, for example, ot 9 dpc, of 12.5 dpc. of 18.5 dpc, of parturition, of one month post- partuπtion, of three months post-partuπtion. or of one year post partuntion. A further embodiment of the invention is the bigenic non-human mammal wherein the transcriptional activator gene is GAL4 Further, the transcriptional activator gene is regulated by a tissue specific promoter, for example, the tissue specific promoter is a wnt promoter or a col II promoter In a further embodiment of the bigenic non-human mammal, the transcnptional activator gene is regulated by an inducible promoter, for example, the inducible promoter is regulated by a fusion of GAL4 protein and a second protein, for example, the second protein is activated by binding an RU486 mitepnstone molecule
A further embodiment ot the invention is a bigenic non-human mammal for use as a model for disease, for example, the disease is cancer, for example, a cancer of the breast, skin, prostate, kidney, lung, and central nervous system In a preferred embodiment, the cancer is a primitive neuroectodermal tumor, or the cancer is a medulloblastoma A further embodiment of the invention provides an isolated cell of a bigenic non- human mammal obtained from the above bigenic mammal The isolated cell of the bigenic non-human mammal is selected from the group consisting of an embryonic-stem cell, a tumor cell, a nerve cell, and a vascular cell
Another embodiment of the invention is a transgenic non-human mammal having an insertion mutation of an Ihh gene, for example, the insertion can comprise a selectible marker, and the insertion can comprise a deletion of the Ihh gene
A further embodiment of the invention provides an isolated population of cells selected from the group consisting of a transgenic non-human mammal, and its bigenic progeny In another aspect, an embodiment of the invention is a method ot identifying the effect of misexpression of a target transgene in a signal transduction pathway that includes a hedgehog protein, in a progeny animal, comprising, (a) forming a first transgenic animal having a first transgene encoding a transcnptional activator of a eukaryotic species different from the animal; (b) forming a second transgenic animal having a second transgene comprising the target gene and having a recognition sequence for the transcnptional activator that is located upstream of the target gene, (c) mating the first and the second transgenic animals to form a bigenic animal, and (d) causing the target gene to be misexpressed in the animal A further aspect of this method of identifying the effect of misexpression of a target transgene provides the transgenic animals formed from an animal which is an animal model disease line, for example, the animal model is selected from the group consisting ot a cancer and an autoimmune disease
A further embodiment of the invention is a method of assaying for a temporal requirement for the presence of a hedgehog protein on progression of a disease, comprising:
(a) forming a bigenic animal according to the method above; (b) treating the bigenic animal for an effective time interval with an agent that interrupts the hedgehog pathway; and
(c) assaying the progression of the disease in the animal in (b) compared to the progression of the disease in the animal in (a).
Another embodiment of the invention is method of assaying for a temporal requirement for the presence of a hedgehog protein during progression of the disease in the bigenic animal in the disease model line, wherein the treatment comprises administration of an agent selected from the group consisting of an inhibitor of cholesteroid biosynthesis, an anti-hedgehog antibody, and a sterol analog.
An embodiment of the invention further provides a method for determining therapeutic efficacy of an agent, comprising: (a) forming a bigenic mouse according to the method above, wherein the misexpressed target gene is a hedgehog gene; (b) administering the agent to the mouse; and (c) determining therapeutic efficacy of the agent. Another method provides that (b) further comprises administering the agent to the mouse in a pharmaceutical carrier at an effective dose. Yet another method provides that (c) further comprises comparing lifespans of the bigenic mouse of (b) with the bigenic mouse of (a), for example where the bigenic mouse in (a) is an embryo.
A further embodiment of the invention is a method of obtaining an expanded population of neural stem cells from a subject, comprising: treating a neural stem cell from the subject with a hedgehog protein, so that proliferation of the stem cell provides an expanded population of neural stem cells. In a preferred embodiment of the method, the hedgehog protein is sonic hedgehog protein. In another embodiment of the method, the subject has a condition selected from the group consisting of Parkinson's disease, Alzheimer's disease, and spinal cord injury. Thus the condition can be treated by administration to the subject of a sample of the expanded cell population.
An embodiment of the invention provides a method for inactivating an Ihh gene in a non-human mammal, comprising: (a) constructing a recombinant vector carrying an Ihh insertion mutation; (b) injecting an embryonic stem cell with the vector; and (c) implanting the stem cell into an adult mammal. In a preferred embodiment of this method for inactivating an Ihh gene, the vector in (a) carries a deletion of exon 1 of the Ihh gene.
Brief Description of the Figures Figure 1 is a schematic representation of a signaling pathway of which exogenously supplied hedgehog functions to effect changes in nuclear gene transcription. HH, hedgehog protein is shown as an extracellular protein that binds a receptor composed of the products of genes indicated PTC (iox patched), and SMO (smoothened). In the absence of HH binding, a cytoplasmic protein complex comprising microtubule protein and Cos-2 (costal-2) and Fu (Fused), functions with a repressor form of Cl (cubitus interruptus), indicated as Rep.-CI= transcriptional repressor. In the presence of HH binding to the receptor, the protein complex dissociates from the microtubule protein, and as a result of a series of protein phosphorylations, an activator form appears, indicated Act.-CI (transcriptional activator). The activator or repressor form of Cl is translocated into the nucleus where it regulates transcription of the HH target family of genes, in the activator form complexed with CBP (CREB binding protein). Figure 2 shows a schematic drawing of transgenes WEXP-GAL4, UAS-/αcZ and
UAS-5 used in the bigenic system for misexpression in the mouse embryonic CNS. (A) Plasmid pWEXP-GA 4 is a driver vector that comprises full-length GALA, which was cloned into the WEXP2 expression vector under control of the Wnt-1 promoter. (B) The reporter transgenic construct, a vehicle vector carrying a UAS-ZACZ, was constructed to utilize the Wnt-1 promoter and 5 copies of the UAS. (C) Plasmid pUAS-S was constructed with full-length mouse Shh cDNA target gene cloned into expression vector WEXP3C. Wnt-1 regulatory sequences were then replaced by 5 copies of the UAS. The arrows indicate sites of hybridization for each of the oligonucleotide primers used in genotyping the various transgenic lines and progeny as described in the Examples. Figure 3 is a diagrammatic representation of the strategy for forming mouse
GAIA Wnt-1 and lacZ reporter transgenic mouse lines suitable for crossing to obtain bigenic progeny. Blue color indicating GAL4 mediated Wnt-1 promoted expression of lacZ was visible in the mouse embryo at the dorsal region of the neck.
Figure 4 shows the GAL4/U AS bigenic system for misexpression of proteins in transgenic (Tg) mice, wherein (a) shows structure of the WEXP-GA 4 transgene; (b) shows structure of the UAS-lacZ transgene and expression of β-galactosidase in the Wnt- 1 pattern in a GAL4II S-lacZ 10.5 dpc (days post coitum) embryo with black arrows indicating expression observed in the midbrain-hindbrain junction and dorsal spinal cord as a blue color; and (c) shows structure of the UAS-Shh (sonic hedgehog) transgene and phenotype of a GAL4/UAS-Shh 10.5 dpc embryo. Ectopic expression of the neural tube floorplate marker, HNF3β is indicated by arrows and occurs in analogous positions to lacZ expression under wnt-1 in the brain (b).
Figure 5 shows data obtained from the GAL4IU AS system for providing ectopic gene expression in the developing CNS. Panels A-D show whole mount histochemical analysis of target reporter β-galactosidase activity in transgenic mouse embryos. A: Lateral view showing pattern of lacZ expression under control of Wnt-1 regulatory sequences. B, C: Lateral views of 10.5 dpc and 12.5 dpc bigenic Wnt-1-Gal4 X UAS-lacZ embryos showing expression pattern of lacZ (arrow indicates roofplate expression in the spinal cord). D: Transverse (top) and bisected (bottom) views of lacZ expression in the rostral spinal cord of a bigenic embryo at 18.5 dpc. Note staining in roofplate oligodendrocytes that project to the ventricular zone (arrows). Panels E-J show morphological analysis of wild-type (left) and Wnt-1 -GAL4 X UAS-Shh bigenic (right) litter mates at: E: 10.5 dpc (arrow indicates anterior neural tube defect); F: 12.5 dpc. Panels G-J show analysis at 18.5 dpc. Lateral views are shown of (G) wild-type and (H) bigenic embryos. Note tissue mass protruding from midbrain which covers cerebral hemispheres (arrow). Panel I: Dorsal view of bigenic embryo showing hyperplastic spinal cord which protrudes from the back covered by a thin epithelial membrane. Note prominent vasculature and hemorrhage (arrow). J: Dorsal view of skeletal preparation of wild-type (left) and bigenic (right) embryo at 18.5 dpc. The membranous skull and dorsal neural arches were observed to be absent, and the vertebral bodies displayed a splayed open configuration (arrows) as a result of ectopic Shh expression. Figure 6 demonstrates hyperplasia in the dorsal central nervous system (CNS) of
Wnt-1 -GAL4 X UAS-Shh (referred to as UAS-Shh Tg) bigenic mice, wherein (a) shows a dorsal view of a 18.5 dpc UAS-Shh Tg embryo demonstrating overgrowth of the brain and spinal cord, and increased vasculature in the dorsal CNS where Shh is ectopically expressed: and (b) shows a transverse section at the level of the forelimb of an 18.5 dpc UAS-Shh Tg embryo. The region dorsal tissue in the spinal cord was observed to be hyperplastic. with hydromyelia (gross enlargement and distension) of the spinal cord central canal. Figure 7 shows the result of misexpression of Shh in the dorsal CNS. Ectopic expression of Shh in the midbrain ventralizes the midbrain. inducing ectopic expression of Shh target gene Hnf-3β in the dorsal CNS. The whole mount was analyzed by Hnf-3β immunostaining. Figure 8 shows the targeting strategy used to generate Ihh mouse knock-out mutants by homologous recombination with a vector in which the first exon at the Ihh locus is deleted, thereby generating a null allele.
Detailed Description of Embodiments We have examined the effect of misexpression of proteins that play a role in the developing embryo. In particular, we have examined the effect of misexpression of hedgehog proteins, more particularly Sonic hedgehog proteins (Shh). using bigenic mouse models and the effect of loss of function of Indian hedgehog in transgenic mouse embryos.
Hedgehog A hedgehog protein includes a member of a family of cell proteins found in invertebrates such as Drosophila and in vertebrate eukaryotes. including humans, which are essential to tissue pattern formation that distinguish the variety of tissues formed during embryonic development. A hedgehog protein molecule is post-translationally modified by addition of a cholesterol molecule. Figure 1 shows the hedgehog signal transduction pathway and the concomitant effects on nuclear transcription of binding of a hedgehog molecule to a cell receptor.
Hedgehog proteins are secreted factors and determinants of dorsal- ventral polarity in the central nervous system (CNS), being essential for induction and subsequent differentiation of ventral cell types. Hedgehog proteins act via signal transduction. Sonic hedgehog appears to induce hypervascularization, hyperplasia and in some situations, neoplasia, a property that is shared with Indian hedgehog protein which appears however to reduce vascularization. Neoplasia is linked not only to hedgehog gene expression but also in humans to the loss of the patched protein receptor (Figure 1). Patched is a membrane protein which down regulates transcription of the genes encoding transforming growth factor (TGF) β and Wnt families, and transcription of its own gene. Patched has been implicated in oncogenesis, including development of basal cell carcinoma and of nevoid basal cell carcinoma syndrome (Gorlin. (1987) Medicine 66:98-113), which includes f ibromas of the ovaπes and heart, cysts of skin and jaw and mesentery, meningiomas and medulloblastomas.
Until now, the effects on the embryo, particularly the prohferative effects, of expression of hedgehog proteins in abnormal amounts or in tissues that do not normally express such proteins have remained incompletely understood. The present invention provides a binary transgenic (bigenic) system in which protein expression exemplified by expression of hedgehog is regulated by a promoter that is not normally recognized in a mammalian cell (described herein by the term "extra- mammalian" promoter; Figures 2,3). The promoter is in turn activated by a transcnptional activator protein, expression of which is under the control of a tissue specific enhancer. A binary transgenic system provides the opportunity to activate otherwise silent transgenes in progeny obtained from a simple genetic cross, because the transcnptional activator is maintained in one line of mouse, while the silent target gene under control of an extra-mammalian promoter is maintained in a second mouse line. Only when the two lines are crossed does abnormal expression of the target gene occur (A. Brand et al. (1993) Development 118:401-415: Ornitz et al. (1991) Proc Natl Acad Sci. USA 88:698-702). Ormtz et al. utilized a bigenic system to study the effects ot misregulatmg ιnt-2, using a mouse mammary tumor virus (MMTV) promoter to transcnbe the activator protein gene. The ιnt-2 gene is expressed in mammalian cells, and is implicated in mammalian neoplasia. In the Ormtz system, tumors resulted from ectopic expression of ιnt-2 only in the mammary and salivary glands Brand et al. created a bigenic system in Drosophila to study the homeobox protein, even skipped.
The term hedgehog as used here and in the claims shall include the hedgehog protein from any organism, for example from an invertebrate or a vertebrate organism, and shall include any polypmoφhic vanant or mutation, including a substitution mutation, a deletion, or an insertion mutation that retains the developmental and differentiation functions of dorsoventral patterning and prohferative function of the wild type hedgehog protein. The term shall further include hedgehog proteins of all members of the hedgehog family, for example, Some hedgehog. Indian hedgehog, desert hedgehog, zebra hedgehog, tiggywinkle. and other members ot the hedgehog family. The hedgehog protein of the invention shall include a hedgehog protein synthesized from a hedgehog-encoding DNA sequence that is at least 70% homologous, at least 807c homologous, at least 90% homologous, at least 95% homologous, and at least 98% homologous to the sonic hedgehog protein which retains the functions of the hedgehog protein. The hdegehog protein includes a protein encoded by a nucleic acid that hybridizes under stringent conditions as defined herein with a portion of a gene encoding a hedgehog protein. The term shall further include any chemical analog or derivative composition of a hedgehog protein, including a peptidomimetic which maintains the hedgehog functions as described in the examples herein.
Hedgehog is a secreted protein that functions as modified by addition of a cholesterol moiety as an intercellular signalling system. Hedgehog signalling can be interrupted by one of several chemical treatments of an animal or a cell in culture, for example, by addition of an anti-hedgehog monoclonal or polyclonal antibody, by addition of an inhibitor of cholesterol biosynthesis such as lovastatin, pravastatin and simvastatin (Merck, Rahway, NJ), or by addition of the steroidal alkaloid cyclopamine (Incardona, J. et al.(1998) Devel. 125:3553-3562). Cyclopamine has been shown to exert teratogenic effects (for example, cyclopia) due to direct antagonism of sonic hedgehog signal transduction. Administration of these agents to a bigenic animal that is an embodiment of the invention, particularly bigenic animals that are formed in an animal line that is an animal model of a disease, at times during embryonic development, can provide a method of assaying for a temporal requirement for hedgehog protein during the progression of a disease.
Definitions
As used in this description and in the accompanying claims, the following terms shall have the meanings indicated unless the context otherwise requires. The term "protein" includes the terms "polypeptide," and "peptide." A "regulatory DNA sequence" is used herein to describe a sequence of DNA to which one or more proteins can bind, so that transcription of a DNA sequence can be initiated or increased or decreased. The regulatory DNA sequence can be a promoter, an operator, or an enhancer site. A regulatory DNA sequence can also be a terminator site, for example, a tract of several adenyl residues at the end of a gene (polyA). A UAS is an upstream activating sequence that can bind a GAL4 protein, such binding resulting in an increase in transcription of DNA downstream from that site. An enhancer site can also increase transcription from downstream DNA. The UAS of the invention (SEQ ID NO 1) is known to function from a location that is upstream of the target gene
A "promoter is a DNA sequence with ability to bind to an RNA polymerase molecule to initiate transcnption Extent of binding is influenced by promoter strength, and by protein tactors that interact with an enhancer site at or adjacent to the promoter A regulatory DNA sequence can be located within a protein coding region of a gene, however, the protein coding region of all or a part ot a gene shall be referred to herein as a gene The engineered vectors used herein generally select a site upstream of a gene for regulation of transcription of the gene, however it is within the scope of the invention to locate a regulatory sequence within the protein coding region of a gene
A "recombinant protein' is a protein that is synthesized in vivo from a transgene or a recombinant gene, so that it can be distinct both in cell location and in regulation of expression from a naturally occurnng homologous gene, if any, within the cell The recombinant proteins that are used in embodiments of the present invention can carry mutations, including without limitation, substitutions, chain terminations, deletions and insertions Further, a recombinant protein can be encoded by DNA that is homologous to the gene encoding the protein, providing that the function of the protein is retained A "bigenic ' animal is the result of a cross between two different transgenic animals, such that a 1 1 1 1 Mendehan progeny ratio is observed, the ratio describing progeny which consist of one wild type, one ot each of the single hemizygous transgenic animals, both of which may have phenotypes identical to the wild type, and one bigenic progeny animal Figure 2 shows vectors for forming transgenic animals, which can be combined by a genetic cross to obtain bigenic progeny Figure 2A shows a "dnver vector" capable of producing GALA, a transcnptional activator protein native to yeast Saccharomyces cerevisiae This vector confers no phenotype itself in a mammalian cell, as GAL4 is ' extra-mammalian' and therefore does not interact with the wild type mouse genome Figure 2B and 2C show "vehicle" or earner" vectors which can express a "target" gene carried on the vehicle, but only in the presence of GAL4 protein, at the time it is synthesized by expression of the GAL4 gene on the driver vector "Temporal requirement" indicates a window of time ot development dunng which a specific factor must be present The temporal requirement may be a period of transient gene expression, tor example, from the period between 9 5 and 12 5 dpc, or mav be of long duration, tor example, from conception, or from 4 5 dpc, up until parturition or even beyond
An "embryo" of an animal is the term used to describe the progeny trom the zygote stage until partuntion An "inducible" gene is capable of being expressed in response to addition to cells or administration to an animal of an exogenous chemical or drug Transcription mediated by a steroid-receptor like protein to which the chemical RU486 (metipnstone; Roussel- Uclaf , Hoechst) has been bound is inducible by administration to an animal or addition to cells in culture of this chemical A "fusion" protein is a non-naturally occurnng protein obtained from genetic manipulation of two or more genes encoding respectively amino acid sequences derived from two or more different proteins, to create a fusion gene having the two or more proteins tranlated in the same reading frame In an embodiment ot the present invention, the GALA protein can be fused to all or a portion of another protein, for example to confer inducibility. such that mitepnstone (RU486) can be added to cell medium or administered to a transgenic or bigenic animal to induce expression of another gene
' Homology' refers to sequence similanty between two peptides or between two nucleic acid molecules Homology can be determined by companng a position in each sequence which may be aligned for puφoses of companson When a position in the compared sequence is occupied by the same base or amino acid, then the molecules are homologous or identical at that position A degree of homology between sequences is a function of the number of matching or identical positions shared by the sequences
A "gene" encoding for a hedgehog protein, for example a sonic hedgehog or an Indian hedgehog protein within the scope of an embodiment of the invention if it encodes a protein that has substantially the same function of the wild-type hedgehog protein. A hedgehog gene that is within the scope of the present invention may have a mutation, for example without limitation, a point mutation resulting in an amino acid substitution or chain termination, a deletion, an insertion, it the encoded protein retains hedgehog function Further, a gene that is homologous to a hedgehog gene that encodes a protein capable of confernng a normal hedgehog phenotype is within the scope of the embodiment of the invention
Preferred regulatory sequences encode a UAS sequence which is at least 764% homologous (having 13 homologous and 4 nonhomologous nucleotide residues), more preferably at least 82 3% homologous (having 14 homologous and 3 nonhomologous nucleotide residues), more preferably at least 88 3% homologous (having 15 homologous and 2 nonhomologous nucleotide residues), and even more preferably at least 94 1% homologous (having 16 homologous and 1 nonhomologous nucleotide residues). A GAL4 protein, which is an embodiment of the invention is one compnsing an amino acid sequence which retains the functions of binding to a UAS and activating transcription, and has an amino sequence which is at least 60% homologous, more preferably 70% homologous and most preferably 80%. 90%, or 95% homologous with the wild type GALA amino acid sequence (Brand, A et al , 1993)
Another aspect ot the invention provides a nucleic acid which hybndizes under high stnngency conditions to a ' probe '. which is a nucleic acid which encodes a portion of an inserted transgene sequence as shown in SEQ ID Nos 2, 3, and 4 A suitable probe is at least 12 nucleotides in length, is single-stranded, and is labeled, for example, radiolabeled or fluorescently labeled Appropnate moderate conditions of stringency of conditions of formation of double-strandedness which promote DNA hybridization, for example, 6 0 x sodium chlonde/sodium citrate (SSC) at about 45°C. are followed by successive washes of increased stnngency, e g , 2 0 x SSC at 50°C, and are known to those skilled in the art or can be found in Current Protocols in Molecular Biology, John Wiley & Sons. N Y (1989), 6 3 1-6 3 6 Other suitable stringency conditions include selecting the salt concentration in the wash step trom a low stringency of about 2 0 x SSC at 50°C, and then using a wash of a high stringency condition, of about 0 2 x SSC at 50°C In addition, the temperature in the wash step can be increased from low stringency conditions at room temperature, about 22°C, to high stnngency conditions at about 65°C A GAL4 protein which is an embodiment of the invention is encoded by a gene which hybndizes to the wild type GAL4 gene under stnngent conditions
Conditions for hybridizations are largely dependent on the melting temperature for half of the molecules ot a substantially pure population of a double-stranded nucleic acid, a parameter known as the Tm For nucleic acids of sequence 11 to 23 bases, the Tm can be calculated in degrees C as 2(number of A+T residues) + 4(number of C+G residues) Hybndization or annealing of the probe to the nucleic acid being probed should be conducted at a temperature lower than the Tm, e g . 15 °C. 2ϋ°C. 25 °C or 30°C lower than the Tm. The effect of salt concentration (in M of NaCl) can also be calculated, see for example. Brown. A., "Hybndization" pp. 503-506, in The Encyclopedia of Molec. Biol, J. Kendrew. Ed., Blackwell, Oxford (1994).
An "animal model" for a disease is an animal treated with a chemical composition, or a mutant animal, that displays symptoms identical or similar to a human subject having the disease. The mouse mutant Patched, for example, is an animal model of cancer. Animal models for human cancers can be formed using the bigenic animals that are embodiments of the present invention, for example, misexpression of a hedgehog protein causing ectopic proliferation of nerve stem cells in the CNS can be an animal model of a brain tumor
A "therapeutic effect ' resulting from addition to a cell culture or administration to an animal of a chemical or a protein agent can be observed as a prevention or a remediation of symptoms of disease, in companson to cells or animals not receiving the chemical. For remediation or prevention ot symptoms in the present invention, a therapeutic effect is a demonstration of effectiveness of an agent to cause a phenotype which is more normal than a phenotype observed from ectopic expression of a hedgehog protein, for example, in the bigenic animals of the invention
An "effective dose" is that amoung of exogenously added or administered, or in vivo generated Shh protein or other hedgehog protein, or other chemical entity, capable of achieving a successful endpoint of a therapeutic effect
Advantages of the bigenic system include reduction in cost and time compared with forming transgenic animals de novo by micro-injection and genotypic screening prior to performing each experiment. Large numbers of bigenic embryos can be generated by cross breeding. Bigenic transgenic systems may be formed as follows: a first or "carrier" vector is made having a regulatory sequence placed adjacent to and upstream of a target gene of interest. The regulatory sequence is recognized by an extra-mammalian regulatory protein, for example the extra-mammalian upstream sequence may be a regulatory sequence from yeast (for example, UAS) or from heφes virus (for example, LPE). A second or "dnver" vector contains DNA encoding a gene for a transcnptional activator wherein the expression of this gene is capable of tnggenng the regulatory sequence in front of the target gene on the first earner vector, for example yeast transcriptional activator (GAL4). or heφes transcnptional activator (VP16) A tissue specific regulatory sequence may be used to promote the expression of the transcriptional activator such as wnt-1 enhancer and promoter which target gene expression to cells of the nervous system (Figures 2, 4). The Wnt-1 enhancer is ideally suited for directing gene expression in the roofplate of the CNS (Echelard et al., Development (1994) 120:2213-2224), and it has been used to misexpress chicken Shh in transgenic mice (Echelard et al., Cell (1993) 75: 1417-1430); however in studies by Echelard et al. (1993, 1994) the CNS malformation resulting from Wnt-1 control of Shh expression was lethal, and no transgenic embryos survived to birth.
Other tissue specific regulatory sequences may be used, including those that target bone (for example collagen type π enhancer), skin (keratin- 14 enhancer), kidney (pax-2 enhancer), and CNS (nestin, neuron specific enolase. transerythrin). These tissue specific promoters may in turn be regulated by inducible enhancer sequences. An example of an inducible system utilizes RU486 which binds to a membrane receptor protein and is translocated to the nucleus (Wang et al., Nature Biotechnology (1997) 15:239-243) and therefore has particular utility for regulating expression of hedgehog protein. Another example of an inducible system having utility in this invention is a tetracycline regulated system in which the tet repressor from Escherichia coli is fused to the Heφes simplex virus viral protein 16 (VP16) transcriptional activation domain (Schockett et al. Nature Biology (1997) 15:217) such that addition of tetracycline induces VP16-promoter regulated expression.
The present invention uses a regulated gene expression system to cause selective expression of hedgehog proteins, for example Sonic hedgehog protein (Shh), and also to express lacZ as a convenient marker ("reporter") system, well known in the art, to monitor the activity of enhancers, promoters and transcriptional activator sequences. The lacZ reporter is used as a control in parallel with studies on hedgehog gene expression (Figures 2-4).
Each of two types of vectors is introduced into a mouse to yield two types of lines of novel transgenic mice, each having a normal phenotype. The target gene is not expressed until the two mouse strains are cross bred and progeny embryos are obtained. The progeny of the cross can express the target gene, and therefore the phenotype observed in the progeny of the cross is different from that of each of the two parental lines. Because the extra-mammalian transcriptional activator exemplified by GALA is not normally present in mouse cells, genes with lethal effects on the embryo can be stably maintained in transgenic mice under control of the extra-mammalian promoter (exemplified by UAS). An embodiment of the invention uses this novel system to determine the effects of synthesis of abnormal amounts of regulatory proteins during embryogenesis
The bigenic mouse model as used herein illustrates the prohferative effects of Sonic hedgehog protein in the CNS of animals as exemplified by the following:
(a) CNS hypeφlasia was analyzed to determine the constraints, if any, on competence to respond to Hedgehog signaling by neural cells: (b) The impact of Shh on patterning and cellular induction was determined.
Using the bigenic system embodiment of the invention, it was here observed that abnormally high levels of Sonic hedgehog expression resulted in increased vasculanzation in the nervous tissue of the brain and the dorsal CNS (Figures 4-6)
In the novel transgenic mouse progeny, unexpected changes in vasculanzation of the nervous system were observed herein to arise when hedgehog proteins were defective. The bigenic mouse provides a system for analyzing in vivo vasculanzation of the brain, and an assay system to identify novel factors to enhance or diminish such vasculanzation. Furthermore, an embodiment of the invention provides explant cultures of the hypervasculanzed tissue, which when cultured in vitro, provide a system for analysis of translocation of drugs across the blood brain barrier, tor identifying agents that affect translocation, for analyzing hyperplastic including neoplastic properties of the cells, and for analyzing agents that modulate or reverse the hypeφlasia.
An embodiment of the invention provides a system in which for the first time abnormal activation of hedgehog signal transduction in specific neural cells can be associated with generation of neoplasia. Further, over-expression of Shh in the brain unexpectedly caused the surface of the mouse brain, usually smooth, to become wrinkled, an appearance normally associated with higher animals such as cats and humans. Consequently, the bigenic mouse models of the invention can be used to study regulation of brain size and density as well as cellular composition and thereby provide a system for testing therapeutic agents that can reverse the neuronal deficit seen in patients with neurodegenerative diseases. The expanded zone of neural growth have cell precursors may also be a useful tissue for obtaining neural stem cells tor therapeutic purposes. The bigenic animal system of the present invention is further suited for analysis of medulloblastoma. For example, an inducible RU486-GAL4 transcriptional activator that relies on Pax-2 enhancer to target hedgehog protein expression to the cerebellum ensures that over-expression occurs after early brain development. This system avoids the abnormal development of the early brain that is observed in response to over-expression of hedgehog, and consequently enables formation of a cerebellum prior to activation of the regulatory protein.
The bigenic mouse model of the invention provides a means for modulating hedgehog gene expression for analyzing the effect of varied amounts of hedgehog, and an assay system for testing chemicals and cells as agents for therapeutic benefit for patients having abnormal hedgehog protein or suffering from the effect of abnormal levels of hedgehog.
Methods and Uses
The methods that are embodiments of the invention have utility in analyzing any of the components of hedgehog signaling pathways (Figure 1), both in terms of the biological activity of the individual components, and methods of modulating the activity of these compounds.
Screens for agents that reverse an ectopic hedgehog expression phenotype An object of an embodiment of the present invention is the use of methods of assay with the bigenic animal and cell lines, mutants, vector constructs, and methods of the present invention, to identify, for example, the effect of misexpression of a target transgene. The misexpression of the transgene can be that of a reporter transgene, for example, a reporter gene on a vector that causes a color development such as lacZ as described in the examples herein. Methods of screening, including synthesis of chemical libraries and culture and assay of screen organisms in sterile multi-well plastic dishes containing for example 96 or 354 wells per dish, robots for delivery of samples to each well using devices such as automated multi-pipeters, and for processive manipulation of each dish, and for computerized reading of growth as optical density or production of light absorbant material at a given wavelength in each well, are well known to those of ordinary skill in the art of design of screens of chemical agents. The methods that are embodiments of the invention herein are suitable for automated and robotic applications, for example, by use of solvent systems to soluble a colored reaction product or product capable of absorption of light of a particular wavelength Programs for collection, analysis, storage and retneval of assay data for each animal or cell line and vector at each condition of development and post-harvest incubation are available
Such methods can be used to monitor potential inhibition of proliferation of tissues or cells of a bigenic animal in the presence and absence of a vanety of chemical entity agents, and to record the extent of proliferation ot cells and/or tissue differentiation in the presence and absence of the candidate chemical, and of control animal or cells under these conditions.
Pharmacological Methods An agent, for example a hedgehog composition or analog or peptidomimetic, identified by an embodiment of the invention that is a method ot assay can be subjected to a pre-clinical trial in an animal or a subject. For such a method, a "pharmaceutically acceptable carrier" includes any and all solvents, dispersion media, e.g , human albumin or cross-linked gelatin polypeptides, coatings, antibactenal and antifungal agents, lsotonic, e.g., sodium chloride or sodium glutamate, and absoφtion delaying agents, and the like that are physiologically compatible. The use ot such media and agents for pharmaceutically active substances is well known in the art Preferably, the carrier is suitable for oral, topical, intravenous, intramuscular, subcutaneous, parenteral, spinal or epidermal administration (e.g., by injection or infusion) Depending on the route of administration, the active compound can be coated in a material to protect the compound from the action of acids and other natural conditions that can inactivate the compound. Routes of administration also include, without limitation, lntrauteπne, intraartenal, intrathecal. intracapsular, intraorbital, intracardiac, mtradermal, intrapentoneal, transtracheal, subcutaneous, subcuticular, intraarticular, subcapsular, subarachnoid, intraspinal. epidural and intrastemal injection and infusion. Administration of an agent to a maternal parent of an embryo progeny animal is within the scope of the invention.
Dosage regimens are adjusted to provide the optimum desired response, e.g., a therapeutic response, such as restoration of a normal CNS prohferative response. For example, a single bolus can be administered, several divided doses can be administered over time or the dose can be proportionally reduced and administered over a time period by infusion, or increased, as indicated by the exigencies of the therapeutic situation
One ot ordinary skill in the art can determine and prescribe the effective amount of the pharmaceutical composition required. For example, one could start doses at levels lower than that required in order to achieve the desired therapeutic effect and gradually increase the dosage until the desired effect is achieved. In general, a suitable daily dose of a composition of the invention will be that amount of the composition which is the lowest dose effective to produce a therapeutic effect. Such an effective dose will generally depend upon the factors described above.
The invention is further illustrated by the following examples, which should not be construed as further limiting. The contents of all references, pending patent applications and published patents, cited throughout this application, are hereby expressly incorporated by reference.
Examples 1-3 describe materials and methods used in preparation of a bigenic mouse system which is capable of expressing a lethal mutation in the hedgehog protein. Example 1 describes construction of the vectors used in producing the parental transgenic mice, the genotype characterizations of which are described in Example 2. Procedures for analysis of mouse tissues by in situ hybridization and immunostaining are given in
Example 3. Methods of measuring cell proliferation and apoptosis are given in Example 4, and the results observed show that misexpression of sonic hedgehog from 9.5 to 18.5 dpc caused hyperplasia of the embryonic CNS when Shh was under GAL4IU AS control. A lethal phenotype was observed in Example 5 to result from micro-injection of the Wnt-1 enhancer-mouse Shh transgene into mouse embryos. In Example 6. the phenotypes of progeny from a cross of parental lines was examined, and 25% (the bigenic progeny) were found to have a lethal phenotype characterized by the presence of an open neural tube in the midbrain region. Example 7 describes construction of a knock-out mutation of Indian hedgehog is constructed. In Example 8, the lethal phenotype of mouse embryos carrying an Indian hegehog null mutation was found to be due to a defect in formation of blood or blood supply.
Examples Example 1. Construction of vectors for forming transgenic parents of bigenic animals An overall strategy of the embodiment of the invention comprising bigenic animals is first constructing each of the two transgenic parents, then crossing them as shown in Figures 2-3 to obtain bigenic animals in the Mendelian proportion of one- quarter of the progeny. Vectors were constructed so that one transgenic parent contains a driver vector which expresses an extra-mammalian transcnptional activator, and the other parent contains a vehicle vector capable of expressing a target gene in the presence of the transcnptional activator.
To construct these vectors, strategy of adding or removing gene sequences was utilized in forming the wnt-1 -GAL4 vector and the pUAS-Shh transgene vectors. As descnbed below, pWEXP-2 (containing wnt-1) and pGaTB (containing GAL4) were combined to produce the tissue specific transcnptional activator vector. A second transgene vector carrying UAS-Shh was formed by inserting pUAS-shuttle into pWEXP3C-S/z z and removing the wnt-1 enhancer, resulting in a ^UAS-Shh product. (a) Constructing a vector containing a transcnptional activation sequence.
The plasmids pGaTB and pUAST encoding, respectively, full length GAL4 and a pentamer array of its cognate DNA binding sequence, and the "upstream activating sequence" (UAS, 5 -CGG AGT ACT GTC CTC CG-3'; SEQ LD NO:l). were combined (Brand et al, 1993). To generate the transgene pWEXPGA 4, the Wnt-1 expression vector pWEXP-2 (Echelard et al., 1993) was digested with Nrul and treated with calf intestine alkaline phosphatase (CLAP). The plasmid pGaTB was digested with HindUI and Fspl to release a DNA fragment encoding GAL4; this was end-filled with the Klenow fragment of DNA polymerase I and cloned into the pWEXP-2 vector. The transgene was purified from vector sequences by digestion with A tll. (b) Constructing a vector carrying a hedgehog gene regulated by an extra- mammalian promoter.
To generate the transgene pUAS-S , a shuttle vector. pUAS Shuttle, was constructed as follows. A Kpnl and BglTL fragment of plasmid XB3 was replaced with an ohgonucleotide polylinker encoding an Xhol site. This construct was digested with Notl and Kpnl, and was treated with CLAP. To this vector a Notl-Kpnl fragment of pUAS-/αcZ, compnsing five copies of UAS, was added, generating plasmid pUAS-Shuttle. Finally, pUAS-Shuttle was digested with Xhol and BgJR and was treated with CIAP. A Sall-BgRl fragment of pWEXP-3C was isolated and cloned into the vector, creating plasmid pUAS-S z z. The transgene was punfied from vector DΝA by digestion with Sail and BglU prior to micro-iniection.
DΝA sequencing of these constructs was carried out using both the ABI dye terminator and the di-deoxy chain termination methodologies. The genotyping determinations for pWEXP2-GAL4, pWEXP3C-5/z/z. and UAS-Shh mice and embryos employed an upstream oligonucleotide primer from exon 1 of untranslated sequence of Wnt-1 pner (5 -TAA GAG GCC TAT AAG AGG CGG-3'. SEQ ID NO: 2), which primes approx 60 bp upstream of the Wnt-1 translational initiation site: a downstream primer from within GALA (5'-ATC AGT CTC CAC TGA AGC-3', product size ca. 600bp; SEQ ID NO: 3); or mouse Shh (5 -CTC ATA GTG TAG AGA CTC CTC-3', product size ca. 600bp; SEQ ID NO:4). The following PCR conditions were used: 30sec. 93 °C, 30sec, 55 °C. and lmin, 72 °C for 40 cycles: then 5mιn, 72 °C
(c) Constructing a vector carrying a reporter gene regulated by an extra- mammalian promotor
To generate the reporter transgene pUAS-/αcZ, the plasmid XB3 (Echelard et al.. 1994) was digested with Notl and treated with CLAP The pentamer array of UAS sequences from plasmid pUAST was amplified by PCR using primers that incoφorated Notl and Eagl recognition sequences. The PCR products were digested and cloned into the XB3 vector to produce pUAS-/αcZ. The transgene was punfied from vector DΝA by digestion with Sail, and was micro-injected into control mouse embryos to confirm the specificity of gene expression under the tissue specific enhancer.
(d) Constructing a vector carrying a hedgehog gene regulated by an extra- mammalian promoter. To generate the mouse Sonic hedgehog misexpression transgene pWEXP3C-S/z/7, the full length cDΝA of Shh was digested from plasmid 6 1 (Echelard. et al., 1993) with the enzymes EcoRl and Spel. end-filled and cloned into vector pWEXP-3C (Danielian P. et al. (1996) Cell 75:1417-1430) using standard splicing and ligation reactions. The transgene pWEXP3C-S/z/ι was punfied from vector DΝA by digestion with Sail, and was micro-injected into control mouse embryos to determine that the Shh gene encoded the correct functional protein and caused the lethal phenotype. Example 2. Production and genotyping of transgenic mice
Transgenic mice were generated by micro-injection of linear DΝA fragments obtained from vector DΝA into pronuclei of B6CBAF1/J (C57BL/6J x CBA J) zygotes as descnbed (Echelard et al., 1994). The transgenic mouse line Wnt-1/GALA was produced by injection of transgene pWEXP2-GA 4. All transgenic mice were made following standard protocols as descnbed in "Manipulating the Mouse Embryo" B Hogan, 2nd Ed Cold Spring Harbor Press, Cold Spring Harbor, NY (1994).
Founder (G0) transgenic mice were identified by Southern blot of E ?/?I-digested genomic DNA using probes for GAL4 (line WΕXP2-GAL4) or lacZ (lines UAS-/αcZ and UAS-Shh; probes described in Rowitch et al.. 1999, Devel Neurosci., in press, incoφorated herein by reference). Subsequent genotyping of UAS-/αcZ transgenic embryos or mice by PCR was carried out as described in Echelard, et al. (1994). Genotyping of WEXP2-GA 4 and UAS-Shh transgenic embryos or mice was performed using the upstream primer described supra (SEQ LD NO:2) from exon 1 of the untranslated sequence of Wnt-1 and the downstream primer described supra (SEQ LD NO:3) from within GALA or mouse Shh (SEQ ID NO:4) , respectively. PCR conditions were as described in Echelard et al. (1994).
The transgenic mice carrying any one of the vectors that are embodiments of the invention exhibited normal wild-type phenotypes in comparison to parental mice which had not received a transgene. Example 3. Whole mount and section histology, in situ hybridization and immunohistochemistry for assay of misexpression
Analysis of embryos for β-galactosidase activity was carried out as described by Whiting, J. et al. (1992) Genes Devel.5:2048-2059). For analysis of skeletal elements, 18.5 dpc bigenic embryos were processed as described by McLeod. J. et al. (1990) Teratol. 22:229-230.
For analysis of tissues by histological analysis or in situ hybridization, embryos were harvested between 9.5-18.5 dpc, dissected in phosphate buffered saline (PBS) and fixed overnight in 4% paraformaldehyde. Whole mount in situ hybridization was carried out per standard lab protocols. Embryos for histologic analysis, BrDU incorporation, and in situ hybridization, were fixed in either Bouin's or 4% paraformaldehyde overnight or up to 24 hrs, embedded in paraffin wax and sectioned at 6-7 μm. Sections were stained with hematoxylin-eosin or toluidine blue.
In situ hybridization on paraffin sections with radiolabeled anti-sense RNA probes was carried out on either paraformaldehyde or Bouin's fixed tissues according to Wilkinson, D. (1992) In situ hybridization: a practical approach. BRL Press. Darkfield photomicrographs were collected on a Leitz Orthoplan or Nikon E600 compound microscope using a 35 mm camera and Fuji Velva film or a SPOT I digital camera (Diagnostic Imaging). In situ hybridization on frozen sections of paraformaldehyde-fixed tissues with digoxigenin labeled anti-sense probes was carried out as described in Ma, Q. et al. (1997) J. Neurosci.17:3644-3652, and photomicrographs were collected as above. For immunohistochemistry, embryos were either fresh frozen or fixed between 6-24 hrs prior to freezing and cryostat sectioning. Photography of live embryos was carried out in PBS on an Olympus SZH10 microscope using Kodak 64T film, or a Nikon camera and daylight film, respectively. Example 4. Misexpression of hedgehog causes excessive cellular proliferation
For analysis of proliferation, BrDU (Sigma. St. Louis, MO) incoφoration was measured using a dose of 50 μg/kg injected intraperitoneally into pregnant mice exactly 3 hrs before sacrifice at 12.5 and 18.5 dpc. Embryos were fixed either in Bouin's or 4% paraformaldehyde and sectioned as described above. Dividing cells that had incorporated BrDU were identified using monoclonal IgG (Becton-Dickenson) and immunoperoxidase staining (Vector Labs; Burlingame, CA) employing FTTC-tyramide (NEN; Boston, MA). Apoptotic death was measured by techniques established in the art, for example, the TUNEL procedure (Gavrieli. Y. et al.(1992) J.Cell Biol. 119:493-501) on adjacent sections, and electron microscopy. Reagents TdT and biotinylated-16dUTP were obtained from (Boehringer-Mannheim).
To investigate the embodiment of the invention comprising proliferative effects of Shh in the spinal cord, Shh was placed under GAL4IU AS regulation which gives consistent expression of Shh at ectopic locations such as the roofplate of transgenic mouse embryos. The phenotype observed to result from Shh misexpression included hypeφlasia of the dorsal CNS, and activation of Hedgehog transcriptional targets, e.g., Patched and Gli, and was observed in embryos from 9.5-18.5 dpc (Figures 4-6). Suφrisingly, increased cellular proliferation as measured by BrDU incoφoration was observed at 12.5 dpc but not at 18.5 dpc. despite continuous exposure to Shh. Hypeφlastic tissues were predominantly nestin-positive, however, dispersion of tissue samples into cell culture medium yielded differentiation of cells into neurons, astrocytes and oligodendrocytes. Markers of ventral progenitor populations in the spinal cord were expressed with an altered pattern as a consequence of ectopic Shh expression. Example 5. The effect of a lethal mutation in hedgehog protein
To determine whether the Wnt-1 enhancer-mouse Shh transgene (WEXP3c-Shh, which is not under GAL4 regulation) was lethal, approximately 300 mouse embryos were injected and harvested at 10.5 dpc. The phenotype of all embryos that expressed this transgene was the presence of an open neural tube, indicating that the transgene was lethal, unlike the bigenic UAS-Shh mouse line animals having a UAS-GA dependent regulation above.
In one embodiment of a transgenic line of the invention, the yeast transcription factor GALA was expressed in the dorsal CNS under the control of the Wnt- 1 enhancer (WEXP-GA 4: Figure 3). A second transgenic line (UAS-lacZ) directed expression of reporter gene β-galactosidase (lacZ), under control of UAS (Figure 3). When the UAS-lacZ heterozygous animals were mated with WEXP-GAL heterozygotes, 25% of progeny embryos showed β-galactosidase expression in the Wnt-1 pattern of tissues and cells. The progeny capable of expressing β-galactosidase in the Wnt-1 pattern were otherwise normal in phenotype.
This experiment demonstrates that GALA was capable of functioning at its cognate DNA-binding sequence in cells of the developing CNS, that the pattern of gene expression with respect to time and cells of a tissue was programmed by Wnt-1, and that the vector system was capable of activating gene expression of a bacterial reporter transgene under the control of the UAS.
Example 5. The effects of sonic hedgehog misexpression in the embryonic CNS in bigenic mouse progeny
In order to study the effects of Shh misexpression in the embryonic CNS, a transgenic mouse line containing Shh under control of the UAS enhancer (UAS-SAΛ) was generated in Example 2. The UAS-Shh mouse line was observed to be stable, and animals showed no detrimental effects of Shh. However, when animals were crossed to mice from the ΨEXP-GALA line, 25% of embryos were observed at 10.5 dpc to have each developed an open neural tube in the region of the midbrain (Figure 5, Panel E), as a result of ectopic expression of Shh. At 18.5 dpc. the gross phenotype of progeny of the UAS-Shh x WEXP-GAL4 cross (referred to as Shh-Tg) was substantial hypeφlasia of the dorsal brain and spinal cord, as well as hydromyelia (Fig.5). The phenotype was consistent among the progeny observed, indicating 100% penetrance of the Shh gene, i.e., that the phenotype and the genotype of animals coincided in every case, and was observed in at least 50 Shh-Tg progeny embryos. Example 6. Construction of an Indian hedgehog loss of function mutation
The Indian hedgehog gene Lhh has been thought to be expressed in the yolk sac of visceral endoderm from 8 dpc (Farrington, S., et al. (1997) Mech.Dev. 62:197-211), in the gut epithelium lining mid-and hindgut from 10.5 dpc and in the hindstomach and columnar epithelium of inestine and rectum (Bitgood, M. et al. (1995) Dev. Biol. 172:126-138), in tooth dental lamina from 9.5 dpc (Kronmiller, J. et al. (1996) Arch.Oral.Biol.41 :577-583), in the metanephros of the kidney from 14.5 dpc and in adult kidney and proximal tubules, in the retina of the eye (Jensen, A. et al. (1997) Devel.124: 363-371), in chondrocyte cartilage nodules from 11.5 dpc and in maturing chondrocytes overlalpping with prohferative and hypertrophic zones (Bitgood et al.. 1995), and in osteoblast cell lines and osteoblasts enriched cultures from neonatal rat calvariae (Murakami, S. et al. (1997) Endocrinol. 138:1972-1978).
No homozygous mutants have been isolated or constructed, however, to permit further analysis and identification these presumed Lhh tissue targets. To determine whether Lhh is an essential gene, i.e., whether a potential lethal phenotype is demonstrated by an Lhhllhh homozygotes, a targeting vector (Figure 8) based on the structure and restriction sites of the Lhh gene was constructed. The targeting vector carries a DNA with a deletion of the El of Lhh replaced by neo. and having DNA encoding TK following E2 and E3 of the Lhh gene. Following successful isolation of mice carrying the markers of the targeting vector, probes for distinguishing the wild type and insertion knock-out mutant Lhh genes by digestion and analysis of Xhol and Ncol fragments were used, and the predicted sizes of Xhol and Ncol fragments that hybridized with the probes and that were used to identify each genotype, are also shown in Figure 8. Mice carrying the Lhh knockout gene, and heterozygous for the normal Lhh gene were thus constructed.
Example 7. Crossing knock-out heterozygotes to determine the effects of an Indian hedgehog loss of function mutation among homozygous progeny
Mice carrying the knockout mutation constructed in the previous example were bred, and embryos having each of a homozygous wild type genotype, a heterozygous genotype, and a homozygous mutant Ihh genotype were harvested from among all embryos as a function of time after the matings. It was here observed that the significant loss of the embryos having the homozygous mutant Ihh genotype, observed as an overall deviation from the Mendehan ratio of 1:2:1, indicated that embryos of this class have substantially less viability from between 10.5 to 12 5 dpc (Table 1) The data in Table 1 indicate that loss had occurred of a significant fraction of the embryos of the homozygous mutant class ot progeny, compared to the stable numbers ot embryos observed of wild- type and heterozygote classes over this time penod (maintained as a stable ratio of homozygous wild type to Ihh heterozygotes of 1 :2). A dramatic loss in viability of Ihh mutant homozygotes occured after 1 .5 dpc with further decline occurring also after this time point
Embryonic death of Ihh homozygotes was determined to be due to a defect in formation of the blood or the blood supply. A further aspect of the phenotype was a reduction in the size of the main blood vessels observed in the null double Ihh mutant embryos compared with normal embryos (homozygotes and heterozygotes) at 11 5 dpc. These results show that a knockout system utilizing the Ihh gene provides a useful model for the study of vasculogenesis in a mammalian animal Example 8. Collagen π enhancer from early chondrocytes
Bigenic mice were formed by crossing a first parental mouse line having a driver vector with the collagen II enhancer (col II: Metsarante. M. et al. (1995) Dev. Dyn. 204:202-210) used to express GAL4, with a second mouse line having a earner vector with UAS upstream of Ihh. Expression in the embryonic progeny of this cross was compared to that of progeny from crossing the first parent with each of UAS-/αcZ and UAS-Shh. The data show that expression of GALA under control of the collagen LI enhancer restricts expression to chondrocytes, and further that Lhh expression can be specifically activated in chondrocytes.
These data, in combination with data obtained from using Wnt-1 -GAL4 to cause expression specifically in the CNS show that it is possible to combine different transgenic animal lines to achieve new combinations of gene expression in bigenic progeny animals.
Figure imgf000028_0001
Genotypes of embryos from Ihh +/- intercrosses
Figure imgf000028_0003
Table
Figure imgf000028_0002

Claims

What is claimed is-
1. A transgenic non-human mammal, substantially all of whose cells contain a non- viral regulatory DNA sequence linked to a recombinant hedgehog gene introduced into the mammal or an ancestor of the mammal at an embryonic stage.
2. A transgenic non-human mammal according to claim 1, the mammal having an endogenous coding sequence substantially the same as a coding sequence ot the recombinant hedgehog gene.
3. A transgenic non-human mammal according to claim 2, wherein the mammal is a rodent.
4 A transgenic non-human mammal according to claim 3, wherein the rodent is a mouse.
5 A transgenic non-human mammal according to claim 1, wherein the regulatory sequence compnses a UAS sequence (SEQ ID NO:l)
6 A bigenic non-human mammal, substantially all of whose cells contain a non-viral regulatory DNA sequence linked to a recombinant hedgehog gene sequence; and a transcnptional activator sequence, introduced into the mammal or an ancestor ot the mammal at an embryonic stage.
7. A bigenic non-human mammal according to claim 6. having an overexpressed vascular system in the central nervous system.
8. A bigenic non-human mammal according to claim 7. wherein the mammal is an embryo.
9. A bigenic non-human mammal according to claim 8, wherein the mammal is a mouse and is capable of a lit espan of at least 9 dpc
10. A bigenic non-human mammal according to claim 6, wherein the transcriptional activator gene is GAL4.
1 1. A bigenic non-human mammal according to claim 6. wherein the transcriptional activator gene is regulated by a tissue specific promoter.
12. A bigenic non-human mammal according to claim 6, wherein the tissue specific promoter is a wnt promoter.
13. A bigenic non-human mammal according to claim 6. wherein the tissue specific promoter is a col LL promoter.
14. A bigenic non-human mammal according to claim 6. wherein the transcriptional activator gene is regulated by an inducible promoter.
15. A bigenic non-human mammal according to claim 14. wherein the inducible promoter is regulated by a fusion of GAL4 protein and a second protein.
16. A bigenic non-human mammal according to claim 15. wherein the second protein is activated by binding an RU486 mifepristone molecule.
17. A bigenic non-human mammal according to claim 6. for use as a model for disease.
18. A bigenic non-human mammal according to claim 17, wherein the disease is cancer.
19. A bigenic non-human mammal according to claim 18. wherein the cancer is selected from the group consisting of a cancer of the breast, skin, prostate, kidney, lung, and central nervous system.
20. A bigenic non-human mammal according to claim 18. wherein the cancer is a pnmitive neuroectodermal tumor.
21. A bigenic non-human mammal according to claim 19. wherein the cancer is a medulloblastoma
22 An isolated cell of a bigenic non-human mammal obtained from the mammal of claim 6
23. An isolated cell of the bigenic non-human mammal according to claim 22, selected from the group consisting ot an embryonic-stem cell, a tumor cell, a nerve cell, and a vascular cell
24 A transgenic non-human mammal having an insertion mutation of an Lhh gene.
25. A transgenic mammal non-human according to claim 24, wherein the insertion compnses a selectible marker.
26. A transgenic mammal non-human according to claim 25, wherein the insertion compnses a deletion of the Lhh gene
27. An isolated population of cells selected from the group consisting of a transgenic non-human mammal according to claim 1, and its bigenic progeny
28. A method of identifying the effect of misexpression of a target transgene in a signal transduction pathway that includes a hedgehog protein, in a progeny animal, comprising:
(a) forming a first transgenic animal having a first transgene encoding a transcnptional activator of a eukaryotic species different from the animal; (b) forming a second transgenic animal having a second transgene comprising the target gene and having a recognition sequence for the transcnptional activator that is located upstream of the target gene. (c) mating the first and the second transgenic animals to form a bigenic animal; and
(d) causing the target gene to be misexpressed in the animal.
29. A method of identifying the effect of misexpression of a target transgene according to claim 28. wherein the transgenic animals are formed from an animal which is an animal model disease line.
30. A method of identifying the effect of misexpression of a target transgene according to claim 28, wherein the animal model is selected from the group consisting of a cancer and an autoimmune disease.
31. A method of assaying for a temporal requirement for the presence of a hedgehog protein on progression of a disease, comprising: (a) forming a bigenic animal according to the method of claim 28;
(b) treating the bigenic animal for an effective time interval with an agent that interrupts the hedgehog pathway: and
(c) assaying the progression of the disease in the animal in (b) compared to the progression of the disease in the animal in (a).
32. A method of assaying for a temporal requirement for the presence of a hedgehog protein during progression of the disease according to claim 31 , wherein the treatment comprises administration of an agent selected from the group consisting of an inhibitor of cholesteroid biosynthesis, an anti-hedgehog antibody, and a sterol analog.
33. A method for determining therapeutic efficacy of an agent, comprising:
(a) forming a bigenic mouse according to claim 28, wherein the misexpressed target gene is a hedgehog gene:
(b) administering the agent to the mouse; and (c) determining therapeutic efficacy of the agent.
34. A method according to claim 33, wherein in (b) further comprises administering the agent to the mouse in a pharmaceutical carrier at an effective dose.
35. A method according to claim 34. wherein (c) further comprises comparing lifespans of the bigenic mouse of (b) with the bigenic mouse of (a).
36. A method according to claim 29, wherein the bigenic mouse in (a) is an embryo.
37. A method of obtaining an expanded population of neural stem cells from a subject, comprising: treating a neural stem cell from the subject with a hedgehog protein, so that proliferation of the stem cell provides an expanded population of neural stem cells.
38. A method according to claim 37, wherein the hedgehog protein is sonic hedgehog protein.
39. A method according to claim 37, wherein the subject has a condition selected from the group consisting of Parkinson's disease, Alzheimer's disease, and spinal cord injury.
40. A method according to claim 39, wherein the condition is treated by administration to the subject of a sample of the expanded cell population.
41. A method for inactivating an Lhh gene in a non-human mammal, comprising:
(a) constructing a recombinant vector carrying an Lhh insertion mutation;
(b) injecting an embryonic stem cell with the vector: and
(c) implanting the stem cell into an adult mammal.
42. A method for inactivating an Lhh gene according to claim 41, wherein the vector in (a) carries a deletion of exon 1 of the Lhh gene.
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