Regulation of Axon Guidance by Second Messengers

描述（申请人提供）：神经系统的发育需要神经元的适当分化、迁移和形态发生。单个神经元的形态发生和组成人类神经系统的数万亿神经元连接的组装是通过轴突和树突的引导延伸发生的。我们研究的长期目标是更好地理解细胞内信号级联和效应机制，它们负责轴突的生长和发育中的大脑的指导。为此，我们必须了解神经生长锥如何在其环境中检测、整合和响应可溶性以及细胞和基质相关的指导分子。参与轴突引导信息检测和转导到定向神经突生长的基因突变可能导致许多认知功能缺陷，包括自闭症、阅读障碍、心理障碍和智力迟钝。轴突延伸是通过一系列的过程进行的，包括由肌动蛋白聚合驱动的前缘膜突出，随后是粘附和突出稳定。不粘附的新突出物被收回，现有的不粘附的突出物也是如此。虽然广泛的研究集中在控制膜的伸缩回的信号上，但令人惊讶的是，对粘附的调节知之甚少。生长锥突对细胞外基质（ECM）配体的稳定发生在称为点接触的特殊粘附位点。点接触是包含结构蛋白和信号蛋白的大分子复合物，通过跨膜整合素受体将细胞骨架与ECM连接起来。我们的研究重点是了解控制点接触组装、成熟和拆卸的分子信号事件，以及轴突引导线索如何影响这些过程以控制轴突寻路。重要的是，我们的证据表明，促进生长的轴突引导线索刺激点接触的组装和更换，而抑制性线索减慢新的点接触的组装和减少更换。我们假设轴突的正确目标引导和突触接触的稳定需要调节整合素依赖的点接触。我们将在三个具体目标中使用各种方法和模型系统来检验这一假设。在Aim 1中，我们将研究Focal Adhesion Kinase （FAK）在响应轴突引导信号时，在丝状面尖端控制粘附动力学、面纱突出和磷酸酪氨酸信号传导中的作用。在Aim 2中，我们将研究p21活化激酶（PAK）蛋白在整合素依赖性粘附、细胞突出和轴突生长的调节中的作用。最后，在Aim 3中，我们将在爪蟾和斑马鱼胚胎的几个选择点确定粘附位点动力学在轴突引导中的作用。

DESCRIPTION (provided by applicant): The development of the nervous system requires the proper differentiation, migration and morphogenesis of neurons. The morphogenesis of individual neurons and the assembly of the trillions of neuronal connections that compose the human nervous system occurs through guided extension of axons and dendrites. The long-term objective of our research is to better understand the intracellular signaling cascades and effector mechanisms that are responsible for axon outgrowth and guidance in the developing brain. For this we must understand how nerve growth cones detect, integrate and respond to soluble, as well as cell- and substratum-associated guidance molecules in their environment. Mutations in genes involved in the detection and transduction of axon guidance information into directed neurite outgrowth are likely responsible for many deficits in cognitive function, including autisms, dyslexias, psychological disorders and mental retardations. Axon extension proceeds through a sequential process that involves leading edge membrane protrusion driven by actin polymerization, followed by adhesion and protrusion stabilization. New protrusions that do not adhere are retracted, as do existing protrusions that de-adhere. While extensive research has focused on the signals that control membrane protrusion and retraction, surprisingly little is known about the regulation of adhesion. Stabilization of growth cone protrusions to extracellular matrix (ECM) ligands occurs at specialized adhesion sites called point contacts. Point contacts are macromolecular complexes, containing both structure and signaling proteins, which link the cytoskeleton to the ECM through transmembrane integrin receptors. Our research is focused on understanding the molecular signaling events that control point contact assembly, maturation and disassembly and how axon guidance cues influence these processes to control axon pathfinding. Importantly, our evidence suggests that growth promoting axon guidance cues stimulate point contact assembly and turnover, while inhibitory cues slow the assembly of new point contacts and reduce turnover. We hypothesize that guidance of axons to their proper targets and stabilization of synaptic contacts requires modulation of integrin-dependent point contacts. We will test this hypothesis using a variety of approaches and model systems in three specific aims. In Aim 1, we will examine the role of Focal Adhesion Kinase (FAK) in the control of adhesion dynamics, veil protrusion and phosphotyrosine signaling at filopodial tips in response to axon guidance cues. In Aim 2, we will examine the role of p21-Activated Kinase (PAK) proteins in the regulation of integrin-dependent adhesion, cellular protrusion and axon outgrowth. Finally, in Aim 3, we will determine the role of adhesion site dynamics in axon guidance at several choice point in both Xenopus and zebrafish embryos.