Molecular Mechanisms of Axon Branching in Synaptic Development

描述（申请人提供）：轴突分支允许神经元与多个伙伴通信，并帮助建立形态和功能上不同的神经网络。为了确保正确的突触连接，分支受到信号通路的严格调节，这些信号通路允许环境线索指示轴突何时何地产生分支。本研究的长期目标是研究这种调节的分子和细胞基础，了解它如何促进突触连接的初始发育和随后的可塑性重排，并为损伤后如何再生新分支和功能连接提供见解。以背根神经节和三叉神经节为模型，我们发现了一种细胞外信号通路，涉及分泌分子Slit促进轴突分支的发展。此外，我们的初步研究表明，cGMP途径为分支调节提供了细胞内信号传导机制。利用原代感觉神经元培养和敲除小鼠，我们提出了以下三个目标来进一步表征cGMP信号的作用：1)通过体内分析建立cGMP信号作为调节多种刻板感觉轴突分支发育的一般信号机制；2)明确cGMP活性在感觉轴突分支中的下游信号机制；3)确定轴突分支时空控制的细胞机制。这些目标应该有助于建立调节轴突分支的独特信号通路，并填补我们对突触连接重要过程的理解的主要空白。此外，由于突触稳定性的丧失是许多神经系统疾病的标志，我们对这一基本过程的研究应该为这些疾病的病因学提供新的见解。公共卫生相关性：本研究的目的是研究轴突分支的分子和细胞基础，轴突分支是突触连接和神经网络建立的重要过程。我们将结合分子、细胞和遗传方法来描述关键的分子通路，并确定轴突分支调节的信号机制。从这项研究中获得的知识不仅有助于理解大脑发育，而且还为许多神经系统疾病的分子基础以及如何促进中风和损伤后的神经再生提供了新的见解。

DESCRIPTION (provided by applicant): Axon branching allows a neuron to communicate with multiple partners and helps establish morphologically and functionally distinct neural networks. To ensure proper synaptic connections, branching is tightly regulated by signaling pathways that allow environmental cues to instruct axons when and where to make branches. The long term goal of the proposed research is to investigate the molecular and cellular basis of this regulation, understand how it contributes to the initial development and the subsequent plastic rearrangement of synaptic connections, and provide insights into how to regenerate new branches and functional connections after injury. Using the development of stereotypic axonal branches of rodent sensory neurons from the dorsal root ganglion and trigeminal ganglion as models, we have identified an extracellular signaling pathway involving the secreted molecule Slit in promoting axon branching. In addition, our preliminary studies have demonstrated that the cGMP pathway provides an intracellular signaling mechanism for branching regulation. Using primary sensory neuron cultures and knockout mice, we propose the following three aims to further characterize the role of cGMP signaling: 1) use in vivo analysis to establish cGMP signaling as a general signaling mechanism in regulating the development of diverse yet stereotypic sensory axon branches; 2) identify the downstream signaling mechanism mediating the cGMP activity in sensory axon branching; 3) determine the cellular mechanism underlying the spatial and temporal control of axon branching. These aims should help establish a distinct signaling pathway in regulating axon branching and fill in a major gap in our understanding of an important process in making synaptic connections. In addition, since loss of synaptic stability is the hallmark of many neurological disorders, our study of this fundamental process should provide new insights into the etiology of these diseases. PUBLIC HEALTH RELEVANCE: The goal of the proposed research is to investigate the molecular and cellular basis of axon branching, an important process in making synaptic connections and establishing neural networks. We will use a combination of molecular, cellular and genetic approaches to characterize key molecular pathways and identify the signaling mechanisms underlying the regulation of axon branching. The knowledge obtained from this study will not only help understand brain development, but also provide new insights into the molecular basis of many neurological disorders as well as how to promote nerve regeneration after stroke and injury.