Role of the m6A methyltransferase Mettl16 in Drosophila development.

N6-methyladenosine (m6A), one of the most abundant chemical modifications on RNA, is installed by METTL3 and several other methyltransferases, including METTL16. Although METTL16 has been characterized in several model organisms, its function in Drosophila remains unknown. Here, we show that, unlike in mammals, Drosophila Mettl16 mutants are viable but exhibit multiple developmental and behavioral defects. Both male and female mutants are sterile, with severe gametogenesis defects. Mettl16 mutant germ cells can pass the mitotic and meiotic stages, but are defective in spermatid elongation and individualization. Mettl16-GFP localizes predominantly to the nucleus, and its absence does not impair global protein synthesis in wing disc epithelial cells. MeRIP-Seq analysis indicates that Mettl16 loss affects m6A on only a small subset of transcripts, in contrast to the broad effect of Mettl3. We further demonstrate that Mettl16 interacts with U6 snRNA and is required for its m6A modification. Accordingly, Mettl16 mutants display widespread alterations in alternative splicing. Together, the pleiotropic phenotypes of Mettl16 mutants likely stem from its role in m6A deposition and U6-dependent splicing regulation of specific target transcripts.