Targeted disruption of murine ornithine aminotransferase gene: Surprising neonatal lethality rescued by arginine therapy and possible mouse model for gyrate atrophy
- Johns Hopkins Univ. School of Medicine, Baltimore, MD (United States); and others
Deficiency of ornithine-{delta}-aminotransferase (OAT) in humans results in gyrate atrophy (GA), an autosomal recessive blinding disorder characterized by progressive chorioretinal degeneration and hyperornithinemia. GA patients are otherwise asymptomatic. The explanation for the unique susceptibility of retina to this inborn error is not known. Poor understanding of the pathophysiology hampers development of effective therapy. To address these problems, we undertook targeted disruption of the murine OAT gene. We isolated a 13 kb genomic DNA fragment containing the first five exons of OAT from an AB1 mini-genomic library and made a replacement type targeting vector with the NEOR gene inserted into OAT exon 3 at codon 40. Following electroporation and selection, 4.4% of G418 resistant ES clones had undergone homologous recombination. Chimeric animals produced by blastocyst injection transmitted the disrupted OAT allele. Mice homozygous for OAT disruption (-/-) have no detectable OAT activity in their tissues. Although normal at birth, they die within 10 to 48 hrs. We hypothesize this lethality results from a block in gut arginine biosynthesis, a pathway that requires {open_quotes}reverse{close_quotes} OAT flux and is apparently critical for rapidly growing neonatal mice. Amino acid measurements reveal extreme reduction in urea cycle intermediates in dying mice. With i.p. arginine administration for the first 14 days of life, we have successfully obtained adult (-/-) mice. Plasma amino acids on these mice show a 10-15 fold increase in ornithine and a 2 fold decrease in lysine, biochemical hallmarks of GA. ERG and retinal histopathologic studies are in progress to examine the ocular phenotypes. These mice will provide an invaluable model to test strategies to reduce ornithine accumulation and should also prove useful in understanding the pathophysiology of retina degeneration.
- OSTI ID:
- 133277
- Report Number(s):
- CONF-941009-; ISSN 0002-9297; TRN: 95:005313-0004
- Journal Information:
- American Journal of Human Genetics, Vol. 55, Issue Suppl.3; Conference: 44. annual meeting of the American Society of Human Genetics, Montreal (Canada), 18-22 Oct 1994; Other Information: PBD: Sep 1994
- Country of Publication:
- United States
- Language:
- English
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