A Novel Role For Plexin A in Photoreceptor Axon Targeting

项目摘要 复杂神经回路的形成必须在发育过程中得到精确控制 神经系统。轴突通过检测远距离和近距离信号来导航到它们的目标 由环境中的细胞呈现，可用作引诱剂或驱避剂。轴突缺陷 指导和靶向可导致许多神经发育障碍，如癫痫， 精神分裂症、自闭症谱系障碍和智力残疾。果蝇的视觉系统 是研究轴突引导和神经回路基本机制的优秀模型系统 队形。R7和R8感光细胞的终末负责色觉的不同方面， 被分成不同的延髓靶层，延髓是视觉处理的中心区域 大脑。光感受器还必须以视网膜定位的方式投射，以保持对 大脑内的视野。在控制彩色光感受器轴突的分子的屏幕上 利用RNAi靶向、击倒大脑中的丛状蛋白A(PlexA)导致R7光感受器 过早地终止于延髓的R8靶层，无法扩大轴突终末。一个 编码外显子插入Minos元件导致plexA(PlexAMb09499)蛋白零突变 对R7轴突也有同样的影响。R7在神经元中需要丛状A，但在光感受器中不需要 正确的目标层。PlexA蛋白在靠近这一靶层的地方表达，这表明它可能起作用 作为R7轴突的一个有吸引力的信号，与其在排斥L3板层神经元轴突中的已知作用相反 从这一层。马赛克分析将被用来确认这是PlexA动作的部位。 光感受器过度表达PlexA或缺失细胞质结构域的截短形式的结果 在轴突的过度分裂和提前终止中。这种错误表达的表型将是 用来描述PlexA的作用机制并检验PlexA作为 对光感受器有吸引力或粘性的信号。已知的丛状A受体和配体--Semaphorin- 1A不是R7光感受器正常靶向所必需的。我们将调查PlexA是否 与未鉴定的幼崽结构域蛋白CG6024相互作用；敲除CG6024 使用RNAi的光感受器也会破坏R7的靶向。PlexA的同系物已在 脊椎动物视网膜的组织，网络蛋白家族成员也参与调节 免疫反应、心脏和血管的形成，甚至癌症的进展。初步结果 提示PlexA通过一种新的信号机制控制R7靶向，与那些 如前所述。因此，这项工作可能会提供新的洞察力，以控制一种 高等生物体的发育和疾病过程的多样性。

Project Summary Formation of complex neural circuits must be precisely controlled during the development of the nervous system. Axons navigate to their targets by detecting both long-range and short-range signals presented by cells in the environment that can act as attractants or repellants. Defects in axon guidance and targeting can result in a number of neurodevelopmental disorders, such as epilepsy, schizophrenia, Autism Spectrum Disorders, and intelligence disabilities. The Drosophila visual system is an excellent model system for studying the basic mechanisms of axon guidance and neural circuit formation. The terminals of R7 and R8 photoreceptors, responsible for different aspects of color vision, are segregated into distinct target layers of the medulla, a central region of visual processing in the brain. Photoreceptors also must project in a retinotopic manner to maintain a precise representation of the visual field within the brain. In a screen for molecules that control color photoreceptor axon targeting, knocking down plexin A (plexA) in the brain using RNAi caused R7 photoreceptors to prematurely terminate in the R8 target layer of the medulla and fail to expand their axon terminals. A protein null mutation in plexA (plexAMb09499) caused by a Minos element insertion in a coding exon has the same effect on R7 axons. plexA is required in neurons, but not in photoreceptors, for R7 to reach the correct target layer. PlexA protein is expressed close to this target layer, suggesting that it may act as an attractive signal for R7 axons, in contrast to its known role in repelling L3 lamina neuron axons from this layer. Mosaic analysis will be used to confirm that this is the site of PlexA action. Overexpression of PlexA or a truncated form lacking the cytoplasmic domain in photoreceptors results in hyperfasciculation and premature termination of their axons. This misexpression phenotype will be used to characterize the mechanism of PlexA action and test the hypothesis that PlexA acts as an attractive or adhesive signal for photoreceptors. The known receptor and ligand for PlexA, Semaphorin- 1a, is not required for normal targeting of R7 photoreceptors. We will investigate whether PlexA instead interacts with an uncharacterized CUB domain protein, CG6024; knocking down CG6024 in photoreceptors using RNAi also disrupts R7 targeting. Homologs of PlexA have been studied in the organization of the vertebrate retina, and Plexin family members also participate in regulation of the immune response, heart and vessel formation, and even the progression of cancer. Preliminary results suggest that PlexA controls R7 targeting through a novel signaling mechanism, distinct from those previously described. Therefore, this work may provide new insight into the mechanisms that control a variety of developmental and disease processes in higher organisms.