Molecular and Cellular Mechanisms of Axon Branching in Neural Circuit Development

描述（由申请人提供）：轴突分支是开发对人类行为至关重要的神经回路的关键步骤。在胚胎发育期间，轴突分支的形成在时间和空间上受到高度调节，并且正常控制的破坏可导致与许多神经和精神疾病相关的突触缺陷。虽然在过去的十年中已经开始确定的分子机制，轴突分支的精确的时间和空间控制知之甚少。背根神经节中感觉神经元的中央投射形成在许多脊椎动物中发现的刻板分支。它们包括脊髓背侧的轴突分叉，将疼痛和触觉等躯体感觉信息传递给大脑，以及侵入白色物质并形成局部反射弧的侧支。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好模型。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，拟议的研究将使用两种体外培养物 和小鼠突变体来研究这两种结构形成的机制。具体来说，我们将结合联合收割机分子，遗传，生物化学和细胞生物学的方法来解决三个关键问题：1）细胞外的线索如何合作和调节细胞内的机器，以确保分叉发生一次，只有一次在一个确定的位置？2)细胞骨架蛋白MAP 7是如何作为信号中心调节感觉侧支形成的？3)转录辅助因子Ldb 1/2的表达如何影响侧枝形成的发育时间控制？这些问题的答案将有助于理解支配分支的时间和空间调节的机制，这对感觉回路的发育至关重要。考虑到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对轴突分支研究的一个主要空白。我们还希望，这里获得的知识可以转化为理解其他脑回路。因此，这些研究与脑研究的使命高度相关 功能和障碍。

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.