The biology of epithelial cell tight junctions in the kidney.

Nearly 50 years have lapsed since the tight junction between epithelial cells was first identified by electron microscopy. The tight junction was once viewed as a static structure providing a barrier to paracellular movement and restricting proteins to the apical or basolateral membrane. Recent insights into the molecular composition of tight junctions reveal surprising complexity and dynamic regulation. Epithelia along the nephron exemplify a diversity of tight junctions that contribute to more than a 100-fold difference in permeability from the proximal tubule to the collecting duct. Tight junctions along the nephron form during kidney development and must reassemble after tubular injury. Hereditary diseases, animal models, and cell culture studies provide a variety of new perspectives on the function of tight junctions in health and disease.