PROLIFERATION AND DIFFERENTIATION OF TROPHOBLAST IN ESTABLISHMENT OF RAT CHORIOALLANTOIC PLACENTA

  • 1 January 1977
    • journal article
    • research article
    • Vol. 124  (DEC) , 675-687
Abstract
The morphological differentiation of the elements contributing to the chorio-allantoic placenta of the rat was studied between days 6-16 of gestation and DNA synthetic activity was investigated in animals killed 1 h after injection of 3H-thymidine. The chorionic lamina was formed from the epithelial cells lining the ectoplacental cavity although a contribution may also arise from ectoplacental cone cells at the mesometrial pole of the cavity. From day 8 onwards a high proportion of cells were labeled in both cone and lamina with the labeling index reaching a peak of about 80% at 10-11 days. There was no corresponding peak in mitotic activity, which remained at a high level in all regions up to day 12. The amount of thymidine incorporation, as judged by grain count/nucleus, was variable. At 9 days a significantly higher grain count was obtained in a central core of cells in the ectoplacental cone and at day 10 the grain density of labeling in the cone was very much heavier than in the lamina. This difference in labeling intensity was maintained until day 12 and there was no evidence of an influx of heavily labeled cells from the cone into the developing labyrinth.