The regulation of early phase development of mammalian embryos

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This study was undertaken to elucidate the mechanism underlying the inability of mouse embryos to develop in culture past the 2-cell stage (2-cell block). Sodium fluoride (NaF, an inhibitor of enolase in glycolysis) significantly improved the rate of further development of 2-cell embryos in a dose-fashion manner. The removal of glucose and phosphate from the conventional medium improved the rate of development of 2-cell embryos to* 3 cell (42%), but the rate of development of 2-cell embryos to* 3 cells was enhanced (77%) when NaF at 2.5 mM was added to the medium without glucose and phosphate. The effect of NaF at 2.5 mM on ^<14>CO_2 and [^<14>C] lactate production form [^<14>C] glucose was also examined. NaF at 2.5 mM significantly inhibited both ^<14>CO_2 and [^<14>C] lactate production from [6-^<14>C] glucose, but not ^<14>CO_2 production from [1-^<14>C]-glucose, although it had no effect on the uptake of [^3H] deoxy-D-glucose (a non-metabolizable analogue of glucose) by the embryos. When the intracellular level of adenosine triphosphate (ATP) during early development of mouse embryos was examined, it was higher before rather than after cleavage. In addition, the ATP level was much higher before the 2nd cleavage 30 hr after insemination in unblocked embryos than that in blocked ones. These results suggest that the flow rate of glucose in glycolysis may regulate the development of 2-cell embryos to*3 cells, and that the intracellular level of ATP may be critical to early phase of mouse embryo development in vitro.