Global DNA methylation, DNA methyltransferase and stress-related gene expression in ovine oocytes and embryos after exposure to metabolic stressors.

DNA methylation, considered the most prominent epigenetic mark was important for the gene regulation in embryonic development. The present study aimed at evaluating the effects of metabolic stressors [Non-esterified fatty acid (NEFA), β-hydroxy-butyric acid (BHB), ammonia and urea] exposure during the in vitro ovine oocyte maturation, global DNA methylation, DNA methyltransferase and stress-related gene expression. Colorimetric analysis of global DNA methylation and the expression of the DNA methyltransferase genes (DNMT1, DNMT3A, and DNMT3B) were assessed in the matured oocytes, 2-cell embryos and blastocysts produced in vitro from oocytes exposed with the metabolic stressors during 24 h of the in vitro maturation (IVM). Further, the mRNA expression of the stress-related genes (SOD1, SOD2) in the matured oocytes, 2-cell embryos and blastocysts produced was assessed. Significant difference in global DNA methylation levels between all the treatments tested was observed when compared with control in oocytes, two-cell embryos and blastocysts. Elevated concentration of metabolic stressors resulted in increased expressions of several stress-related genes, i.e., SOD1, SOD2 and in mRNA expression of DNA methyltransferase genes. The present study is the first to report that the DNA methylation was sensitive to the effects of the metabolic stressors in ovine oocytes/embryos. The aberrant expressions of genes during oocyte development targeted in the present study can provide evidence for the early embryo developmental arrest and blastocysts quality. These results highlighted the sensitivity of the early embryogenesis and more precisely of the reprogramming period to metabolites challenges, in a realistic situation of elevated concentration of metabolic stressors.