Cytoskeletal Signaling and Axon Guidance

细胞形状和极性的建立和维持在多细胞生物的发育中起着关键作用。在发育中的神经系统中，神经元将轴突发送到正确的目标，形成轴突支架，在轴突支架上建立功能性神经元连接。该提议涉及新生神经系统中轴突寻路至其目标的机制。细胞外线索提供指导信息，并由生长锥上存在的跨膜受体检测到，生长锥是延伸轴突远端的感觉运动结构。响应于此类线索，介导生长锥运动的生长锥的肌动蛋白细胞骨架发生改变，以实现生长锥的定向迁移。我们对秀丽隐杆线虫的研究表明，三种 Rac GTP 酶在轴突寻路中定义了三种冗余的细胞骨架信号传导途径，并且 GTP 交换因子 UNC-73 Trio 控制着所有三种途径。我们发现肌动蛋白结合蛋白 UNC-115 在三个 Rac 通路之一的下游起作用，可能响应 Rac 信号传导直接调节肌动蛋白结构。此外，我们还发现了一种新型 Rac 调节因子，即 7-WD 重复蛋白 SWR-1，它直接结合 UNC-115 和 Racs，并抑制神经元形态发生中的 Rac 活性。这里描述的实验旨在阐明 Rac 信号转导在轴突寻路中的作用，包括 Rac 信号转导中新分子的识别和表征，以及分析这些分子在轴突寻路中如何相互关联。第一个目的是表征新型 DAD 结构域在下游 Rac 细胞骨架效应器 UNC-115 轴突寻路功能中的作用。第二个目的是确定 Rac 负调节因子 SWR-1 抑制 Rac 的分子机制。第三个目标是通过利用轴突寻路中 Rac 功能的冗余来识别和表征新分子以及与 Rac 信号传导的相互作用。了解细胞骨架信号传导的分子机制对于开发旨在减轻中枢神经系统创伤（例如脊髓损伤和中风）以及肿瘤转移影响的疗法至关重要

The establishment and maintenance of cell shape and polarity play key roles in the development of multicellular organisms. In the developing nervous system, neurons send axons to their correct targets to form an axon scaffold upon which functional neuronal connections are made. This proposal involves mechanisms of axonal pathfinding to their targets in the nascent nervous system. Extracellular cues provide guidance information and are detected by transmembrane receptors present on the growth cone, the sensory-motile structure at the distal tip of an extending axon. In response to such cues, the actin cytoskeleton of the growth cone, which mediates growth cone movement, is altered to achieve directed migration of the growth cone. Our studies in Caenorhabditis elegans have revealed that three Rac GTPases define three redundant cytoskeletal signaling pathways in axon pathfinding, and that the GTP exchange factor UNC-73 Trio controls all three pathways. We have found that the actin-binding protein UNC-115 acts downstream of one of the three Rac pathways, possibly to directly modulate actin structure in response to Rac signaling. Further, we have identified a novel Rac regulator, the 7-WD repeat protein SWR-1, which directly binds to both UNC-115 and Racs and represses Rac activity in neuronal morphogenesis. Experiments described here aim to elucidate the role of Rac signal transduction in axon pathfinding, including identification and characterization of new molecules in Rac signaling and analyses of how these molecules relate to one another in axon pathfinding. The first aim is to characterize the role of the novel DAD domain in the function of the downstream Rac cytoskeletal effector UNC-115 in axon pathfinding. The second aim is to determine the molecular mechanisms of Rac repression by the Rac negative regulator SWR-1. The third aim is to identify and characterize new molecules and interactions with Rac signaling by exploiting the redundancy of Rac function in axon pathfinding. Understanding the molecular mechanisms of cytoskeletal signaling could prove critical for developing therapies aimed at mitigating the effects of central nervous system trauma (e.g. spinal cord injury and stroke) as well as tumor metastasis