Clustering Postsynaptic Proteins at Neuromuscular Synapses: From Dok-7 to Rapsyn

聚集蛋白/Lrp 4/MuSK/Dok-7信号转导级联对突触发生至关重要。聚集蛋白和Lrp 4之间的结合刺激MuSK的酪氨酸磷酸化和Dok-7的募集和酪氨酸磷酸化。人类聚集蛋白、MuSK或Dok-7中的亚型突变损害了它们的功能，导致先天性肌无力，其特征在于结构和功能缺陷的突触，导致肌肉无力和疲劳，强调了这一信号通路的临床相关性。一旦磷酸化，Dok-7招募Crk和Crk-L，两种相关的衔接蛋白。聚集蛋白/Lrp 4/Dok-7/Crk/Crk-L信号通路最终与细胞骨架相交，导致AChR和其他蛋白质在突触后膜中积累。本实验旨在揭示Crk/Crk-L的募集与乙酰胆碱受体（AChR）在发育和成年突触的再分布和锚定之间的分子和机制。拟议的实验将确定与Rapsyn相关的蛋白质，Rapsyn是一种AChR相关蛋白质，对聚集AChR至关重要，并分析这些新发现的突触蛋白质，包括Vezatin，如何调节突触分化。这些研究具有临床意义，因为Agrin、MuSK、Dok-7和Rapsyn的突变会导致先天性肌无力，因此了解这些蛋白质的工作原理将有助于更好地了解这些疾病，并可能导致新的治疗策略。此外，Crk/Crk-L下游基因的突变同样可能导致先天性肌无力，因此鉴定Crk/Crk-L下游途径可能揭示导致先天性肌无力的新基因。

The Agrin/Lrp4/MuSK/Dok-7 signal transduction cascade is critical for synaptogenesis. Binding between Agrin and Lrp4 stimulates tyrosine phosphorylation of MuSK and recruitment and tyrosine phosphorylation of Dok-7. Hypomorphic mutations in human Agrin, MuSK or Dok-7, which impair their function, cause congenital myasthenia, characterized by structurally and functionally defective synapses, leading to muscle weakness and fatigue, emphasizing the clinical relevance of this signaling pathway. Once phosphorylated, Dok-7 recruits Crk and Crk-L, two related adapter proteins. The Agrin/Lrp4/Dok-7/Crk/Crk-L signaling pathway ultimately intersects with the cytoskeleton to cause accumulation of AChRs and other proteins in the postsynaptic membrane. The experiments in this proposal are designed to reveal the molecules and mechanisms that link recruitment of Crk/Crk-L to the redistribution and anchoring of acetylcholine receptors (AChRs) at developing and adult synapses. The proposed experiments will identify proteins that associate with Rapsyn, an AChR-associated protein that is essential to cluster AChRs, and analyze how these newly identified synaptic proteins, including Vezatin, regulate synaptic differentiation. These studies are clinically relevant, as mutations in Agrin, MuSK, Dok-7 and Rapsyn cause congenital myasthenia, so understanding how these proteins work will contribute to a better understanding of these diseases and may lead to novel therapeutic strategies. Moreover, mutations in genes that are downstream from Crk/Crk-L may likewise cause congenital myasthenia, so identifying the pathway downstream from Crk/Crk-L may reveal new genes responsible for congenital myasthenia.