Nuclear m6 A reader YTHDC1 suppresses proximal alternative polyadenylation sites by interfering with the 3' processing machinery. Nuclear m6 A reader YTHDC1 suppresses proximal alternative polyadenylation sites by interfering with the 3' processing machinery

N6-methyladenosine (m6 A) and alternative polyadenylation (APA) are important regulators of gene expression in eukaryotes. Recently, it was found that m6 A is closely related to APA. However, the molecular mechanism of this new APA regulation remains elusive. Here, we show that YTHDC1, a nuclear m6 A reader, can suppress proximal APA sites and produce longer 3' UTR transcripts by binding to their upstream m6 A sites. YTHDC1 can directly interact with the 3' end processing factor FIP1L1 and interfere with its ability to recruit CPSF4. Binding to the m6 A sites can promote liquid-liquid phase separation of YTHDC1 and FIP1L1, which may play an important role in their interaction and APA regulation. Collectively, YTHDC1 as an m6 A "reader" links m6 A modification with pre-mRNA 3' end processing, providing a new mechanism for APA regulation. Overall design: We knockdowned YTHDC1 in HEK293T and MCF-7cell with siRNA and applied a alternative polyadenylation high sequencing (IVT-SAPAS) method to detect dynamic change of 3‘UTR length.

N6-甲基腺嘌呤（N6-methyladenosine, m6A）与可变多聚腺苷酸化（alternative polyadenylation, APA）均为真核生物基因表达的重要调控元件。近期研究表明，m6A与APA存在紧密关联，但此类新型APA调控的分子机制仍未阐明。本研究发现，细胞核内m6A识别蛋白YTHDC1可通过结合靶基因上游的m6A位点，抑制近端APA位点的使用，进而生成更长的3'非翻译区（3' UTR）转录本。YTHDC1可直接与3'端加工因子FIP1L1相互作用，并干扰其招募CPSF4的能力。结合m6A位点可促进YTHDC1与FIP1L1发生液液相分离，这一过程可能在二者相互作用及APA调控中发挥重要功能。综上，作为m6A识别蛋白的YTHDC1将m6A修饰与前体mRNA 3'端加工过程相偶联，为APA调控提供了全新的分子机制。实验设计概述：本研究通过小干扰RNA（siRNA）在HEK293T与MCF-7细胞中敲低YTHDC1的表达，并采用可变多聚腺苷酸化高通量测序（IVT-SAPAS）方法，检测3'非翻译区长度的动态变化。