Applications of imaging techniques to studies of epithelial tight junctions

The intercellular junctional complex, which consists of the tight junction (TJ), adherens junction, and desmosomes, mediates cell-cell adhesion in epithelia and endothelia. The TJ forms the apical-most portion of this complex in epithelia, serving as a fence to lateral diffusion of apical and basolateral membrane components and as a semi-permeable barrier or gate to the flow of ions and solutes through the paracellular pathway. The TJ consists of a series of integral membrane and cytoplasmic plaque proteins with complex interactions. Included among the TJ proteins are the claudins, which play a major role in mediating the charge and solute selectivity of the junction. Yet, the profile of claudin and associated protein expression differs among epithelia and the function and regulation of many of the TJ proteins remain unknown. This review discusses the application of techniques to discern the function, localization, and regulation of epithelial TJs based on examples from published studies.