INVESTIGATION OF PROTOCADHERIN-10 IN MEF2- AND FMRP-MEDIATED SYNAPSE ELIMINATION

描述(申请人提供)：脆性X综合征(FXS)是迄今为止发现的最常见的精神发育迟滞和自闭症的遗传形式。FXS是由Fmr1基因转录沉默或功能丧失突变引起的，Fmr1基因编码脆性X智力低下蛋白(FMRP)。FXS最具特征性的表型之一是树突棘过多，这是兴奋性突触的接触点，这与FXS是由于突触消除缺陷而导致的观点相联系。我们实验室最近的工作表明，FMRP是由转录因子肌细胞增强因子2(MEF2；Pfeiffer等人，Neuron，2010)触发的活性依赖性突触消除所必需的。证据表明，FMRP调节MEF2产生的转录本的翻译或运输，以调节突触消除。这一应用的拟议研究集中在自闭症谱系障碍(ASD)基因Protocadherin-10(PCDH10)(Morrow等人，Science，2008)上，旨在表征PCDH10消除MEF2和FMRP介导的突触的机制。我们的初步数据表明，1)PCDH10的表达受MEF2和FMRP的调控；2)PCDH10参与了突触数量的调节；3)PCDH10介导了突触后支架蛋白PSD-95的泛素化和降解。电生理学以及生化分析将被应用于了解PCDH10是否以及如何调节PSD-95的降解，并有助于MEF2诱导的突触消除，这需要FMRP。这些实验数据将提供MEF2和FMRP介导的突触消除的分子机制以及ASD基因在神经系统中的功能。

DESCRIPTION (provided by applicant): Fragile X Syndrome (FXS) is the most common inherited form of mental retardation and autism identified so far. FXS is caused by transcriptional silencing or loss-of-function mutations in the Fmr1 gene, which encodes for the Fragile X mental retardation protein (FMRP). One of the most characterized phenotypes of FXS is an excess of dendritic spines, the point of contact of excitatory synapses, which links the idea that FXS results from a deficit in synapse elimination. Recent work from our laboratory demonstrated that FMRP is required for activity- dependent synapse elimination triggered by the transcription factor Myocyte Enhancer Factor 2 (MEF2; Pfeiffer et al., Neuron, 2010). The evidence suggests that FMRP functions to regulate translation or transport of MEF2 generated transcripts to mediate synapse elimination. The proposed research of this application focuses on an autism-spectrum-disorders (ASD) gene, protocadherin-10 (PCDH10) (Morrow et al., Science, 2008) and aims to characterize the mechanisms underlying MEF2- and FMRP-mediated synapse elimination by PCDH10. Our preliminary data suggests that 1) the expression of PCDH10 is regulated by MEF2 and FMRP; 2) PCDH10 is involved in regulating synapse number; and 3) PCDH10 mediates ubiquitination and degradation of postsynaptic scaffold protein, PSD-95. Electrophysiology, as well as biochemical assays, will be applied to understand whether and how PCDH10 regulates PSD-95 degradation and contributes to MEF2-induced synapse elimination, which requires FMRP. The data from proposed experiments will provide molecular mechanism of MEF2- and FMRP-mediated synapse elimination as well as the function of an ASD gene in nervous system.