Is oncofetal fibronectin a trophoblast glue for human implantation?

Using an antibody probe specific for the class of fibronectins that contain the oncofetal domain, it was shown that oncofetal fibronectin (onfFN) is present wherever trophoblasts make contact with extraplacental extracellular matrix (ECM). In normal human implantation sites, onfFN was localized to a highly specific region-the ECM connecting extravilous trophoblasts and trophoblastic cell columns to the uterine decidua. This same zone of onfFN was present in an analogous location in extrauterine gestations. Like these in vivo extravillous trophoblasts, isolated cytotrophoblasts in primary culture synthesized and secreted onfFN as they underwent differentiation. Furthermore, when cocultured with an ECM gel, cytotrophoblast aggregates deposited onfFN at cell-ECM contact sites, resembling early implanting trophoblasts in vivo. In the presence of cyclic AMP agonists, onfFN synthesis was inhibited markedly. It is concluded from these results that onfFN is a trophoblast protein that, under cAMP regulation, could mediate implantation and placental-uterine attachment throughout gestation.