Molecular and Cellular Mechanisms of Axon Branching in Neural Circuit Development

描述(由申请人提供)：轴突分支是发展神经回路的关键步骤，神经回路对人类行为至关重要。在胚胎发育过程中，轴突分支的形成在时间和空间上受到高度调控，正常控制的中断可导致与许多神经和精神疾病相关的突触缺陷。虽然分子机制在过去的十年里已经开始被发现，但对轴突分支的精确的时间和空间控制还知之甚少。脊神经节感觉神经元的中央投射形成了许多脊椎动物都有的定型分支。它们包括背侧脊髓的轴突分叉，将躯体感觉信息(如疼痛和触摸)传递到大脑，以及侵入白质并形成局部反射弧的侧枝。这些分支的形成在发育过程中受到精确的调控，使它们成为了解轴突分支的分子和细胞机制的极佳模型。在我们最近确定了分叉的细胞外线索和侧支形成的内在决定因素之后，拟议的研究将使用这两种体外培养方法。 和小鼠突变体来研究这两种结构形成的机制。具体地说，我们将结合分子、遗传、生化和细胞生物学的方法来解决三个关键问题：1)细胞外信号如何协调和调节细胞内的机制，以确保在指定的位置发生一次且仅一次的分叉；2)细胞骨架蛋白MAP7如何作为信号中心来调节感觉侧支的形成？3)转录辅助因子LDB1/2的表达如何有助于侧支形成的发育时间控制？对这些问题的回答将有助于理解对感觉回路发育至关重要的分支的时间和空间调节机制。鉴于这些分子的广泛表达和两个分支过程的频繁出现，我们对这种进化保守的细胞模型的研究将填补我们在轴突分支研究中的一个主要空白。我们还希望这里获得的知识可以转化为理解其他大脑回路。因此，拟议的研究与研究大脑的使命高度相关 功能和紊乱。

DESCRIPTION (provided by applicant): Axon branching is a key step in developing neural circuits that are critical to human behaviors. During embryonic development, formation of axonal branches is high regulated in time and space, and disruption of normal control can cause synaptic defects associated with many neurological and psychiatric disorders. Although molecular mechanisms have begun to be identified in the past decade, the precise temporal and spatial control of axon branching is poorly understood. The central projection of the sensory neurons in the dorsal root ganglion develops stereotypic branches that are found in many vertebrates. They include axon bifurcation at the dorsal spinal cord that relays somatosensory information such as pain and touch to the brain, and collateral branches that invade the white matter and form local reflex arcs. Formation of these branches is precisely regulated during development, making them excellent model to understand molecular and cellular mechanisms of axon branching. Following our recent identification of extracellular cues for bifurcation and intrinsic determinants for collateral formation, the proposed study will use both in vitro cultures and mouse mutants to investigate the mechanisms underlying the formation of both structures. Specifically, we will combine molecular, genetic, biochemical, and cell biological approaches to address three key questions: 1) How do extracellular cues cooperate and regulate the intracellular machineries to ensure bifurcation happens once and only once at a defined location? 2) How does a cytoskeleton protein MAP7 serve as a signaling center to regulate sensory collateral formation? 3) How does the expression of transcriptional co-factors Ldb1/2 contribute to the developmental time control for collateral formation? Answers to these questions will help understand the mechanisms governing the temporal and spatial regulation of branching that is critical to sensory circuit development. Given the wide expression of these molecules and the frequent appearance of the two branching processes, our proposed studies of this evolutionarily conserved cell model will fill in a major gap in our study of axon branching We also expect that the knowledge obtained here can be translated to understanding other brain circuits. Thus the proposed studies are highly relevant to the mission of investigating brain functions and disorders.