Intra-axonal signaling pathways triggered by attractive guidance cues.

描述（由申请人提供）：在神经系统发育期间，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靶标。轴突寻路的复杂调节过程中的干扰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，轴突寻路的改变被认为是导致各种神经发育障碍的原因。Netrin-1和NGF是诱导轴突更快生长速率的有吸引力的引导线索，以及生长锥的精细化和有吸引力的转向。这些形态学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，并且大量的先前研究已经解决了支配这些细胞骨架变化的轴突内信号传导途径。然而，除了细胞骨架生长外，轴突伸长和生长锥的形成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向。目前，尚不清楚这两个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，PPV的细胞骨架重排和极化胞吐，是如何整合和共调节netrin-1和NGF信号传导的下游，以导致特征性轴突生长和生长锥转向，其表征轴突对有吸引力的指导线索的形态反应。基于初步研究，本研究建议的一个特别重点是了解轴突内mRNA翻译对两种途径共激活的功能意义。这项研究的成功完成将提供一个连贯的观点的信号级联，确保时空并发的细胞骨架动力学和膜扩张的远端轴突和生长锥刺激有吸引力的指导线索。

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.