Progress in characterization of pre-implantation factor in embryo culturesand in vivo

PROBLEM: Pre-implantation factor (PIF), a small, embryo-derived peptide is detected in the maternal serum prior to implantation and is associated with successful pregnancy outcome. However, its identity is not known. METHOD OF STUDY: PIF was isolated from mouse embryo conditioned media and f rom pregnant porcine sera, using high-performance liquid chromatography (HP LC) followed by mass spectrometry. RESULTS: Conditioned culture media was separated by gel filtration chromato graphy followed by reversed phase chromatography. At each step, PIF activit y was determined by the lymphocyte/platelet binding autorosette assay (LPBA ). Mass spectrometry yielded a single peak with a mass of 1300 Da. The pept ide is, however, present in very low concentrations (fM), which has so far precluded complete identification. Pregnant porcine sera that exhibit poten t PIF activity were deproteinated by acetone and further fractionated by re versed phase HPLC. Active fractions contain peptides of molecular masses 52 3 and 551 Da. CONCLUSION: PIF, likely to be peptides, represents a novel substance relate d to pregnancy initiation and maintenance.