Abstract
Chinese Mutations in serologically defined colon cancer autoantigen protein 8 ( SDCCAG8) were first identified in retinal ciliopathy families a decade ago with unknown function. To investigate the pathogenesis of SDCCAG8-associated retinal ciliopathies in vivo, we employed CRISPR/Cas9-mediated homology-directed recombination (HDR) to generate two knock-in mouse models, Sdccag8Y236X/Y236X and Sdccag8E451GfsX467/E451GfsX467 , which carry truncating mutations of the mouse Sdccag8, corresponding to mutations that cause Bardet-Biedl syndrome (BBS) and Senior-Løken syndrome (SLS) (c.696T>G p.Y232X and c.1339-1340insG p.E447GfsX463) in humans, respectively. The two mutant Sdccag8 knock-in mice faithfully recapitulated human SDCCAG8-associated BBS phenotypes such as rod-cone dystrophy, cystic renal disorder, polydactyly, infertility, and growth retardation, with varied age of onset and severity depending on the hypomorphic strength of the Sdccag8 mutations. To the best of our knowledge, these knock-in mouse lines are the first BBS mouse models to present with the polydactyly phenotype. Major phototransduction protein mislocalization was also observed outside the outer segment after initiation of photoreceptor degeneration. Impaired cilia were observed in the mutant photoreceptors, renal epithelial cells, and mouse embryonic fibroblasts derived from the knock-in mouse embryos, suggesting that SDCCAG8 plays an essential role in ciliogenesis, and cilium defects are a primary driving force of SDCCAG8-associated retinal ciliopathies. 虽早在十年前就从视网膜纤毛病家族中首次检出结肠癌血清学检测自身抗原蛋白8（ SDCCAG8）基因突变，但仍不知其蛋白功能。为了开展SDCCAG8相关视网膜纤毛病致病机制的体内研究，我们利用CRISPR/Cas9介导的同源重组技术（HDR）成功构建携带 Sdccag8截短突变的两个基因敲入小鼠模型， Sdccag8Y236X/Y236X 和 Sdccag8E451GfsX467/E451GfsX467 。它们所对应的人类 SDCCAG8基因突变c.696T>G p.Y232X 和 c.1339–1340insG p.E447GfsX463分别致巴德毕式综合征（BBS）和洛肯综合征（SLS）两种视网膜纤毛病。两个基因敲入小鼠模型准确复制SDCCAG8相关BBS综合征的表型，包括视杆-视锥营养不良、肾囊肿、多趾畸形、不育和生长发育迟缓。其表型始发年龄和严重程度与 Sdccag8突变的亚等位基因强度成正比。它们是迄今首次表现多趾畸形的BBS基因敲入小鼠模型。虽然，小鼠感光细胞发生退化后，主要光传导相关蛋白出现表达错位。但是，我们在突变小鼠的感光细胞、肾小管上皮细胞和小鼠胚胎成纤维细胞中都发现纤毛异常，提示SDCCAG8在纤毛发生中发挥着重要作用，纤毛异常是导致SDCCAG8相关视网膜纤毛病的根本原因。.