Tight Junctions and Gap Junctions

Abstract

Tight junctions have several major functions. They seal the intercellular space in epithelial and endothelial cell layers and prevent free paracellular passage of substances. They determine the polarity of epithelial cells by creating a boundary between the apical domain of the plasma membrane and the basolateral domain and prevent diffusion of lipids and proteins between them. Tight junctions recruit multiple cytoskeletal and signalling molecules at their cytoplasmic surfaces, which is seen in connection with regulatory processes involving the actinomyosin cytoskeleton and with intercellular adhesion signalling within epithelia and endothelia. Tight junctions may occur independently of other cell contacts but are more often part of junctional complexes forming an occluding belt in the top position (cf. Fig. 83).