Mechanisms of Synaptic Specificity in C. elegans

描述（由申请人提供）： 化学突触是神经元与其突触伙伴细胞之间的特化细胞连接结构。突触是中枢神经系统中神经元之间的重要通讯手段。在发育过程中，突触的形成是连接神经系统的最终步骤。解剖学和生理学证据都表明，局部回路中神经元之间形成的突触是特定的和定型的。目前还不清楚突触特异性背后的分子机制是什么：突触伴侣将彼此与其他非靶标接触神经突区分开来的能力。从长远来看，我们希望了解特异性机制的本质，以及这些机制如何导致功能性突触的组装。 我们在C.线虫已经建立了一个遗传系统来研究突触特异性。我们标记了一组来自运动神经元HSNL的特定突触。我们询问了HSNL的突触伙伴是如何选择的，以及突触的定位是如何确定的。我们发现，两个跨膜免疫球蛋白超家族蛋白，SYG-1和SYG-2，是必不可少的，以确定HSNL的靶特异性。在syg-1和syg-2突变体中，HSNL不能突触到其正常的突触后靶点上。相反，异位突触在异常的目标上形成。SYG-1在突触前神经元HSNL中自主发挥细胞功能，并在突触形成的早期定位于突触部位。SYG-2在路标细胞中作为SYG-1的配体起作用，以将SYG-1聚集到突触。SYG-1和SYG-2在生物化学测定中直接与各自结合。因此，两种IgSF蛋白之间的相互作用定义了HSNL中的突触特异性。 在这项研究中，我们打算了解SYG-1和SYG-2的相互作用如何导致突触形成和突触靶点选择。我们将对SYG-1和SYG-2进行结构-功能分析。我们将测试这种相互作用是否足以触发突触的形成和目标选择。我们将通过表征和克隆syg-3和其他特异性突变体来扩展我们的遗传分析，以识别突触特异性中的更多分子参与者。我们将研究SYD-2在突触囊泡聚集中的作用，以了解特异性机制如何导致突触的组装。 突触特异性是如何实现的是发育神经生物学中的一个基本问题。理解这个问题应该提供对功能神经元回路在发育过程中如何构建的见解，将可能导致针对神经损伤和神经退行性疾病的新治疗策略。

DESCRIPTION (provided by applicant): Chemical synapses are specialized cellular junction structures between neurons and their synaptic partner cells. Synapses are essential means of communication between neurons in central nervous systems. During development, synapse formation is the ultimate step in wiring the nervous system. Both anatomical and physiological evidence suggest that synapses formed between neurons in local circuits are specific and stereotyped. It is not understood what molecular mechanisms underlie the synaptic specificity: the ability of synaptic partners to distinguish each other from other non-target contacting neurites. In the long term, we would like to understand the nature of specificity mechanisms and how these mechanisms lead to the assembly of functional synapses. Our previous work in C. elegans has established a genetic system to study synaptic specificity. We labeled a specific set of synapses from a motor neuron, HSNL. We asked how the synaptic partners of HSNL were selected and how the localization of synapses was determined. We discovered that two transmembrane immunoglobulin superfamily proteins, SYG-1 and SYG-2, were essential to determine the target specificity of HSNL. In both syg-1 and syg-2 mutants, HSNL fails to synapse onto its normal postsynaptic targets. Instead, ectopic synapses are formed onto abnormal targets. SYG-1 functions cell autonomously in the presynaptic neuron HSNL and localizes to synaptic sites at early stage of synapse formation. SYG-2 functions in the guidepost cells as a ligand of SYG-1 to cluster SYG-1 to synapses. SYG-1 and SYG-2 directly bind to each in biochemical assays. Therefore, interaction between two IgSF proteins defines synaptic specificity in HSNL. In this grant, we propose to understand how the SYG-1 and SYG-2 interaction leads to synapse formation and synaptic target selection. We will perform structure-function analysis on SYG-1 and SYG-2. We will test if this interaction is sufficient to trigger synapse formation and target selection. We will expand our genetic analysis to identify more molecular players in synaptic specificity by characterizing and cloning syg-3 and other specificity mutants. We will study the role of SYD-2 in synaptic vesicle clustering to understand how specificity mechanisms lead to the assembly of synapses. How synaptic specificity is achieved is a fundamental question in developmental neurobiology. Understanding this question should provide insights into how functional neuronal circuits are constructed during development, will potentially lead to new therapeutic strategies against nerve injuries and neurodegenerative diseases.