A Mettl16/m6A/Mybl2b/Igf2bp1 axis ensures cell cycle progression of embryonic hematopoietic stem and progenitor cells

Prenatal lethality associated with mouse knockout of METTL16, a recently identified RNA N6-methyladenosine (m6A) methyltransferase, has hampered characterization of the essential role of METTL16-mediated RNA m6A modification in early embryonic development. Here, using cross-species single-cell RNA sequencing analysis, we found that during early embryonic development, METTL16 is more highly expressed in vertebrate hematopoietic stem and progenitor cells (HSPCs) than other methyltransferases. In Mettl16-deficient zebrafish, proliferation capacity of embryonic HSPCs is compromised due to G1/S cell cycle arrest, an effect whose rescue requires Mettl16 with intact methyltransferase activity. We further identify the cell-cycle transcription factor Mybl2b as a directly regulated by Mettl16-mediated m6A modification. Mettl16 deficiency resulted in the destabilization of Mybl2b mRNA, likely due to lost binding by the m6A reader Igf2bp1 in vivo. Moreover, we found that the METTL16-m6A-MYBL2-IGF2BP1 axis controlling G1/S progression is conserved in humans. Collectively, our findings elucidate the critical function of METTL16-mediated m6A modification in HSPC cell cycle progression during early embryonic development.

METTL16是新近鉴定的RNA N6-甲基腺苷（RNA N6-methyladenosine, m6A）甲基转移酶，针对该基因的小鼠敲除模型会引发胚胎致死，这一障碍阻碍了对METTL16介导的RNA m6A修饰在早期胚胎发育中核心作用的解析。本研究借助跨物种单细胞RNA测序分析，发现在早期胚胎发育过程中，脊椎动物造血干细胞与祖细胞（hematopoietic stem and progenitor cells, HSPCs）中METTL16的表达水平高于其他甲基转移酶。在METTL16缺陷型斑马鱼中，胚胎造血干细胞与祖细胞的增殖能力因G1/S期细胞周期阻滞而受损，且该效应的挽救需要具备完整甲基转移酶活性的METTL16。本研究进一步鉴定出细胞周期转录因子Mybl2b是受METTL16介导的m6A修饰直接调控的靶点。METTL16缺陷会导致Mybl2b mRNA的稳定性下降，这可能是由于体内m6A阅读蛋白Igf2bp1丧失了结合能力所致。此外，本研究发现，调控G1/S期进程的METTL16-m6A-MYBL2-IGF2BP1调控轴在人类中具有保守性。综上，本研究阐明了METTL16介导的m6A修饰在早期胚胎发育过程中造血干细胞与祖细胞的细胞周期进程中的关键作用。