Role of Hakai in m(6)A modification pathway in Drosophila

N6-methyladenosine (m(6)A), 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 m(6)A writer components, and Hakai mutants exhibit typical m(6)A pathway defects in Drosophila, such as lowered m(6)A 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 m(6)A modification is mostly distributed in 5’ UTRs in Drosophila, in contrast to the mammalian system. Interestingly, we demonstrate that m(6)A modification is deposited onto the Sxl mRNA in a sex-specific fashion, which depends on the m(6)A writer. Together, our work not only advances the understanding of mechanism and regulation of the m(6)A writer complex, but also provides insights into how Sxl cooperate with the m(6)A pathway to control its own splicing.