Changes in the distribution of fibronectin in the placenta during normal human pregnancy.

The distribution of fibronectin, a major extracellular glycoprotein with various activities that affect the proliferation and differentiation of cells, was studied by immunofluorescence staining in first-, second- and third-trimester placentas from normal human pregnancy. In early chorionic villi, fibronectin was localized mainly in the trophoblastic basement membranes; this fluorescence became weaker after 10 weeks' gestation. In term placenta, fibronectin was densely deposited around the fetal vessels but not in the trophoblastic basement membranes. Both syncytiotrophoblasts and cytotrophoblasts of the villous epithelium were virtually negative throughout pregnancy. However, the pericellular matrices of nonvillous trophoblasts in early chorionic villi were strongly stained. These findings suggest that fibronectin plays an important role in the proliferation of trophoblastic cells and the tissue organization of the placenta.