Cellular Mechanisms of Convergence Among Autism Spectrum Disorder Genes

摘要 遗传学的最新进展已经发现了100多个与自闭症谱系障碍（ASD）相关的基因。 确定ASD候选基因之间的收敛点是翻译基因的下一个关键步骤 脑回路病理生理变化的发现。ASD风险基因会聚的一个中心位点 前额叶皮层（PFC）第5层锥体神经元。这些神经元有专门的树突状乔木， 作为在其基底心轴上的本地输入和在其基底心轴上的远程调制输入之间的重合检测器， 它们的顶端毛簇因此，锥体细胞树突可能是突触整合的主要位点。异常枝晶 兴奋性被假设为导致通常观察到的社交、认知和交流缺陷的原因 在ASD中，但这些缺陷如何在细胞水平上表现仍不清楚。在这里，我建议， 树突整合和树突兴奋性是ASD的核心细胞表型。具体来说，我将测试 一个中心假设，即受损的树突兴奋性是多个高置信度的收敛点， ASD风险基因我们的实验室最近发现了小鼠的树突状细胞损伤，单倍不足的最高ASD风险 基因、Scn 2a. Scn 2a编码电压门控钠通道NaV1.2，其对于反向传播是关键的 动作电位的顶端树突调节突触整合，稳定性和可塑性。有趣的是， 几个高危ASD基因可能与Scn 2a相互作用-通过膜支架或基因 表达的方式，也可能导致受损的树突兴奋性。例如锚蛋白是一个家族 已知将钠通道定位于轴突起始段和Ranvier节点的支架蛋白， 动作电位的启动和传播。在这里，我们提出，锚-B，ASD相关的产品， 基因ANK 2是将Nav1.2定位在树突中的主要锚蛋白。与树枝状纳伏的缺失一致， 我的初步数据表明Ank 2 +/-和Scn 2a +/-锥体细胞在兴奋性突触中有相同的缺陷 功能在这种直接相互作用的上游，ASD风险基因Fmr 1和Tbr 1已被证明调节 Scn 2a或AnkB表达。因此，我们预计，当这些神经元中的任何一个被激活时，树突的兴奋性都会受损。 基因受到影响。我们将通过追求三个具体目标来测试我们的假设：目标1：评估 Ank 2对树突状钠通道功能和兴奋性的影响。目的2：研究受损的聚合 ASD风险基因小鼠模型的树突兴奋性。目的3：确定Scn 2a的作用 单倍不足对基底与顶端树突兴奋性的影响。这项工作有望揭示树突状细胞是否 兴奋性确实是高风险ASD基因的一个趋同点，为了进一步确定 在这些情况下，树突兴奋性方面受到最大影响。我们的结果将产生积极的影响，因为 这项工作将揭示导致树突兴奋性改变的机制，这反过来可能会给我们带来 更深入地了解ASD的病理生理学。

ABSTRACT Recent progress in genetics has uncovered over 100 genes associated with autism spectrum disorder (ASD). Identifying points of convergence among ASD candidate genes is the next critical step to translate gene discoveries to pathophysiological changes in brain circuitry. One central locus at which ASD risk genes converge are prefrontal cortex (PFC) layer 5 pyramidal neurons. These neurons have specialized dendritic arbors thought to act as coincidence detectors between local inputs on their basal arbors and long-range modulatory inputs on their apical tufts. Thus, pyramidal cell dendrites may be a major locus for synaptic integration. Abnormal dendritic excitability is hypothesized to contribute to the social, cognitive, and communication deficits typically observed in ASD, but how these deficits manifest at the cellular level remains unclear. Here, I propose that deficits in dendritic integration and dendritic excitability are a core cellular phenotype of ASD. Specifically, I will test the central hypothesis that impaired dendritic excitability is a point of convergence across multiple high-confidence ASD risk genes. Our lab has recently identified dendritic impairments in mice haploinsufficient for a top ASD risk gene, Scn2a. Scn2a encodes the voltage-gated sodium channel NaV1.2, which is critical for the backpropagation of action potentials to apical dendrites to regulate synaptic integration, stability, and plasticity. Interestingly, several high-risk ASD genes may interact with Scn2a—either through membrane scaffolding or gene expression—in ways that could also result in impaired dendritic excitability. Ankyrins, for example, are a family of scaffolding proteins known to localize sodium channels to the axon initial segment and nodes of Ranvier, sites of action potential initiation and propagation. Here, we propose that ankyrin-B, the product of the ASD-associated gene ANK2, is the primary ankyrin that localizes Nav1.2 in dendrites. Consistent with a loss of dendritic NaVs, my preliminary data indicate that Ank2+/- and Scn2a+/- pyramidal cells have identical deficits in excitatory synapse function. Upstream of this direct interaction, the ASD risk genes Fmr1 and Tbr1 have been shown to regulate either Scn2a or AnkB expression. As a result, we expect dendritic excitability to be impaired when any of these genes are affected. We will test our hypothesis by pursing three specific aims: Aim 1: To evaluate the effects of Ank2 loss on dendritic sodium channel function and excitability. Aim 2: To investigate convergence of impaired dendritic excitability in mouse models of ASD risk genes. Aim 3: To determine the effects of Scn2a haploinsufficiency on basal versus apical dendritic excitability. This work is expected to reveal whether dendritic excitability is indeed a point of convergence across high-risk ASD genes, and to further determine precisely what aspects of dendritic excitability are most affected in these cases. Our results will have a positive impact because this work will reveal mechanisms that contribute to altered dendritic excitability, which, in turn, may give us greater insight to the pathophysiology of ASD.