STRUCTURAL AND FUNCTIONAL-PROPERTIES OF TROPHOBLAST CELLS OF MOUSE EGG-CYLINDERS INVITRO

Embryos at the egg-cylinder stage were obtained by culturing blastocys ts in vitro on an agarose surface for 4 days. The adhesiveness and out growth activity of the trophoblast of the egg-cylinder were compared w ith those properties of the flushed adhesive blastocyst. Trophoblast c ells of egg-cylinders were found to be more adhesive and their outgrow th activity greater than in the case of trophoblast cells of adhesive blastocysts. The cultured egg-cylinders presented two subpopulations o f giant trophoblast cells. They represent probably two stages of diffe rentiation of the same trophoblast population. The most distinctive mo rphological differences of these subpopulations were that the surface of one was covered with small blebs and the cytoplasm had relatively f ew ribosomes, while the surface of the other subpopulation was covered with large blebs and microvilli and the cytoplasm was rich in ribosom es and large, dense granules. The two types of giant trophoblast cells of the day 7 implantation site consist of one subpopulation whose cyt oplasm has few organelles, and the other subpopulation, whose cytoplas m is rich in ribosomes, lysosome-like bodies, and heterophagosomes. He nce, we conclude that the in vitro grown trophoblast cells have counte rparts in the in vivo implanting embryos. The lectin binding pattern o f the agarose cultured egg-cylinder trophoblast cells was similar to t hat of the adhesive and/or invasive trophoblast cells grown in vivo. T hus, the in vitro grown egg-cylinders are appropriate material for the analysis of trophoblast cells at the invasive stage of implantation.