Canine rod transducin a-1: cloning of the cDNA and evaluation of the gene as a candidate for progressive retinal atrophy

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Abstract
Progressive retinal atrophy (PRA) represents a heterogeneous group of retinal dystrophies, distinct forms of which occur in different canine breeds. The present study was undertaken to evaluate the gene for the alpha-1 subunit of the rod specific G-protein transducin (GNAT1), a member of the phototransduction pathway, as a candidate for progressive rod cone degeneration (pred) in poodles, early retinal degeneration (erd) in elkhounds, and rod cone dysplasia 2 (rcd2) in collies.Oligonucleotide primers were designed from the consensus region of known cDNA sequences for GNAT1 from other species. Canine GNAT1 cDNA was cloned and sequenced after reverse transcription (RT) and polymerase chain reaction (PCR) of total retinal RNA, and PCR amplification of specific sequences from a canine retinal cDNA library. Large, intron containing fragments of the canine transducin alpha-1 subunit gene were amplified from genomic DNA of individuals in PRA informative pedigrees, using canine-specific primers. PCR products were digested with Nci I, to enable typing of individuals in the PRA affected pedigrees for a previously identified GNAT1 restriction fragment length polymorphism (RFLP).The sequence of canine GNAT1 cDNA is reported (GenBank accession no. U65376). Over the coding region, the canine GNAT1 cDNA sequence presented here shares 92-95% identity with human, bovine and murine sequences. The canine cDNA encodes a polypeptide of 350 amino acids; its theoretical translation is 98-99% identical with the corresponding GNAT1 sequence from each of the other 3 species and it has no unique amino acids. In rcd2 and erd pedigrees informative for both the disease locus and the GNAT1 Nci I RFLP, a minimum of 3 and 2 recombinants were identified, respectively. Similarly, in a prcd pedigree, 3 of 7 progeny informative for both prcd and this RFLP were obligate recombinants.The canine GNAT1 gene has been excluded as a candidate for prcd, erd and rcd2. Sequence information of canine GNAT1 gene will enable testing this locus as a candidate in other canine hereditary retinal degenerations.