Role of MEF2 and neural activity in cortical synaptic weakening and elimination

项目摘要：皮质结构(海马体和新皮质)对认知和 知觉，以及它们的不正确功能与智力残疾和自闭症有关。成立了 正确的大脑皮层回路需要神经活动和基因程序的复杂相互作用，这些程序控制 特定突触连接的形成和消除。结构性兴奋性突触的研究，如 脊椎发现，在出生后发育的早期有一个快速的突触发生时期，随后是一个后期 消除(或修剪)-在人类和小鼠身上。重要的是，感觉体验和回路活动 推动体内脊椎的修剪。脊柱消除也是由成年人的学习引发的，并可能在 对保持记忆的电路的改进。然而，棘突是突触的间接测量 关于修剪如何调节特定神经元的突触功能和连接性的信息很少。 大脑皮层通路。此外，对活性的细胞和分子机制几乎一无所知。 以及大脑皮层神经元中感觉经验依赖的突触消除。使用突触功能的分析 在孤立的皮质通路中，我们积累的证据表明，活动依赖的突触 修剪受肌细胞增强因子2(MEF2)家族转录因子的激活调节。 我们发现，MEF2-2需要RNA结合蛋白--脆性X智力低下蛋白(FMRP)。 通过调节MEF2生成的转录本的翻译触发突触消除-包括 Protocadherin 10(Pcdh10)和Arc/Arg3.1。我们发现Arc和Pcdh10介导突触的消除 通过不同的机制。重要的是，MEF2C、FMRP和Pcdh10的功能突变丢失是相关的 智障(ID)、自闭症和巡回过度兴奋。对生理和体内的情况知之甚少 导致皮层神经元上功能性突触连接消失的条件以及如果或如何这样做 涉及MEF2C、FMRP、Pcdh10和Arc。在目标1中，我们将使用光遗传学来诱导生理模式 以确定MEF2亚型、Fmr1和Pcdh10在CA1神经元放电和突触消除中的作用 依赖生理活动的突触消除。在目标2中，我们将确定内源性MEF2 亚型有助于功能性兴奋性突触连接到皮质的发育修剪 活体中的神经元。我们也有新的数据表明，一种新的体验激活了MEF2依赖的Arc 激活代谢性激活时启动CA1神经元长期突触抑制的转录 谷氨酸受体(mGluR-Ltd.)。MGluR-LTD的新奇启动可能是突触消除的前驱 并有助于形成记忆的稀疏皮质网络表征。在目标3中，我们建议 为了确定MEF2是否有助于新颖性诱导的基因表达、mGluR-LTD的启动和新颖性 习惯化。在目标4中，我们将利用光遗传学和电刺激建立一种体外模型。 新颖性诱导的LTD启动以揭示细胞机制。

Project Summary: Cortical structures (the hippocampus and neocortex) are critical for cognition and perception, and their improper function is implicated in intellectual disability and autism. The establishment of proper cortical circuits requires a complex interaction of neural activity and genetic programs that control the formation and elimination of specific synaptic connections. Studies of structural excitatory synapses, such as spines, find there is a rapid period of synaptogenesis early in postnatal development followed by a later period of elimination (or pruning) - in both humans and mice. Importantly, sensory experience and circuit activity drives the pruning of spines in vivo. Spine elimination is also triggered by learning in adults and may mediate the refinement of circuits that maintain memories. However, spines are an indirect measure of synaptic number and provide little information about how pruning regulates synaptic function and connectivity of specific cortical pathways. Furthermore, virtually nothing is known of the cellular and molecular mechanisms of activity and sensory experience-dependent synapse elimination in cortical neurons. Using assays of synaptic function in isolated cortical pathways, we have accumulated evidence indicating that activity-dependent synaptic pruning is regulated by the activation of the Myocyte-Enhancer Factor 2 (MEF2) family of transcription factors. We find that the RNA binding protein, Fragile X Mental Retardation Protein (FMRP) is required for MEF2- triggered synapse elimination by regulating the translation of MEF2-generated transcripts - including Protocadherin10 (Pcdh10) and Arc/Arg3.1. We find that Arc and Pcdh10 mediate elimination of synapses through distinct mechanisms. Importantly, loss of function mutations in MEF2C, FMRP and Pcdh10 are linked to intellectual disability (ID), autism and circuit hyperexcitability. Little is known of the physiological and in vivo conditions that lead to elimination of functional synaptic connections on cortical neurons and if or how this involves MEF2c, FMRP, Pcdh10, and Arc. In Aim 1 we will use optogenetics to induce physiological patterns of CA1 neuron firing and synapse elimination to determine the role of MEF2 isoforms, Fmr1 and Pcdh10 in physiological activity-dependent synapse elimination. In Aim 2 we will determine if endogenous MEF2 isoforms contribute to developmental pruning of functional excitatory synaptic connections onto cortical neurons in vivo. We also have new data suggesting that a novel experience activates MEF2-dependent Arc transcription which primes CA1 neurons for long-term synaptic depression upon activation of metabotropic glutamate receptors (mGluR-LTD). Novelty-priming of mGluR-LTD may be a precursor to synapse elimination and contribute to the formation of sparse cortical network representations of memories. In Aim 3 we propose to determine if MEF2 contributes to novelty-induced gene expression, priming of mGluR-LTD, and novelty habituation. In Aim 4 we will use optogenetics and electrical stimulation to establish an in vitro model of novelty-induced priming of LTD to reveal cellular mechanisms.