Development of golden hamster embryos through the two-cell block in chemically defined medium.

The effect of increasing the embryo:medium volume ratio on overcoming the hamster two-cell block was examined. Two-cell golden hamster embryos from each superovulated female were cultured in microdrops (estimated at 0.75 microliter) or 100 microliter macrodrops of chemically defined medium (modified Tyrode's solution [TLP] plus glutamine, isoleucine, methionine, phenylalanine, and taurine). In 11 trials (i.e., with embryos from 11 donors), 28.6% of 269 embryos developed to the four-cell stage in microdrops, whereas only 2 (0.7%) embryos developed in the macrodrops. When two microdrops were used to culture the two-cell embryos from each donor (n = 8), 17.8% of 304 embryos developed to four cells. Increasing the embryo:medium volume ratio further by culturing all of the embryos from each donor (n = 10) in single microdrops resulted in 53.1% of 397 embryos developing to four cells. Conditioning of the culture medium by these embryos could not be demonstrated. Increasing the embryo:medium volume ratio may protect against loss of some intracellular component essential for growth of early-stage hamster embryos. Alternatively, increasing this ratio may permit embryos to reduce the concentration of a substance detrimental to their growth. This work represents the first report of cleavage of hamster two-cell embryos in vitro. These findings are a significant step towards our goal of obtaining complete preimplantation developmental of hamster embryos in vitro and may be helpful for solving the in vitro developmental blocks in embryos from other species.