FTO-dependent demethylation of N6-methyladenosine regulates mRNA splicing and is required for adipogenesis

The role of Fat Mass and Obesity-associated protein (FTO) and its substrate N6-methyladenosine (m 6 A) in mRNA processing and adipogenesis remains largely unknown. We show that FTO expression and m 6 A levels are inversely correlated during adipogenesis. FTO depletion blocks differentiation and only catalytically active FTO restores adipogenesis. Transcriptome analyses in combination with m 6 A-seq revealed that gene expression and mRNA splicing of grouped genes are regulated by FTO. M 6 A is enriched in exonic regions flanking 5′- and 3′-splice sites, spatially overlapping with mRNA splicing regulatory serine/arginine-rich (SR) protein exonic splicing enhancer binding regions. Enhanced levels of m 6 A in response to FTO depletion promotes the RNA binding ability of SRSF2 protein, leading to increased inclusion of target exons. FTO controls exonic splicing of adipogenic regulatory factor RUNX1T1 by regulating m 6 A levels around splice sites and thereby modulates differentiation. These findings provide compelling evidence that FTO-dependent m 6 A demethylation functions as a novel regulatory mechanism of RNA processing and plays a critical role in the regulation of adipogenesis.