Cycloleucine negatively regulates porcine oocyte maturation and embryo development by modulating N6-methyladenosine...

Maturation of oocytes and early embryo development are regulated precisely by numerous factors at transcriptional and posttranslational levels through precise mechanisms. N6-methyladenosine (m⁶A) is the most common modification in mRNA which regulates RNA metabolism and gene expression. However, the role of RNA m⁶A on porcine oocyte maturation and early embryogenesis is largely unknown. Here, we found that oocytes treated with cycloleucine (CL), an RNA m⁶A inhibitor, express impaired cumulus expansion, increased production of reactive oxygen species (ROS) in the mitochondria, and delayed maturation of oocytes by disrupting spindle organization and chromosome alignment. Also, CL halted the development of embryos at the 4-cell stage and resulted in low-quality blastocysts. Furthermore, CL treatment decreased the RNA m⁶A, H3K4me3, and H3K9me3 levels, but increased the acetylation level of H4K16 during parthenogenetic embryonic development in pigs. Single-cell RNA-seq (scRNA-seq) analysis further revealed that CL treatment dramatically up-regulated the expression of metabolism-related genes (SLC16A1, and MAIG3 etc.) and maternal related genes, including BTG4, WEE2, and BMP15 among others, at the blastocyst stage. Taken together, inhibition of RNA m⁶A by CL impaired meiosis of oocytes and early embryonic development of porcine via RNA m⁶A methylation, histone modifications, and altering the expression of metabolism-related genes in blastocysts.