Superovulation, or ovarian stimulation is a commonly used ART for treatment of human infertility/subfertility. Recent studies suggest that superovulation unaffects methylated imprints acquisition in mouse oocytes during oogenesis, whereas disrupts DNA methylation maintenance in embryos during preimplantation development. However, the mechanisms of defects in methylation maintanence caused by superovulation remain largely unclear. We hypothesized that superovulation may disrupt the expression of DNA methyltransferases (Dnmts), the enzymes which catalyze DNA methylation acquisition and maintenance. The mice were subjected to superovulate with low (6 IU) and high (10 IU) dosage hormone. We examined the global DNA methylation levels in zygotes and DNA methylation of repeated sequences (IAP and Line 1) in blastocyst stage embryos. In addition, we investigated the expression of Dnmts (Dnmt3a, Dnmt3b, Dnmt3l and Dnmt1o) in ovulated oocytes and zygotes. Through staining with antibody 5mC and Di-H3K9 coupled with confocal microscopy, we found that global methylation profiles in zygotes derived from females after low or high dosage hormone treatment were not affected when compared to control counterpart. Moreover, methylation at IAP in blastocysts also was unaffected by superovulation, irrespective of hormone dosage. In contrast, methylation level at Line 1 decreased when the females were administered by high dosage hormone. Furthermore, expression of de novo DNA methyltransferase Dnmt3a, Dnmt3b, Dnmt3L, as well as maintenance Dnmt1o in MII oocytes and zygotes was not disrupted by superovulation. Given superovulation adversely affected methylation maintenance in blastocysts during preimplantation development but with normal expression of Dnmts in oocytes and zygotes, it is indicated that defects of embryonic methylation didn’t originate from abnormal expression of Dnmts.

Epigenetic modification dependent DNA methyltransferases (DNMTs) play an important role in tissue- and stage-specific gene regulation and normal mammalian development. In this study, we show that DNMTs are expressed at different levels during hematopoietic stem cell (HSC) differentiation to proerythrocytes. DNMT1, DNMT3A, and DNMT3B were highly expressed at day 7 after differentiation. We used specific siRNA as a tool to probe the relationship between the expression of DNMTs and erythropoietic differentiation. When introduced siRNA of DMNT1 and DMNT3b in human CD34+ cells, these more differentiated into erythrocytes. This was confirmed by glycophorin A (GPA) positive cell analysis and globin gene expression. GPA+ cells increased up to 20～30%, and γ- and ε-globin genes increased in siRNA transfected cells. Therefore, our data suggest that suppression of DNA methylation can affect positively differentiation of HSC and may contribute to expression of erythrocyte lineage genes including GPA and globins.

There are replete numbers of reports which have apparently shown that established patterns of methylation are critical for normal mammalian development. Here, we report expression of the DNA methyltransferases (Dnmts) family during mouse early development. Transcription of Dnmt1o occurs in one-cell and morula stage embryos, whereas Dnmt1s transcripts were detectable in all cells and tissues examined during the study. Dnmt3a1 transcript was detected in all cells and Dnmt3a2 transcript was particularly detected in the oocyte and 1-cell stages. Low level Dnmt3b1 transcripts were expressed ubiquitously in oocyte, 1-cell, and preimplantation embryos except 2～4 cell stages. Dnmt3b3 transcripts were only detected in E7.5 embryo and ovary. Furthermore, Dnmt3l transcripts were detectable in all cells and tissues examined. Unlike Dnmt1, both Dnmt3a and Dnmt3b proteins existed in the nucleus of preimplantation embryos till the morula stage. These Results suggest that differences Dnmts expression level exist and genomic DNA methylation patterns may be determined partly through differential expression of Dnmts during early development.