DEVELOPMENTAL-CHANGES IN MOUSE PLACENTAL CELLS FROM SEVERAL STAGES OF PREGNANCY INVIVO AND INVITRO

Developmental changes in mouse placentae from the 6th to the 18th day of pregnancy were studied in vivo and in vitro. Placental volume increased from the 6th to the 18th day of pregnancy; however, the total number of cells per placenta reached a plateau on the 14th day. Decidual cells were predominant in the placenta on the 6th day. Placentae obtained from the 10th to the 18th day contained decidual cells, trophoblastic (labyrinth and spongiotrophoblast) cells, and trophoblast giant cells. Decidual cells increased in number from the 6th to the 10th but decreased on the 14th day, whereas trophoblastic cells increased linearly until the 14th day. Two types of placental cells were distinguished in vitro: small fibroblast-like cells and large flattened cells containing 2-3 nuclei. The large cells reacted to anti-desmin antibody, indicating their decidual character. The small cells reacting to anti-keratin antibody appeared to be trophoblastic cells. Decidual cells from all days of gestation were nonproliferative, regressing with time in culture. 17Beta-estradiol (E, 10(-9) and 10(-8) M), progesterone (P, 10(-10), 10(-9), and 10(-8) M), and a combination of E and P (10(-9) M each) stimulated proliferation of the trophoblastic cells only from the 6th and the 10th days. Keoxifene (2 x 10(-7) M), but not tamoxifen, significantly inhibited the E-induced proliferation of the trophoblastic cells. Both mouse and human epidermal growth factor (EGF, 10 and 100 ng/ml) and human transforming growth factor alpha (TGFalpha, 10 ng/ml) stimulated the proliferation of trophoblastic cells from the 6th and the 10th days but not from the 14th or the 18th day. The present results indicate that E, P, EGF, and TGFalpha were effective in stimulating the proliferation in vitro of placental trophoblastic cells from early pregnancy, but were ineffective in stimulating the proliferation of decidual cells from any day of gestation and that of trophoblastic cells from the 14th and the 18th days.