Adhesion molecules in implantation.

At implantation, trophectoderm attaches to the apical uterine luminal epithelial cell surface. Molecular anatomy studies in humans and mice, and data from experimental models have identified several adhesion molecules that could take part in this process: integrins of the alpha v family, trophinin, CD44, cad-11, the H type I and Lewis y oligosaccharides and heparan sulfate. The endometrial cell surface mucin MUC1 may play a role in both steric inhibition of attachment and selective glycan display. After attachment, interstitial trophoblast invasion occurs requiring a new repertoire of adhesive interactions with maternal extracellular matrix as well as stromal and vascular cell populations. Human anchorage sites contain columns of cytotrophoblasts in which self-attachment gives way progressively to adhesion to extracellular matrix and then interstitial migration. The beta 1 integrins are important during these later stages of implantation and placentation.