Mettl3 downregulation in germinal vesicle oocytes inhibits mRNA decay and the first polar body extrusion during maturation†.

In oocytes, mRNA decay is essential for maturation and subsequent events, such as maternal-zygotic transition, zygotic genomic activation, and embryo development. Reversible N6-methyladenosine RNA methylation directly regulates transcription, pre-mRNA splicing, mRNA export, mRNA stability, and translation. Here, we identified that downregulation of N6-methyladenosine modification by microinjecting a methyltransferase-like 3 (Mettl3)-specific small interfering RNA into mouse germinal vesicle oocytes led to defects in meiotic spindles and the first polar body extrusion during maturation in vitro. By further quantitative real-time polymerase chain reaction and Poly(A)-tail assay analysis, we found that N6-methyladenosine methylation mainly acts by reducing deadenylation of mRNAs mediated by the carbon catabolite repression 4-negative on TATA less system, thereby causing mRNA accumulation in oocytes. Meanwhile, transcriptome analysis of germinal vesicle oocytes revealed the downregulation of transcripts of several genes encoding ribosomal subunits proteins in the Mettl3 small interfering RNA-treated group, suggesting that N6-methyladenosine modification might affect translation. Together, our results indicate that RNA methylation accelerates mRNA decay, confirming the critical role of RNA clearance in oocyte maturation.