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S Kameya, B Chang, NL Hawes, JR Heckenlively, JK Naggert, PM Nishina; A novel Candidate Gene is Mutated in the Mouse retinal degeneration 6 . Invest. Ophthalmol. Vis. Sci. 2002;43(13):833.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The retinal degeneration 6 (rd6) mouse mutation causes an autosomal recessive, progressive retinal degeneration similar to human retinitis punctata albescens. Fundus examination of mice homozygous for rd6 shows discrete dots distributed across the retina. The purpose of this study is to elucidate the molecular genetic defect of rd6 mice. Methods: We have used a positional cloning approach to identify the gene responsible for rd6. Previous genetic mapping had localized rd6 to mouse chromosome 9 approximately 24 cM from the centromere. To locate rd6 precisely, we constructed a high resolution genetic map of the region. A total of 657 F2 progeny from the C57BL/6J-rd6/rd6 x CAST intercross were genotyped with markers D9MIT329 and D9MIT23 and phenotyped using indirect ophthalmoscopy. A physical map of the critical area was assembled using bacterial artificial chromosome clones. Transcript map of the critical region was assembled using comparative in silica analysis. Candidate genes were tested by Northern blot , sequencing, and in situ hybridization analyses. Results: The maximum estimated genetic distance for the chromosome 9 segment containing rd6 was 0.45 cM (6 recombinants/1314 meiosis). One of the candidate genes showed an altered hybridization pattern to mRNA derived from rd6 mutant mice in that they expressed a slightly smaller transcript. By sequencing the corresponding cDNA derived from eyes of rd6, we found that exon 4 was missing. We also found 4 bp deletion in the splice donor sequence of intron 4 in rd6 genomic DNA. We examined the expression of the gene in adult tissues by Northern blot analysis and identified a 4.4 kb transcripts that is predominantly expressed in the eye and at a lower level in the brain. In situ hybridization showed that the mRNA of the gene is expressed in retinal pigment epithelium (RPE) and ciliary epithelium. Conclusions: We identified the disease causing mutation in rd6 mice, a model for human flecked retinal diseases. Spatial expression of the gene suggests that the interaction between photoreceptors and RPE may be central to the retinal degeneration seen in rd6.
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