Vitrification at the germinal vesicle stage does not affect the methylation profile of H19 and KCNQ1OT1 imprinting centers in human oocytes subsequently matured in vitro

Abstract

To evaluate the integrity of genomic imprinting in oocytes vitrified at the germinal vesicle (GV) stage and in vitro matured (IVM) after thawing. Clinical research and application. University-based fertility center. Immature oocytes were donated for research by patients who were included in an intracytoplasmic sperm injection program. Immature oocyte retrieval after ovarian stimulation, followed by oocyte vitrification, thawing, and IVM. Methylation profile of H19 and KCNQ1OT1 imprinting control regions, H19DMR and KvDMR1, respectively. Among 184 vitrified GV oocytes, 102 survived thawing (55.4%), 77 (75.5%) of which reached the meiosis II (MII) stage after IVM. One hundred twenty control GV oocytes were only subjected to IVM; 70.8% reached the MII stage. GV vitrified as well as control oocytes acquired full imprint at KvDMR1 after IVM and generally retained the unmethylated state of H19DMR. For the first time, we show that oocyte vitrification does not affect the methylation profile of H19DMR and KvDMR1: during their IVM, vitrified GV oocytes acquire DNA methylation in the maternally imprinted KCNQ1OT1 gene with the same efficiency as fresh GV oocytes; the vitrification process does not alter the unmethylated state of the paternally imprinted H19 gene.