A Degenerin Cation Channel Drives Activity-Dependent Remodeling of GABA Synapses

描述（由申请人提供）：神经回路在发育过程中被广泛地完善，因为突触要么被创建，要么被破坏，以改变大脑功能。已知神经活动调节这些重塑事件，但驱动突触重组的分子机制尚不清楚。本研究验证了一个假设，即DEG/ENaC阳离子通道家族的一个成员在神经活动和突触稳定性之间起着分子联系的作用。这项工作利用了线虫的突触重塑事件，在幼虫发育过程中，DD类GABA神经元的腹侧突触被重新定位到与背肌的新连接。这种突触重塑程序被VD运动神经元中的UNC-55/COUP TF转录因子阻断，VD运动神经元通常与腹侧肌肉突触。Miller实验室在细胞特异性分析策略中利用这种UNC-55功能来鉴定19个在突触重塑中起作用的保守基因。我的工作现在已经表明，这些UNC-55靶点之一，变性素/上皮钠通道（DEG/ENaC）， UNC-8，在gaba能信号激活的机制中促进突触重塑。这一发现很重要，因为DEG/ENaC蛋白与学习和记忆有关，但连接DEG/ENaC功能与突触可塑性的分子途径在很大程度上是未知的。特异性目的1验证了GABA神经元活动在细胞自主机制中驱动重塑过程的预测。特异性目的2验证了关键假设，即UNC-8定位于GABA神经元的突触前区域，并在这些细胞中发挥促进重塑的功能。特异性目的3测试了新的预测，即UNC-8被伴随GABA释放的细胞外钙的短暂耗尽激活，这种效应触发突触前装置的解体。结果是

DESCRIPTION (provided by applicant): Neural circuits are extensively refined during development as synapses are either created or destroyed to modify brain function. Neural activity is known to regulate these remodeling events but the molecular mechanisms that drive synaptic reorganization are poorly understood. This study tests the hypothesis that a member of the DEG/ENaC family of cation channels functions as a molecular link between neural activity and synaptic stability. This work exploits a synaptic remodeling event in the nematode C. elegans in which ventral synapses for the DD class of GABA neurons are re-located to new connections with dorsal muscles during larval development. This synaptic remodeling program is blocked by the UNC-55/COUP TF transcription factor in VD motor neurons, which normally synapse with ventral muscles. The Miller lab exploited this UNC-55 function in a cell-specific profiling strategy to identify 19 conserved genes with roles in synaptic remodeling. My work has now shown that one of these UNC-55 targets, the degenerin/epithelial sodium channel (DEG/ENaC), UNC-8, promotes synaptic remodeling in a mechanism that is activated by GABAergic signaling. This finding is important because DEG/ENaC proteins have been implicated in learning and memory but the molecular pathways that connect DEG/ENaC function to synaptic plasticity are largely unknown. Specific Aim 1 tests the prediction that GABA neuron activity drives the remodeling process in a cell autonomous mechanism. Specific Aim 2 tests the key hypothesis that UNC-8 localizes to the presynaptic regions of GABA neurons and functions in these cells to promote remodeling. Specific Aim 3 tests the novel prediction that UNC-8 is activated by the transient depletion of extracellular calcium that accompanies GABA release and that this effect triggers disassembly of the presynaptic apparatus. The results of this study will provide a better understanding of the cellular mechanisms that connect circuit activity to dynamic events at the synapse. Additionally, this study may provide insights that reveal the biological basis of mental disorders that arise from dysfunctional synaptic connectivity.