The Actin Cytoskeleton of Photoreceptor Inner Segments

描述（由申请人提供）：本项目的目标是了解光感受器内段的肌动蛋白细胞骨架如何参与光感受器的形态发生、维持和存活，从而影响视力。光感受器内节细胞骨架由平行的肌动蛋白丝束组成，终止于环绕外节基部的指状萼突。本研究验证了这些束对光感受器形态发生、内外段对齐以及内段与瞳孔对齐至关重要的假设。它还检验了这些束在核周肌样区和外段之间为肌球蛋白依赖的货物运输提供轨道的假设。有几种蛋白质专门定位于这些结构，包括两种肌动蛋白交联剂，束状蛋白和纤维蛋白，以及Myo3A，一种III类肌球蛋白。筋膜蛋白突变的患者患有视网膜炎，Myo3A过表达也会导致感光细胞肌动蛋白细胞骨架异常。虽然细胞缺陷的性质及其如何导致视网膜功能障碍尚未对束状蛋白突变进行研究，但它说明了视网膜内段肌动蛋白细胞骨架的重要性。本研究验证了一个假设，即肌动蛋白丝束的交联和调控成核协调了它们的正常组装和维护，因此是维持健康的光感受器所必需的。本研究将首先集中于fastin， fiimbrin和Myo3A。为了研究光感受器的肌动蛋白细丝束，将采用两种动物模型系统，鱼和爪蟾，每一种都独特地适合回答某些问题。由于鳟鱼视网膜具有一个包含所有感光细胞发育阶段的增殖区，因此将利用鳟鱼视网膜研究发育过程中内部肌动蛋白丝束和萼过程的形态发生。我们还将使用鱼类（鲈鱼和绿色太阳鱼）来鉴定光感受器内/外段细胞骨架的其他蛋白质成分，因为可以使用光感受器内外段的均匀制备，并且鱼类的大小使生物化学变得容易。这些研究将为光感受器内部丝束和萼突的组成、组装和功能提供新的信息，从而增加对光感受器形态发生、功能和存活的基本机制的理解。

DESCRIPTION (provided by applicant): The goal of this project is to understand how the actin cytoskeleton of the photoreceptor inner segment contributes to the morphogenesis, maintenance and survival of photoreceptors, and hence to vision. The photoreceptor inner segment cytoskeleton is comprised of parallel bundles of actin filaments terminating in fingerlike calycal processes that surround the base of the outer segment. This research tests the hypothesis that these bundles are critical to photoreceptor morphogenesis, to inner and outer segment alignment, and to alignment of the inner segment with the pupil. It also examines the hypothesis that these bundles provide tracks for myosin-dependent transport of cargo between the perinuclear myoid region and the outer segment. Several proteins localize specifically to these structures including two actin cross-linkers fascin and fimbrin and Myo3A, a class III myosin. Patients with a mutation in fascin suffer from retinitis pimentosa, and Myo3A over-expression also causes abnormalities in the photoreceptor actin cytoskeleton. While the nature of the cellular defect and how it contributes to retinal dysfunction has not been studied yet for the fascin mutation, it illustrates the importance of the inner segment actin cytoskeleton in the retina. This research tests the hypothesis that the cross-linking and regulated nucleation of actin filament bundles orchestrates their proper assembly and maintenance, and thus is required for maintenance of healthy photoreceptors. This study will initially focus on fascin, fimbrin and Myo3A. In order to study the actin filament bundles of photoreceptors, two animal model systems will be employed, fish and Xenopus, each of which is uniquely suited to answer certain questions. The morphogenesis of the inner segment actin filament bundles and calycal processes during development will be studied using trout retinas, since they possess a proliferative zone containing all stages of photoreceptor development. We will also identify other protein components of the photoreceptor inne/outer segment cytoskeleton using fish (Bass and green sunfish), because homogeneous preparations of photoreceptor inner outer segments can be used, and the size of the fish makes biochemistry tractible. These studies will provide new information about the constituents, assembly and functions of the inner segment filament bundles and calycal processes and will thereby increase or understanding of mechanisms fundamental to photoreceptor morphogenesis, function and survival.