Intra-axonal signaling pathways triggered by attractive guidance cues.

描述（由申请人提供）：在神经系统的发育过程中，轴突通过对轴突和生长锥施加排斥或吸引作用的引导因子被定向到其同源突触靶点。在复杂调节的轴突寻路过程中，干扰了正确突触连接的建立和适当神经元回路的形成。因此，轴突寻径的改变被认为是引起多种神经发育障碍的原因。Netrin-1和NGF是极具吸引力的引导信号，可诱导轴突更快的生长速率，以及生长锥的细化和极具吸引力的转向。这些形态变化是由生长锥内高度动态的肌动蛋白和微管细胞骨架的重排介导的，大量的先前研究已经解决了控制这些细胞骨架变化的轴突内信号通路。然而，除了细胞骨架生长外，轴突伸长和生长锥体发育的过程还需要细胞表面快速、大量的扩大。构成新生质膜的磷脂以质膜前体囊泡（PPVs）的形式沿轴突顺行运输。这些ppv与生长锥膜融合，从而扩大轴突和生长锥的表面，这一过程被称为极化胞外作用。质膜扩张和细胞骨架动力学必须在同一地点同时发生，以实现轴突的生长或转动。目前，尚不清楚这两个看似独立的通路之间的同步性是如何建立的。本应用程序的目的是了解ppv的细胞骨架重排和极化胞外分泌这两种分子途径如何整合并共同调节netrin-1和NGF信号的下游，从而导致轴突的特征性生长和生长锥转向，这是轴突对有吸引力的引导信号的形态学反应的特征。在初步研究的基础上，本研究计划的一个特别重点是了解轴突内mRNA翻译对这两种途径共激活的功能意义。这项研究的成功完成将为信号级联提供一个连贯的观点，该信号级联确保了细胞骨架动力学和膜扩张在远端轴突和生长锥内的时空同步，并受到有吸引力的引导线索的刺激。

DESCRIPTION (provided by applicant): During the development of the nervous system, axons are directed to their cognate synaptic targets by guidance factors that exert either a repulsive or an attractive effect onto axons and growth cones. Disturbances in the intricately regulated process of axonal pathfinding interfere with the establishment of correct synaptic connections and the formation of proper neuronal circuitry. Consequently, alterations of axonal pathfinding are thought to cause a wide variety of neurodevelopmental disorders. Netrin-1 and NGF are attractive guidance cues that induce faster growth rates in axons, as well as growth cone elaboration and attractive turning. These morphological changes are mediated by the rearrangement of the highly dynamic actin and microtubules cytoskeleton within growth cones, and a great amount of prior research has addressed the intra-axonal signaling pathways governing these cytoskeletal changes. However, besides cytoskeletal growth the process of axon elongation and growth cone elaboration requires the rapid, massive enlargement of the cell surface. The phospholipids that make up the nascent plasma membrane are anterogradely transported along the axons from the cell bodies in the form of plasma membrane precursor vesicles (PPVs). These PPVs fuse with the growth cone membrane thereby enlarging the surface of axons and growth cones in a regulated process called polarized exocytosis. Plasma membrane expansion and cytoskeletal dynamics have to occur at the same site and at the same time to achieve axon outgrowth or turning. Currently, it is unknown how this synchronicity between two seemingly separate pathways is established. The goal of this application is to understand how these two molecular pathways, cytoskeletal rearrangement and polarized exocytosis of PPVs, are integrated and co-regulated downstream of netrin-1 and NGF signaling to result in the characteristic axonal outgrowth and growth cone turning that characterize the morphological response of axons to attractive guidance cues. Based on preliminary studies, a special focus of this research proposal is to understand the functional significance of intra-axonal mRNA translation for the co-activation of both pathways. The successful completion of this research will provide a coherent view of the signaling cascades that ensure the temporal-spatial concurrence of cytoskeletal dynamics and membrane expansion within distal axons and growth cones stimulated with attractive guidance cues.