Tight junction proteins connect epithelial and endothelial cells and, importantly, form selective barriers and channels for paracellular transportation. Two types of tight junction proteins--the claudin family (claudins-1 to -27) and the TAMP family (occludin, Marvel-D2, and tricellulin)--can be distinguished molecularly and functionally. Recent work has focused on delineating the functional significance of differences in selective permeability, for example, by examining the regulatory mechanisms of tight junctions. This work is of great clinical importance as many inflammatory or...