Molecular mechanisms of photoreceptor outer segment morphogenesis

这项提议解决了视觉中最基本的未解决的问题之一：分子和细胞 负责构建和维持脊椎动物感光细胞的光敏细胞器的机制， 外段。外节是充满一叠椎间盘膜的纤毛结构， 用于光捕获的广阔表面和包含光转导机制的蛋白质的港湾。光盘更新 以抵消光暴露的不利影响，并且光盘更新的保真度是至关重要的 维持感光细胞健康和正常视力。以前的研究表明，感光盘是 形成为外节基部质膜的连续外翻。然而，分子机制 负责执行这些膜转化的机制仍然知之甚少。研究策略 在这个提议中所概述的是建立在最近发现的感光细胞中的盘形成之间的相似性之上的 以及许多其他纤毛类型的基本特性-释放小的纤毛外囊泡的能力，称为 外体光感受器纤毛也具有释放大量外体的先天能力。 然而，在正常的光感受器中，这一过程被盘特异性蛋白，外周蛋白-2， 将芽生膜保持在外节基部，从而使它们能够变形为圆盘。 睫状体和感光盘的形成都需要肌动蛋白细胞骨架的作用， 最近的证据表明，外泌体的释放也依赖于ESCRT蛋白复合物。因此，Aim 1将探讨肌动蛋白细胞骨架和ESCRT蛋白之间是否存在类似的相互作用， 进行感光盘形成的第一步骤。目标2将探讨 外周蛋白-2将感光纤毛的功能状态从释放外体转变为保留外体， 外节基部的膜，并将它们转化为盘。阐明这些机制至关重要 促进了我们对感光细胞生物学和病理生物学机制的理解， 光感受器变性常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. Previous studies established that photoreceptor discs are formed as serial evaginations of the plasma membrane at the outer segment base. Yet, the molecular mechanisms responsible for performing these membrane transformations remain poorly understood. The research strategy outlined in this proposal is built upon the recently uncovered analogy between disc formation in photoreceptor cells and a fundamental property of many other cilia types - the ability to release small extraciliary vesicles, called ectosomes. The photoreceptor cilium also has an innate ability to release massive amounts of ectosomes. However, in normal photoreceptors this process is suppressed by the disc-specific protein, peripherin-2, which retains the budding membranes at the outer segment base, thereby enabling them to be morphed into discs. The formation of both ciliary ectosomes and photoreceptor discs requires the action of the actin cytoskeleton, and recent evidence suggests that ectosome release also relies on the ESCRT protein complex. Therefore, Aim 1 will explore whether a similar interplay between the actin cytoskeleton and ESCRT proteins is responsible for performing the first steps of photoreceptor disc formation. Aim 2 will explore the mechanism by which peripherin-2 transforms the functional state of the photoreceptor cilium from releasing ectosomes to retaining membranes at the outer segment base and transforming them into discs. 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.