Mechanisms of neural circuit formation in C. elegans

 描述（由申请人提供）：神经回路形成是大脑发育的关键步骤，神经回路形成的破坏会导致许多出生条件。功能电路的形成需要多个步骤的复杂编排，包括 命运决定、迁移、轴突/树突分化、轴突生长和突触形成和消除。然而，目前还不清楚单个神经元在发育过程中是如何组装成功能回路的。在这里，我们建议使用一个定义的神经元回路在秀丽隐杆线虫的RME电路的发展，研究神经回路形成的分子机制。RME回路的发育利用了哺乳动物皮层发育的所有关键步骤，并涉及神经元-神经元、神经元-神经胶质和神经元-肌肉相互作用。该系统使我们能够分析从神经元诞生到功能回路成熟的神经回路形成。在本研究中，我们着重于解决两个重要问题：胶质细胞如何通过缝隙连接来指导神经元的极性，以及突触消除中细胞死亡途径的局部调节机制是什么。在我们的初步研究中，我们发现了神经胶质细胞在神经元发育过程中的一个先前未知的功能，其中神经胶质细胞与附近的神经元形成间隙连接，以调节微管极性和神经元极性。我们建议研究这一观察的分子机制。回路形成的最后一步是通过消除突触来细化突触连接。我们发现，突触消除需要细胞死亡途径的局部激活，而这种局部激活需要线粒体的存在。在本申请中，我们概述了一种策略，以解决该领域的长期问题：如何在不引起细胞死亡的情况下局部激活凋亡途径，以及在神经元发育中半胱天冬酶的下游靶点是什么。这一提议的完成将导致发现新的神经回路形成机制，建立RME回路的发展作为一个强大的模型来研究神经回路的形成，并产生新的工具，为进一步的研究。鉴于许多神经系统疾病与神经回路形成缺陷有关，希望该项目将有助于了解生理和病理条件下的大脑发育。

 DESCRIPTION (provided by applicant): Neural circuit formation is a critical step of brain development, and disruption of neural circuit formation causes many birth conditions. The formation of a functional circuit requires the intricate orchestration of multiple steps, including fate determination, migration, axon/dendrite differentiation, axon growth, and synapse formation and elimination. However it is still unclear how individual neurons are assembled into the functional circuits during development. Here, we propose to use the development of a defined neuronal circuit in Caenorhabditis elegans-the RME circuit- to study molecular mechanisms of neural circuit formation. RME circuit development utilizes all the critical steps of mammalian cortex development and involves neuron- neuron, neuron-glia, and neuron-muscle interactions. This system has enabled us to analyze neural circuit formation from the birth of neurons to the maturation of functional circuits. In this proposal we focus on address two important questions: how do glial cells instruct neuronal polarity through gap junctions, and what is the local regulatory mechanism of the cell death pathway in synapse elimination. In our preliminary studies we uncovered a previous unknown function of glial cells during neuronal development in which glial cells form gap junctions with nearby neurons to regulate microtubule polarity and neuronal polarity. We propose studies of the molecular mechanism underlying this observation. The final step of the circuit formation is refinement of synaptic connections through synapse elimination. We found that local activation of the cell death pathway is required for synapse elimination, and this local activation needs the presence of mitochondria. In this application we outline a strategy to address the long time questions in the field: how the apoptotic pathway is locally activated without causing cell death, and what are the downstream targets of caspases in neuronal development. Completion of this proposal will lead to the discovery of novel mechanisms of neural circuit formation, establish the development of RME circuit as a powerful model to study neural circuit formation, and generate new tools for further studies. Given that many neural disorders are associated with defects in neural circuit formation, it is hopeful that this project will help to understand brain development under both physiological and pathological conditions.