Exclusion of GNGT1 Gene as a Positional Candidate for Canine rcd2 Disease

Abstract

Abstract: : Rod cone dysplasia type 2 (rcd2) is an early onset form of canine progressive retinal atrophy (PRA) phenotypically similar to rcd1 of Irish setters. In difference from rcd1, which is caused by a mutation in PDE6B subunit, a number of phototransduction cascade genes have been excluded as candidates underlying the rcd2 disease. Purpose: To identify the genetic linkage between rcd2 and chromosomal loci and to evaluate GNGT1 gene as a positional candidate for rcd2 disease. Methods: A set of rcd2 informative pedigrees has been generated and genotyped with microsatellite markers from standard canine genome wide scan set. Based on identified genetic linkage the positional candidate gene approach has been applied. Results: 13 rcd2 informative three-generation pedigrees have been screened with 97 canine microsatellites. Genotyping data was analysed by best two-point option of MultiMap software and genetic linkage between rcd2 disease and CFA14 markers (FH3725, lod 2.25; FH2547 lod 1.98; C14.390 lod 1.976) has been found. Comparison of CFA14 with human ortholog (HSA7) has revealed GNGT1 gene as a positional candidate for rcd2. Based on canine RH map 5000 cR the GNGT1 gene is located on CFA14 in the region of interest, its chromosomal position on CFA14 between markers FH3725 and FH2060 was also confirmed on canine RH panel 3000 cR. The cDNAs of GNGT1 from rcd2 affected and normal dogs have been cloned and sequenced. The polymorphism involves an A to G change in the nucleotide 298 in the 3’ UTR of the canine GNGT1 cDNA has been found. A fragment of GNGT1 cDNA was used as a probe for canine BAC library screening and 3 polymorphic microsatellites were found in selected canine BAC clones. Identified microsatellites and SNP were used for genotyping of rcd2 families. Recombinants between GNGT1 and rcd2 have been observed by "Identity by Descent" approach as well as by linkage analyses of rcd2 informative pedigrees. Conclusions: GNGT1 gene has been excluded as a positional candidate for rcd2 disease. CR: N Supported by EY06855 and EY13132, the Foundation Fighting Blidness, American Border Collie Association , Morris Animal Foundation/ The Seeing Eye, Inc., and the Van Sloun Fund for Canine Genetics Research

Keywords: retinal degenerations: hereditary • retina • animal model