Cellular and molecular mechanisms underlying the function of SRGAP2 during synaptic development

摘要 在发育过程中，严格调节的机制在兴奋性（E）和兴奋性（E）之间建立适当的平衡。 抑制性（I）对每种神经元细胞类型进行的突触输入。几种神经发育障碍是 被认为是由E/I突触失衡引起的，包括自闭症谱系障碍（ASD）和 精神分裂症然而，协调兴奋性和抑制性突触发育的机制仍然是未知的。 不太了解。我们最近发现SRGAP 2是一种突触后蛋白，在体内起着关键作用， 促进兴奋性和抑制性突触成熟的速率，并限制这两种类型的突触的密度。 在发育中的皮层中锥体神经元上形成的突触。在上一个融资期，我们首先 在解剖SRGAP 2在兴奋性和兴奋性两种功能的分子机制方面取得了重大进展， 和抑制性突触，发现它促进兴奋性突触成熟的能力需要它的能力 与Homer 1结合，Homer 1是兴奋性突触的关键突触后支架蛋白，但促进抑制性突触形成。 通过其与抑制性突触的关键支架蛋白Gephyrin结合的能力促进突触成熟。 最后，SRGAP 2调节锥体神经元上的兴奋性和抑制性突触的密度 通过其Rac 1-GAP活性。 其次，我们和其他人发现SRGAP 2特异性地经历了几次部分基因复制， 在人类血统中。这些基因中只有一个被称为SRGAP 2C（人类基因的祖先拷贝）。 SRGAP 2A基因已在人类群体中固定，并在发育中表达。 人脑我们发现SRGAP 2C在突触形成过程中与SRGAP 2A结合并抑制其功能。 发展当人特异性SRGAP 2C在小鼠皮质锥体神经元中体内表达时， 诱导突触成熟的显著延迟（幼态持续）和兴奋性和 抑制性突触密度。 本建议是一个全面的、多学科的方法，以解决一些基本问题。 上一个资助期的结果提出了一些问题：SRGAP 2A及其人类特异性 旁系同源物只参与突触发育还是也调节突触可塑性？哪些类型 在SRGAP 2C人源化后，小鼠皮层回路中出现了功能特性 表情？由SRGAP 2A及其人源性蛋白诱导的结构变化的后果是什么？ 特异性paraffin SRGAP 2C对皮层回路组织和功能以及行为 表演？我们的目的是测试是否人类特异性的SRGAP 2A基因重复，导致出现的， SRGAP 2C代表了一种进化相关的底物，用于在细胞中出现新的功能特性。 皮层回路该项目将以前所未有的相关性解决基因之间的关系， 在人类皮层发育和进化的框架中的神经回路和行为。

ABSTRACT During development, tightly regulated mechanisms establish the proper balance between excitatory (E) and inhibitory (I) synaptic inputs made onto each neuronal cell type. Several neurodevelopmental disorders are thought to have emerged from E/I synaptic imbalance including autism spectrum disorders (ASD) and schizophrenia. However, the mechanisms coordinating excitatory and inhibitory synaptic development are still poorly understood. We recently discovered that SRGAP2 is a postsynaptic protein playing key roles in vivo in promoting the rate of excitatory and inhibitory synapses maturation and limiting the density of both types of synapses made onto pyramidal neurons in the developing cortex. In the previous funding period, we first made significant progress in dissecting the molecular mechanisms underlying SRGAP2 function at both excitatory and inhibitory synapses, discovering that its ability to promote excitatory synaptic maturation requires its ability to bind to Homer1, a key postsynaptic scaffolding protein at excitatory synapses, but promotes inhibitory synapse maturation through its ability to bind to Gephyrin, a key scaffolding protein at inhibitory synapses. Finally, SRGAP2 regulates the density of excitatory and inhibitory synapses made onto a pyramidal neuron through its Rac1-GAP activity. Secondly, we and others discovered that SRGAP2 has undergone several partial gene duplications specifically in the human lineage. Only one of these gene duplications, called SRGAP2C (the ancestral copy of the human gene was renamed SRGAP2A) has been fixed in the human population and is expressed in the developing human brain. We discovered that SRGAP2C binds to and inhibits the functions of SRGAP2A during synaptic development. When human-specific SRGAP2C is expressed in mouse cortical pyramidal neurons in vivo, it induces significant delay (neoteny) of synaptic maturation and significant increase in both excitatory and inhibitory synapse density. The present proposal constitutes a comprehensive, multi-disciplinary approach to address some fundamental questions raised by our results from the previous funding period: Is SRGAP2A and its human-specific paralogs only involved in synaptic development or is it also regulating synaptic plasticity? What types of functional properties emerge in mouse cortical circuits following humanization of SRGAP2C expression? What are the consequences of structural changes induced by SRGAP2A and its human- specific paralog SRGAP2C on cortical circuit organization and function as well as behavioral performance? Our aim is to test if human-specific gene duplication of SRGAP2A that led to the emergence of SRGAP2C represented an evolutionary relevant substrate for the emergence of new functional properties in cortical circuits. This project will tackle with unprecedented relevance the relationship between genes, neural circuits and behavior in a framework of human cortical development and evolution.