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DJ Sidjanin, J Lowe, C Mellersh, EA Ostrander, B Milne, D Sargan, GD Aguirre, GM Acland; Identification of a Mutation Responsible for Hereditary Cone Degeneration in Dog . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3671.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Cone degeneration (cd) is an autosomal recessive canine disease that is phenotypically similar to human achromatopsia, a heterogeneous autosomal recessive disorder that maps to at least three loci: ACHM1 (HSA14q), ACHM2 (HSA2q11) and ACHM3 (HSA8q21-22). Causative mutations for ACHM2 and ACHM3 have been identified in the CNGA3 and CNGB3 gene respectively. Both the canine and human diseases are characterized by day-blindness, absent cone function and normal rod function as detected by electroretinogram. The cd locus has been mapped to CFA29 in a region homologous to HSA8q21-22 suggesting that cd in the dog might be a locus homolog of ACHM3 in human. To test this hypothesis, we cloned the canine CNGB3 gene and screened for a mutation in cd dogs. Methods:A canine CNGB3 cDNA sequence was amplified from a canine retinal cDNA library using primers based on human CNGB3 sequence. The canine CNGB3 cDNA was then used as a probe to screen a canine BAC library. A CNGB3 positive canine BAC clone was isolated and 3x sequenced. The canine CNGB3 specific BAC was used as a probe for FISH on metaphase chromosome spreads from cd/+, cd/cd and wild type dogs. Results:The open reading frame of canine CNGB3 is 2346 bp (782 aa). The polyadenylation signal sequence AATAA was present 448 bp from the stop codon. Canine genomic CNGB3 contains 18 exons. Primers were designed flanking each exon (∼50 bp from each intron/exon boundary) and used to screen for mutations by exon scanning in cd/cd and cd/+ dogs. For all cd/cd dogs tested we could not obtain a PCR product from any of the 18 exons. In contrast, we could not detect any sequence difference in cd/+ dogs when compared to homozygous normal (+/+) dogs. The results from FISH showed absence of any sequence from the CNGB3 specific BAC in affected cd chromosomes. Conclusion:Our data indicate that the entire CNGB3 gene is deleted in the cd dog. The deletion is at least 150 kb or more. The cd dogs are the only animal model for human ACHM3 achromatopsia offering a unique animal model for study of achromatopsia both as a disease model as well as a model for gene therapy directed specifically at cone photoreceptors.
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