Molelcular determinants of synaptic plasticity

描述(申请人提供)：随着突触在新的位置被创建，在其他位置被拆除，发育中的神经回路被积极地重塑。这些动态事件受神经元活动的调节，以产生具有特定生理功能的成熟回路。这种现象在整个动物系统发育过程中都可以观察到，这表明潜在的途径是保守的。然而，驱动突触重塑的分子机制在很大程度上是未知的。在这里，我们提出了一种策略，利用简单的模式生物体，线虫，来定义一个发展计划，以重塑GABA能回路的突触结构。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背侧的新位置。这种突触重构程序被正常与腹肌突触的VD运动神经元中的UNC-55/COUP-TF转录因子阻断。我们利用了UNC-55的这一功能，采用了一种强大的细胞特异性图谱策略，确定了19个在突触重构中起作用的保守基因。我们现在已经证明，这些UNC-55靶点之一，DEG/ENaC阳离子通道，UNC-8，以一种由GABA能信号激活的机制促进突触重构。这一发现很重要，因为DEG/ENaC蛋白与学习和记忆有关，但将DEG/ENaC功能与突触可塑性联系起来的机制尚不清楚。特定目标1测试了关键预测，即UNC-8与由UNC-8活动重塑的GABA能突触密切相关。特定目的2旨在测试这一新的假设，即钙依赖机制将神经活动与UNC-8阳离子转运联系在一个反馈环路中，该反馈环路拆除突触前机制。特定目的3定义了所提出的调节UNC-8并促进GABA能突触重构的活性依赖途径的细胞起源和分子组成。总之，这些方法为描绘控制突触可塑性的复杂分子途径提供了一个强大的机会。此外，哺乳动物中这些重塑成分的保守认为，这项工作的结果可能会揭示调节人脑突触可塑性的基本机制。

DESCRIPTION (provided by applicant): Developing neural circuits are actively remodeled as synapses are created in new locations and dismantled in others. These dynamic events are regulated by neuronal activity to produce mature circuits with specific physiological functions. This phenomenon has been observed throughout animal phylogeny which suggests that the underlying pathways are conserved. However, the molecular mechanisms that drive synaptic remodeling are largely unknown. Here we propose a strategy that exploits the simple model organism, C. elegans, to define a development program that remodels the synaptic architecture of a GABAergic circuit. Ventral synapses for DD class GABA neurons are relocated to new sites on the dorsal side 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. We exploited this UNC- 55 function in a powerful cell-specific profiling strategy that identified 19 conserved genes with roles in synaptic remodeling. We have now shown that one of these UNC-55 targets, the DEG/ENaC cation channel, 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 mechanism that links DEG/ENaC function to synaptic plasticity is poorly understood. Specific Aim 1 tests the key prediction that UNC-8 is closely associated with GABAergic synapses that are remodeled by UNC-8 activity. Specific Aim 2 is designed to test the novel hypothesis that a Ca2+-dependent mechanism links neural activity to UNC-8 cation transport in a feedback loop that dismantles the presynaptic machinery. Specific Aim 3 defines the cellular origin and molecular components of the proposed activity-dependent pathway that regulates UNC-8 and promotes GABAergic synaptic remodeling. Together, these approaches offer a powerful opportunity to delineate an intricate molecular pathway that controls synaptic plasticity. Moreover, the conservation of these remodeling components in mammals argues that the results of this work are likely to reveal fundamental mechanisms that regulate synaptic plasticity in the human brain.