Morphological and functional analysis of tight junction by overexpression or suppression of tight junction plaque protein ZO-1

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The carboxyl terminus of claudin-1, an integral membrane protein at tight junctions, binds to ZO-1 which is a plaque protein at tight junctions, and the actin binding region (ABR) localized at the carboxyl terminal half of ZO-1 binds to actin filaments. Our previous report showed that aberrant tight junction strands were formed along entire lateral plasma membrane when claudin-1 with myc-epitope at its carboxyl terminus was expressed in MDCK cells. In this study, we examined whether 1CL-ZO1Cmyc or 1CL-ZO1CΔABRmyc caused aberrant tight junction strands in MDCK cells. 1CL-ZO1Cmyc consisted of claudin-1, carboxyl terminal half containing ABR, and myc epitope. 1CL-ZO1CΔABRmyc consisted of claudin-1, carboxyl terminal half without ABR, and myc epitope. The frequency of aberrant strands was reduced both in 1CL-ZO1Cmyc- or 1CL-ZO1CΔABRmyc-expressing MDCK cells, but they still existed. These results suggest that other factors may be necessary for maintaining tight junction strands at the most apical region of lateral membranes.Claudin-1 which forms tight junction strands localized along the entire lateral membrane of rat epididymal epithelium, and this raises the possibility that aberrant tight junction strands may exist along lateral membrane. We found using freeze fracture method that aberrant strands only occasionally existed in lateral membrane of epididymal epithelium. This result suggests that claudin-1 may exist as a monomer and function as a pool of protein in lateral membrane. We reported immunohistochemical localization of claudin-2 and -10 in rat epididymis and condition of RT-PCR for mouse claudin transcripts.