(50) Maternal OGT is Required for the Asymmetry of Epigenetic Modifications in Mouse Zygotes

Haoxue Wang 1; Shuntaro Ikeda 1
1. Laboratory of Reproductive Biology, Graduate School of Agriculture, Kyoto University, Kyoto, Japan

Abstract Text:

After fertilization in mammals, there is an asymmetry in epigenetic modifications reflected by the differences in DNA demethylation and histone modifications between the female and male pronuclei. This dynamic process is directly related to proper embryogenesis. This study focused on O-GlcNAc transferase (OGT), a key regulator for O-GlcNAcylation that is highly expressed in mammalian oocytes and zygotes. OGT was reported to interact with the ten-eleven-translocation family of proteins 3 (TET3), the key factor that triggers DNA demethylation, and co-related with many histone modifications that show asymmetric patterns between two pronuclei during the zygote stage. Thus, we approached its potential roles in the asymmetric epigenetic modifications in mouse zygotes. We inhibited OGT function by a specific small molecular inhibitor and the small interfering RNA (siRNA) separately during oocyte maturation. Then, we examined how the inhibitor treatment impacts the levels of 5-methylcytosine (5mC), 5-hydroxymethylcytosine (5hmC, an intermediate product toward DNA demethylation from 5mC), and several histone methylations by using immunostaining. Our results revealed that inhibiting OGT during oocyte maturation can cause postfertilization embryonic arrest at the 2- or 4-cell stage; however, the siRNA-mediated decrease of maternal Ogt mRNA had less effect on preimplantation development. The asymmetric pattern of DNA demethylation was disrupted, represented by the decreased levels of 5hmC in the male pronucleus. The histone methylations in male pronuclei were altered by maternal OGT inhibition. In contrast, there were no significant differences in DNA demethylation and histone modifications in female pronuclei. These findings highlight maternal OGT's importance in mammalian early embryogenesis through its influence on epigenetic remodeling and provide insights into exploring potential therapeutic approaches targeting OGT to improve fertility. In addition, they gave us a new gateway to explore parental pronuclear interaction after fertilization.