Roles of DNMT3B and DNMT3L enzymes during oocyte maturation

DNA methylation plays a fundamental role in the epigenetic regulation of gene expression. This study aimed to investigate the specific roles of DNMT3B and DNMT3L enzymes in oocyte maturation in mice, and to evaluate the reciprocal regulatory effects of DNMT3B and DNMT3L proteins on each other, as well as the potential compensatory responses of other DNMT enzymes, namely DNMT1 and DNMT3A, in the event of gene silencing. In the study, siRNA specific to DNMT3B or DNMT3L was applied to germinal vesicle (GV) stage oocytes, which were then cultured under in vitro conditions. At the end of the culture period, metaphase II (MII) oocytes were collected, and DNMT protein expression levels and global DNA methylation status were analyzed using immunofluorescence staining specific to DNMT proteins and 5-methylcytosine (5mC), respectively. The results showed that silencing DNMT3B led to a significant decrease in DNMT3L protein levels, and vice versa (p < 0.001). DNMT3L silencing resulted in a significant increase in DNMT1 expression (p < 0.001), while DNMT3B silencing caused no significant change in DNMT1 levels. Both gene silencing conditions led to a significant reduction in DNMT3A expression (p < 0.001) and global DNA methylation levels (p < 0.001). Oocyte maturation was assessed by the proportion of GV-stage oocytes reaching the MII stage. A decreased maturation rate was observed in both DNMT3B and DNMT3L siRNA-treated groups. These findings indicate that DNMT3B and DNMT3L regulate each other and other DNMT enzymes, and play a key role in oocyte maturation by controlling DNA methylation dynamics.