RT Journal Article SR Electronic T1 The RNA demethylase FTO targets m6Am in snRNA to establish distinct methyl isoforms that influence splicing JF bioRxiv FD Cold Spring Harbor Laboratory SP 327924 DO 10.1101/327924 A1 Jan Mauer A1 Miriam Sindelar A1 Théo Guez A1 Jean-Jacques Vasseur A1 Andrea Rentmeister A1 Steven S. Gross A1 Livio Pellizzoni A1 Françoise Debart A1 Hani Goodarzi A1 Samie R. Jaffrey YR 2018 UL http://biorxiv.org/content/early/2018/05/23/327924.abstract AB Small nuclear RNAs (snRNAs) are core spliceosome components and mediate pre-mRNA splicing. During their biogenesis, snRNAs acquire several constitutive nucleotide modifications. Here we show that snRNAs also contain a regulated and reversible nucleotide modification causing them to exist as two different methyl isoforms, m1 and m2, reflecting the methylation state of the adenosine adjacent to the snRNA cap. We find that snRNA biogenesis involves the formation of an initial m1-isoform with a single-methylated adenosine (2’-O-methyladenosine, Am), which is then converted to a dimethylated m2-isoform (N6,2’-O-dimethyladenosine, m6Am). The relative m1- and m2-isoform levels are determined by the RNA demethylase FTO, which selectively demethylates the m2-isoform. We show FTO is inhibited by endogenous metabolites, resulting in increased m2-snRNA levels. Furthermore, cells that exhibit high m2-snRNA levels show altered patterns of alternative splicing. Together, these data reveal that FTO has a central role in snRNA biogenesis and controls a previously unknown step of snRNA processing involving reversible methylation, thereby providing a potential link between reversible RNA modifications and mRNA splicing.