Binding to m6A RNA promotes YTHDF2-mediated phase separation

As the most abundant modification on mRNA in mammal, N6-Methyladenosine (m6A) has been demonstrated to play important roles in various biological processes including mRNA splicing, translation and degradation. m6A reader proteins have been shown to play central roles in these processes. One of the m6A readers, YTHDF2 is localized to the P granules, which are liquid-like droplets where RNA degradation occurs. How YTHDF2 is localized to P granules is unknown. Here we provide evidence that YTHDF2 forms liquid droplets and phase separate, mediated by its low complexity (LC) domains. Interestingly, the ability to phase separate is robustly stimulated by m6A RNAs in vitro. In vivo, YTHDF2 phase separation may in fact be dependent on m6A RNA and YTHDF2 binding to m6A RNA, since a YTHDF2 m6A-binding defective mutant or a wildtype YTHDF2 assayed in cells lacking m6A RNAs, both fail to phase separate. The ability of phase separate is not limited to YTHDF2; we find other members of the YTH-domain m6A readers can also undergo phase separation. Our findings suggest that m6A RNA induced phase separation of m6A readers may play an important role in their distributions to different phase-separated compartments in cells.