m6A修饰调控染色质上新生RNA命运决定的分子机制研究

m6A修饰广泛存在于mRNA上，并且参与调控mRNA的多种生物学功能，但m6A修饰是否存在于新生RNA以及是否参与新生RNA功能的研究相对欠缺。我们前期发现m6A甲基转移酶METTL3，METTL14，WTAP和去甲基化酶ALKBH5可以动态调控新生RNA上的m6A修饰，特别是增强子和启动子转录产生的eRNA和PROMPT这两类新生RNA。具体地，RNA修饰酶可以结合染色质的增强子区域和启动子区域，并且催化其结合位点转录产生的新生RNA的m6A修饰。不同于mRNA上的m6A修饰会被识别子蛋白YTHDF2识别而使其降解，我们发现新生RNA上的m6A修饰是一个稳定信号；在METTL3、METTL14、WTAP敲低或者ALKBH5过表达情况下，细胞内新生RNA含量都会降低。本项目拟鉴定新生RNA上m6A修饰的识别子蛋白，并探讨m6A修饰促进新生RNA稳定的分子机制和潜在的生物学功能。

N6-methyladenosine (m6A) regulates various aspects of mRNA biology. Although m6A methylation has been shown to be co-transcriptionally deposited, its regulatory role on nascent RNAs remains poorly understood. Here, we demonstrate that enhancer- and promoter-derived nascent RNAs are dynamically regulated by the METTL3/METTL14/WTAP m6A methyltransferase complex (MTC) and the demethylase, ALKBH5. Mechanistically, MTC specifically binds promoters and enhancers on chromatin and mediates m6A methylation on local nascent transcripts. In contrast to what has been reported for m6A function in destabilizing mRNA through YTHDF2, our study shows that m6A plays a protective role of the chromatin-associated nascent RNAs derived from promoters and enhancers. Knockdown of MTC or overexpression of ALKBH5 decrease the abundance of nascent RNA. This study aims to define reader protein recognizing m6A on nascent RNA, and understand the mechanism of m6A promoting nascent RNA stability potential biological significance.