Junctions and adhesion molecules in first trimester and term human placentas.

Placental tight and gap junctions and their adhesion molecules were studied by immunochemistry and electron microscopy in early and term placentas in order to clarify their pattern of expression during placental development. Early syncytio-cytotrophoblast contained tight junctions with occludin and gap junctions with connexins 40 and 43. At term, endothelial cells from arterioles had tight and gap junctions following each other. Occludin, claudins 3 and 5 were found at the paracellular clefts of endothelial cells together with connexins 32, 40 and 50. Stromal cells had mixed tight and gap junctions with connexins 32, 43, 50. Capillaries demonstrated interendothelial tight junctions with claudins 3 and 5, and small gap junctions. Taken together these observations showed that the numerous tight and gap junctions of the early placental syncytio-cytotrophoblast are observed in the foetal arterioles and capillaries in the term placenta. We conclude that the tightness of the placenta due to the junctions lying in the syncytio-cytotrophoblast in early pregnancy is maintained by the foetal endothelial layer in term pregnancy, with significant developmental changes of their transmembrane proteins.