FMRP Mechanism and Function

脆性X综合征（FXS）是由脆性X智力迟钝蛋白（FMRP）的遗传性缺失引起的， 最常见的遗传性智力残疾形式和孤独症的主要单基因原因。FMRP 与许多在突触中起关键作用的靶mRNA编码蛋白质结合。FMRP已被证明 抑制许多靶mRNA的翻译，并且已经提出了一些机制。FMRP相互作用 与microRNA的结合已被证明在翻译控制中起作用，但分子机制不是 很好理解。FMRP介导的翻译抑制是可逆调节的，并依赖于转录水平。 FMRP的磷酸化状态。FMRP也被证明是响应于谷氨酸的泛素化 受体的刺激，提供了一种潜在的机制，以动态地消除翻译抑制。它 目前尚不清楚是否有任何上述机制发生局部树突内，以调节局部 翻译对蛋白质合成依赖性突触可塑性很重要。很可能其中一些或全部 机制是相互关联的，但缺乏关键的细节，以了解FMRP介导的翻译控制 以及其对受体信号传导的可逆性。一个关键的差距是缺乏一个统一的模型FMRP 介导的抑制及其在突触处的可逆调节。我们假设FMRP泛素化 和UPS介导的降解反应受体刺激提供了一个统一的机制，以消除 翻译抑制和调节突触处的局部蛋白质合成。E3连接酶的特殊作用 将研究FMRP介导的局部蛋白质合成调节中的Cdh 1-APC。阐明当地 这些机制在树突和棘中的功能，我们将继续开发和应用荧光 报道分子和活培养的海马神经元的单分子成像。使用解离和 器官型切片培养作为模型系统，UPS介导的FMRP降解的作用，作为局部 翻译开关，调节脊柱形态，突触发育和可塑性将进行研究。我们 将分析FMRP突变体的作用，这些突变体对泛素化具有抗性或不能结合Cdh 1-APC， 调节或挽救树突棘发育、突触功能和 可塑性。目的1将检验FMRP去磷酸化，由Cdh 1-APC和UPS泛素化， 介导的降解是调节局部mRNA翻译的动态分子开关的组成部分， 在控制树突棘形态、突触发育和可塑性中起作用。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 RISC/microRNA的靶向。这项研究有望揭示Cdh 1-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。发病机制的发展 基于FXS的治疗策略将受益于对机制的深入理解， FMRP介导的突触局部mRNA翻译控制的功能。

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.