COLOCALIZATION OF PLACENTAL LACTOGEN-I, PLACENTAL LACTOGEN-II, AND PROLIFERIN IN THE MOUSE PLACENTA AT MIDPREGNANCY

This study was undertaken to determine whether mouse placental lactoge n (mPL)-I, mPL-II, and proliferin (PLF) are expressed by the same popu lation of placental giant cells at midpregnancy. Tissue sections from Day 9 of pregnancy were analyzed by double immunofluorescence staining . Sections were stained for PLF by use of a rhodamine-conjugated secon d antibody, and for mPL-I or mPL-II by use of a fluorescein-conjugated second antibody. All three proteins were present in most of the same giant cells. The distribution of mPL-I and PLF among giant cells in vi tro was also examined. When placental cells from Day 7 of pregnancy we re cultured for 5 days, > 90% of the cells that immunostained for mPL- I also immunostained for PLF on the first 3 days of culture. Thereafte r, the percentage of cells that contained both proteins declined rapid ly while the percentage that contained only PLF increased, suggesting continued differentiation of the cells in vitro. These data demonstrat e that the same trophoblast giant cells express mPL-I, mPL-II, and PLF simultaneously at midpregnancy, suggesting that their gestational pro files in maternal blood during this period result at least partly from changes in gene expression in one population of cells and not from di fferentiation of several subsets of giant cells, each expressing only one member of the gene family.