Intra-axonal signaling pathways triggered by attractive guidance cues.

描述(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体施加排斥或吸引作用的引导因素而指向它们的同源突触目标。轴突寻路的复杂调控过程中的干扰干扰了正确突触连接的建立和正确神经元电路的形成。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是有吸引力的指导信号，可以诱导轴突更快的生长速度，以及生长锥体的精加工和有吸引力的转向。这些形态变化是由生长锥体内高度动态的肌动蛋白和微管细胞骨架的重排所介导的，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，除了细胞骨架的生长外，轴突的延长和生长锥的精化过程还需要细胞表面的快速、大规模的扩大。组成新生质膜的磷脂以质膜前体小泡(PPV)的形式从细胞体顺着轴突运输。这些PPV与生长锥膜融合，从而在一种被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同时发生在同一部位，以实现轴突的生长或转向。目前，尚不清楚两条看似独立的通路之间的这种同步性是如何建立的。这项应用的目的是了解这两个分子通路，细胞骨架重排和PPV的极化胞吐，是如何在netrin-1和NGF信号下游整合和共同调节的，从而导致特征性的轴突生长和生长锥体转向，这是轴突对吸引人的指导线索的形态反应的特征。在前期研究的基础上，本研究建议的一个重点是了解轴突内mRNA翻译对于两条通路共同激活的功能意义。这项研究的成功完成将提供对信号级联的一致看法，以确保在有吸引力的指导线索刺激的远端轴突和生长锥体内细胞骨架动力学和膜扩张的时空同步。

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.