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。 识别ASD候选基因之间的汇聚点是翻译基因的下一个关键步骤 大脑回路的病理生理学变化的发现。ASD风险基因汇聚的一个中心基因 前额叶皮质(PFC)第5层锥体神经元。这些神经元具有特化的树突。 充当其基杆上的本地输入与其上的远程调制输入之间的符合探测器 它们的顶端簇毛。因此，锥体细胞树突可能是突触整合的主要部位。异常树枝晶 兴奋性被认为是导致通常观察到的社交、认知和沟通缺陷的原因 在ASD中，这些缺陷是如何在细胞水平上表现出来的仍不清楚。在这里，我建议 树突状整合和树突状细胞兴奋性是ASD的核心细胞表型。具体地说，我将测试 中心假设树突状细胞兴奋性受损是多个高置信度的汇聚点 ASD风险基因。我们的实验室最近在小鼠身上发现了树突状细胞损伤，单倍体不足以成为ASD的主要风险因素 基因，SCN2A型。SCN2A编码电压门控钠通道NaV1.2，这对反向传播至关重要 顶端树突的动作电位调节突触的整合、稳定性和可塑性。有趣的是， 几个高危ASD基因可能通过膜支架或基因与SCN2A相互作用 表达--也可能导致树突状细胞兴奋性受损。例如，Ankyrins是一个大家庭 已知的将钠离子通道定位于轴突起始节段和Ranvier结点的支架蛋白 动作电位的启动和传播。在这里，我们提出了Ankyrin-B，ASD相关的产物 基因ANK2是主要的锚蛋白，定位于树突中的Nav1.2。与树突状神经节的缺失相吻合， 我的初步数据表明，Ank2/-和SCN2A/-锥体细胞在兴奋性突触中存在相同的缺陷 功能。在这种直接相互作用的上游，ASD风险基因Fmr1和Tbr1已被证明调节 SCN2A或AnkB的表达。因此，我们预计当其中任何一种情况下，树突状细胞的兴奋性都会受到损害 基因会受到影响。我们将通过追求三个具体目标来检验我们的假设：目标1：评估 Ank2在树突状钠通道功能和兴奋性上的缺失。目的2：研究受损者的趋同性 ASD危险基因小鼠模型中的树突状兴奋性。目的3：确定SCN2A的作用 基础树突状细胞兴奋性与心尖树突状细胞兴奋性的单倍性不足。这项工作有望揭示树枝状结构 兴奋性确实是高危ASD基因的一个汇合点，并进一步准确地确定 在这些情况下，树突状细胞兴奋性的各个方面受到的影响最大。我们的结果将产生积极的影响，因为 这项工作将揭示有助于改变树突状细胞兴奋性的机制，这反过来可能给我们 对ASD的病理生理学有更深入的了解。

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.