ERM proteins and cell morphology in the retina

视网膜中的 ERM 蛋白和细胞形态

• 批准号: RGPIN-2018-05756
• 负责人: Hocking, Jennifer
• 金额: $ 2.26万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=653671
• 关键词: ERM; proteins; cell; morphology; retina

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.

本实验室的长期目标是研究调节光感受器外段发育和维持的机制。***身体的每一种细胞类型都必须获得并维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，即眼睛的感光细胞，以及它们特殊的感觉末梢，即外部部分。外节段的纤毛被扩大和修饰，纤毛中含有一堆扁平的膜状圆盘，上面装载着视蛋白光色素。为了构建和更新外节段，需要反复地外翻质膜，每次都会产生一个新的磁盘。然而，驱动和控制磁盘扩展的机制尚不清楚。与此同时，微绒毛状突起，被称为萼突，垂直于椎间盘延伸并包围着外节的基部。萼突的作用尚不清楚，但它们的破坏与光感受器变性有关。***在本研究中，我们研究了肌动蛋白细胞骨架和质膜如何合作形成感光器外段的复杂形态。重要的是，萼突由肌动蛋白丝的核心束支撑，但外节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，并且是磁盘起始所必需的。因此，肌动蛋白细胞骨架对萼突和外节都是必需的，但方式不同。由于OS盘没有肌动蛋白核心，我们认为它们是通过气泡形成的，这是一种细胞过程，肌动球蛋白收缩导致细胞内压力增加，并从细胞骨架上释放膜。相比之下，微绒毛样CPs是通过其肌动蛋白核心的延伸形成的。ERM （Ezrin, Radixin, Moesin）蛋白作为细胞骨架和膜之间的连接物，在起泡和微绒毛形成中都有很好的作用。我们假设ERM蛋白Ezrin锚定萼突，但在外节的基部周期性地抑制以允许椎间盘外翻。***我们选择斑马鱼作为我们的模型系统来研究光感受器，因为斑马鱼有很多实验优势，视网膜发育良好，视力也很好。在这里，我们将利用体外和体内实验来研究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)水泡是否驱动光感受器外节盘的外移？2)萼状进程是否限制操作系统磁盘的增长并稳定操作系统？3)肌动蛋白和Ezrin在盏突稳定和外节盘外翻中的具体作用是什么？***影响：本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。