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.