TET Family is Responsible for the Appearance of 5-Hydroxylmethylcytosine During Porcine Embryo Development

After fertilization, a dynamic change in DNA methylation is observed. Recent studies in mouse showed that ten-eleven translocation family (TET 1-3) is involved in these dynamics by converting methylated cytosine (5mec) into 5-hydroxylmethylcytosine (5hmec). Specifically, TET3 is involved in the conversion during early stages, and TET1 is a key regulator during later stages of preimplantation embryo development. Previously we demonstrated that the porcine TET family shows dynamic changes in mRNA expression during oocyte and embryo development. Based on these results, we’ve hypothesized that TET1 and TET3 are important for the maintenance of 5hmec during embryo development. Here we examined the 5hmec signal during preimplantation embryo development, as well as the role of the TET family on the appearance of 5hmec. By using immunocytochemistry, the 5hmec signal was detected in porcine oocytes and embryos, though the signal was weak in the oocytes. To investigate the role of the TET family in maintaining the level of 5hmec, siRNAs against porcine TET1 and TET3 were designed and introduced into porcine oocytes and embryos by microinjection. Both siRNAs could decrease the level of the target transcripts, and TET3 down-regulation before fertilization resulted in the reduction of 5hmec in the zygotes. This indicates that TET3 is responsible for 5hmec conversion in porcine embryogenesis. This is the first report showing the involvement of the TET family in the appearance of 5hmec in non-rodent species. Future studies are focused on the effect of TET1 down-regulation and subsequent gene expression profiles after altering levels of the TET family.