Development of sensory axon pathways in zebrafish

描述（由申请人提供）：在神经发育过程中，轴突在包含大量影响其生长和方向的引导分子的环境中延伸。在复杂的体内环境中，轴突生长锥是如何被引导的，目前还知之甚少。我们对特定的轴突引导问题感兴趣，即一个神经元的两个轴突分支如何沿着不同的路径被引导到不同的目标。神经元通常会将轴突投射到多个目标上，实际上我们对它们的轴突分支是如何被不同地引导的一无所知。我们使用斑马鱼的脊髓感觉神经元作为模型，因为它们是一种简单的神经元类型，具有很好表征的简单轴突轨迹。这些神经元延伸两个主要的轴突分支，中央和外周轴突，它们表现出非常不同的行为和轨迹。该项目的目标是研究这些轴突沿着其特定路径的引导机制，并阐明引导它们的分子线索的功能。斑马鱼胚胎是研究活体轴突引导机制的一个很好的系统，因为我们可以很容易地在完整的活胚胎中操纵引导分子和图像效应对轴突生长锥的动态行为。我们的具体目标是：1)使用活体成像来表征外周轴突最初向中央轴突垂直延伸并退出脊髓时的行为，研究已知对外周轴突延伸重要的两种分子的作用，并研究差异轴突引导下的细胞内信号事件；2)识别和分析参与感觉轴突引导的新分子的功能；3)从感觉轴突通路有缺陷的突变体中鉴定和克隆突变基因。总的来说，我们的研究旨在了解促进和抑制轴突生长的过程，以及神经系统复杂的树突模式。了解这些机制对于理解神经发育疾病和损伤后轴突再生发生的条件是重要的。

DESCRIPTION (provided by applicant): During neural development, axons extend through an environment containing a multitude of guidance molecules that influence their growth and direction. There is still relatively little known about how axonal growth cones are guided in the complex in vivo environment. We are interested in the particular axon guidance question of how two axon branches from one neuron are guided along separate pathways to distinct targets. Neurons often project axons to more than one target, and virtually nothing is known about how their axon branches are differentially guided. We use zebrafish spinal sensory neurons as a model because they are a simple neuronal type with well- characterized simple axon trajectories. These neurons extend two main axon branches, the central and peripheral axons, which display very different behaviors and trajectories. The goal of this project is to investigate mechanisms of guidance of these axons along their particular pathways and to elucidate the function of the molecular cues that guide them. The zebrafish embryo is an excellent system to investigate axon guidance mechanism in vivo because we can readily manipulate guidance molecules and image effects on dynamic behavior of axonal growth cones in the intact living embryo. Our specific aims are 1) to use live imaging in vivo to characterize the behavior of the peripheral axon as it initially extends in an orthogonal direction to the central axon and exits the spinal cord, investigate the roles of two molecules known to be important for peripheral axon extension, and investigate the intracellular signaling events underlying the differential axon guidance; 2) to identify and analyze the function of new molecules involved in sensory axon guidance; and 3) to characterize and clone the mutated gene from a mutant that has defective sensory axon pathways. Overall, our studies are designed to understand the processes involved in promoting and inhibiting axon growth, and patterning the complex arborization patterns of the nervous system. Knowledge of these mechanisms is important for understanding diseases of neural development and the conditions under which axon regeneration after injury can occur. Project Narrative: An understanding of the complex processes involved in promoting and inhibiting neuronal axon growth, and the functions of molecules that guide axons to their correct targets will be crucial for understanding diseases of neural development. Moreover, knowledge of these mechanisms will help to understand the conditions under which axon regeneration after injury can occur.