Insufficient pyruvate in culture medium arrests mouse embryos at the first cleavage stage associated with abnormal epigenetic modifications

Energy is essential for early embryogenesis, and fertilized eggs can successfully develop to blastocyst in in vitro culture medium with an appropriate energy supply. Conversely, embryonic development is negatively affected by a suboptimal energy supply. We previously observed that a low level of pyruvate greatly arrests mouse embryos at the 2-cell stage. However, how methylation modifications are affected at this specific stage remains unknown. In this study, we found that mouse embryos could timely develop to the 4-cell stage in K+simplex optimized medium (KSOM) with control level of pyruvate, but embryos were significantly arrested at the 2-cell stage when pyruvate was reduced to 0.2-fold of the control level. Moreover, the fluorescence intensities of 5 mC, H3K4me2, H3K9me2 and H3K27me2 in the 2-cell stage embryos of the 0.2-fold pyruvate group were notedly lower than those of the control group, but N6-methyladenosine (m6A) fluorescence intensity was higher, suggesting that global genomic DNA, histone and m6A methylation modifications are disrupted with low levels of pyruvate. Consistently, the mRNA levels of genes related to DNA methylation, histone methylation and m6A modifications were also disturbed in the 2-cell stage embryos cultured with low levels of pyruvate. In summary, our findings demonstrate that insufficient pyruvate in culture medium results in mouse embryonic developmental arrest, at least in part due to defects in methylation modifications.