Mechanisms of neural circuit formation in C. elegans

 描述(申请人提供)：神经回路形成是大脑发育的关键步骤，神经回路形成障碍会导致许多出生条件。功能电路的形成需要复杂的多个步骤的协调，包括 命运决定，迁移，轴突/树突分化，轴突生长，以及突触的形成和消除。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电路的。在这里，我们建议利用秀丽隐杆线虫一种已定义的神经元回路--RME回路--的发展来研究神经回路形成的分子机制。RME回路发育利用哺乳动物皮质发育的所有关键步骤，涉及神经元-神经元、神经元-神经胶质细胞和神经元-肌肉相互作用。这个系统使我们能够分析神经回路的形成，从神经元的诞生到功能回路的成熟。在这个建议中，我们重点解决两个重要的问题：胶质细胞如何通过缝隙连接指导神经元的极性，以及细胞死亡途径在突触消除中的局部调控机制是什么。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未知功能，即神经胶质细胞与附近的神经元形成缝隙连接，以调节微管和神经元的极性。我们建议研究这一观察结果背后的分子机制。回路形成的最后一步是通过消除突触来精炼突触连接。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。在这一应用中，我们概述了一种策略来解决该领域的长期问题：如何在不导致细胞死亡的情况下局部激活凋亡途径，以及caspase在神经元发育中的下游靶点是什么。这一提议的完成将有助于发现神经回路形成的新机制，使RME回路的发展成为研究神经回路形成的有力模型，并为进一步的研究提供新的工具。鉴于许多神经障碍与神经回路形成的缺陷有关，这个项目有望有助于理解大脑在生理和病理条件下的发育。

 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.