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

AGRIN/Lrp4/Musk/Dok-7信号转导通路在突触发生中起关键作用。AGRIN和Lrp4结合可刺激麝香的酪氨酸磷酸化和DOK-7的募集和酪氨酸磷酸化。人类Agin、Musk或Dok-7的亚型突变会损害它们的功能，导致先天性肌无力，其特征是突触结构和功能缺陷，导致肌肉无力和疲劳，强调了这一信号通路的临床相关性。一旦被磷酸化，DOK-7就招募到两个相关的接头蛋白--Crk和Crk-L。AGRIN/LRP4/DOK-7/Crk/Crk-L信号通路最终与细胞骨架相交，导致AChRs等蛋白质在突触后膜中积聚。本方案中的实验旨在揭示Crk/Crk-L的招募与乙酰胆碱受体(AChRs)在发育中和成年突触的重新分布和锚定有关的分子和机制。拟议的实验将识别与Rapsyn相关的蛋白质，Rapsyn是一种AChR相关蛋白质，对聚集AChRs至关重要，并分析这些新发现的突触蛋白，包括Vezatin，如何调节突触分化。这些研究具有临床意义，因为Agin、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下游基因的突变也可能导致先天性肌无力，因此识别Crk/Crk-L下游的通路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.