Progressive retinal atrophy in Schapendoes dogs: mutation of the newly identified CCDC66 gene

Abstract

Canine generalized progressive retinal atrophy (gPRA) is characterized by continuous degeneration of photoreceptor cells leading to night blindness and progressive vision loss. Until now, mutations in 11 genes have been described that account for gPRA in dogs, mostly following an autosomal recessive inheritance mode. Here, we describe a gPRA locus comprising the newly identified gene coiled-coil domain containing 66 (CCDC66) on canine chromosome 20, as identified via linkage analysis in the Schapendoes breed. Mutation screening of the CCDC66 gene revealed a 1-bp insertion in exon 6 leading to a stop codon as the underlying cause of disease. The insertion is present in all affected dogs in the homozygous state as well as in all obligatory mutation carriers in the heterozygous state. The CCDC66 gene is evolutionarily conserved in different vertebrate species and exhibits a complex pattern of differential RNA splicing resulting in various isoforms in the retina. Immunohistochemically, CCDC66 protein is detected mainly in the inner segments of photoreceptors in mouse, dog, and man. The affected Schapendoes retina lacks CCDC66 protein. Thus this natural canine model for gPRA yields superior potential to understand functional implications of this newly identified protein including its physiology, and it opens new perspectives for analyzing different aspects of the general pathophysiology of gPRA.

The centriolar satellite protein CCDC66 interacts with CEP290 and functions in cilium formation and trafficking

“…The CEP72 BioID hits also include proteins that were not previously implicated in ciliogenesis. Among these hits is the retinal degeneration gene CCDC66 (Dekomien et al, 2010;Gerding et al, 2011). CCDC66 has been reported to localize to centriolar satellites (Gupta et al, 2015) and its mRNA has been found to interact with microtubules in a screen for microtubule-binding transcripts in Xenopus laevis egg extracts (Sharp et al, 2011).…”

“…Expression studies in dog and mouse tissues via quantitative realtime RT-PCR (qRT-PCR) (Dekomien et al, 2010) and a genomewide analysis of transcription profiles (Krupp et al, 2012) showed that CCDC66 is not only expressed in retina but most tissues including heart, brain, liver and blood. Immunoblotting with an antibody against CCDC66 in RPE1, HeLa and HEK293T cell extracts validated the wide expression profile of CCDC66 ( Fig.…”

“…The interactors identified by this map include both known satellite proteins and previously uncharacterized proteins (Firat-Karalar et al, 2014). Among these proteins, we chose CCDC66, for further study, because it has been previously implicated in microtubule-mediated functions, including spindle pole and centriolar satellite organization (Gupta et al, 2015;Sharp et al, 2011), and its link to retinal degeneration (Dekomien et al, 2010;Gerding et al, 2011). A homozygous mutation in the CCDC66 gene was shown to cause autosomal recessively inherited, generalized progressive retinal atrophy, the canine counterpart of Retinitis pigmentosa (Dekomien et al, 2010).…”

“…Among these proteins, we chose CCDC66, for further study, because it has been previously implicated in microtubule-mediated functions, including spindle pole and centriolar satellite organization (Gupta et al, 2015;Sharp et al, 2011), and its link to retinal degeneration (Dekomien et al, 2010;Gerding et al, 2011). A homozygous mutation in the CCDC66 gene was shown to cause autosomal recessively inherited, generalized progressive retinal atrophy, the canine counterpart of Retinitis pigmentosa (Dekomien et al, 2010). Moreover, CCDC66 knockout in mouse leads to early photoreceptor degeneration, with a slow, progressive retinal phenotype and physiological impairment of the retina (Gerding et al, 2011).…”

Atrofia progressiva generalizada da retina em cães da raça Cocker Spaniel

“…Os testes genéticos são exames laboratoriais que possibilitam a análise de DNA, RNA, cromossomos, proteínas e certos metabólitos do paciente, com o objetivo de detectar a presença de material genético, que pode estar (ou não) relacionado às doenças genéticas e hereditárias em geral (DEKOMIEN et al, 2010;MELLERSH, 2012). Diversas formas de degeneração retiniana são causadas por alterações genéticas.…”