Vitrification of porcine immature oocytes and pronuclear parthenotes delays development at the time of embryonic genome activation: A time-lapse study

Vitrification procedures have become indispensable for the preservation of female germplasm and the storage and transport of embryos despite the potential detrimental effects on embryo viability. The aim of this study was to examine the effects of vitrification on porcine embryo developmental kinetics by time-lapse imaging. In the first comparison, cumulus enclosed oocytes at the germinal vesicle (GV) stage were either vitrified-warmed or not vitrified (control) prior to in vitro maturation (IVM) and artificial activation (AA). In the second comparison, pronuclear (PN) parthenotes produced after IVM and AA were either vitrified-warmed or not vitrified (control). Embryo development was monitored for 6 d using the Primo Vision time-lapse system, and corresponding cohorts were assessed after incubation under standard in vitro culture (IVC) conditions. The cumulative time taken to progress to most of the developmental stages was significantly longer for embryos of the vitrified groups than for those of the control groups. Analysing the duration for each developmental interval revealed that the 4- to 5-cell and 5- to 8-cell periods were remarkably slower in the vitrified groups, compared with the control groups. The incidence of atypical blastomere divisions tended to increase following vitrification of GV oocytes. Under standard IVC conditions, blastocyst formation rates were lower for embryos of the vitrified groups than for those of the control groups. Given that the period of greatest developmental delay coincides with the major embryonic genome activation phase in porcine embryos, we propose that the vitrification of GV oocytes and PN parthenotes adversely impacts epigenetic processes.