A subtractive
cDNA cloning strategy was used to isolate canine retina-specific genes. Canine
phosducin cDNA was cloned from a canine subtracted
retinal cDNA library and was analysed as a candidate for canine generalized progressive
retinal atrophies (gPRA). Canine
phosducin cDNA is 1230 bp in length encoding 245
amino acids. The
nucleotide and amino acid sequences of canine
phosducin are highly conserved when compared with those of five other mammalian species, namely human, cat, cow, rat, and mouse. Northern blot analysis demonstrated that the
mRNA transcript for
phosducin was approximately 1.3 kb in size and was present in canine retina, but showed no visible signals in 13 other canine tissues. The
phosducin gene was examined for polymorphisms in a total of 101 pedigree dogs of eight breeds, including normal, obligate gPRA carriers, and gPRA-affected dogs, by single-stranded conformation polymorphisms (SSCP) analysis. Polymorphisms in the
phosducin gene were detected only in the
3' untranslated region of the gene in two breeds of dogs: allelic heterozygous polymorphisms in miniature poodles suffering from one form of gPRA (progressive rod-cone degeneration, prcd), and a different polymorphism in a single normal Irish wolfhound. The polymorphisms of
phosducin in prcd-affected miniature poodles did not segregate with the autosomal recessive form of gPRA. Heterozygous inheritance of the polymorphisms suggests that
phosducin is very unlikely to carry the mutation causing prcd, so
phosducin was probably excluded as a candidate for prcd-affected miniature poodles in this study.