The Actin Cytoskeleton of Photoreceptor Inner Segments

描述(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对光感受器的形态发生、维持和存活做出贡献，从而对视觉做出贡献。光感受器内节段细胞骨架由平行的肌动蛋白细丝组成，终止于外节底部周围的指状纤毛突起。这项研究验证了这一假说，即这些束对于光感受器的形态发生、内外段的排列以及内段与瞳孔的排列都是关键的。它还检验了这样一种假设，即这些束为肌球蛋白依赖的货物在核周肌样区域和外段之间的运输提供了轨迹。有几种蛋白质特异性地定位于这些结构，包括两个肌动蛋白交联物Fasin和Fimbrin，以及Myo3A，一种III类肌球蛋白。筋膜蛋白突变的患者会患上pimentosa视网膜炎，而Myo3A的过度表达也会导致光感受器肌动蛋白细胞骨架的异常。虽然细胞缺陷的性质及其对视网膜功能障碍的作用尚未被研究，但它说明了内段肌动蛋白细胞骨架在视网膜中的重要性。这项研究验证了一种假说，即肌动蛋白细丝束的交联和受调控的成核协调了它们的正确组装和维护，因此是维持健康光感受器所必需的。这项研究最初将重点放在Fascin、Fimbrin和Myo3A上。为了研究光感受器的肌动蛋白细丝束，将使用两个动物模型系统，FISH和Xenopus，每个系统都唯一适合回答某些问题。内节肌动蛋白细丝束的形态发生和发育过程中的唇突将使用鲑鱼视网膜进行研究，因为它们具有包含光感受器发育的所有阶段的增殖区。我们还将使用鱼类(Bass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质制剂，而且鱼的大小使生物化学具有可伸缩性。这些研究将提供关于内节丝束和花丝突起的组成、组装和功能的新信息，从而增加或理解光感受器形态发生、功能和存活的基本机制。

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.