Shriners Hospitals Pediatric Research Center, Department of Anatomy and Cell Biology, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, 19140, USA.
Shriners Hospitals Pediatric Research Center, Department of Anatomy and Cell Biology, Lewis Katz School of Medicine, Temple University, Philadelphia, PA, 19140, USA.
Dev Biol. 2019 Sep 15;453(2):141-154. doi: 10.1016/j.ydbio.2019.05.008. Epub 2019 May 28.
The Crb1 and 2 (Crumbs homolog 1 & 2) genes encode large, single-pass transmembrane proteins essential for the apicobasal polarity and adhesion of epithelial cells. Crb1 mutations cause degenerative retinal diseases in humans, including Leber congenital amaurosis type 8 (LCA8) and retinitis pigmentosa type 12 (RP12). In LCA8, impaired photoreceptor development and/or survival is thought to cause blindness during early infancy, whereas, in RP12, progressive photoreceptor degeneration damages peripheral vision later in life. There are multiple animal models of RP12 pathology, but no experimental model of LCA8 recapitulates the full spectrum of its pathological features. To generate a mouse model of LCA8 and identify the functions of Crb1/2 in developing ocular tissues, we used an mRx-Cre driver to generate allelic combinations that enabled conditional gene ablation from the optic vesicle stage. In this series only Crb1/2 double knockout (dKO) mice exhibited characteristics of human LCA8 disease: locally thickened retina with spots devoid of cells, aberrant positioning of retinal cells, severely disrupted lamination, and depigmented retinal-pigmented epithelium. Retinal defects antedated E12.5, which is far earlier than the stage at which photoreceptor cells mainly differentiate. Most remarkably, Crb1/Crb2 dKO showed a severely attenuated electroretinogram at the eye opening stage. These results suggest that human LCA8 can be modeled in the mouse by simultaneously ablating Crb1/2 from the beginning of eye development. Importantly, they also indicate that LCA8 is caused by malfunction of retinal progenitor cells during early ocular development rather than by defective photoreceptor-Muller glial interaction, a mechanism proposed for RP12.
Crb1 和 2（Crumbs 同源物 1 & 2）基因编码大型单次跨膜蛋白，对于上皮细胞的顶底极性和黏附至关重要。Crb1 突变导致人类退行性视网膜疾病，包括 Leber 先天性黑蒙 8 型（LCA8）和色素性视网膜炎 12 型（RP12）。在 LCA8 中，感光器发育和/或存活受损被认为会导致婴儿早期失明，而在 RP12 中，感光器进行性退化会损害晚年的周边视力。有多种 RP12 病理学的动物模型，但没有能够重现其全部病理学特征的 LCA8 实验模型。为了生成 LCA8 的小鼠模型并确定 Crb1/2 在眼部组织发育中的作用，我们使用 mRx-Cre 驱动物生成等位基因组合，从而从视囊泡阶段开始实现条件性基因敲除。在这一系列中，只有 Crb1/2 双敲除（dKO）小鼠表现出与人类 LCA8 疾病相似的特征：局部视网膜增厚，出现无细胞的斑点，视网膜细胞位置异常，分层严重受损，视网膜色素上皮脱色素。视网膜缺陷发生在 E12.5 之前，远早于感光细胞主要分化的阶段。最显著的是，Crb1/Crb2 dKO 在睁眼阶段的视网膜电图严重衰减。这些结果表明，通过从眼部发育开始同时敲除 Crb1/2，可在小鼠中模拟人类 LCA8。重要的是，它们还表明 LCA8 是由早期眼部发育过程中视网膜祖细胞的功能障碍引起的，而不是由提出的用于 RP12 的感光细胞-Muller 胶质相互作用缺陷引起的。
