Expression of ZO-1 and occludin in normal human placenta and in hydatidiform moles

Zonula occludens-1 (ZO-1) and occludin are key molecules in cell-cell conta cts. They are tight junction constituents and therefore play a pivotal role in tissue differentiation and organogenesis. In the present report-we have investigated the expression of ZO-1 and occludin in normal human placentae and in hydatidiform moles using immunohistochemical and Western blot analy ses. In normal placentae, ZO-1 and occludin were mainly localized in the ap ical part of the syncytium, in cell-cell contacts between syncytium and vil lous cytotrophoblastic cells as well as between the latter, Extravillous cy totrophoblast of cell islands and cell columns was positive for ZO-1 and oc cludin in the cell layers proximally located to the villous stroma whereas the cytotrophoblastic cells, distally located from the villous stroma, were totally negative, Furthermore, fetal vessels showed a positive staining pa ttern for ZO-1 throughout gestation, whereas a positive reaction for occlud in was produced mainly at term, A striking result was the altered expressio n of ZO-1 and occludin in partial and complete moles. In 11 moles, these tw o molecules were not expressed at all, while in the other nine, their expre ssion was only cytoplasmic in syncytium and villous cytotrophoblastic cells , These findings suggest that ZO-1 and occludin participate in normal place ntal development, maintaining the organization and functions of different t issue components. The down-regulation and/or dysregulation of these two mol ecules may be related to phenotypic changes associated with epithelial cell transformation of the chorionic villi in partial and complete moles.