The syncytiotrophoblast, which regulates maternal-fetal transfer of drugs, consists of a single layer in humans, but two layers, i.e., SynI and SynII, in rodents. Polar distribution of transporters in the apical and basal plasma membranes of syncytiotrophoblast is important for placental function in terms of vectorial transport of substrates, but the mechanisms that control protein distribution in the syncytiotrophoblast remain unclear. We have previously established rat syncytiotrophoblast cell lines, TR-TBT 18d-1 and TR-TBT 18d-2, which retain characteristics of SynI and SynII, respectively. In this study, we aimed to characterize the gene expression profiles in the two layers by using these cell lines. DNA microarray analysis indicated that more than 25 mRNAs, including cytoskeleton binding proteins, ezrin and CLP36, are differentially expressed between TR-TBT 18d-1 and TR-TBT 18d-2. Quantitative real time-polymerase chain reaction (PCR) analysis indicated that mRNA expression of ezrin, CLP36, CCN1, and CCN2 is higher in TR-TBT 18d-1 and mRNA expression of elf-1a, hsc70 and flot2 is higher in TR-TBT 18d-2, compared with their counterparts. Immunohistochemical analysis indicated that ezrin is expressed in rat placental villi in vivo, and is located on the apical membranes of TR-TBT 18d-1, while CLP36 is located in the apical and basal sides of TR-TBT 18d-1. The expression of ezrin was highest at gestational days 14 and 18 and was highest among the ezrin/radixin/moesin (ERM) family members. These results may help to clarify the mechanisms controlling polarization of the syncytiotrophoblast and the significance of the double epithelial layers in rat and mouse.
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