The reversible prevalent N⁶-methyladenosine (m⁶A) modification on mRNAs is catalyzed by methyltransferase complex (METTL3/METTL14/WTAP) and demethylases (FTO and ALKBH5). Recent studies revealed that m⁶A modification mediates various RNA processing steps and participates in a wide range of biological functions. Mettl3 exhibits very important roles in invertebrates and plants. However, elucidation of the in vivo biological functions of Mettl3-mediated m⁶A modification in mammalian tissue development is largely hindered due to the early lethality of Mettl3 knockout mice.

Recently, a study led by Dr. ZHOU Qi and Dr. LI Wei from State Key Laboratory of Stem Cell and Reproductive Biology, Institute of Zoology of the Chinese Academy of Sciences, in collaboration with Dr. Yungui Yang from Beijing Institute of Genomics of CAS, revealed an essential role of Mettl3-mediated m⁶A in regulating spermatogenesis, which is published online in Cell Research and selected as the cover story.

In this study, they first generated Mettl3flox/- Vasa-Cre (Mettl3cKO) mice with specific deletion of Mettl3 in germ cells by employing CRISPR-Cas9 system-assisted homologous recombination approach and found that depletion of Mettl3 blocks spermatogonial differentiation and meiosis at early-spermatogenesis stage.

To determine the regulatory mechanism of Mettl3-mediated m⁶A in spermatogenesis, they further compared the transcriptome data between Mettl3Ctrl and Mettl3cKO mouse testes and found global expression changes of spermatogenesis related genes in Mettl3cKO mouse testes.

Moreover, their comprehensive analysis of alternative splicing events and m⁶A methylome provides valuable evidence that Mettl3-mediated m⁶A methylation influences alternative splicing of spermatogenesis related genes and subsequent regulation of male fertility in mouse.

This collaborative group also provided mechanistic evidence of microRNAs-regulated RNA m⁶A methylation formation. The present findings illustrating the mechanism of Mettl3-mediated m⁶A in regulating spermatogonial differentiation and meiosis initiation provide valuable resource for deciphering the potential biological significance of RNA methylation and open up a new area for mRNA modification in RNA metabolisms.

This research is supported by CAS Strategic Priority Research Programs, Ministry of Science and Technology, Natural Science Foundation of China.