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

描述（由申请人提供）：脆性X综合征（FXS）是迄今为止发现的最常见的遗传性精神发育迟滞和自闭症。FXS是由编码脆性X智力低下蛋白（FMRP）的Fmr 1基因中的转录沉默或功能丧失突变引起的。FXS最具特征的表型之一是树突棘（兴奋性突触的接触点）过多，这与FXS由突触消除缺陷引起的观点有关。来自我们实验室的最近工作证明FMRP是由转录因子肌细胞增强因子2（MEF 2; Pfeiffer et al.，Neuron，2010）。有证据表明，FMRP的功能是调节MEF 2产生的转录本的翻译或转运，以介导突触消除。本申请提出的研究集中在自闭症谱系障碍（ASD）基因，原钙粘蛋白-10（PCDH 10）（Morrow等人，Science，2008），旨在表征PCDH 10对MEF 2和FMRP介导的突触消除的潜在机制。我们的初步数据表明：1）PCDH 10的表达受MEF 2和FMRP的调节; 2）PCDH 10参与调节突触数量; 3）PCDH 10介导突触后支架蛋白PSD-95的泛素化和降解。电生理学，以及生化分析，将被应用于了解是否以及如何PCDH 10调节PSD-95降解，并有助于MEF 2诱导的突触消除，这需要FMRP。实验结果将为MEF 2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提供理论依据。

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.