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Effects of Coculture of Vero Cells on the Development of Frozen-thawed Two-cell Stage ICR Mouse Embryos

Objective : The rate of developmental progression of frozen-thawed embryos is lower than that of nonfrozen embryos in mice, cows, humans and other mammalians. This study was designed and performed to evaluate the beneficial effects of coculture of Vero cells on the development of frozen-thawed two-cell stage embryos of ICR strain mice. Materials and Methods : The late two-cell stage mouse embryos were obtained from oviducts of 56 week old mated ICR mice superovulated with pregnant mare's serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG). Two-cell stage mouse embryos were frozen slowly with 1,2-propanediol and sucrose as cryoprotectants and thawed rapidly, followed by stepwise dilution. The frozen-thawed embryos were cultured in Ham's F-10+10% Fetal Bovine Serum (FBS) basal culture medium with and without Vero cells. The rates of development in both groups were compared every 24 hours for 5 days. Results : Vero cells did not significantly stimulate the rate of embryonal development compared to controls at 24 hours after culture, 124 (69.3%) and 68 (61.3%), respectively (p=0.161). On day 4, however, 55 (30.7%) cocultured embryos had developed to expanded-hatching blastocysts, which was the significantly higher number than that of the embryos in controls: 16 (14.4%) (p=0.002). In addition, more embryos in coculture developed to hatching-hatched blastocysts (43[24.0%]) compared to the controls (10[9.0%]) (p=0.001). Conclusion : Coculture of cryopreserved embryos after thawing with Vero cells seems to be an useful tool to remove the postthaw deleterious effects of freezing and to obtain better quality embryos appropriate for transfer. These beneficial effects of Vero cell coculture appear to become more prominent as the embryonic development progresses over time.