FTO mediates LINE1 m 6 A demethylation and chromatin regulation in mESCs and mouse development.

N 6 -methyladenosine (m 6 A) is the most abundant internal modification on mammalian messenger RNA. It is installed by a writer complex and can be reversed by erasers such as the fat mass and obesity-associated protein FTO. Despite extensive research, the primary physiological substrates of FTO in mammalian tissues and development remain elusive. Here, we show that FTO mediates m 6 A demethylation of long-interspersed element-1 (LINE1) RNA in mouse embryonic stem cells (mESCs), regulating LINE1 RNA abundance and the local chromatin state, which in turn modulates the transcription of LINE1-containing genes. FTO-mediated LINE1 RNA m 6 A demethylation also plays regulatory roles in shaping chromatin state and gene expression during mouse oocyte and embryonic development. Our results suggest broad effects of LINE1 RNA m 6 A demethylation by FTO in mammals.