m6A RNA methylation in mammalian oocytes and preimplantation embryos: implications for developmental competence.

Chemical modifications of RNA molecules, collectively referred to as epitranscriptomics, have emerged as a critical layer of post-transcriptional gene regulation. Among these modifications, N6-methyladenosine (m6A) plays a key role in modulating RNA stability, localization, and translational efficiency without altering the underlying nucleotide sequence. In recent years, epitranscriptomics has been increasingly recognized for its involvement in mammalian reproductive processes. In mammalian oocytes, which undergo an extended period of transcriptional quiescence and rely predominantly on post-transcriptional regulation of maternally stored transcripts, RNA modifications are essential for proper gene expression control. During oocyte maturation and early pre-implantation embryo development, epitranscriptomic mechanisms ensure the timely turnover and translational regulation of maternal mRNAs, thereby supporting the correct execution of the maternal-to-zygotic transition. The proper accomplishment of these processes is crucial for the acquisition of developmental competence. Reversible RNA modifications therefore add an additional layer of complexity to the regulation of gene expression in oocytes and early embryos. This mini-review summarizes current knowledge on the role of m6A RNA methylation in mammalian oocyte developmental competence and early embryogenesis, highlighting recent experimental evidence and discussing potential implications for fertility and assisted reproductive technologies.