Mechanisms of MEF2-dependent synapse elimination

描述（由申请人提供）：突触形成、消除和维持的缺陷被认为是许多神经认知障碍的基础，包括智力迟钝和自闭症，也被认为是导致与药物成瘾相关行为的原因。神经元活动促进突触消除，以修剪在发育过程中形成的多余突触，并自稳态地维持突触连接的稳态数量。转录因子肌细胞增强因子2 （MEF2）是发育和成人大脑中兴奋性突触消除的关键活性依赖调节剂。然而，MEF2控制突触数量的分子和细胞机制尚不清楚。我们的实验室最近发现，rna结合蛋白，脆性X智力迟钝蛋白（FMRP）是mef2诱导的突触消除所必需的。脆性X染色体综合征（FXS）是自闭症中最常见的遗传形式，它是由编码FMRP的Fmr1基因失活引起的。患有FXS的个体和该疾病的小鼠模型Fmr1敲除小鼠，显示皮质树突棘密度增加，表明在

DESCRIPTION (provided by applicant): Deficits in proper synapse formation, elimination, and maintenance, are hypothesized to underlie numerous neurocognitive disorders, including mental retardation and autism, and are also thought to contribute to behaviors associated with drug addiction. Neuronal activity promotes synapse elimination to prune excess synapses formed during development, and to homeostatically maintain a steady-state number of synaptic connections. The transcription factor myocyte enhancer factor 2 (MEF2) is a critical activity-dependent regulator of excitatory synapse elimination in developing and adult brains. However, the molecular and cellular mechanisms by which MEF2 controls synapse number are not well understood. Our lab recently discovered that the RNA-binding protein, Fragile X Mental Retardation Protein (FMRP) is required for MEF2-induced elimination of synapses. Fragile X Syndrome (FXS), the most prevalent inherited form of autism, results from inactivation of the Fmr1 gene, which codes for FMRP. Individuals with FXS and a mouse model for the disorder, Fmr1 knockout mice, display increased cortical dendritic spine density, indicating that deficits in synapse elimination may underlie FXS. We propose that MEF2 and FMRP function together to regulate common transcripts to induce elimination of excitatory synapses and propose Specific Aim 1 to investigate this hypothesis. In this aim, we will utilize CLIP-seq, a technique pairing cross-linking immunoprecipitation (CLIP) followed by high throughput sequencing to identify MEF2-regulated gene targets whose transcripts associate with FMRP. We will then test a requirement for MEF2-regulated and FMRP-associated candidates in structural and functional synapse elimination by performing 2-photon live-cell dendritic spine imaging and whole-cell patch clamp recordings of mEPSCs. In Specific Aim 2, we will characterize the process of MEF2-dependent synapse elimination, examining the kinetics of MEF2-induced structural and functional synapse elimination, as well as the morphological process of MEF2-mediated structural synapse elimination by performing 2-photon microscopy and whole-cell electrophysiology recordings. As synapse elimination defects may contribute to autism, Fragile X Syndrome, and behavioral adaptations associated with drug abuse, we believe that our studies will provide significant implications towards understanding these and related disorders. PUBLIC HEALTH RELEVANCE: The transcription factor myocyte enhancer factor 2 (MEF2) has critical roles in the proper development and maintenance of synaptic connections, in learning and memory, and in behaviors associated with drug addiction; however, the molecular and cellular mechanisms by which MEF2 mediates these effects are not well understood. Here, we propose to investigate the mechanisms by which MEF2 regulates the formation of proper connections in the brain, a study which will have broad implications for understanding autism, Fragile X Syndrome, drug addiction, and related disorders.