Plexin-A4 Signaling Regulates Diverse Cellular Morphologies in the Developing Nervous Ssystem

在发育过程中，神经元生长出称为轴突和树突的结构，专门用于传递信号。这些结构的数量和它们的形状赋予每个神经元一个特定的外观，并允许神经元之间形成特定的连接，从而导致神经系统正常运作的能力。目前，在哺乳动物发育中的神经系统中，分子的特定组合调节轴突和树突形态的方式尚不清楚。先前的科学研究发现了一种叫做信号蛋白的分子家族，它通过与神经细胞外膜上的分子（称为受体）结合来控制轴突和树突的形态。该项目将研究Semaphorin分子与受体结合后发育中的神经细胞内发生的情况，以提供有关细胞内分子控制系统的宝贵新细节，这些系统最终决定了神经元连接和信号功能的正确形成。除了这一科学目标之外，该项目还将通过共同参与STEM丰富机会，为少数民族高中生、本科生和研究生提供研究、指导和教育。由于首席研究员和以色列魏茨曼科学研究所的一名科学家之间的独特合作，还将建立一个交流项目，为女性科学家提供更广泛的国内和国际层面的接触和培训经验。这项研究产生的数据将以报告的形式在国家/国际科学会议上传播，并将发表在同行评议的期刊上，供其他科学家和一般公众查阅。本研究产生的新试剂和资源将与更广泛的科学界免费共享，并将发送到存档数据库和存储库。神经元表现出不同的形态，并在发育过程中获得其特定功能所必需的独特的轴突和树突分支。已知细胞表面受体控制这一复杂的过程，主要是通过在不同的神经元群体中引发吸引/允许或排斥/抑制细胞反应。然而，对受体启动的信号事件的这些多功能反应的细胞内机制仍然知之甚少。结合Semaphorin-3A配体的Plexin-A4受体已知可使感觉神经元轴突上的生长锥塌陷，同时促进皮质神经元树突的形成。本项目的具体目标是：1)阐明Plexin-A4受体这些不同功能的机制逻辑；2)确定在轴突塌陷和树突形成过程中，Plexin-A4细胞质结构域是否激活了相似或不同的细胞内信号级联。为该项目生成的新型小鼠遗传工具将用于确定Plexin-A4的哪些信号胞质结构域是这些不同功能所必需的。一个候选的丛蛋白- a4下游相互作用可能在轴突生长、锥体塌陷和树突发育中发挥关键作用，将在感觉神经元和皮层神经元丛蛋白- a4信号激活后进行研究。高通量、基于形态学的siRNA筛选将用于鉴定调节树突和生长锥行为的Plexin-A4信号级联的其他新的下游组分。这些结果将为神经元如何建立其独特的细胞形态提供关键的机制见解，解释Plexin-A4如何调节轴突和树突行为，并在神经系统发育过程中识别影响神经元连接形成和组织的Semaphorin-3A信号通路中的新分子。

During development, neurons grow structures called axons and dendrites that are specialized for carrying signals. The number of these structures and their shapes give each neuron a particular appearance, and allow neurons to form specific connections with each other that result in the nervous system's ability to function properly. Currently, the ways in which particular combinations of molecules regulate axon and dendrite morphology in the developing nervous system of mammals are not well understood. Previous scientific work has found a family of molecules called Semaphorins that control both axon and dendrite morphology by binding to molecules on the outer membrane of nerve cells (called receptors). This project will investigate what happens inside developing nerve cells after Semaphorin molecules bind to their receptors, in order to provide invaluable new details about the molecular control systems inside cells that ultimately determine the proper formation of neuronal connections and signaling functions. In addition to this scientific goal, this project will integrate research, mentorship and education for minority high school, undergraduate and graduate students through their joint involvement in STEM enrichment opportunities. Due to a unique collaboration between the principal investigator and a scientist at the Weizmann Institute of Science in Israel, an exchange program will also be established to provide female scientists with broader exposure and training experiences at both the national and international level. Data generated from this study will be disseminated in the form of presentations at national/international scientific meetings, and will be published in peer-reviewed journals that can be accessed by other scientists and the general public. New reagents and resources generated from this study will be freely shared with the broader scientific community and will be sent to archiving databases and repositories. Neurons exhibit diverse morphologies, and developmentally acquire the unique axonal and dendritic arborizations necessary for their specific functions. Cell surface receptors are known to control this complex process, mainly by eliciting attractive/permissive or repulsive/inhibitory cellular responses in distinct neuronal populations. However, the intracellular mechanisms underlying these multi-functional responses to receptor-initiated signaling events are still poorly understood. The Plexin-A4 receptor that binds the Semaphorin-3A ligand is known to collapse growth cones on the axons of sensory neurons, while it promotes dendrite formation in cortical neurons. The specific aims of the present project are to 1) elucidate the mechanistic logic underlying these disparate functions of the Plexin-A4 receptor; and 2) to determine whether the Plexin-A4 cytoplasmic domains activate similar or different intracellular signaling cascades during axon collapse and dendrite formation. Novel mouse genetic tools generated for this project will be used to determine which signaling cytoplasmic domains of Plexin-A4 are required for these disparate functions. One candidate Plexin-A4 downstream interactor that may play key roles in both axon growth cone collapse and dendrite elaboration will be examined following semaphorin activation of Plexin-A4 signaling in sensory versus cortical neurons. High-throughput, morphology based siRNA screening will be performed to identify additional novel downstream components of the Plexin-A4 signaling cascade that regulate dendrite and growth cone behaviors. The results will provide key mechanistic insights about how neurons establish their unique cellular morphologies, explain how Plexin-A4 regulates axon and dendrite behavior, and identify novel molecules in the Semaphorin-3A signaling pathway that impact the formation and organization of neuronal connections during nervous system development.