RECAPITULATION OF THE PATHWAY FOR TROPHOBLAST GIANT-CELL DIFFERENTIATION IN-VITRO - STAGE-SPECIFIC EXPRESSION OF MEMBERS OF THE PROLACTIN GENE FAMILY

The trophoblast giant cell lineage is characterized by endoreduplicati on and expression of members of the PRL gene family. This report descr ibes the functional consequences following in vitro manipulation of a rat trophoblast cell line, termed Rcho-1. Rcho-1 cells can be cultured under conditions that promote proliferation or differentiation. Proli feration is maintained by culturing the cells in the presence of fetal bovine serum under subconfluent conditions. Differentiation is induce d by growing the cells to confluence and removing the mitogenic source . Differentiation is characterized by continued synthesis of DNA in th e absence of proliferation (endoreduplication) and the sequential expr ession of members of the PRL gene family. Western and Northern blot an alyses demonstrated that placental lactogen-I (PL-I) was first express ed, followed sequentially by PL-II, PRL-like protein-A, and PRL-like p rotein-C. The ontogeny of expression of members of the PRL gene family by the Rcho-1 cells recapitulated the pattern of in situ expression b y trophoblast giant cells of the junctional zone of the chorioallantoi c placenta. A notable difference between in, vivo trophoblast giant ce ll differentiation and in vitro Rcho-1 cell differentiation is the ter mination of PL-I expression in normal trophoblast giant cells developi ng in vivo and the continued expression of PL-I in differentiated Rcho -1 cell cultures. The Rcho-1 cell line provides a unique in. vitro mod el for investigating the initiation and maintenance of the trophoblast giant cell differentiation pathway.