Neuregulin signaling at the neuromuscular synapse

描述(申请人提供)：发育中的轴突和其靶点之间的突触形成涉及协调分化的突触前和突触后成分，介导突触传递。在神经肌肉突触的发育中，乙酰胆碱受体(AChRs)是定位于肌肉突触后区域的蛋白质之一，它们在发育过程中定位于肌纤维膜的这一小块是突触形成诱导事件的标志。人们认为AChRs的定位部分是由转录机制介导的，因为编码AChR亚单位的基因选择性地转录在位于突触部位的少数肌肉核中。神经调节蛋白(NRGs)是刺激突触特异性基因表达的最佳配体，因为NRGs集中在突触部位，可以诱导培养的肌肉细胞合成AChR。NRG-1诱导的AChR转录需要两个转录调控元件，一个结合GA结合蛋白(GABP)，ETS蛋白GABPα和GABPβ的异源二聚体，另一个结合锌指蛋白Sp1。这项拟议的研究解决了NRGs通过GABP和Sp1传递信号以调节转录反应的机制。其具体目的是确定GABP是否是NRG-L诱导的转录所必需的；确定NRG-1刺激的GABPα的磷酸化是否是诱导转录的关键；确定GABPβ的转录激活域是否是诱导响应NRG-1的转录所必需的；确定Sp1的哪个区域足以调节NRG-1的DNA结合。除了提供有关神经肌肉突触发育的信息外，拟议中的实验还可能深入了解受神经调节蛋白信号影响的其他过程，如细胞转化。

DESCRIPTION (provided by applicant): Synapse formation between a developing axon and its target involves the coordinated differentiation of the pre- and postsynaptic components that mediate synaptic transmission. At developing neuromuscular synapses, acetylcholine receptors (AChRs) are among the proteins that become localized to the postsynaptic region in muscle, and their localization to this small patch of the myofiber membrane during development is a hallmark of the inductive events of synapse formation. It is believed that the localization of AChRs is mediated in part by transcriptional mechanisms because the genes encoding AChR subunits are transcribed selectively in the few muscle nuclei that are situated at synaptic sites. Neuregulins (NRGs) are the best candidates for ligands that stimulate synapse-specific gene expression, because NRGs are concentrated at synaptic sites and can induce AChR synthesis in cultured muscle cells. NRG-1-induced AChR transcription requires two transcriptional regulatory elements, one that binds GA-binding protein (GABP), a heterodimer of the Ets protein GABP alpha and GABP beta, and another that binds Sp1, a zinc finger protein. The proposed research addresses the mechanisms by which NRGs signal through GABP and Sp1 to mediate a transcriptional response. The specific aims are to determine if GABP is required for NRG-l-induced transcription; determine if NRG-1-stimulated phosphorylation of GABP alpha is critical for inducing transcription; determine if a transcriptional activation domain of GABP beta is required for inducing transcription in response to NRG-1; identify the region of Sp1 that is sufficient for regulating DNA binding in response to NRG-1. In addition to providing information on development of the neuromuscular synapse, the proposed experiments may also yield insight into other processes which are influenced by neuregulin signaling, such as cellular transformation