SIGNALING BY MUSK, A COMPONENT OF THE AGRIN RECEPTOR

描述（研究者摘要）神经肌肉突触形成为 运动神经元和肌肉纤维之间的感应相互作用的结果。 在与发育中的运动神经元的生长锥接触后， 发育中的肌纤维在骨骼肌中经历复杂的分化程序， 突触区域，来自肌肉的信号反过来被认为是调节 突触前末梢的分化。 两种不同的信号 途径导致乙酰胆碱受体（AChRs）的定位， 突触部位 一种途径的信号是聚集蛋白， 由运动神经元合成，并分泌到基底层， 突触部位 无论是聚集蛋白的受体还是 然而，聚集蛋白介导的信号传导是已知的。 肌肉的发现 特异性激酶MuSK及其在聚集蛋白介导的信号传导中的作用提供了 我们对agrin如何向肌肉发出信号的理解取得了重要进展。 目前的数据支持MuSK是聚集蛋白的关键组分的观点， 受体复合物，但需要另一种肌管特异性活性， 结合聚集蛋白并激活MuSK。 调查人员将使用最少的， 功能活性形式的聚集蛋白，其刺激MuSK但不结合 α-肌营养不良聚糖，作为亲和试剂，以鉴定和分离 电鳐电器突触后功能性聚集蛋白受体 膜。 此外，他们还将确定功能性聚集蛋白 受体与MuSK免疫共沉淀，因为免疫共沉淀可能 作为鉴定和纯化功能性聚集蛋白的独立手段 受体的 这些实验将导致分离编码 agrin受体。 MuSK所需的分子 聚集蛋白和启动突触蛋白的聚集是未知的。 他们 将采用已成功应用于研究其他 受体酪氨酸激酶，以确定蛋白质是酪氨酸 被聚集蛋白磷酸化。 因为被MuSK激活的蛋白质可能 与MuSK相关，他们还将鉴定出 与MuSK共免疫沉淀。 它们会识别并抑制 通过聚集蛋白/MuSK激活的途径来确定，如果有的话， 聚集突触蛋白需要信号通路。 他们将 确定AChR是否需要聚集其他突触蛋白， 是否需要聚集蛋白刺激的AChR酪氨酸磷酸化， 簇AChRs和其他突触蛋白。 这些研究将提供一个 更好地理解聚集蛋白通过MuSK发出信号的机制， 调节乙酰胆碱受体和其他突触蛋白的聚集， 突触后分化

DESCRIPTION (Investigator's Abstract) Neuromuscular synapses form as a result of inductive interactions between motor neurons and muscle fibers. Following contact with the growth cone of a developing motor neuron, developing muscle fibers undergo a complex differentiation program in the synaptic region, and signals from the muscle in turn are thought to regulate the differentiation of the presynaptic terminals. Two different signaling pathways lead to the localization of acetylcholine receptors (AChRs) at synaptic sites. The signal for one pathway is agrin, a protein which is synthesized by motor neurons and which is secreted into the basal lamina at synaptic sites. Neither the receptor for agrin nor the mechanisms of agrin-mediated signaling, however, are known. The discovery of the muscle specific kinase , MuSK, and its role in agrin-mediated signaling provide an important advance in our understanding of how agrin signals to muscle. Current data support the idea that MuSK is a critical component of the agrin receptor complex but that another myotube-specific activity is required to bind agrin and to activate MuSK. The investigators will use minimal, functionally active forms of agrin, which stimulate MuSK but do not bind to alpha-dystroglycan, as affinity reagents to identify and isolate the functional agrin receptor from Torpedo electric organ postsynaptic membranes. In addition,they will determine whether the functional agrin receptor co-immunoprecipitates with MuSK, since co-immunoprecipitation may serve as an independent means to identify and purify the functional agrin receptor. These experiments will lead to the isolation of cDNAs encoding the agrin receptor. The molecules that are required for MuSK to respond to agrin and to initiate clustering of synaptic proteins are not known. They will adopt strategies that have been successfully applied to study other receptor tyrosine kinases to identify proteins that are tyrosine phosphorylated by agrin. Because proteins that are activated by MuSK may associate with MuSK, they will also identify proteins that co-immunoprecipitate with MuSK. They will identify and inhibit signaling pathways which are activated by agrin/MuSK to determine which, if any, signaling pathways are required for clustering synaptic proteins. They will determine whether AChRs are required to cluster other synaptic proteins and whether agrin-stimulated AChR tyrosine phosphorylation is required to cluster AChRs and other synaptic proteins. These studies will provide a better understanding of the mechanisms by which agrin signals through MuSK, regulates clustering of AChRs and other synaptic proteins, and organizes postsynaptic differentiation.