Understanding Photoreceptor Trafficking Pathways to the Outer Segment

摘要 视觉的第一步发生在视网膜，光线被视网膜的外节细胞器捕获 杆状和锥状感光器。外段是一个修改的初级纤毛，它包含一叠扁平的 盘状膜。这种结构安排通过迫使光子 穿过成百上千层密密麻麻的吸光蛋白--视蛋白。一个 光吸收的副产品是光氧化损伤，光感受器通过 不断地用新的蛋白质和脂肪材料取代其整个富含膜的外段。 外节的运输、形成和功能缺陷最终导致光感受器细胞的丢失 并导致广泛的遗传性视网膜营养不良，包括视网膜色素变性、视锥视杆细胞 营养不良和Stargardt病。现在公认的是，光感受器利用多次运输 将结构和信号蛋白运送到对光敏感的外节细胞器的途径； 然而，这些途径是如何协调的，调节运输的分子过程，为什么是货物 选择一条具体的路线在很大程度上仍然不得而知。我们提案的目标是调查 驻留在视盘(视紫红质)内的外节段膜货物的运输路径 环状突起(外周蛋白-2和ABCA4)和围绕盘的质膜(CNG通道)。这 全面的方法将使我们能够了解特定的 此外，我们还将研究贩运路径，并建立通往外部段的细胞内路径的完整概览。我们的 AIMS利用邻近标记方法来发现体内的运输伙伴以及基因传递 快速筛选候选目标缺陷并发现控制常规的信号的技术 和非常规递送到老鼠棒的外部节段。完成我们的目标将提供 洞察外部部分传输路径如何协作以提供结构性和功能性 形成感光外节细胞器所需的蛋白质以及这些过程如何失败 在疾病期间。展望未来，我们的提案旨在提供有关膜的基础知识 传输到一般的感觉纤毛，以及帮助为患者未来的治疗策略提供信息 患有遗传性失明。

ABSTRACT The first step of vision takes place in the retina where light is captured by the outer segment organelle of rod and cone photoreceptors. The outer segment is a modified primary cilium that contains a stack of flat disc-shaped membranes. This structural arrangement maximizes light detection by forcing photons to pass through hundreds of membrane layers densely packed with the light absorbing protein, opsin. A byproduct of light absorption is photooxidative damage, which the photoreceptor overcomes by continuously replacing its entire membrane-rich outer segment with new protein and lipid material. Defects in outer segment trafficking, formation, and function ultimately result in photoreceptor cell loss and cause a broad spectrum of inherited retinal dystrophies including retinitis pigmentosa, cone-rod dystrophy and Stargardt disease. It is now well established that photoreceptors utilize multiple trafficking pathways to deliver structural and signaling proteins to the light-sensitive outer segment organelle; however, how these pathways are coordinated, the molecular processes regulating delivery, why a cargo chooses a specific route remains largely unknown. The goals of our proposal are to investigate the trafficking pathways of outer segment membrane cargos that reside within the discs (rhodopsin), the disc rims (peripherin-2 and ABCA4) and the plasma membrane surrounding the discs (CNG channel). This comprehensive approach will allow us to understand shared and divergent features between specific trafficking pathways as well as build a complete overview of intracellular routes to the outer segment. Our aims utilize proximity labeling approaches to uncover transport partners in vivo as well as gene delivery techniques to rapidly screen candidates for targeting defects and uncover signals governing conventional and unconventional delivery to the outer segment in mouse rods. Completion of our aims will provide insight into how outer segment trafficking pathways cooperate to deliver the structural and functional proteins necessary to form the light-sensing outer segment organelle as well as how these processes fail during disease. Looking forward, our proposal aims to provide fundamental knowledge about membrane trafficking to sensory cilia in general as well as help to inform future therapeutic strategies for patients suffering from inherited blindness.