ERM proteins and cell morphology in the retina

该实验室的长期目标是研究调节光感受器外节发育和维持的机制。身体的每种细胞类型都必须获得并保持与其功能相适应的特定形态。我们的实验室专注于光感受器，眼睛的感光细胞，及其专门的感觉末梢，外节。外节扩张和修改纤毛包含堆叠的扁平膜盘装载视蛋白色素。为了建立和更新一个外节，需要反复外翻质膜，每次产生一个新的磁盘。然而，驱动和控制磁盘扩展的机制尚不清楚。同时，微绒毛状突起，称为萼突，垂直于花盘延伸并包围外节的基部。肾盏突起的目的尚不清楚，但其破坏与感光细胞变性有关。* 在这项研究中，我们研究了肌动蛋白细胞骨架和质膜如何合作创造感光细胞外节的复杂形态。重要的是，花萼过程是由核心束的肌动蛋白丝，但外节磁盘外翻没有任何细胞骨架。然而，肌动蛋白存在于新形成的磁盘附近，并且是磁盘启动所需的。因此，肌动蛋白细胞骨架是必要的花萼过程和外节，但在不同的方式。由于OS磁盘没有肌动蛋白核心，我们建议，他们形成通过起泡，细胞的过程，其中肌动球蛋白收缩导致细胞内压力增加和释放的膜从细胞骨架。相比之下，微绒毛样CP通过其肌动蛋白核心的延伸形成。ERM（Ezrin，Radixin，Moesin）蛋白充当细胞骨架和膜之间的连接体，并且在起泡和微绒毛形成中具有充分描述的作用。我们假设ERM蛋白Ezrin锚定了肾盏突起，但在外节的基部被周期性地抑制，以允许盘外翻。我们使用斑马鱼作为我们的模型系统来研究光感受器，因为它们具有许多实验优势，发育良好的视网膜和出色的视觉。在这里，我们将利用体外和体内测定来研究ERM蛋白Ezrin和肌动蛋白细胞骨架如何促进外节的生长，通过提出三个主要问题：1）起泡是否驱动感光细胞外节盘的外翻？2)肾盏过程是否限制了操作系统磁盘的增长并稳定了操作系统？3)肌动蛋白和Ezrin在肾盏突稳定和外节盘外翻中的具体功能是什么？*影响：这项研究将提高我们对膜-细胞骨架相互作用如何控制复杂细胞形态的理解。

The long-term objective of the lab is to study the mechanisms regulating development and maintenance of the photoreceptor outer segment.*** Each cell type of the body must acquire and maintain a specific morphology adapted to its function. Our lab focuses on photoreceptors, the light-sensing cells of the eye, and their specialized sensory endings, the outer segments. Outer segments are expanded and modified cilia containing stacks of flattened membranous disks laden with opsin photopigments. To build and renew an outer segment requires repeated evagination of the plasma membrane, each time giving rise to a new disk. However, the mechanisms driving and controlling disk expansion are unclear. At the same time, microvilli-like protrusions, called calyceal processes, extend perpendicular to the disks and surround the base of the outer segment. The purpose of calyceal processes is unknown, but their disruption is associated with photoreceptor degeneration. *** In this grant, we look at how the actin cytoskeleton and plasma membrane co-operate to create the complex morphology of the photoreceptor outer segment. Importantly, calyceal processes are supported by a core bundle of actin filaments, but outer segment disks evaginate without any cytoskeleton. Actin is however present adjacent to newly forming disks and is required for disk initiation. Therefore, the actin cytoskeleton is necessary for both calyceal processes and outer segments, but in distinct ways. As OS disks do not have an actin core, we propose that they form through blebbing, a cellular process whereby actomyosin contraction leads to increased intracellular pressure and release of the membrane from the cytoskeleton. In contrast, the microvilli-like CPs form by extension of their actin core. ERM (Ezrin, Radixin, Moesin) proteins act as linkers between the cytoskeleton and membrane and have well-described roles in both blebbing and microvilli formation. We hypothesize that the ERM protein Ezrin anchors calyceal processes, but at the base of the outer segment is periodically inhibited to allow for disk evagination.*** We use zebrafish as our model system to study photoreceptors because of their many experimental advantages, well-developed retina and excellent vision. Here, we will take advantage of both in vitro and in vivo assays to examine how the ERM protein Ezrin and the actin cytoskeleton promote growth of the outer segment, by asking three main questions:1) Does blebbing drive evagination of photoreceptor outer segment disks? 2) Do calyceal processes limit growth of OS disks and stabilize the OS? 3) What are the specific functions of actin and Ezrin in calyceal process stabilization and outer segment disk evagination?***Impact: This research will improve our understanding of how membrane-cytoskeletal interactions control the morphologesis of complex cells.