Morphodynamics of outgrowths of mouse trophoblast in the presence and absence of a monolayer of uterine epithelium.

Mouse blastocysts were cultured in the presence and absence of a confluent uterine, luminal, epithelial monolayer in order to assess (10 comparative developmental abilities and (2) the existence and nature of embryo-uterine intercellular contacts. Embryonic development and mural trophoblast outgrowth were examined by light, transmission and scanning electron microscopy, and by time-lapse cinematography. The results demonstrate that cultured mouse blastocysts are capable of development that is essentially equivalent to the early egg cylinder stage in the presence and absence of a uterine epithelial substratum. Penetration of the endometrium and displacement of uterine luminal epithelial cell in vivo is paralleled in vitro by the displacement of uterine cells from the advancing edge of outgrowing mural trophoblast. The ability of mural trophoblast to continue to outgrow and displace uterine cells persists for a finite period of time. The findings are discussed with respect ot (1) the nature of embryo-uterine contact in vivo and (2) mechanisms proposed to explain trophoblastic displacement of uterine luminal epithelial cells during normal implantation.