Mouse embryos and uterine epithelia show adhesive interactions in culture.

To investigate the cellular mechanisms in preimplantation adhesion of the mammalian blastocyst to uterine epithelium, it is essential to avoid the complexities of the maternal environment but at the same time prevent the introduction of competing artificial surfaces, to which embryos preferentially adhere. We demonstrate here that sealed vesicles of isolated uterine epithelium cultured together with blastocysts in hanging drops provide an optimum system for encouraging and observing the adhesive interactions. The responses of the embryonic and maternal cells were identical to those known in vivo. Microvilli were seen on both surfaces, and in places the membranes were drawn into close apposition with some desmosomelike junctions. After blastocyst adhesion occurred trophoblast cells invaded the epithelium and showed phagocytic activity, closely resembling the invasion that follows adhesion during normal pregnancy in mice. Key words blastocyst, cell adhesion, implantation, microvilli, phagocytosis, trophoblast.