两类环形RNA的生成加工机制研究及其功能探索

While most annotated long noncoding RNAs (lncRNAs) appear indistinguishable from mRNAs, having 5'cap structures and 3'poly(A) tails, recent work has revealed new formats. Such lncRNAs are processed and stabilized by other mechanisms, such as capped by snoRNP complexes at both ends or by forming circular structures. Importantly, these lncRNAs have also been implicated in gene expression regulation in mammalian cells. In fact, the majority of these lncRNAs with new formats are circular RNAs. With the non-poly(A) selection and RNase R enrichment, we and others have very recently reported ten thousands of circular RNAs from many loci in mammals. Circular RNAs can be produced from back splice circularization of exons (exon circularization) or from excised introns owing to a failure in debranching (circular intronic RNAs, ciRNAs). We have demonstrated that exon circularization is dependent on RNA pairing formed by complementary sequences across flanking introns. Importantly, the competition of RNA pairing formation across flanking introns or within individual introns significantly affects exon circularization and leads to alternative circularization, resulting in multiple circular RNA transcripts produced from a single gene. On the other hand, the processing of ciRNAs depends on a consensus motif near the 5'splice site and the branchpoint site. In addition, some ciRNAs largely accumulate to their sites of transcription and boost the transcription of their parent genes. Together, our findings greatly extend the complexity of mammalian co-/post-transcriptional regulation.. However, the biogenesis and function of these two classes of circular RNAs have largely remained elusive. This proposal is aiming to further decipher the detailed processing mechanisms of these circular RNAs, including the coordination of exon/intron circularization with transcription and splicing regulation, the identification of key cis-elements and trans-factors involved in different types of RNA circularization, and the functional implications of circular RNAs in gene regulation. Taken together, our study will lead to a better understanding of circular RNA biogenesis and provide new insights into the mechanistic basis for their functional implications.

近十年来在生物体内发现了大量与mRNA结构类似，却不具备编码功能蛋白质能力的长链非编码RNA。利用新的富集手段结合高通量分析，最近我们报导了人体内存在上万条具有特殊结构的长非编码RNAs，其中多数为环形RNAs（circular RNAs）。环形RNAs不具有5'末端帽子和3'末端poly(A)尾巴，以共价键成环，并具有潜在的生物学功能。根据其产生机制不同，分为外显子来源和内含子来源的环形RNAs。我们研究证明RNA序列互补对外显子环形RNAs的产生和可变环化调控至关重要；而内含子环形RNAs的生成则依赖于一些关键核酸序列。本项目旨在前期研究基础之上，揭示环形RNAs生成转录和剪接的协调互作、阐明两类环形RNAs的加工成熟机制、探索环形RNAs调控基因表达的功能。获得成果将为深入认识环形RNAs的生成加工代谢及生物学功能提供坚实的分子基础和理论依据，有望在本领域继续保持国际领先的研究进展。

环形RNAs不具有5'末端帽子和3'末端poly(A)尾巴，以共价键成环，并具有潜在的生物学功能。本项目旨在前期研究基础之上，揭示环形RNAs生成转录和剪接的协调互作、阐明环形RNAs的加工成熟机制、探索环形RNAs调控基因表达的功能。同时也注重发掘其它新类型RNA分子，深入研究它们的产生机制和生物学功能。.在本项目执行过程中，我们 ①系统解析环形RNAs生成、结构和降解机制并首次揭示环形RNAs在细胞天然免疫反应过程中具有重要生物学功能：揭示环形RNAs降解过程和二级结构调控天然免疫过程PKR的激活，并发现环形RNAs异常低表达与红斑狼疮疾病发生密切关联(Cell, 已接受)；揭示调控环形RNAs生成的蛋白因子并首次发现环形RNAs在细胞天然免疫中发挥作用(Mol Cell, 2017)；阐析外显子反向剪接成环与Pol II 转录的偶联机制(Cell Rep, 2016)；合作揭示和证明可变环化及其发生机制(Genome Res, 2016；RNA Biol, 2017)。②揭示新型lncRNA分子家族及其功能作用机制并探索RNA表观修饰调控：发现两端以Box H/ACA snoRNA结尾的新型SLERT lncRNA，在细胞核仁功能和Pol I 转录过程的重要调控机制(Cell, 2017)；发现多聚顺反子转录本加工来源的5' 端以snoRNA 结尾的SPA lncRNA新家族，揭示其与小胖威利症密切相关(Mol Cell, 2016)；发现lncRNA NEAT1转录调控新机制及其线粒体功能发挥和mRNA出核过程的重要意义(Nat Cell Biol, 2018；Genes Dev, 2015)；发现A-to-I编辑酶ADAR1调控miRNA前体加工而影响人源干细胞神经分化的新功能(Cell Res, 2015)；合作揭示m6A修饰和A-to-I编辑两种普遍的RNA修饰间的互作调控机制 (Mol Cell, 2018)。.研究工作系统揭示了环形RNA及其它新型lncRNA的加工代谢机制和功能作用机制，为深入认识环形及lncRNA生成和代谢提供理论依据，为理解RNA 参与重大疾病提供新思路和新认识。基于这些原创系统的发现，项目期间受邀为Nat Rev Mol Cell Bio、Mol Cell 及Trends系列等权威期刊撰写环形及长非编RNA重要综述10余篇。