Early Pregnancy Factor is Required at Two Important Stages of Embryonic Development in the Mouse

PROBLEM: The importance of early pregnancy factor (EPF) at the pre‐implantation stage of development (days 1–3 post‐coitum [p.c.]) has been previously established in this laboratory. However, the role of EPF at the implantation stage (days 4.5–5 p.c.) has not been determined. This present study therefore investigates the role of EPF at this important developmental stage, both in vivo and in vitro. METHOD OF STUDY: Mated mice were passively immunized with anti‐EPF antibodies at the peri‐implantation stage (days 3.5–4 p.c.) and embryo implantation recorded. Parallel studies were conducted in vitro, where the effect of anti‐EPF antibodies on trophoblast outgrowth of blastocysts was determined. RESULTS: Administration of anti‐EPF antibodies in vivo at the peri‐implantation stage of development resulted in failure of embryos to implant. Similarly, trophoblastic outgrowth of blastocysts was adversely affected in the presence of anti‐EPF antibodies. CONCLUSIONS: These results, together with previous findings that anti‐EPF antibodies retard embryonic development when administered at the early pre‐implantation stage, clearly demonstrate that EPF is required by the embryo at two important developmental stages – the one–two‐cell stage and the peri‐implantation stage.