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引导至其同源突触目标。轴突寻路的复杂调节过程的干扰会干扰正确突触连接的建立和适当神经元回路的形成。因此，轴突寻路的改变被认为会导致多种神经发育障碍。 Netrin-1 和 NGF 是有吸引力的引导线索，可诱导轴突更快的生长速度，以及生长锥的精细化和有吸引力的转向。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，大量先前的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，除了细胞骨架生长之外，轴突伸长和生长锥细化的过程需要细胞表面的快速、大量扩大。构成新生质膜的磷脂以质膜前体囊泡 (PPV) 的形式从细胞体沿着轴突顺行运输。这些 PPV 与生长锥膜融合，从而在称为极化胞吐作用的调节过程中扩大轴突和生长锥的表面。质膜扩张和细胞骨架动力学必须在同一部位同时发生，以实现轴突生长或转动。目前，尚不清楚两条看似独立的途径之间的同步性是如何建立的。本申请的目的是了解这两种分子途径（细胞骨架重排和 PPV 的极化胞吐作用）如何在 netrin-1 和 NGF 信号下游进行整合和共同调节，从而导致特征性轴突生长和生长锥转动，从而表征轴突对有吸引力的引导线索的形态反应。基于初步研究，本研究计划的一个特别重点是了解轴突内 mRNA 翻译对两种途径共同激活的功能意义。这项研究的成功完成将为信号级联提供一个连贯的视图，确保在有吸引力的引导信号刺激下远端轴突和生长锥内细胞骨架动力学和膜扩张的时空并发。

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.