ABSTRACT
Note Added in Proof..............................................................................................385 Acknowledgments..................................................................................................385 References..............................................................................................................385
Multicellular organisms are formed by compartments of different composition. To maintain this compartmentalization, they possess specialized cells, epithelia and endothelia, that form selective barriers. These cells are polarized in an apical and a basolateral cell surface domain and establish an intercellular junctional complex. In epithelial cells, the most apical structure of the junctional complex is the zonula occludens or tight junction (TJ) (see Chapter 1 by Anderson and Cereijido and Chapter 2 by Schneeberger and Lyunch; Farquhar and Palade, 1963). TJs act as a
