Inhibition of METTL5 improves preimplantation development of mouse somatic cell nuclear transfer embryos.

N6-methyladenosine (m6A) is one of the most important epigenetic modifications in eukaryotic RNAs, which regulates development and diseases. It is identified by several proteins. Methyltransferase-like 5 (METTL5), an enzyme that methylates 18S rRNA m6A, controls the translation of proteins and regulates pluripotency in embryonic stem cells. However, the functions of METTL5 in embryonic development have not been explored. Here, we found that Mettl5 was upregulated in somatic cell nuclear transfer (SCNT) embryos compared with normal fertilized embryos. Therefore, we hypothesized that METTL5 knockdown during the early stage of SCNT would improve the developmental rate of SCNT embryos. Notably, injection of Mettl5 siRNA (si-Mettl5) into enucleated oocytes during nuclear transfer increased the rate of development and the number of cells in blastocysts. Moreover, inhibition of METTL5 reduced the activity of phosphorylated ribosomal protein S6, decreased the levels of the repressive histone modification H3K27me3 and increased the expression of activating histone modifications H3K27ac and H3K4me3 and mRNA levels of some 2-cell-specific genes. These results expand our understanding of the role of METTL5 in early embryonic development and provide a novel idea for improving the efficiency of nuclear transfer cloning.