An Adversarial DNA N6-methyladenine-Sensor Network Preserves Polycomb Silencing

Adenine N6 methylation in DNA (6mA) is widespread among bacteria and phage and is detected in mammalian genomes, where its function is largely unexplored. Here we show that 6mA deposition and removal are catalyzed, respectively, by the Mettl4 methyltransferase and Alkbh4 dioxygenase, and that 6mA accumulation in genic elements corresponds with transcriptional silencing. Inactivation of murine Mettl4 depletes 6mA and causes sublethality and craniofacial dysmorphism in incross progeny. We identify distinct 6mA sensor domains of prokaryotic origin within the MPND deubiquitinase and ASXL1, a component of the Polycomb repressive deubiquitinase (PR-DUB) complex, both of which act to remove monoubiquitin from histone H2A (H2A-K119Ub), a repressive mark. Deposition of 6mA by Mettl4 triggers the proteolytic destruction of both sensor proteins, thereby preserving H2A-K119Ub levels. Expression of the bacterial 6mA methyltransferase Dam, in contrast, fails to destroy either sensor. These findings uncover a native, adversarial 6mA network architecture that preserves Polycomb silencing. Analysis of 6mA, Asxl1, MPND distribution by ChIP-seq and 6mA MeDIP-seq in wild-type and Mettl4 knockout (KO) mouse ES cells. RNA-seq profiling in wild-type and Mett; 4 KO mouse ES cells. analysis of E9.5 wild-type and Srap1 KO embryos.