FMRP Mechanism and Function

脆性X综合征(FXS)是由脆性X智力低下蛋白(FMRP)的遗传缺失引起的 遗传性智力残疾的最常见形式，也是导致自闭症的主要单基因原因。FMRP 结合许多靶向mRNAs，编码在突触中起关键作用的蛋白质。FMRP已被证明是 抑制许多靶mRNAs的翻译，并提出了一些机制。FMRP交互作用 对于microRNAs，已经证明在翻译控制中发挥作用，但分子机制还没有 很好理解。FMRP介导的翻译抑制是可逆调节的，并依赖于 FMRP的磷酸化状态。FMRP也被证明是泛素化的，对谷氨酸的反应 受体刺激，提供了一种潜在的机制，动态地消除翻译抑制。它 目前尚不清楚上述任何机制是否在树突内局部发生，以调节局部 翻译对依赖蛋白质合成的突触可塑性很重要。很可能其中的一些或全部 机制是相互关联的，但缺乏关键细节来理解FMRP介导的翻译控制 以及它对受体信号反应的可逆性。一个关键的差距是缺乏FMRP的统一模型 中介抑制及其在突触的可逆调节。我们假设FMRP泛素化 而UPS介导的对受体刺激的降解提供了一种统一的机制来去除 翻译抑制和调节突触的局部蛋白质合成。E3连接酶的特殊作用 将研究CDH1-APC在FMRP介导的局部蛋白质合成调节中的作用。为了澄清当地的 这些机制在树突和棘内的作用，我们将继续开发和应用荧光 记者和活培养海马神经元的单分子成像。使用DISABLED AND 器官型切片培养作为模式系统，UPS介导FMRP降解的作用，作为局部 翻译开关，以调节脊柱的形态，突触的发育和可塑性将被研究。我们 将分析泛素化抗性或不能结合CDH1-APC的FMRP突变体的作用 调节或挽救FXS相关的树突棘发育、突触功能和 可塑性。目的1将检验假设FMRP去磷酸化，泛素化的CDH1-APC和UPS- 介导性降解是动态分子开关的组成部分，用于调节局部mRNA翻译 调控树突棘形态、突触发育和可塑性的功能。目标2将测试 假设FMRP泛素化和UPS介导的降解提供了一种调节机制 靶向RISC/microRNAs。这项研究有望揭示CDH1-APC和FMRP的新作用 泛素化在调节microRNA和局部蛋白质合成中的作用。疾病机制的发展 FXS的基础治疗策略将受益于对其机制和 FMRP对突触局部mRNA翻译的调控作用

Fragile X syndrome (FXS), caused by the inherited loss of the Fragile X Mental Retardation Protein (FMRP), is the most common form of inherited intellectual disability and the leading monogenetic cause of autism. FMRP binds to many target mRNAs encoding proteins that play key roles at the synapse. FMRP has been shown to repress translation of many target mRNAs, and a few mechanisms have been proposed. FMRP interactions with microRNAs have been shown to play a role in translational control but the molecular mechanisms are not well understood. FMRP mediated repression of translation is reversibly regulated and dependent on the phosphorylation status of FMRP. FMRP has also been shown to be ubiquitinated in response to glutamate receptor stimulation, providing a potential mechanism to dynamically remove translational repression. It remains unclear whether any of the above mechanisms occur locally within dendrites to regulate local translation important for protein synthesis dependent synaptic plasticity. It is likely that some or all of these mechanisms are inter-related but critical details are lacking to understand FMRP mediated translational control and its reversibility in response to receptor signaling. A critical gap is lack of a unifying model for FMRP mediated repression and its reversible regulation at the synapse. We hypothesize that FMRP ubiquitination and UPS-mediated degradation in response to receptor stimulation provides a unifying mechanism to remove translational repression and regulate local protein synthesis at the synapse. The specific role of the E3 ligase Cdh1-APC in FMRP mediated regulation of local protein synthesis will be investigated. To elucidate the local functions of these mechanisms within dendrites and spines, we will continue to develop and apply fluorescent reporters and single molecule imaging of live cultured hippocampal neurons. Using dissociated and organotypic slice cultures as model systems, the role of UPS mediated FMRP degradation, as a local translational switch, to regulate spine morphology, synapse development and plasticity will be investigated. We will analyze the role of FMRP mutants that are resistant to ubiquitination or unable to bind Cdh1-APC to modulate or rescue FXS-associated impairments in dendritic spine development, synapse function and plasticity. Aim 1 will test the hypothesis that FMRP dephosphorylation, ubiquitination by Cdh1-APC and UPS- mediated degradation are components of a dynamic molecular switch to regulate local mRNA translation that functions in control of dendritic spine morphology, synapse development and plasticity. Aim 2 will test the hypothesis that FMRP ubiquitination and UPS-mediated degradation provides a mechanism to regulate targeting of RISC/microRNAs. This research is expected to uncover a novel role for Cdh1-APC and FMRP ubiquitination in regulation of microRNAs and local protein synthesis. The development of disease mechanism based therapeutic strategies for FXS will benefit from this in depth understanding of the mechanism and function of FMRP mediated control of local mRNA translation at synapses.