Regulation of Axon Guidance by Second Messengers

描述（由申请人提供）：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通过轴突和树突的引导延伸发生。我们研究的长期目标是更好地了解负责轴突生长和指导发育中大脑的细胞内信号级联和效应机制。为此，我们必须了解神经生长锥如何检测，整合和响应可溶性，以及细胞和基质相关的指导分子在其环境中。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是许多认知功能缺陷的原因，包括自闭症、阅读障碍、心理障碍和智力迟钝。 轴突延伸通过一个连续的过程进行，该过程涉及由肌动蛋白聚合驱动的前缘膜突起，然后是粘附和突起稳定。不粘附的新突起被缩回，脱离粘附的现有突起也被缩回。虽然广泛的研究集中在控制膜突出和收缩的信号上，但令人惊讶的是，对粘附的调节知之甚少。生长锥突起对细胞外基质（ECM）配体的稳定发生在称为点接触的专门粘附部位。点接触是大分子复合物，包含结构和信号蛋白，其通过跨膜整合素受体将细胞骨架连接到ECM。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来控制轴突寻路。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组装和营业额，而抑制线索减慢组装新的点接触，减少营业额。我们假设，轴突的指导，其适当的目标和稳定的突触接触需要调制的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测试这一假设。在目的1中，我们将研究粘着斑激酶（FAK）在控制粘着动力学，面纱突起和磷酸酪氨酸信号在丝状伪足尖端响应轴突导向线索的作用。在目标2中，我们将研究p21激活激酶（PAK）蛋白在调节整合素依赖性粘附，细胞突起和轴突生长中的作用。最后，在目标3中，我们将确定在非洲爪蟾和斑马鱼胚胎的几个选择点的轴突指导的粘附位点动力学的作用。

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.