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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.

To study the biochemical and molecular characteristics of the lysosomal enzyme beta-glucuronidase (GUSB) in the retinal pigment epithelium (RPE) and other tissues of different species.Freshly isolated and cultured cells were harvested, and GUSB activity was measured fluorimetrically in cell homogenates or tissue culture media using the synthetic substrate 4-methyl-umbelliferyl beta-D-glucuronide (4-MUG). The temperature and pH optima, and thermal stability of GUSB in the RPE and fibroblasts were established. Distribution of glycosaminoglycans (GAGs), the natural substrates of GUSB, in the RPE and fibroblast cell layer and media was examined by cellulose acetate electrophoresis following 72 h of metabolic labeling with Na2(35)SO4. Total or poly A(+)-RNA isolated from cells or tissues of different species were examined in Northern blots to identify GUSB mRNA transcripts.Among all the species, the activity of GUSB and its mRNA level was found to be consistently high in RPE cells. In RPE cultures, the activity was detected in the cell layer and the media, and the activity decreased in both compartments with serial passage. While the temperature and pH optima for the enzyme activity was similar across the species, the thermal stability was remarkably different. The GAG profiles in RPE cells were different from fibroblasts. Supplementation of the cultured cells with selected GAGs moderately increased the GUSB activity. A GUSB transcript was detected in all the tissues examined. In man, mouse, dog, and cat the size of the transcript was 2.4 kb, while the rat GUSB transcript was 2.7 kb.The ubiquitous distribution of GUSB was evident from the biochemical and molecular studies. Presence of a high level of GUSB activity in the RPE makes it an ideal model for studies of this enzyme both in normal as well as in diseases resulting in GUSB deficiency.

Purpose. To develop an improved diagnostic test for rod-cone dysplasia type 1 (rcdl). The rcdl phenotype is an early onset, autosomal recessive disease caused by a mutation in the canine rod cyclic GMP phosphodiesterase (β-subunit (PDE6B) gene. A G to A transition in codon 807 at nucleotide position 2420 results in a stop codon. This is the only disease causing mutation detected so far in the canine PDE6B gene.Methods. Allele specific primers were designed in which the 3' end had the nucleotide corresponding to either the wild type or the mutant rcdl allele. PCR was done using the allele specific primers in combination with a common primer complementary to the opposite strand to distinguish between the wild type and the rcdl alleles.Results. The wild type and rcdl alleles were identified successfully in two independent ASPCRs done with two different sets of allele specific primers. Further, both alleles could be amplified in a single tube and distinguished based on the size difference of the PCR products ...

Rod-cone dysplasia type 1 (rcd1) is one of several canine photoreceptor degenerations, collectively termed progressive retinal atrophy (PRA), that afflict different breeds of dogs. The rcd1 phenotype is an early onset autosomal recessive disease caused by a nonsense amber mutation, at codon 807, in the canine gene for the beta-subunit of rod cyclic GMP phosphodiesterase (canine PDEB). The mutation involves a G to A transition at nucleotide position 2420, which presumably would cause premature termination of the canine PDEB protein by 49 amino acid residues. In both a small pedigree study of Irish setters from the United Kingdom and in larger canine pedigree studies in the United States, this gene defect has been found to be the only mutation causing rcd1. Here we report development of a diagnostic test which unequivocally distinguishes the three genotypes at the rcd1 locus: rcd1/rcd1 (homozygous mutant, affected); rcd1/+ (heterozygous, carrier); and +/+ (homozygous normal, wildtype).

In the developing photoreceptor cells of the homozygous rds mutant mice S-antigen is localized over the ciliary protrusion as in the control mice, and to a lesser extent over the inner segments, perikaryal cytoplasma and the cell terminals. As the outer segments develop in the normal retina, the discs become increasingly immunoreactive. In the rds/rds retina the outer segments fail to develop but small membrane bound vesicles, immunoreactive for S-antigen are extruded and phagocytized by the retinal pigment epithelium. In the retina of older mutant mice, as the photoreceptor cells degenerate slowly, the surviving cells continue to show persistent immunoreactivity for S-antigen in the different regions of the photoreceptor cells. In the heterozygotes the outer segments are reduced and appear abnormal, but the localization of S-antigen is similar to normal. In the receptor region of the normal retina and in the deviant membranous structures in the mutant retina the localization of S-antigen is similar to that of opsin. However, some differences in the subcellular localization of these two photoreceptor specific proteins have been observed. It is concluded that the rds gene acts subsequent to the synthesis of these proteins and possibly at the site of disc assembly.