Elucidating the Function of Class 4 Semaphorins in GABAergic Synapse Formation

描述（由申请人提供）：突触是介导神经系统中神经元之间通信的细胞-细胞接触的专门位点。关于哺乳动物中枢神经系统中这些关键结构形成的分子机制仍有许多有待发现。虽然最近的进展有助于我们了解兴奋性突触的形成，介导抑制性突触形成的过程仍然不清楚。此外，据推测，异常的突触形成和功能有助于神经系统疾病，如精神发育迟滞，自闭症谱系障碍和癫痫。为了理解突触功能障碍如何导致这些广泛的神经损伤，重要的是首先要了解突触如何形成，维持和在非病理状态下发挥作用。为此，我们在培养的海马神经元中开发了一种新的基于正向遗传RNA干扰（RNAi）的筛选方法，该方法已经确定了突触形成所需的新分子。使用这种技术，我们发现RNAi介导的4类脑信号蛋白Sema 4D的敲低导致抑制性突触密度的降低，而对兴奋性突触形成没有明显影响。因此，Sema 4D是迄今为止鉴定的少数几种优先调节抑制性突触形成的分子之一。此外，Sema 4D似乎在抑制性突触组装突触后特化中发挥特定作用。因此，了解Sema 4D在这一过程中的作用机制，有望对哺乳动物中枢神经系统中抑制性突触的组装产生关键的见解。

DESCRIPTION (provided by applicant): Synapses are specialized sites of cell-cell contact that mediate communication between neurons in the nervous system. Much remains to be discovered about the molecular mechanisms that underlie formation of these critical structures in the mammalian central nervous system. While recent advances have contributed to our understanding of excitatory synapse formation, the processes that mediate inhibitory synapse formation remain poorly defined. In addition, it is hypothesized that aberrant synapse formation and function contributes to neurological disorders such as mental retardation, autism spectrum disorders and epilepsy. To appreciate how synapse dysfunction contributes to these widespread neurological impairments, it is important to first understand how synapses are formed, maintained, and function in the non-pathological state. To this end, we developed a novel, forward genetic RNA interference (RNAi)-based screen in cultured hippocampal neurons that has identified new molecules required for synapse formation. Using this technique, we discovered that RNAi-mediated knockdown of a class 4 Semaphorin, Sema4D, led to a decrease in the density of inhibitory synapses without an apparent effect on excitatory synapse formation. Thus, Sema4D is one of only a few molecules identified thus far that preferentially regulates inhibitory synapse formation. Further, Sema4D appears to be playing a specific role in assembling the postsynaptic specialization at inhibitory synapses. Therefore, understanding the mechanism of action of Sema4D in this process promises to yield key insights into the assembly of inhibitory synapses in the mammalian central nervous system.