Elucidating the Function of Class 4 Semaphorins in GABAergic Synapse Formation

描述（由申请人提供）：突触是神经系统中细胞与细胞接触的特殊部位，介导神经元之间的交流。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待发现。虽然最近的进展有助于我们对兴奋性突触形成的理解，但介导抑制性突触形成的过程仍然不明确。此外，有假说认为异常的突触形成和功能会导致神经系统疾病，如智力低下、自闭症谱系障碍和癫痫。要了解突触功能障碍如何导致这些广泛的神经损伤，首先要了解突触在非病理状态下是如何形成、维持和功能的。为此，我们在培养的海马神经元中开发了一种新的基于前向遗传RNA干扰（RNAi）的筛选方法，该筛选方法已经确定了突触形成所需的新分子。利用这项技术，我们发现rnai介导的第4类信号蛋白Sema4D的敲低导致抑制性突触密度的降低，而对兴奋性突触的形成没有明显的影响。因此，Sema4D是迄今为止确定的少数优先调节抑制性突触形成的分子之一。此外，Sema4D似乎在抑制性突触的突触后特化组装中起着特定的作用。因此，了解Sema4D在这一过程中的作用机制有望为哺乳动物中枢神经系统中抑制性突触的组装提供关键见解。

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.