Abstract：
Mutations in the apicobasal polarity gene CRB1 lead to diverse retinal diseases, such as Leber congenital amaurosis, cone-rod dystrophy, retinitis pigmentosa (with and without Coats-like vasculopathy), foveal retinoschisis, macular dystrophy, and pigmented paravenous chorioretinal atrophy. Limited correlation between disease phenotypes and CRB1 alleles, and evidence that patients sharing the same alleles often present with different disease features, suggest that genetic modifiers contribute to clinical variation. Similarly, the retinal phenotype of mice bearing the Crb1 retinal degeneration 8 (rd8) allele varies with genetic background. Here, we initiated a sensitized chemical mutagenesis screen in B6.Cg-Crb1rd8/Pjn, a strain with a mild clinical presentation, to identify genetic modifiers that cause a more severe disease phenotype. Two models from this screen, Tvrm266 and Tvrm323, exhibited increased retinal dysplasia. Genetic mapping with high-throughput exome and candidate-gene sequencing identified causative mutations in Arhgef12 and Prkci, respectively. Epistasis analysis of both strains indicated that the increased dysplastic phenotype required homozygosity of the Crb1rd8 allele. Retinal dysplastic lesions in Tvrm266 mice were smaller and caused less photoreceptor degeneration than those in Tvrm323 mice, which developed an early, large diffuse lesion phenotype. At one month of age, Müller glia and microglia mislocalization at dysplastic lesions in both modifier strains was similar to that in B6.Cg-Crb1rd8/Pjn mice but photoreceptor cell mislocalization was more extensive. External limiting membrane disruption was comparable in Tvrm266 and B6.Cg-Crb1rd8/Pjn mice but milder in Tvrm323 mice. Immunohistological analysis of mice at postnatal day 0 indicated a normal distribution of mitotic cells in Tvrm266 and Tvrm323 mice, suggesting normal early development. Aberrant electroretinography responses were observed in both models but functional decline was significant only in Tvrm323 mice. These results identify Arhgef12 and Prkci as modifier genes that differentially shape Crb1-associated retinal disease, which may be relevant to understanding clinical variability and underlying disease mechanisms in humans.
摘要：
根尖极性基因CRB1的突变导致不同的视网膜疾病，比如Leber先天性黑蒙,锥杆营养不良,视网膜色素变性（有和没有Coats样血管病变），视网膜中央凹，黄斑营养不良,和色素性左侧脉络膜视网膜萎缩。疾病表型和CRB1等位基因之间的有限相关性，并且有证据表明，共享相同等位基因的患者通常具有不同的疾病特征，表明遗传修饰剂有助于临床变异。同样，携带Crb1视网膜变性8（rd8）等位基因的小鼠的视网膜表型随遗传背景而变化。这里,我们在B6中启动了敏化的化学诱变筛选。Cg-Crb1rd8/Pjn,临床表现轻微的菌株，鉴定导致更严重疾病表型的遗传修饰剂。这个屏幕上的两个模型，Tvrm266和Tvrm323表现出增加的视网膜发育不良。高通量外显子组和候选基因测序的遗传作图鉴定了Arhgef12和Prkci的致病突变，分别。两个菌株的上位分析表明，发育不良表型的增加需要Crb1rd8等位基因的纯合性。与Tvrm323小鼠相比，Tvrm266小鼠的视网膜发育不良病变较小，引起的光感受器变性较少，它开发了一个早期的，大弥漫性病变表型。一个月大的时候，两种修饰品系在发育不良病变处的Müller胶质细胞和小胶质细胞错误定位与B6相似。Cg-Crb1rd8/Pjn小鼠但感光细胞错位更广泛。外界膜破坏在Tvrm266和B6中相当。Cg-Crb1rd8/Pjn小鼠,但在Tvrm323小鼠中更温和。出生后第0天小鼠的免疫组织学分析表明，Tvrm266和Tvrm323小鼠的有丝分裂细胞分布正常，表明正常的早期发育。在两种模型中均观察到异常的视网膜电图反应，但功能下降仅在Tvrm323小鼠中明显。这些结果确定了Arhgef12和Prkci是差异塑造Crb1相关视网膜疾病的修饰基因，这可能与理解人类的临床变异性和潜在的疾病机制有关。
