Expression of integrins by human trophoblast and differential adhesion to laminin or fibronectin

The process of placental implantation involves a series of transformationsof trophoblast from a single polarized epithelial layer restingon a basement membrane (villous trophoblast), to cellular aggregates(trophoblast columns) which ultimately disperse to invade uterinedecidua as individual cells (interstitial trophoblast). Suchtissue re-modelling is associated with changes in the constituentsof the extracellular matrix and in the expression of matrixreceptors by the cells, the most relevant being the family ofintegrins which bind to laminin and fibronectin. In this studywe show, by immunohistology and flow cytometry, a gradual lossof laminin receptors with the concomitant acquisition of fibronectinreceptors as trophoblast is transformed from the villous phenotype,through the cell columns, into the extravillous population.The pattern of staining for the ₅, ₆, ₁ and ₄ subunits indicatesthat the integrins expressed by trophoblast are predominantlythe ₅₁ and the ₆₄ heterodimers. We have also shown that isolatedtrophoblast cells assume a flattened, sessile phenotype whencultured on laminin but exhibit a more spreading, motile morphologywhen plated on fibronectin. In addition, numerous multinucleatedgiant cells are observed on a fibronectin substrate. Our datasuggest that the relative expression of laminin and fibronectinreceptors may determine the morphology and behaviour of trophoblastduring the process of implantation.