Role of Hakai in mA modification pathway in Drosophila.

N6-methyladenosine (mA), the most abundant internal modification in eukaryotic mRNA, is installed by a multi-component writer complex; however, the exact roles of each component remain poorly understood. Here we show that a potential E3 ubiquitin ligase Hakai colocalizes and interacts with other mA writer components, and Hakai mutants exhibit typical mA pathway defects in Drosophila, such as lowered mA levels in mRNA, aberrant Sxl alternative splicing, wing and behavior defects. Hakai, Vir, Fl(2)d and Flacc form a stable complex, and disruption of either Hakai, Vir or Fl(2)d led to the degradation of the other three components. Furthermore, MeRIP-seq indicates that the effective mA modification is mostly distributed in 5' UTRs in Drosophila, in contrast to the mammalian system. Interestingly, we demonstrate that mA modification is deposited onto the Sxl mRNA in a sex-specific fashion, which depends on the mA writer. Together, our work not only advances the understanding of mechanism and regulation of the mA writer complex, but also provides insights into how Sxl cooperate with the mA pathway to control its own splicing.