ROLE OF TIGHT JUNCTIONS IN ESTABLISHING AND MAINTAINING CELL POLARITY

Supplementary Data

• Figure 4. The relationship between TJs and polarity: E-cadherin participates in polarization and formation of TJs. This is illustrated in confluent monolayers corresponding to monolayers of mixed MDCK (not stained) and MA104 cells stained before mixing with (5-(and6)-(((4-chloromethyl)benzoyl)amino)tetramethyl rodamine) (red), as seen in upper (A,B,C) and lateral (a,b,c) views. Green staining corresponds to E-cadherin (A,a), ZO-1 (B,b), and Na⁺,K⁺-ATPase (C,c) of MDCK cells. Notice that whereas E-cadherin and Na⁺,K⁺-ATPase expression requires neighboring cells to be of the same type (i.e. MDCK-MDCK), ZO-1 is expressed between MDCK-MDCK, MDCK-Ma104 and Ma104-Ma104. The fact that ZO-1 depends on the activation of E-cadherin, but can be expressed even in regions of MDCK cells where E-cadherin is absent, indicates that this molecule is not restricted to holding two neighboring cells together but can trigger a cascade of reactions (described by Balda et al 1991) that influences the distribution of ZO-1. On the contrary, expression of Na⁺,K⁺-ATPase, which is also triggered by Ca-activated cell-cell contacts (24), requires both neighboring cells to be of the same type.