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

摘要 在发育过程中，严格调控的机制在兴奋性(E)和兴奋性(E)之间建立适当的平衡 抑制性(I)对每种神经细胞类型的突触输入。几种神经发育障碍是 被认为是E/I突触失衡，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 人们对此知之甚少。我们最近发现SRGAP2是一种突触后蛋白，在体内发挥着关键作用 促进兴奋性和抑制性突触成熟并限制这两种类型突触的密度 突触形成发育中的皮质中的锥体神经元。在上一个资助期，我们首先做出了 SRGAP2在两种兴奋性疾病中作用的分子机制研究进展 以及抑制性突触，发现它促进兴奋性突触成熟的能力需要它的能力 与突触后关键支架蛋白Hmer 1结合，但促进抑制性突触 突触的成熟是通过与抑制突触上的关键支架蛋白--吉菲林结合来实现的。 最后，SRGAP2调节锥体神经元上兴奋性和抑制性突触的密度 通过它的rac1-GAP活动。 其次，我们和其他人发现SRGAP2经历了几次特定的部分基因复制 在人类血统中。这些基因中只有一个被称为SRGAP2C(人类的祖先副本 基因被重新命名为SRGAP2A)已经在人类群体中固定并在发育中表达 人脑。我们发现SRGAP2C在突触过程中结合并抑制SRGAP2A的功能 发展。当人特异性SRGAP2C在活体小鼠皮质锥体神经元中表达时，它 导致突触成熟显著延迟(新生)，兴奋性和兴奋性 抑制性突触密度。 目前的提议是一种综合的、多学科的方法，以处理一些基本问题 我们从上一个资助期的结果提出的问题：SRGAP2A及其人类特有的 Paralog只参与突触的发育，还是也调节突触的可塑性？什么类型？ 随着SRGAP2C的人源化，小鼠皮质回路中出现了功能特性的变化 表情？SRGAP2A及其人类-的结构变化会产生什么后果？ 关于皮层回路组织和功能以及行为的特定Paralog SRGAP2C 表现如何？我们的目的是测试是否人类特有的SRGAP2A基因复制导致了 SRGAP2C代表了一种与进化相关的底物，用于出现新的功能特性 大脑皮层回路。这个项目将以前所未有的相关性处理基因之间的关系， 人类大脑皮层发育和进化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.