Neuregulin signaling at the neuromuscular synapse

描述（由申请人提供）：发育中的轴突与其靶之间的突触形成涉及介导突触传递的突触前和突触后组分的协调分化。在发育神经肌肉突触时，乙酰胆碱受体（AChR）是定位于肌肉中突触后区域的蛋白质之一，并且它们在发育期间定位于肌纤维膜的这一小片是突触形成的诱导事件的标志。据信，AChR的定位部分是由转录机制介导的，因为编码AChR亚基的基因在位于突触位点的少数肌核中选择性地转录。神经调节蛋白（NRG）是刺激突触特异性基因表达的配体的最佳候选者，因为NRG集中在突触位点，并且可以诱导培养的肌肉细胞中AChR的合成。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GABP α和GABP β的异二聚体，另一个结合Sp1，锌指蛋白。拟议的研究解决了NRG通过GABP和Sp1介导转录反应的机制。具体目的是确定GABP是否是NRG-1诱导转录所必需的;确定NRG-1刺激的GABP α磷酸化是否是诱导转录的关键;确定GABP β的转录激活结构域是否是诱导NRG-1应答转录所必需的;鉴定Sp1足以调节NRG-1应答DNA结合的区域。除了提供有关神经肌肉突触发育的信息外，所提出的实验还可以深入了解受神经调节蛋白信号传导影响的其他过程，例如细胞转化。

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-1-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.