Differential behavior of E-cadherin and occludin in their colocalization with ZO-1 during the establishment of epithelial cell polarity

At the initial stage of cell-cell contact of epithelial cells, primordial s pot-like junctions are formed at the tips of thin cellular protrusions radi ating from adjacent cells, where E-cadherin and ZO-1 are precisely coconcen trated (Yonemura et al., 1995, J. Cell Sci. 108:127-142). In fully polarize d epithelial cells, E-cadherin and ZO-1 are completely sorted into belt-lik e adherens junctions (AJ) and tight junctions (TJ), respectively. Here we e xamined the behavior of occludin, an integral membrane protein consisting o f TJ, during the establishment of epithelial cell polarity. Using confocal immunofluorescence microscopy, we quantitatively compared the spatial relat ionship of occludin/ZO-1 with that of E-cadherin/ZO-1 during epithelial cel lular polarization by replating or wounding cultured mouse epithelial cells (MTD1-A). At the initial stage of cell-cell contact, E-cadherin and ZO-1 a ppeared to be simultaneously recruited to the primordial form of spot-like junctions at the tips of cellular processes which showed no concentration o f occludin. Then, as cellular polarization proceeded, occludin was graduall y accumulated at the ZO-1-positive spot-like junctions to form belt-like TJ , and in a complementary manner E-cadherin was sorted out From the ZO-1-pos itive spot-like junctions to form belt-like AJ. The molecular mechanism of TJ/AJ formation during epithelial cellular polarization is discussed with s pecial reference to the roles of ZO-1. (C) 1999 Wiley-Liss, Inc.