Investigating the effect of superovulation on the DNA methyltransferase genes expression in mouse oocytes and early embryos

DNA methylation is one of the epigenetic mechanisms which plays critical role at mammalian oocyte and preimplantation embryo development. DNA methylation materializes by adding a methyl group to the fifth carbon atom of the cytosine residues within cytosine-phosphate-guanine (CpG) and non-CpG dinucleotide sites. DNA methyltransferase (DNMT) enzymes play roles at de novo and maintenance methylation processes. In studies, DNMT1, DNMT3A and DNMT3B which are DNMT enzymes were identified to have important assignments in oocyte and preimplantation embryo development. In this study propose that superovulation which is used frequently in IVF applications and experimental researches that identification expression of protein levels and in subcellular localization of DNMT1, DNMT3A and DNMT3B. In this study, three groups were formed which included control, normal dose [5 IU pregnant mare's serum gonadotropin (PMSG) and 5 IU human chorionic gonadotropin (hCG)] and high dose (7.5 IU PMSG and 7.5 IU hCG) from 4-5 weeks female mice (BALB/C). Protein expression level and cellular localization of DNMT1, DNMT3A and DNMT3B were defined by immunofluorescence technique at oocyte [germinal vesicle (GV), metaphase II (MII)] and preimplantation embryos (1-cell and 2-cell) which were picked up in predetermined set of time chart. The images obtained were analyzed by ImageJ software and One Way Anova statistical test so that relative expressions were identified. According to the results of our study, DNMT1 we identified weak expression pattern in nuclear region, more intensive in cytoplasmic region and the most intensive expression pattern in near the membrane regions at analyzed oocytes and preimplantation embryos for three groups. DNMT3A and DNMT3B expressions have shown intensive localizations in nuclear regions and normal expression in cytoplasmic regions. Additionally, DNMT1, DNMT3A and DNMT3B protein expressions were observed significantly different in normal and high dose groups compared with control groups at GV and MII oocytes, 1-cell and 2-cell embryos (P<0.05). In conclusion, this study has demonstrated for the first time that superovulation alters expression levels of DNMT proteins. Subcellular localizations of these proteins were examined in detail for the first time at oocytes and embryos obtained from a control group of females. Superovulation is commonly used in experimental studies and assisted reproductive techniques that its effect should be further investigated in the oocytes and preimplantation embryos. Keywords: DNMT, Embryo, Oocyte, Immunofluorescence, Superovulation