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.