The Drosophila Nab2 RNA binding protein inhibits m⁶A methylation and male-specific splicing of Sex lethal transcript in female neuronal tissue

The Drosophila polyadenosine RNA binding protein Nab2, which is orthologous to a human protein lost in a form of inherited intellectual disability, controls adult locomotion, axon projection, dendritic arborization, and memory through a largely undefined set of target RNAs. Here, we show a specific role for Nab2 in regulating splicing of similar to 150 exons/introns in the head transcriptome and focus on retention of a male-specific exon in the sex determination factor Sex-lethal (Sxl) that is enriched in female neurons. Previous studies have revealed that this splicing event is regulated in females by N6-methyladenosine (m(6)A) modification by the Mettl3 complex. At a molecular level, Nab2 associates with Sxl pre-mRNA in neurons and limits Sxl m(6)A methylation at specific sites. In parallel, reducing expression of the Mettl3, Mettl3 complex components, or the m(6)A reader Ythdc1 rescues mutant phenotypes in Nab2 flies. Overall, these data identify Nab2 as an inhibitor of m(6)A methylation and imply significant overlap between Nab2 and Mettl3 regulated RNAs in neuronal tissue.