WO2003064658A1 - Alpha 1,3 galactosyltransferase mutant pigs - Google Patents

Abstract

The invention is directed to genetically modified animals bearing mutations at a pre-selected genetic locus and methods of generating such genetically modified animals. In particular, the invention is directed to genetically modified mutant pigs bearing mutations in the alpha 1,3 galactosyltransferase (GGTA1) gene and methods of obtaining such animals by co-administration of Drosophila Recombination-Associate Protein (DRAP) or a DRAP function conserved variant and an oligonucleotide complementary to the GGTA1 gene.

Description

ALPHA 1,3 GALACTOSYLTRANSFERASE MUTANT PIGS

CROSS REFERENCE TO RELATED APPLICATION

The present application claims benefit of priority under 35 U.S.C. § 119(e) of provisional application serial no. 60/353,946, filed February 2, 2002, which is hereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention is directed to genetically modified animals bearing mutations at a pre-selected genetic locus and methods of generating such genetically modified animals. In particular, the invention is directed to genetically modified mutant pigs bearing mutations in the alpha 1,3 galactosyltransferase (GGTAl) gene and methods of obtaining such animals by co-administration of Drosophila Recombination- Associate Protein (DRAP) or a DRAP function conserved variant and an oligonucleotide complementary to the GGTAl gene.

BACKGROUND OF THE INVENTION

A shortage of human organs and tissues available for transplant has lead to a search for suitable animal organ and tissue sources for xenotransplantation into humans. Pigs are a likely source of tissues and organs for human xenotransplantation because of anatomical and physiological similarities to humans and the ease with which they can be obtained in large numbers. A major barrier to using pigs as donors for human xenotransplantation is the hyperacute rejection of transplanted pig tissue that has been transplanted into primates, leading to organ failure. Reducing or eliminating hyperacute rejection is therefore an important goal in the development of pigs as donors for human xenotransplantation.

Hyperacute rejection is due to the presence of terminal α-1,3- galactosyl (gal) epitopes on the surface of pig cells. In the course of evolution, humans and Old World monkeys have lost the galactosyltransferase that adds the - 1,3 gal epitopes and therefore produce "natural" anti-α-1,3 gal antibodies (i.e., antibodies present without prior known immunization) to the epitope. Xenotransplantation induces further amounts of anti-α-1,3 antibodies. Hyperacute rejection is caused by rapid activation of complement, triggered by the binding of the anti- -1,3 gal antibodies to epitopes present on the surface of cells in transplanted tissue or organs.

Hyperacute rejection of porcine tissue and organs can be delayed or avoided by removing circulating anti- -1,3 gal antibodies and slowing complement activation. These measures are only temporary, however. Transplanted tissue and organ are ultimately rejected, due to returning antibody acting in concert with complement. Similarly, efforts to reduce the level of epitope on the surface of pig cells indirectly has lead to partial reduction of epitope, but has failed to yield donor pig cells with extended tissue or organ survival in primate hosts. In contrast to indirect methods of lowering α-1, 3 gal epitopes that reduce, but fail to eliminate, epitopes from cells, mutant pigs lacking activity of the porcine α-1,3 galactosyltransferase gene (GGTAl) would lack the epitope and provide protection from hyperacute rejection.

Two groups have recently reported obtaining pigs bearing a targeted disruption of a single GGTAl allele (Dai, et al, Nature Biotech., 20: 251-255, 2002; Lai, βt al, Science, 295:1089-1092, 2002). In both instances, a single GGTAl allele was mutated by targeted disruption of porcine somatic cells in vitro, followed by nuclear transfer of the mutated somatic cells and subsequent embryo transfer. Starting with a cell line bearing the single GGTAl allele disruption, one of these groups subsequently used a second round of mutagenesis of cultured somatic cells to select for a cell line that failed to express α-1,3 gal on the surface of cells, followed by nuclear transfer of the cell and embryo transfer, to obtain α-1,3 galactosyltransferase-deficient pigs lacking α-1,3 gal epitopes on their cell surfaces (Phelps, et al, Science, 299:411-414, 2003). The transferase-deficient pigs thus obtained contained one GGTAl allele with a point mutation and a second GGTAl allele with an insertion of a neomycin resistance gene. (Phelps, et al, Science, 299:411-414, 2003). The transferase-deficient pigs were apparently normal, indicating that in pigs, as previously found in mice, α-1,3 galactosyltransferase activity is apparently not necessary for normal development and survival. The results obtained using nuclear transfer methods to obtain GGTAl mutants demonstrate the feasibility of obtaining α-1,3 galactosyltransferase deficient pigs for use in xenotransplantation. The nuclear transfer methods used to obtain the GGTAl knockouts, however, have several weaknesses. Nuclear transfer-based methods require first performing targeted gene disruption in cell culture, followed by nuclear transfer. The method therefore requires two steps. Furthermore, these steps yield pigs with a mutation in only a single GGTAl allele. Generation of mutant pigs with mutations in both GGTAl alleles requires either a second round of mutagenesis of cells cultured in vitro followed by a second round of nuclear transfer, or the mating of single allele mutants. In either case, the generation of pigs with both GGTAl alleles mutated is delayed. Additionally, the GGTAl mutants generated by nuclear transfer techniques have the undesirable characteristic of including heterologous DNA, typically an antibiotic resistance gene, at the GGTAl locus. Finally, in some instances, use of nuclear transfer methods to generate mutations can lead to errors in genetic imprinting that may be associated abnormal development or future growth disturbances.

Accordingly, there is a need for improved methods of obtaining porcine GGTAl mutants that are efficient, easy to practice and which do not require the insertion of heterologous DNA at the GGTAl locus and which do hold the potential for genetic imprinting errors. As disclosed in U.S. Patent Application Serial

No. 09/621,377, filed July 21, 2000, now U.S. Patent No. , the present inventor has previously found that mutations can be targeted to a pre-selected gene by co-administering Drosophila Recombination- Associated Protein (DRAP) and an oligonucleotide complementary to the pre-selected gene, i the present application, the inventor shows that when DRAP and oligonucleotides complementary to GGTAl are co-injected into pig embryos that are then reimplanted into surrogate mothers, the derived genetically modified pigs have reduced α-1,3 gal epitopes on their cell surfaces. Examination of GGTAl alleles from the genetically modified pigs indicates that in at least some instances DRAP mediated mutation at the GGTA locus leads to multiple mutations on each GGTAl allele. The methods described herein can be used for a new rapid one-step method for obtaining GGTAl bi-allelic mutant pigs. Mutants with reduced amounts or lacking α-1,3 gal epitopes are will be useful as donors for human xenotransplantation. SUMMARY OF THE INVENTION

In certain embodiments, the invention provides a method of promoting mutation of the porcine alpha 1,3 galactosyltransferase (GGTAl) gene in a cell comprising introducing DRAP or a function-conserved variant thereof and one or more oligonucleotide complementary to GGTAl into the cell to promote said mutation, hi a preferred embodiment, the cell is a pig cell.

In other embodiments the invention provides a method for generating a genetically modified pig bearing a bi-allelic mutant GGTAl that does not comprise an inserted heterologous sequence, comprising introducing DRAP or a function- conserved variant thereof and an oligonucleotide complementary to the GGTAl gene into a porcine cell capable of developing into said genetically modified pig and thereby causing in one step one or more mutation in each allele of the GGTAl gene, wherein said GGTAl gene of said cell does not comprise an inserted heterologous sequence, and implanting said cell into a recipient female capable of bearing the cell to term, and allowing the cell to develop to term, thereby obtaining said genetically modified animal.

In other embodiments, the invention provides a genetically modified pig comprising a bi-allelic knockout of the GGTAl gene that does not comprise an inserted heterologous nucleic acid sequence in said GGTAl gene, wherein said bi- allelic knockout in said genetically modified pig is produced by a single step process comprising introducing DRAP or a function-conserved variant thereof and an oligonucleotide complementary to said GGTAl gene into a porcine cell capable of developing into said genetically modified pig and which cell does not comprise an inserted heterologous nucleic acid sequence in its GGTAl gene, transplanting said cell into a recipient female animal capable of bearing said cell to term, and allowing the cell to develop to term, thereby obtaining said genetically modified pig with a knockout of the GGTA gene without the step of mating mono-allelic knockout animals. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 depicts the level of lectin FITC-IB4 staining of fibroblast cell lines derived from pigs that developed from embryos co-injected with DRAP and mutant GGTAl oligonucleotides. Fig. 2 depicts the distribution of staining levels of the cell lines depicted in Fig. 1.

DETAILED DESCRIPTION OF THE INVENTION

All patent applications, patents and literature references cited in this specification are hereby incorporated by reference in their entireties.

The present invention provides for genetically modified animals bearing mutations at a pre-selected genetic locus and methods of generating such genetically modified animals. In particular, the invention provides for mutant pigs bearing mutations in the α-1,3 galactosyltransferase (GGTAl) gene and methods of obtaimng such animals by co-administration of Drosophila Recombination- Associate Protein (DRAP) or a DRAP function conserved variant and an oligonucleotide complementary to the GGTAl gene. The GGTAl alleles of animals generated by such methods can then be analyzed, e.g., sequenced, to determine the effect of the co- injection method. Co-injection of DRAP or a DRAP function-conserved variant and an oligonucleotide complementary to the GGTAl gene lead to mutations on one or both GGTAl alleles.

The methods for obtaining mutations in the porcine GGTAl gene described herein are have an advantage over methods known in the art in that the present methods can yield bi-allelic GGTAl mutants in a single-round of DRAP- or DRAP conserved-function variant-mediated mutagenesis. Accordingly, the present method affords a "single-step" method of obtaining bi-allelic GGTAl mutants, without having to undergo additional steps of generating a GGTAl in cultured cells and/or crossing GGTAl mono-allelic mutants to obtain a GGTAl bi-allelic mutant.

Porcine 1,3 alpha galactosyltransferase gene

The GGTAl genomic sequence is available from, e.g., Genbank, or other database well known to those of ordinary skill in the art. The sequences of the GGTAl cDNA and the α-1,3 galactosyltransferase enzyme encoded by the GGTAl cDNA are given respectively in SEQ ID NO: 1 and SEQ ID NO: 2. The enzyme catalytic site is found within exon 9 of the GGTCA1 cDNA, which begins at nucleotide 438 of the cDNA sequence and extends through the end of the cDNA (see SEQ ID NO: 1). Exon 9 includes the third base of the triplet encoding amino acid 141 of the α-1,3 galactosyltransferase enzyme through the remainder of the 371 amino acid coding sequence (see SEQ ID NO: 1 and 2).

Oligonucleotides for use in methods of DRAP-mediated recombination

Oligonucleotides used to generate porcine GGTAl mutations can be complementary to GGTAl intron or exon sequences, or both intron and exon sequences. In a preferred embodiment, GGTAl oligonucleotides are complementary to GGTAl exon sequences, most preferably GGTAl exon 9.

Oligonucleotides for use with DRAP may be provided as, without limitation, single stranded 5 'OH oligonucleotides, 3 'OH oligonucleotides or 5' phosphate (5'P) oligonucleotides. Double stranded duplex oligonucleotides may also include these modifications, which may be found independently at the ends of either strand. The strands of a double stranded oligonucleotide may be completely complementary. Such a double stranded oligonucleotide is fully duplex. Alternatively, one or both of the single strand oligonucleotides that comprise the double stranded oligonucleotide may include a sequence that is not complementary to a sequence on the opposite strand, and which therefore extends from the end of the duplex base-paired region, thus forming a single stranded extension ("overhang"). Overhangs may be present at either one end or both ends of the double stranded oligonucleotide. It will be appreciated that a double stranded oligonucleotide may comprise overhangs on one or both strands. The overhangs may be either 5 ' or 3 'overhangs.

The length of oligonucleotides may vary from about 9 nucleotides to about 8000 nucleotides in length. Preferred oligonucleotides are from about 9 to about 100 nucleotides in length. More preferred are oligonucleotides from about 15 to about 45 nucleotides in length. Most preferred are oligonucleotides from about 30 to about 35 nucleotides in length. The length of a double stranded oligonucleotide is defined as the number of complementary nucleotide base-pairs plus the number of any non-complementary nucleotides that are present (i.e., plus the number of nucleotides in any overhang). For example, a double stranded oligonucleotide comprising a central duplex region of 20 complementary base-pairs and two 5 'OH overhangs of 10 nucleotides each is defined as 40 nucleotides in length.

The single stranded extensions found on double stranded oligonucleotides may be of varied length. Preferably the single stranded extensions are about 1 to 50 nucleotides in length. More preferably the single stranded extensions are about 4 to 32 nucleotides in length. Still more preferably the single stranded extensions are about 4 to 15 nucleotides in length. Most preferably the single stranded extensions are about 9 to 15 nucleotides in length. Double stranded duplex oligonucleotides may be formed by any method known in the art. In a preferred method, double stranded nucleotides are formed, for example, by mixing single stranded oligonucleotides that are either completely or substantially complementary, thereby causing the single stranded oligonucleotides to anneal and form duplexes. The single stranded nucleotides need not be completely complementary and may include, for example, mismatches, within an otherwise complementary string of nucleotides. In preferred embodiments, the single stranded oligonucleotides that are to be annealed contain nucleotide sequences at their respective 5' or 3' ends that are not complementary. Annealing such oligonucleotides provides double stranded duplex oligonucleotides with, depending on the position of the non complementary region, either 5' or 3 ' single strand extensions (i.e., "overhangs").

Double stranded duplex oligonucleotides with extensions can also be produced by digestion of duplex DNA by a variety of restriction enzymes, either alone or in conjunction with the use of specific exo- and endo-nucleases, chemical degradation of DNA ends or by ligating linker-adaptors with single stranded extensions to blunt-ended DNA. Such methods extend the range of potential substrates useful for the modification of an endogenous locus with DRAP. They also provide a direct and rapid route for the identification of any disease phenotype- causing mutant gene that can be localized to a restriction fragment with small single stranded extensions. In the latter case, a series of restriction fragments from an affected animal could be tested for its causal relationship to the disease by co- injection with DRAP to produce an animal having the disease phenotype.

Oligonucleotides may comprise nucleic acid (RNA, DNA, PNA or other DNA- compatible chemically-derived purine/pyrimidine base-pairing oligonucleotide) having a native or mutant sequence to homologous regions in any duplex DNA such as genomic DNA, isolated linear DNA or cloned DNA in vivo or in vitro.

DRAP and DRAP function-conserved variant

DRAP protein may be obtained from natural sources or from recombinant sources. Methods for purifying DRAP are described in U.S. Patent Application Serial No. 09/621,377, filed July 21, 2000, now U.S. Patent No. . Preferably, DRAP is produced recombinantly, e.g., as described in application serial no. 09/621, 377, supra. It is also preferred that DRAP protein be isolated and purified for use.

Recombinant DRAP can be isolated following expression of a DRAP cDNA clone of [SEQ ID NO: 3], a DNA encoding the longest Open Reading Frame (ORF) contained within the isolated cDNA clone sequence which corresponds to nt 104-610 of the isolated cDNA clone [SEQ ID NO: 4] or a DNA encoding DRAP corresponding to nt 134-610 of the isolated cDNA clone [SEQ ID NO: 5]. The DRAP polypeptide comprises the sequence of SEQ ID NO: 6. DNA vectors and transformed cells suitable for recombinant expression of DRAP can be used.

DRAP protein exhibits both recombinase (homology-dependent strand transferase) and topoisomerase activity. This combination of properties makes DRAP useful for to methods of using DRAP and oligonucleotides to perform recombination events, including, for example, homologous recombination and gene conversion events. Hence, DRAP can be used in procedures to produce, for example, genetically modified animals. Mutagenesis can also be performed using DRAP function-conserved variants of DRAP. A "function-conserved" variant of DRAP is defined as a polypeptide that is encoded by a nucleic acid that hybridizes to a DRAP-encoding nucleic acid, e.g., a nucleic comprising a DRAP nucleic acid of sequence SEQ ID NO: 3-5, and which has topoisomerase and recombinase activities. One of ordinary skill in the art will appreciate that function-conserved variants of DRAP will have

DRAP activity or activity substantially similar to DRAP and will thus be useful in the methods of mutagenesis described herein. Function-conserved variants of DRAP can include, for example and without limitation, DRAP fusion proteins or DRAP polypeptides bearing one or more conserved amino acid changes, or a change of one or more in-frame insertion of 1, 2 or 3 amino acids or a change of one more in-frame deletion of 1, 2 or 3 amino acids, or combination of any of the foregoing changes. In a preferred embodiment, a DRAP function-conserved variant is at least 90% identical to DRAP (SEQ ID NO: 6). Further preferred is where a DRAP function-conserved variant is at least 95% identical to DRAP (SEQ ID NO: 6). Still further preferred is where a DRAP function-conserved variant is at least 99% identical to DRAP (SEQ ID NO: 6). As used herein, percent identity to DRAP is determined using the Bestfit program available from Accelrys (formerly Genetics Computer Group (GCG)) set to standard parameters. In other preferred embodiments, a DRAP function-conserved variant differs from DRAP SEQ ID NO: 6 at 1-16 positions, wherein each such differences are determined by aligning DRAP SEQ ID NO: 6 with a DRAP function- conserved variant and summing the number of positions between the first and final amino acids of SEQ ID NO: 6, inclusive, wherein the function-conserved variant contains an amino acid that is not identical to the amino acid at the corresponding position of SEQ ID NO: 6 or the function-conserved variant includes an amino acid insertion or deletion at a position relative to a corresponding position of SEQ ID NO: 6, wherein the function-conserved variant and SEQ ID NO: 6 are aligned to minimize such differences. Further preferred is where a DRAP function-conserved variant differs from DRAP SEQ ID NO: 6 at 1, 2, 3, 4, 5 , 6, 7, 8, 9 or 10 positions. Still further preferred is where a DRAP function-conserved variant differs from DRAP SEQ ID NO: 6 at 1, 2, 3, 4, or 5 positions. Preferred differences between a DRAP function-conserved variant and DRAP are conservative amino acid changes. With regard to the aforementioned differences between DRAP and a DRAP function- conserved variant, preferably, 1-16 of said differences are conservative amino acid changes; more preferably, 5-16 of said differences are conservative amino acid changes; still more preferably, 11, 12, 13, 14, 15 or 16 of said differences are conservative amino acid changes; and, most preferably, all of said differences are conservative amino acid changes. Conservative substitution tables providing functionally similar amino acids are well known in the art. The following six groups each contain amino acids that are conservative substitutions for one another: (1)

Alanine (A), Serine (S), Threonine (T); (2) Aspartic acid (D), Glutamic acid (E); (3) Asparagine (N), Glutamine (Q); (4) Arginine (R), Lysine (K); (5) Isoleucine (I), Leucine (L), Methionine (M), Valine (V); and (6) Phenylalanine (F), Tyrosine (Y), Tryptophan (W). See also, Creighton, Proteins W.H. Freeman and Company, 1984. Definitions:

"Gene" as used herein refers to a region of nucleic that when under the control of an appropriate promoter is transcribed into an RNA that is ultimately translated into a protein encoded by the region of the nucleic acid or a region of nucleic acid that had previously had the capacity when under the control of an appropriate promoter to be transcribed into an RNA and translated into a protein, but which as been mutated to a form such that it no longer has the capacity when under the control of a promoter to be transcribed into RNA and/or no longer has the capacity to encode an RNA that is translated into a protein.

In diploid mammalian cells, each gene comprises two alleles. A "wild- type" gene comprises non-mutated alleles, each having a sequence found in normal naturally occurring members of a species and encoding a normal active "wild-type" protein. Mutant genes may be mono-allelic or bi-allelic, i.e., may comprise one or two mutant alleles. One of ordinary skill in the art will appreciate that mutant genes may contain one or more point mutation, which may be a missense or nonsense mutation, or one or more insertion or deletion, each of which may either by an in- frame or frameshift mutation. Insertion mutations can be formed by inserting "heterologous DNA" into a gene, wherein "heterologous DNA" refers to a DNA sequence that is not found in the wild-type type and has been inserted into the gene by recombination of the gene with an isolated nucleic acid comprising the "heterologous DNA." Heterologous DNA may include, for example and without limitation, an antibiotic resistance gene.

"Recombinase activity" as used herein refers to the promotion of homologous pairing and DNA strand exchange. Recombinases can be site-specific or general and can operate in a variety of biological contexts by a variety of biochemical mechanisms. "Topoisomerase activity" as used herein refers to the ability of a protein to change the linking number of DNA. The "linking number" as used herein refers to the number of times the two strands of a closed DNA duplex cross over each other. Methods for measuring recombinase activity and topoisomerase activity are described in application serial no. 09/621, 377, supra.

"Nucleic acid" or "polynucleotide" as used herein refer to purine- and pyrimidine-containing polymers of any length, either polyribonucleotides or polydeoxyribonucleotides or mixed polyribo-polydeoxyribo nucleotides. This includes single- and double-stranded molecules, i.e., DNA-DNA, DNA-RNA and RNA-RNA hybrids, as well as "protein nucleic acids" (PNA) formed by conjugating bases to an amino acid backbone. This also includes nucleic acids containing modified bases. An "isolated" polypeptide or nucleic acid is defined as one that is unaccompanied by at least some of the material with which it is associated in its natural state. Generally, an isolated polypeptide constitutes at least about 1%, preferably at least about 10%, and more preferably at least about 50% by weight of the total protein in a given sample. Included in the polypeptide weight are alternative forms such as differentially glycosylated or phosphorylated or otherwise post- translationally modified forms. An "isolated" nucleic acid sequence is present as other than a naturally occurring chromosome or transcript in its natural state and typically is removed from at least some of the proteins with which it is normally associated on a natural chromosome. A "partially pure" nucleotide sequence constitutes at least about 5%, preferably at least about 30%, and more preferably at least about 90% by weight of total nucleic acid present in a given fraction.

Also encompassed for use by the invention are nucleic acids that are hybridizable to, or derived from, the DRAP sequences described above.

A nucleic acid or polypeptide sequence that is "derived from" a designated sequence refers to a sequence that is related in nucleotide or amino acid sequence to a region of the designated sequence. For nucleic acid sequences, this encompasses sequences that are homologous or complementary to the sequence, as well as "sequence-conserved variants" and "function-conserved variants." For polypeptide sequences, this encompasses "function-conserved variants." Sequence- conserved variants are those in which a change of one or more nucleotides in a given codon position results in no alteration in the amino acid encoded at that position. Function-conserved variants are those in which a given amino acid residue in a polypeptide has been changed without altering the overall conformation and function of the native polypeptide, including, but not limited to, replacement of an amino acid with one having similar physico-chemical properties (such as, for example, acidic, basic, hydrophobic, and the like, see, e.g., supra). "Function-conserved" variants of

DRAP are described supra.

Nucleic acids are "hybridizable" to each other when at least one strand of nucleic acid can anneal to another nucleic acid strand under defined stringency conditions. Stringency of hybridization is determined, e.g., by a) the temperature at which hybridization and/or washing is performed, and b) the ionic strength and polarity (e.g., formamide concentration) of the hybridization and washing solutions, as well as other parameters. Hybridization requires that the two nucleic acids contain substantially complementary sequences; depending on the stringency of hybridization, however, mismatches may be tolerated. The appropriate stringency for hybridizing nucleic acids depends on the length of the nucleic acids and the degree of complementarity, variables well known in the art.

In certain embodiments, the invention relates to nucleic acids capable of hybridizing with DRAP nucleic acid sequences or with their complements under high stringency hybridization conditions, an example of which is defined below.

-- Prehybridization treatment of the support (e.g., nitrocellulose filter or nylon membrane), to which is bound the nucleic acid capable of hybridizing with that of D. melanogaster DRAP, at 65°C for 6 hours with a solution having the following composition: 4 x SSC, 10 x Denhardt (IX Denhardt is 1% Ficoll, 1% polyvinylpyrrolidone, 1% BSA (bovine serum albumin); 1 x SSC consists of 0.15M of NaCl and 0.015M of sodium citrate, pH 7);

~ Replacement of the pre-hybridization solution in contact with the support by a buffer solution having the following composition: 4 X SSC, 1 X Denhardt, 25 mM NaPO₄, pH 7, 2 mM EDTA, 0.5% SDS, 100 μg/ml of sonicated salmon sperm DNA containing a nucleic acid derived from the sequence of the DRAP as probe, in particular a radioactive probe, and previously denatured by a treatment at

100°C for 3 minutes;

~ Incubation for 12 hours at 65°C; ~ Successive washings with the following solutions: (i) four washings with 2 X SSC, 1 X Denhardt, 0.5% SDS for 45 minutes at 65°C; (ii) two washings with 0.2 X SSC, 0.1 % SDS for 45 minutes at 65°C; and (iii) 0.1 x SSC,

0.1% SDS for 45 minutes at 65°C.

It will be understood that the conditions of hybridization defined above constitute preferred conditions for high stringency hybridization, but are in no way limiting and may be modified without in any way affecting the properties of recognition and hybridization of the probes and nucleic acids mentioned above.

The salt conditions and temperature during the hybridization and the washing of the membranes can be modified in the sense of a greater or lesser stringency without the detection of the hybridization being affected. For example, it is possible to add formamide in order to lower the temperature during hybridization.

Expression of DRAP and DRAP function-conserved variants A large number of vectors, including plasmid and fungal vectors, have been described for expression in a variety of eukaryotic and prokaryotic hosts. Such vectors will often include one or more replication systems for cloning or expression, one or more markers for selection in the host, e.g., antibiotic resistance, and one or more expression cassettes. The inserted DRAP or DRAP function-conserved variants coding sequences may be synthesized, isolated from natural sources, prepared as hybrids, etc. Ligation of the coding sequences to the transcriptional regulatory sequences may be achieved by known methods. Suitable host cells may be transformed/transfected/infected by any suitable method including electroporation, CaCl₂ mediated DNA uptake, fungal infection, microinjection, microprojectile, or other established methods known in the art.

A wide variety of host/expression vector combinations may be employed in expressing DNA sequences encoding DRAP and DRAP function- conserved variants. Useful expression vectors, for example, may consist of segments of chromosomal, non-chromosomal and synthetic DNA sequences. Suitable vectors include derivatives of SN40 and known bacterial plasmids, e.g., E. coli plasmids col El, pCRl, pBR322, pMal-C2, pET, pGEX (Smith et al, Gene 67:31-40, 1988), pMB9 and their derivatives, plasmids such as RP4; phage DΝAs, e.g., the numerous derivatives of phage 1, e.g., ΝM989, and other phage DNA, e.g., M13 and filamentous single stranded phage DNA; yeast plasmids such as the 2 micron plasmid or derivatives thereof; vectors useful in eukaryotic cells, such as vectors useful in insect or mammalian cells; vectors derived from combinations of plasmids and phage DNAs, such as plasmids that have been modified to employ phage DNA or other expression control sequences; and the like.

Appropriate host cells for expressing protein include bacteria, Archaebacteria, fungi, especially yeast, and plant and animal cells, especially mammalian cells. Of particular interest are E. coli, B. subtϊlis, S. cerevisiae, Sf9 cells,

C129 cells, 293 cells, Neurospora, and CHO cells, COS cells, HeLa cells, and immortalized mammalian myeloid and lymphoid cell lines. Preferred replication systems include Ml 3, ColEl, SN40, baculovirus, lambda, adeno virus, and the like. A large number of transcription initiation and termination regulatory regions have been isolated and shown to be effective in the transcription and translation of heterologous proteins in the various hosts. Examples of these regions, methods of isolation, manner of manipulation, etc. are known in the art. Under the appropriate expression conditions, host cells can be used as a source of recombinantly produced DRAP or DRAP function-conserved variants.

Advantageously, vectors may also include a promoter sequence operably linked to the DRAP or DRAP function-conserved variant-encoding portion. The encoded DRAP or DRAP function-conserved variant may be expressed by using any suitable vectors and host cells, using methods disclosed or cited herein or otherwise known to those skilled in the relevant art. The particular choice of vector/host is not critical to the invention.

A "promoter sequence" is a DNA regulatory region capable of binding RNA polymerase in a cell and initiating transcription of a downstream (3' direction) coding sequence. For purposes of defining the present invention, the promoter sequence is bounded at its 3' terminus by the transcription initiation site and extends upstream (5' direction) to include the minimum number of bases or elements necessary to initiate transcription at levels detectable above background. Within the promoter sequence will be found a transcription initiation site (conveniently defined for example, by mapping with nuclease SI), as well as protein binding domains (consensus sequences) responsible for the binding of RNA polymerase.

Expression of DRAP or DRAP function-conserved variants maybe controlled by any promoter/enhancer element known in the art, but these regulatory elements must be functional in the host selected for expression. Promoters which may be used to control DRAP or DRAP-function conserved variant gene expression include, but are not limited to, Cytomegalovirus ("CMN") immediate early promoter (CMN promoter; US Patent Νos. 5,385,839 and 5,168,062) the SN40 early promoter region (Benoist and Chambon, 1981, Nature 290: 304-310), the promoter contained in the 3' long terminal repeat of Rous sarcoma virus (Yamamoto, et al, 1980, Cell 22: 787-797), the herpes thymidine kinase promoter (Wagner et al, 1981, Proc. Natl. Acad. Sci. U.S.A. 78: 1441-1445), the regulatory sequences of the metallothionein gene (Brinster et al, 1982, Nature 296: 39-42); prokaryotic expression vectors such as the β-lactamase promoter (Nilla-Kamaroff, et al, 1978, Proc. Νatl. Acad. Sci. U.S.A. 75: 3727-3731), or the tac promoter (DeBoer, et al, 1983, Proc. Natl. Acad. Sci. U.S.A. 80: 21-25); see also "Useful proteins from recombinant bacteria" in Scientific American, 1980, 242: 74-94; promoter elements from yeast or other fungi such as the Gal 4 promoter, the ADC (alcohol dehydrogenase) promoter, PGK (phosphoglycerol kinase) promoter, alkaline phosphatase promoter; and the animal transcriptional control regions, which exhibit tissue specificity and have been utilized in transgenic animals: elastase I gene control region which is active in pancreatic acinar cells (Swift et al, 1984, Cell 38: 639-646; Ornitz et al, 1986, Cold Spring Harbor Symp. Quant. Biol. 50: 399-409; MacDonald, 1987, Hepatology 7: 425-515); insulin gene control region which is active in pancreatic beta cells (Hanahan, 1985, Nature 315: 115-122), immunoglobulin gene control region which is active in lymphoid cells (Grosschedl et al, 1984, Cell 38: 647-658; Adames et al, 1985, Nature 318: 533-538; Alexander et al, 1987, Mol. Cell. Biol. 7: 1436-1444), mouse mammary tumor virus control region which is active in testicular, breast, lymphoid and mast cells (Leder et al, 1986, Cell 45: 485-495), albumin gene control region which is active in liver (Pinkert et al, 1987, Genes and Devel. 1: 268-276), alpha-fetoprotein gene control region which is active in liver (Krumlauf et al, 1985, Mol. Cell. Biol. 5: 1639-1648; Hammer et al, 1987, Science 235:53-58), alpha l-antitrypsin gene control region which is active in the liver (Kelsey et al, 1987, Genes and Devel. 1: 161-171), beta-globin gene control region which is active in myeloid cells (Mogram et al, 1985, Nature 315: 338-340; Kollias et al, 1986, Cell 46: 89-94), myelin basic protein gene control region which is active in oligodendrocyte cells in the brain (Readhead et al, 1987, Cell 48: 703-712), myosin light chain-2 gene control region which is active in skeletal muscle (Sani, 1985, Nature 314: 283-286), and gonadotropic releasing hormone gene control region which is active in the hypothalamus (Mason et al, 1986, Science 234: 1372-1378).

"Purification" of DRAP or DRAP function-conserved variants refers to the isolation of the polypeptide in a form that allows its recombinase/topoisomerase activity to be measured without interference by other components of the cell in which the polypeptide is expressed. Methods for polypeptide purification are well-known in the art, including, without limitation, preparative disc-gel electrophoresis, isoelectric focusing, HPLC, reversed-phase HPLC, gel filtration, ion exchange and partition chromatography, and countercurrent distribution. For some purposes, it is preferable to produce the polypeptide in a recombinant system in which the protein contains an additional sequence tag that facilitates purification, such as, but not limited to, a polyhistidine ("His₆") sequence. The polypeptide can then be purified from a crude lysate of the host cell by chromatography on an appropriate solid-phase matrix. Alternatively, antibodies produced against DRAP or DRAP function-conserved variants can be used as purification reagents. Other purification methods known in the art are possible.

ot-1,3 galactosyltransferase mutant swine

DRAP and DRAP function-conserved variant- mediated gene disruption can be carried out in order to generate mutations in the porcine GGTAl gene. Such mutations may be, for example and without limitation, missense, nonsense, insertion, deletion, transition or transversion mutations. A mutation in the GGTAl gene may lower the expression of one or both alleles of the GGTAl gene and/or lower the activity of the protein expressed by the mutated allele. Alternatively, a mutation in the GGTAl gene may prevent, i.e., "knockout," expression of GGTAl protein from one or both GGTAl gene alleles. A GGTAl "knockout pig" is a pig wherein one or both GGTAl alleles has been inactivated by co-administration of DRAP or DRAP function-conserved variant and oligonucleotide complementary to the GGTAl gene, wherein "inactivation" refers to the loss of activity of a gene product. A knockout pig includes both a mono-allelic knockout (i.e., one defective allele and one wild-type GGTAl allele) and a bi-allelic knockout (i.e., two defective GGTAl alleles) animals.

Preparation of a knockout pig requires first introducing DRAP or a DRAP function-conserved variant and a GGTAl oligonucleotide into an a pig embryo. The injected embryo is then implanted into a foster mother, i.e., either a sow or gilt, for the duration of gestation. As used herein, the an implanted embryo that is allowed to "develop to term" has been allowed to proceed through gestation to the point at which the fetus has completed development. Accordingly, the phrase "develop to term" does not imply that an animal is delivered by a natural process. In particular, an implanted embryo that has been allowed to "develop to term" may be delivered either naturally or by surgical intervention. Methods for obtaining and microinjecting pig embryos, implanting the injected embryos in surrogate mothers and having the implanted embryos proceed to term are well known by those of ordinary skill in the art. Such methods are described, e.g., in U.S. Patent No. 6,258,998; Betthauser, et al., Nature Biotech., 18:1055-1059, 2000; Dai, et al, Nature Biotech., 20: 251-255, 2002; Lai, et al, Science, 295:1089-1092, 2002.

A pig in which a gene has been mutated by co-administration of DRAP or a DRAP function-conserved variant and one or more oligonucleotide is defined herein as a "genetically modified pig." Preferably, the genetically modified pig has been mutated in the GGTAl gene.

Use of DRAP or a DRAP function-conserved variant thus provides for the targeting of a specific mutagenic oligonucleotide or oligonucloetides to one or more pre-selected cognate gene or genes in a complex genome. As used herein a "mutagenic oligonucleotide" means a DNA sequence that contains a mutation of change within the corresponding endogenous gene sequence. Non-limiting examples of oligonucleotides to be used include those with one or more base substitutions, deletions or insertions in such cognate gene, intron, exon or regulatory element. DRAP or a DRAP function-conserved variant, in conjunction with endogenous DNA repair and recombination proteins known to those skilled in the art, effects a direct modification of the targeted locus. Direct co-injection of protein with mutagenic oligonucleotides into the pronucleus of fertilized pig embryos results in viable genetically modified mammals.

As shown in the example below, recombinant DRAP can be co- injected with a mutagenic oligonucleotide to induce gene mutation events resulting in genetically modified pigs with targeted mutations in the genome of such pigs. This direct mutagenic approach is considerably easier and less expensive to perform than other methods currently in practice and produces bi-allelic changes at the GGTAl locus in a single step and without the use of heterologous DNA.

Example: Generation of α-1,3, galactosyltransferase mutant pigs

DRAP Protein and Oligonucleotides

Recombinant DRAP protein was purified using the procedure described U.S. Patent Application Serial No. 09/621,377, filed July 21, 2000, now

U.S. Patent No. . Purified DRAP was stored at 4°C in low ionic strength

TG (transgenic) buffer and used from 1 day to 4 months following purification. Prior to use in co-injection protocols, DRAP activity was confirmed by measuring topoisomerase activity. Oligonucleotides for co-injection with DRAP corresponded to sequences from the porcine GGTAl containing a one base mis-match. GGTAl gene sense nucleotides were selected from the sequences SEQ ID NO: 7 (ATACATTGAGCATTAATTGGAGGAGTTCTTA) and SEQ ID NO: 8 (TCCTGGCCCACATCCAGCACTAGGTGGACTT). GGTAl gene anti- sense nucleotides were selected from the sequences SEQ ID NO: 9 (GCAGAAGAGGAAGTCCACCTAGTGCTGGATG) and SEQ ID NO: 10 (TATATGATAATCCCATCAGTATTCTGGGGAT). The last 20 nucleotides respectively of oligonucleotides of SEQ ID NO: 8 and 9 are complementary. SEQ ID NO: 8 and 9 were annealed in some instances to form double strand oligonucleotides comprising 20 base pairs of duplex DNA and 10 base pair 5 '-overhangs at each respective end. Annealing was performed by mixing equal molar amounts of each oligonucleotide, heating to at least 80°C for 10 min, and cooling slowly to room temperature.

DRAP Injection and Isolation of Piglets

DRAP co-injection with oligonucleotide into pig egg pronuclei was performed using the methods described in U.S. Patent Application Serial No. 09/621 ,377, filed July 21 , 2000, now U.S. Patent No. , for co-injection of

DRAP and oligonucleotide into mouse embryos. In separate protocols, DRAP was co-injected with individual single stranded oligonucleotide selected from SEQ ID NO: 7-10, non-complementary pairs of oligonucleotides SEQ ID NO: 7 and 10 or SEQ ID NO: 8 and 10, or double strand oligonuclotide formed by annealing SEQ ID NO: 8 and 9. DRAP protein and oligonucleotides were mixed in a ratio of 500,000 to 50,000 molecules, respectively, per picoliter and 1-4 pi was microinjected into one of the two pronuclei of an in vitro fertilized pig egg. The pronuclei of the fertilized pig egg were rendered visible by stratifying the organelles in the zygote through low speed centrifugation as is commonly performed in the art of making genetically modified pigs. Microinjected eggs were re-implanted into recipient sows using methods well known in the art and allowed to come to term. The pronuclear microinjection technique is commonly used to make conventional genetically modified animals. The protocol resulted in 17 successful pregnancies and total of 96 live-born piglets. A summary of the results of each successful pregnancy are shown in Table 1. Table 1. Successful Pregnancies With Injected Embryos

Injected Total Live- Still oliεonucleotide(s) Offspring Born born wτ^α MUTANT"

SEQ ID NO: 10 4 3 1 2 2

SEQ ID NO: 10 6 5 1 0 6

SEQ ID NO: 10 6 6 0 5 1

SEQ ID NO: 10 9 9 0 1 8

SEQ ID NO: 9 13 13 0 2 11

SEQ ID NO: 7 6 5 1 5 1

SEQ ID NO: 7 4 4 0 3 1

SEQ ID NO: 7 + 10 6 6 0 2 4

SEQ ID NO: 8 4 4 0 0 4

SEQ ID NO: 8 + 10 6 5 1 1 4

SEQ ID NO: 8/9 7 7 0 0 7

(Double stranded)

SEQ ID NO: 8/9 11 8 3 6 5

(Double stranded)

SEQ ID NO: 8/9 5 4 1 0 5

(Double stranded)

SEQ ID NO: 8/9 11 10 1 0 10

(Double stranded)

SEQ ID NO: 8/9 7 7 0 2 7

(Double stranded")

Total: 105 96 29 76

a) WT (wild type) and Mutant GGTAl phenotype determined by FITC-IB4 staining of isolated fibroblasts

Identification of GGTAl Mutants

GGTAl mutant offspring were identified by screening offspring peripheral blood lymphocytes (PBL) and offspring-derived fibroblast cell lines for reduced binding of isolectin B4 (B34), which binds specifically to α-1,3 gal epitopes. Fibroblasts from individual piglets were isolated by trypsinization of skin removed from piglet ears or the tails at 1-2 days after birth according to standard methods. The fibroblasts were grown according to standard methods know to those skilled in the art of tissue culture. Fibroblast cell lines were trypsinized and washed prior to staining. PBL were isolated as follows. Blood was collected from piglets 48 days after birth and diluted 1 : 1 with PBS. The blood:PBS mixture (6 ml)was layered over ficoll (3 ml) in 15 ml conical tubes, followed by centrifugation at 720 x g for 45 min ( gentle start and no brake) followed by collection of the buffy coat containing lymphocytes. The collected lymphocytes were washed with PBS and re-pelleted. Erythrocyte lysis buffer (1.0 ml) was added to lymphocyte pellet followed by incubation for 5 min at room temperature. The lymphocytes were then washed and pelleted. The erythrocyte lysis step was repeated if necessary.

Analysis of GGTAl activity was quantitatively assessed by staining whole PBL or fibroblasts with FITC-labeled IB4 (FITC-IB4) to measure of the amount of alpha 1,3 galactosyl-containing sugars on the cell surface. Cells were fixed with 4.0 % parafbrmaldehyde for 10 min. at room temperature, washed, and resuspended in PBS + 0.4% BSA with 5.0, 1.0, or 0.5 μg/ml FITC-IB4. Cells were stained at approximately 37°C for 30-40 min. Stained cells were washed twic with PBS/BSA and resuspended in 400 μl PBS/BSA for flow cytometry. Typically, for flow cytometry 10,000 events were collected for each sample. Flow cytometry data is reported as the adjusted geometric mean of the population (AGM) and is calculated by dividing the geometric mean intensity value for the gated events by the value of the cells in the absence of staining with FITC-IB4. Data was collected for fibroblast cell lines and PBL from each piglet and compared to four control cell lines: a commercial wild-type swine, a wild-type mini-swine, a mini-swine mono-allelic cell line made by disruption of one allele by homologous recombination and selection and human null cell line (SK neuroblastoma cells; American Type Culture Collection). FACS staining intensities obtained for fibroblast cell line and PBL from each piglet and control cells are listed in Table 2 and depicted in Fig. 1. The distribution of the FITC-IB4 staining intensities is depicted in the Fig. 2. There are two peaks. Peak 1 corresponds to a reduction in total staining. Peak 2 corresponds to staining consistent with wild-type total GGTAl activity. The majority of the cell lines exhibit reduced staining indicative of a reduction in total GGTAl activity. This reduction in total GGTAl activity is due to induced mutations on one or both GGTAl alleles.

Table 2. FACS Staining Intensities Using FITC-IB4

AVG AGM Line Fibroblasts PBLs

+/+ swine 36.71 44.81

+/+ mini-swine 23.14 17.65

+/- mini-swine 10.54 11.95

-/- human 1.51 1.10

PL586 40.10 26.40

PL587 34.40 25.80

PL588 12.20 N.D.

PL589 11.40 N.D.

PL590 38.40 18.20

PL591 35.50 20.80

PL592 37.80 25.20

PL593 27.50 20.00

PL594 29.30 23.60

PL595 38.70 34.60

PL596 32.40 17.20

PL597 41.00 26.30

PL602 15.30 N.D.

PL603 19.85 19.60

PL604 17.75 19.50

PL605 17.50 21.60

PL606 18.45 27.80

PL607 22.55 21.50

PL608 22.20 14.90

PL609 17.50 24.80

PL610 22.20 23.80

PL611 19.15 22.40

PL612 16.80 32.80

PL613 20.80 N.D. PL614 20.30 N.D.

PL615 18.00 67.60

PL616 18.90 71.40

PL617 18.00 67.00

PL624 15.45 N.D.

PL625 30.50 32.00

PL626 29.80 55.80

PL627 26.60 36.30

PL628 28.70 47.30

PL629 35.20 38.70

PL638 45.90 N.D.

PL639 53.60 44.60

PL640 42.50 41.30

PL641 43.20 N.D.

PL642 33.20 35.60

PL643 42.10 42.50

PL644 35.10 49.80

PL645 33.30 29.40

PL646 31.50 40.90

PL647 24.10 32.80

PL650 22.30 35.70

PL651 29.80 35.70

PL652 24.70 34.60

PL653 29.20 37.80

PL654 26.20 34.80

PL655 28.00 32.00

PL656 20.30 37.70

PL657 23.00 30.40

PL658 31.90 N.D.

PL661 16.90 53.60

PL662 24.30 66.10

PL663 20.30 72.30

PL664 23.00 64.60

PL665 13.20 83.40 PL666 16.00 88.50

PL667 27.20 58.00

PL668 16.30 64.80

PL669 17.30 74.80

PL670 24.70 59.90

PL671 24.10 35.40

PL672 32.90 24.20

PL673 37.30 37.50

PL674 27.70 38.30

PL675 23.90 32.30

PL676 14.10 33.20

PL677 26.20 38.70

PL678 18.80 N.D.

PL679 28.10 N.D.

PL680 27.30 N.D.

PL681 27.30 N.D.

PL682 23.20 N.D.

PL683 18.40 N.D.

PL684 36.50 N.D.

PL685 23.20 N.D.

PL686 27.80 N.D.

PL687 25.40 N.D.

PL688 28.00 N.D.

PL689 23.50 N.D.

PL690 23.10 N.D.

PL691 25.30 N.D.

PL692 22.20 N.D.

PL693 30.70 N.D.

PL694 24.50 N.D.

PL695 28.00 N.D.

PL696 27.50 N.D.

PL697 23.30 N.D.

PL698 30.90 N.D.

PL699 24.30 N.D. PL714 45.00 38.10

PL715 37.20 27.20

PL716 33.50 26.60

PL717 28.20 27.50

PL718 33.00 27.10

PL719 38.70 29.90

PL736 43.60 N.D.

PL737 35.10 N.D.

PL738 36.70 N.D.

PL739 23.60 N.D.

N.D. = not determined

Sequence Analysis of Mutant Mutations in GGTAl exon 9 that were induced by co-injection of

DRAP and oligonucleotide were determined by sequencing exon 9 alleles that had been PCR-amplified. A 1.2 kbp fragment encompassing the coding portion of GGTAl exon 9 plus several hundred bp of flanking sequence was amplified from genomic DNA by a PCR protocol designed to yield long accurate products. Piglet DNA was isolated from fibroblasts grown to confluence in a 100 mm dish using a DNeasy tissue kit (Qiagen, Chatsworth, CA) protocol for cultured cells, according to the manufacturers protocol. Genomic PCR reactions contained the following: 5.0 μl lOx LA-Taq buffer, 8.0 μl 2.5 mM dNTPs, 0.5 μl LA Taq (Takara), 0.5 μl Taq Start Ab (Clontech), 1.0 μl 5.0 μM forward primer (5'-CCACTCCACCTCCCCAAAG; SEQ ID NO: 11), 1.0 μl 5.0 uM reverse primer (5 '-CCCCCTCAACCCAGAACAG; SEQ ID NO: 12), template DNA (250-500 ng) and dH₂O to a final reaction volume of 50 μl. PCR reactions were performed as follows: (95°C, 2 min), (95°C, 1 min— 61 °C, 0.5 min- 72°C, 2 min x 30 cycles), (72°C, 10 min) and 4°C, hold.

The PCR reactions yielded products that were all of the expected (1.2 kbp) size. The PCR amplified material was cloned into a Topo-TA cloning vector (Invitrogen), used to transform E. coli and then spread on LB-ampicillin plates. After overnight incubation, 96 individual colonies containing an insert were isolated and grown in individual wells. Plasmid DNA was isolated for use as a template for automated fluorescent sequencing.

The high quality insert sequences were trimmed of vector sequences and analyzed for mutations. Two long overlapping sequences were derived from each of 8 clones. The sequences were then clustered with ClustalW (Higgins et al., Nucl. Acid Res., 22:4673-4680, 1994) to determine which had been derived from a common allele. Sequences from a common allele (i.e., four from each allele) were assembled using the CAP EST Assembler (Huang, X., Genomics 18-25, 1992) to generate a consensus sequences. The consensus sequence from each allele was then compared to GenBank entries for pig GGTAl using the BLAST program (Altschul, et al, J Mol. Biol 215:403-410, 1990) to identify mutations in the GGTAl nucleotide sequence, using the Paired BLAST tool. Nucleotide changes were related to amino acid changes using the BLASTX program.

The differences found in GGTAl exon 9 alleles for male piglet PL676 having the lowest amount of FITC-IB4 staining relative to the closest wild-type GGTAl sequence found in GenBank were as follows. The notation lists in order XYZ (aal M aa2), where Y represents the nucleotide position in the GGTAl cDNA sequence set forth in SEQ ID NO: 1, X represents the nucleotide present at position Y in the wild-type reference GGTAl allele, Z represents the nucleotide present at position Y in an allele from piglet PL676 and aal, aa2 and M represent respectively the amino acids found in the reference wild-type allele (aal) and the PL676 allele (aa2) at position M of the GGTAl polypeptide sequence set forth in SEQ ID NO: 2, wherein Y is a nucleotide in the triplet that encodes the amino acid at position M. The differences between the GGTAl wild-type reference sequence for exon 9 and the PL676 alleles were as follows:

PL676 allele 1: T570C (R185R), C687T (L224L), C690T (F225F). PL676 allele 2: T570C (R185R), C998T (L295L), A938C (D308A), C982T (L323L), ClOOOn (L229?), C1020T (I335I)

Multiple differences were observed between the GGTAl exon 9 sequence of the wild-type reference gene and each of the PL676 alleles. The three nucleotide differences detected between PL676 allele 1 and the wild-type GGTAl reference were silent mutations and that did not lead to amino acid changes in PL676, relative to the wild-type gene. Six of the eight observed sequence differences between PL676 allele 2 and the wild-type GGTAl reference were similarly silent mutation. The "A" to "C" transversion detected at nucleotide position 938 in exon 9, however, would cause substitution of an uncharged alanine residue for aspartic acid at position 308 of the α-1,3 galactosyltransferase protein, which could lower enzyme activity and account for the reduced level of α-1,3 gal on the surface of cells from PL676.

The analysis of PL676 indicates that DRAP can induce bi-allelic mutants bearing multiple mutations on each GGTAl allele. PL676 retains residual α- 1,3 galactosyltransferase activity. The ability to use DRAP to induce such bi-allelic GGTAl mutations and the high efficiency at which pigs with reduced α-1,3 galactosyltransferase activity are recovered following DRAP -mediated mutagenesis indicate that the DRAP -mediated mutagenesis will yield genetically modified pigs lacking α-1,3 galactosyltransferase activity.

Claims

WHAT IS CLAIMED:

1. A method of promoting mutation of the porcine alpha 1 ,3 glactosyl transferase (GGTAl) gene in a cell comprising introducing DRAP or a function-conserved variant thereof and one or more oligonucleotide complementary to the GGTAl gene into the cell to promote said mutation.

2. The method of claim 1 wherein said cell is a pig zygote or somatic cell.

3. The method of claim 2 wherein introduction of DRAP and the oligonucleotide promotes one or more mutations in one GGTAl allele.

4. The method of claim 3 wherein introduction of DRAP and the oligonucleotide promotes one or more mutations in each of two GGTAl alleles.

5. The method of claim 1 wherein said oligonucleotide is complementary to GGTAl exon 9.

6. The method of claim 5 wherein said oligonucleotide comprises a wild type sequence from exon 9.

7. The method of claim 5 wherein said oligonucleotide comprises a mutant exon 9 sequence.

8. A method for generating a genetically modified pig bearing a bi-allelic mutant GGTAl that does not comprise an inserted heterologous sequence, comprising introducing DRAP or a function-conserved variant thereof and an oligonucleotide complementary to the GGTAl gene into a porcine cell capable of developing into said genetically modified pig and thereby causing in one step one or more mutation in each allele of the GGTAl gene, wherein said GGTAl gene of said cell does not comprise an inserted heterologous sequence, and implanting said cell into a recipient female capable of bearing the cell to term, and allowing the cell to develop to term, thereby obtaining said genetically modified animal.

9. The method of claim 8 wherein said cell is an embryo.

10. The method of claim 8 wherein said oligonucleotide is complementary to GGTAl gene exon 9.

11. The method of claim 8 wherein at least one GGTAl allele bears a mutation in an exon.

12. The method of claim 11 wherein the genetically modified pig is a GGTAl mono-allelic knockout.

13. The method of claim 8 wherein both GGTAl alleles bear mutations in exons.

14. The method of claim 13 wherein the genetically modified pig is a GGTAl bi-allelic knockout.

15. A genetically modified pig comprising a bi-allelic mutant of the GGTAl gene that does not comprise an inserted heterologous sequence in said GGTAl gene, wherein said bi-allelic mutant in said genetically modified pig is produced by a single step process comprising introducing DRAP or a function-conserved variant thereof and an oligonucleotide complementary to said GGTAl gene into a porcine cell capable of developing into said genetically modified pig and which cell does not comprise an inserted heterologous sequence in its GGTAl gene, transplanting said cell into an animal capable of bearing said cell to term, and allowing the cell to develop to term, thereby obtaining said bi-allelic mutant of the GGTA gene without the step of mating mono-allelic mutant animals.

16. The method of claim 14 wherein the genetically modified pig is a GGTAl bi-allelic knockout.