Embryonic alkaline phosphatase (EAP) is expressed during the preimplantation period of mouse development; however, its function is unknown. To determine whether the absence of an EAP gene affects development of preimplantation embryos, we studied mice homozygous for the disrupted EAP gene (EAP.ko mice). Time to reach morphologically definedpreimplantation stages, preimplantation loss, cell count, gestation length, and litter size were monitored, and it was found that EAP.ko embryos have slower development and higher rates of degeneration during in vitro preimplantation development. In vivo, EAP.ko mice had a longergestation, smaller litter size, and fewer cells at 93 hr after human chorionic gonadotropin injection. Furthermore, there was no compensation for the absence of EAP gene in EAP.ko embryos by other isozymes of alkaline phosphatase. We conclude that the presence of an active EAP gene is beneficial for preimplantation development of the mouse embryo, and its absence leads to fewer blastocysts in vitro, delayed parturition, and reduced litter size in vivo.

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