Genome-Wide Maps of m6A circRNAs Identify Widespread and Cell-Type-Specific Methylation Patterns that Are Distinct from mRNAs

Summary N 6 -methyladenosine (m 6 A) is the most abundant internal modification of mRNAs and is implicated in all aspects of post-transcriptional RNA metabolism. However, little is known about m 6 A modifications to circular (circ) RNAs. We developed a computational pipeline (AutoCirc) that, together with depletion of ribosomal RNA and m 6 A immunoprecipitation, defined thousands of m 6 A circRNAs with cell-type-specific expression. The presence of m 6 A circRNAs is corroborated by interaction between circRNAs and YTHDF1/YTHDF2, proteins that read m 6 A sites in mRNAs, and by reduced m 6 A levels upon depletion of METTL3, the m 6 A writer. Despite sharing m 6 A readers and writers, m 6 A circRNAs are frequently derived from exons that are not methylated in mRNAs, whereas mRNAs that are methylated on the same exons that compose m 6 A circRNAs exhibit less stability in a process regulated by YTHDF2. These results expand our understanding of the breadth of m 6 A modifications and uncover regulation of circRNAs through m 6 A modification.