Dynamic reprogramming of 5-hydroxymethylcytosine during early porcine embryogenesis.

摘要

DNA active demethylation is an important epigenetic phenomenon observed in porcine zygotes, yet its molecular origins are unknown. Our results show that 5-methylcytosine (5 mC) converts into 5-hydroxymethylcytosine (5 hmC) during the first cell cycle in porcine in vivo fertilization (IVV), IVF, and SCNT embryos, but not in parthenogenetically activated embryos. Expression of Ten-Eleven Translocation 1 (TET1) correlates with this conversion. Expression of 5 mC gradually decreases until the morula stage; it is only expressed in the inner cell mass, but not trophectoderm regions of IVV and IVF blastocysts. Expression of 5 mC in SCNT embryos is ectopically distinct from that observed in IVV and IVF embryos. In addition, 5 hmC expression was similar to that of 5 mC in IVV cleavage-stage embryos. Expression of 5 hmC remained constant in IVF and SCNT embryos, and was evenly distributed among the inner cell mass and trophectoderm regions derived from IVV, IVF, and SCNT blastocysts. Ten-Eleven Translocation 3 was highly expressed in two-cell embryos, whereas TET1 and TET2 were highly expressed in blastocysts. These data suggest that TET1-catalyzed 5 hmC may be involved in active DNA demethylation in porcine early embryos. In addition, 5 mC, but not 5 hmC, participates in the initial cell lineage specification in porcine IVV and IVF blastocysts. Last, SCNT embryos show aberrant 5 mC and 5 hmC expression during early porcine embryonic development.