Abstract
Tight junctions (TJ) are composed of a branching network of sealing strands. TJ regulate paracellular conductance and ionic selectivity. TJ components include the peripheral protein ZO-1, junctional adhesion molecules (JAM) and the integral proteins such as occludin and claudin. Claudins are a family of proteins that are the most important components in the tight junctions. The established paracellular transport barriers that control transportation of molecules within intercellular space. The present study focused on the expression of claudin, suggesting as major working molecules in the paracellular transport system. To study the regulation and roles of claudin family, we examined expression of mouse placental claudin family. Fifteen pregnant C57/BL6 mice were used in this study and TJ proteins including Claudin-1 to Claudin-24 expressions by real-time RT–PCR and Western blotting. The mice were divided into 3 groups depending on the gestational day (on Days 12, 16, and 20 of gestation).The localization of TJ proteins were examined by immunohistochemistry. After we identified the fluctuation of claudin expression during pregnancy, we assumed that the hormones are one regulator for claudin family. Therefore, we performed an in vivo study with hormone receptor antagonists (ICI 182, 780, and RU-486) for examining hormonal effect on claudin expression in the placenta. Forty-nine mice were divided into 7 groups. The changes of claudin expression were examined with real-time RT-PCR and Western blotting. In the transcription levels, Claudin-1, claudin-2, claudin-4, and Claudin-5 expression levels were relatively high compared to others in the claudin family in all periods of the pregnancy. The claudin-4 expression, which reduces permeability of ions, increased over a period of time. However, caludin-5 expression that is the responsive protein for a decrease in paracellular conductance, were decreased. Claudin-1 and -4 have been known as responsive genes for a decrease in paracellular conductance. On the other hand, claudin 2 and 5 have been known as increasing paracellular conductance. In addition, immunohistochemistry was performed to identify their localization for inferring permeability in placenta. In summary, we analysed the claudin expressions and presented possible important claudins among its family. Furthermore, their localization was also examined in the mouse placenta. In addition, the regulation of critically expressed claudins by pregnancy-associated hormones, E2 and P4, was examined. These results may provide functional and structural roles of claudins and their involvement in the maternal-fetal interaction and in the transportation of placental materials.
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