Retinal degeneration in a knock–out model of HRG4 (UNC119)

Abstract

Abstract: : Purpose: HRG4 (UNC119) is a novel photoreceptor protein we have isolated by a differential cloning approach (Higashide et al., J. Biol. Chem. 271:1797–1804,1996). The HRG4 gene has been mapped to chromosome 17q11.2 and shown to consist of five exons (Higashide et al, Genomics. 57:446–450, 1999). HRG4 protein is localized in the rod and cone photoreceptor synapses (Higashide et al, Invest Ophthalmol Vis Sci. 1998 Apr;39(5):690–8). A truncation mutation of HRG4 has been shown to cause late–onset cone–rod dystrophy in a patient, and a transgenic model expressing the identical mutation has been shown to develop late–onset retinal degeneration with ERG abnormality just as in the patient (Kobayashi et al, Invest Ophthalmol Vis Sci. 2000 Oct;41(11):3268–77). To further investigate the function and pathogenicity of HRG4, we have constructed a knock–out model of this gene and begun to analyze its phenotype. Methods: Western blot analysis of retinal proteins and immunofluorescent staining of retinal sections were carried out to confirm the targeted knock–out of HRG4 and to investigate the changes in selected retinal proteins. Fundus photography and histologic analysis of retinal sections were carried out to examine the phenotypic changes in the retina. Results: In younger homozygous knock–out mice up to 16 months of age, slight changes in the retina consisting of white spots in the fundus and 20∼30% decrease in the thickness of the photoreceptor layer were seen. Dramatic onset of severe retinal degeneration was observed starting around the age of 17 months with only 3∼4 layers of photoreceptors remaining in the entire retina. A decrease in synaptic vesicle proteins, synaptotagmin and synaptobrevin, was observed. Conclusions: A targeted knock–out of HRG4 results in severe late–onset retinal degeneration, supporting the importance of HRG4 for retinal integrity. This knock–out model should be very useful for elucidation of the function and pathogenic mechanism of HRG4. CR: None Support: NIH Grant EY10848, Foundation Fighting Blindness, Research to Prevent Blindness

Keywords: retinal degenerations: hereditary • transgenics/knock–outs • photoreceptors