Loss of methylation imprint of Snrpn in postovulatory aging mouse oocyte.

Prolonged residence of postovulatory oocyte in the oviduct or prolonged culture in vitro can lead to oocyte aging, which significantly affects pre- and post-implantation embryo development. In this study, we employed bisulfite sequencing and COBRA methods to investigate the DNA methylation status of differentially methylated regions (DMRs) of Snrpn and Peg1/Mest, two maternally imprinted genes, in postovulatory oocytes aged in vivo and in vitro. The results showed that Snrpn DMR was clearly demethylated in oocytes aged in vivo at 29h post-hCG and in denuded oocytes aged in vitro for the same time period. However, Peg1/Mest did not show any demethylation in all aged groups at 29h post-hCG. These data indicate that oocytes undergo time-dependent demethylation of Snrpn DMR during the process of postovulatory aging.