In vitro oocyte maturation is associated with altered OCT4 promoter methylation, DNMT expression, and early embryonic development in transgenic mouse embryos

Objective: In vitro oocyte maturation (IVM) is widely used in assisted reproductive technologies; however, its potential effects on epigenetic regulation and embryonic development remain incompletely understood. In this study, we compared the developmental competence and epigenetic characteristics of transgenic mouse embryos derived from in vitro-matured and in vivo-matured oocytes. Methods: A human OCT4-enhanced green fluorescent protein (EGFP) construct was microinjected into fertilized oocytes, and embryo development was evaluated by assessing cleavage and blastocyst formation rates. The methylation status of the OCT4 promoter was assessed using methylation-specific polymerase chain reaction (PCR), and the expression levels of DNA methyltransferases (Dnmt1, Dnmt3a, Dnmt3b, and Dnmt3l) and endogenous Oct4 were analyzed using quantitative real-time PCR. Results: Embryos derived from IVM oocytes exhibited significantly reduced cleavage and blastocyst formation rates compared with those derived from in vivo-matured oocytes. In addition, differences in OCT4 promoter methylation patterns and altered expression of DNMTs were observed between the two groups. In particular, increased Dnmt3a expression and decreased Oct4 expression were associated with embryos derived from IVM oocytes. Conclusion: These findings suggest that IVM is associated with epigenetic alterations that may influence early embryonic development and the quality of transgenic embryos. Improved understanding of these effects may contribute to the optimization of IVM protocols and outcomes in assisted reproductive technologies.