Molecular mechanisms of photoreceptor disc morphogenesis

这一建议解决了视觉中最基本的未解决的问题之一：分子和细胞 负责建立和维持脊椎动物感光细胞感光细胞器的机制， 最外层的部分。外段是填充有盘膜堆叠的纤毛结构，该盘膜提供 巨大的表面光捕捉和窝藏蛋白质组成的光转导机制。光盘需要续订 为了抵消光照的不利影响，光盘更新的保真度是至关重要的 用于维持感光器健康和正常视力。现在公认的是，每个新的形成 视盘开始于由分支肌动蛋白网络的扩张驱动的睫状质膜外翻 在一种类似于运动细胞中形成片状脂肪的机制中。仍然完全未知的是分子 以大约80次的惊人周期启动每个新盘的形成的机构 哺乳动物的一天。确定这一机制是本应用程序的总体目标。我们最近的工作表明，这 肌动蛋白网络是由波浪蛋白复合体组成的，其独特的亚基组成特别适合于 执行此功能。因为波复合体在上游信号通路和 下游的肌动蛋白网络，这为阐明周期性 肌动蛋白在视盘形态发生部位的组装和拆解。为了实现这一目标，我们将结合 两个实验室的努力，这将提供独特的专业知识和两个互补的遗传模式 改良动物：小鼠和非洲爪蛙。我们提议的实验将研究肌动蛋白的调节。 细胞骨架动力学，包括活的光感受器，由两类调节分子：小分子 GTP酶和肌醇磷脂。阐明这些机制对于促进我们对基本知识的理解至关重要 感光细胞生物学及常见感光细胞变性的病理生物学机制 与外节形态发生缺陷有关。

This proposal addresses one of the most fundamental unsolved problems in vision: the molecular and cellular mechanism responsible for building and maintaining the light-sensitive organelle of vertebrate photoreceptor cells, the outer segment. The outer segment is a ciliary structure filled with a stack of disc membranes, which provide vast surfaces for light capture and harbor proteins comprising the phototransduction machinery. Discs are renewed on a daily basis in order to counteract the adverse effects of light exposure, and the fidelity of disc renewal is critical for maintaining photoreceptor health and normal vision. It is now well-established that the formation of each new disc begins with an evagination of the ciliary plasma membrane driven by an expansion of branched actin network in a mechanism akin the formation of lamellipodia in motile cells. What remain entirely unknown are the molecular mechanism that initiate the formation of each new disc with the striking periodicity of approximately 80 times per day in mammals. Pinpointing this mechanism is the overall goal of this application. Our recent work shows that this actin network is nucleated by the WAVE protein complex whose unique subunit composition is specifically fitted to perform this function. Because WAVE complexes mediate between the upstream signaling pathways and downstream actin networks, this opens doors to elucidating the entire mechanism responsible for the periodic assembly and disassembly of actin at the disc morphogenesis site. To accomplish this goal, we will combine the efforts of two laboratories, which will contribute unique expertise and two complementary models of genetically modified animals: mice and Xenopus frogs. Our proposed experiments will investigate the regulation of the actin cytoskeleton dynamics, including that in living photoreceptors, by two classes of regulatory molecules: small GTPases and phosphoinositides. Elucidating these mechanisms is critical for advancing our understanding of basic photoreceptor cell biology and pathobiological mechanisms underlying photoreceptor degeneration frequently associated with defects in outer segment morphogenesis.