Fragile X Phenotypes Modulated by Altered Signaling to the Synaptic Cytoskeleton

描述（由申请人提供）：树突棘的小尺寸掩盖了它们在兴奋性突触传递和最终复杂行为中发挥的复杂作用。脊柱的细胞骨架结构主要由肌动蛋白丝组成。这些细丝，乍一看可能看起来很简单，但也令人惊讶地复杂。它们动态地组装成不同的结构，并作为一个平台，在脊柱发生和经验依赖的可塑性过程中协调脊柱的复杂反应。在人类和小鼠中，调节突触肌动蛋白的通路突变与神经系统疾病（人类）和相关的内表型（小鼠）有关。我的实验室研究了一种信号通路，通过激活Rac下游的WAVE1来驱动脊柱中肌动蛋白的重新聚合。本应用程序的目的是分析脆性X综合征的致病基因Fmr1与WAVE1之间的上位性。我们的中心假设是，WAVE1的升高和肌动蛋白的失调显著地促进了脆性X综合征的突触和行为表型。这一假设是基于以下强有力的初步数据：1)在Fmr1缺失的小鼠中，Rac活性升高，Rac抑制使LTD正常化。2)我们之前的工作表明，WAVE1缺失导致的突触表型与Fmr1缺失相反。3) WAVE1 mRNA是FMRP的直接靶点，我们的初步数据显示，在Fmr1缺失的小鼠中，WAVE1蛋白增加。4)我们的数据表明，突触肌动蛋白动力学在小鼠FXS模型中显着改变，过度活跃的Rac信号模拟了这种异常。5)我们的初步数据显示，Fmr1零记忆损伤在同样杂合Wave1的小鼠中得到拯救。该资助的具体目的是：1)定量分析脊柱肌动蛋白动力学与FMRP丧失之间的联系；2)检测WAVE1基因减少是否使Fmr1零缺陷正常化；3)通过WAVE1在体内过表达来模拟Fmr1空表型。由于本研究采用多学科方法分析Fmr1缺失如何导致WAVE1水平异常、脊柱肌动蛋白动力学改变和行为缺陷，因此可以预测脆性X综合征模型中肌动蛋白信号传导与神经元功能障碍之间的联系机制的根本进展。因此，拟议的研究与NIH的使命有关，即研究将基因突变与神经系统疾病的机制联系起来的机制。

DESCRIPTION (provided by applicant): The small size of dendritic spines belies the elaborate role they play in excitatory synaptic transmission and ultimately complex behaviors. The cytoskeletal architecture of the spine is predominately composed of actin filaments. These filaments, which at first glance might appear simple, are also surprisingly complex. They dynamically assemble into different structures and serve as a platform for orchestrating the elaborate responses of the spine during spinogenesis and experience-dependent plasticity. Mutations in pathways that regulate synaptic actin in humans and mice are associated with neurological disorders (humans) and related endophenotypes (mice). My laboratory studies a signaling pathway that drives de novo actin polymerization in spines by the activation of WAVE1 downstream of Rac. The objective of this application is to analyze epistasis between Fmr1, the causative gene in Fragile X Syndrome, and WAVE1. Our central hypothesis is that elevated WAVE1 and dysregulation of actin significantly contributes to the synaptic and behavioral phenotypes of Fragile X Syndrome. This hypothesis is guided by strong preliminary data based on: 1) In Fmr1 null mice, Rac activity is elevated and inhibition of Rac normalizes LTD. 2) Our previous work showing that loss of WAVE1 results in synaptic phenotypes opposite those of Fmr1 loss. 3) WAVE1 mRNA is a direct target of FMRP and our preliminary data shows an increase in WAVE1 protein in Fmr1 null mice. 4) Our data that demonstrates synaptic actin dynamics are significantly altered in a mouse model of FXS and overactive Rac signaling mimics this abnormality. 5) Our preliminary data showing Fmr1 null memory impairments are rescued in mice also heterozygous for Wave1. The specific aims of this grant are: 1) quantitatively analyze the link between spine actin dynamics and loss of FMRP; 2) test if genetic reduction of WAVE1 normalizes Fmr1 null deficits; and 3) test for mimicry of Fmr1 null phenotypes by WAVE1 overexpression in vivo. Because this proposal utilizes a multidisciplinary approach to analyze how loss of Fmr1 results in abnormal WAVE1 levels, altered spine actin dynamics, and behavioral deficits, a fundamental advance in understanding the mechanisms linking actin signaling to neuronal dysfunction in a model of Fragile X Syndrome can be anticipated. Thus the proposed research is relevant to that part of NIH's mission that pertains to the investigation of the mechanisms linking genetic mutations to mechanisms of neurological disease.