MeCP2 Interacts with the Super Elongation Complex to Regulate Transcription (RNA-Seq)

Loss-of-function mutations in methyl-CpG binding protein 2 (MECP2) cause the neurodevelopmental disorder, Rett syndrome (RTT). The molecular mechanisms underlying MeCP2 function remain poorly understood. Here, using a MECP2 gain-of-function Drosophila model, we screened for genetic modifiers of MECP2-induced toxicity. Our approach identified several subunits of the Drosophila super elongation complex (SEC), a P-TEFb containing elongation factor that releases promoter-proximally paused RNA polymerase II (RNA pol II), as genetic interactors of MECP2. MeCP2 directly interacts with AFF4, the scaffold of the SEC, and facilitates its binding on a subset of genes that regulate neuronal development and synaptic function in the mouse cortex. Furthermore, genes with reduced AFF4 binding showed reduced RNA pol II binding in their genebody and decreased RNA expression in Mecp2 null mice. Taken together, we propose that MeCP2 interacts with the SEC to facilitate the release of RNA pol II and thereby support gene expression. Gene expression profiling in wildtype and Mecp2 null cortex at 7-weeks of age甲基CpG结合蛋白2（methyl-CpG binding protein 2, MECP2）的功能丧失型突变可引发神经发育障碍——雷特综合征（Rett syndrome, RTT）。目前学界对MeCP2发挥功能的分子机制仍缺乏深入认知。本研究借助MECP2功能获得型果蝇模型，对MECP2诱导毒性的遗传修饰因子进行了筛选。研究鉴定出果蝇超级延伸复合物（super elongation complex, SEC）的多个亚基作为MECP2的遗传互作因子；该复合物是一类包含正性转录延伸因子b（positive transcription elongation factor b, P-TEFb）的延伸因子，可释放启动子近端暂停的RNA聚合酶II（RNA polymerase II, RNA pol II）。MeCP2可直接与SEC的支架蛋白AFF4结合，并促进其在小鼠皮层中调控神经发育与突触功能的部分靶基因上的结合。此外，在Mecp2敲除小鼠中，AFF4结合水平降低的基因，其基因体区域的RNA pol II结合水平与RNA表达量均显著下调。综上，我们提出MeCP2可通过与SEC互作，促进RNA pol II的释放，进而维持靶基因的正常表达。本研究对7周龄野生型与Mecp2敲除小鼠的皮层开展了基因表达谱分析。