Improvement of development of vitrified two-cell mouse embryos by vero cell coculture

The purpose of this study was to determine the developmental potential of two-cell mouse embryos resulting from vitrification could increased using monolayer of Vero cells.

Two-cell mouse embryos were divided into vitrified and nonvitrified groups. Embryos in the vitrified group were frozen with a combination of 10% ethylene glycol, 30% ficoll, and 0.5% M sucrose (EFS10) as cryoprotectants, and thawed rapidly with 0.5 M sucrose. The survived embryos were cultured either with Vero cells monolayer or in T6 medium. Accordingly the embryos of the nonvitrified group were also cultured. The rates of the development in all the groups were daily determined and statistically compared. At the end of the cultivation period, several expanded blastocysts from each group were stained with ethidium bromide and the mean number of the blastomers were counted and statistically compared.

After 4 days of culture, the developmental potential of vitrified-thawed embryos were significantly reduced in Vero cell-free medium, and the mean cell number of embryos reaching the expanded blastocyst stage were also lower than that of nonvitrified embryos. With exception of last day of culture, Vero cell coculture, resulted in a significant increase in the rate of development of vitrified-thawed embryos as well as improved the mean cell number of expanded blastocysts. On the other hand, the mean cell number of expanded blastocysts of nonvitrified group was significantly improved in coculture group. However, the rate of embryo development except for the first day of culture was similar to that of medium alone.

The developmental potential of vitrified-thawed embryos appears to be retarded in conventional medium and Vero cell monolayer is capable to eliminate the postthaw deleterious effect of vitrification during the first 3 days of cultivation, but not for a longer period.