Fig. 1

Many different cell types utilize tight junction (TJ)-dependent barriers. TJs are comprised of occludin (also called tricellulin), junctional adhesion molecules (JAMs), and claudins. Variability in the claudin component (claudin-1 through -24) dictates the permselectivity of the barrier while JAMs may also vary (JAM-A, -B, or -C), although their functional impact is less well understood. TJs are linked to the cytoskeleton through adapter proteins like zonula occludens (ZO-1, -2, and -3). a Columnar or cuboidal epithelia found in the upper airway, GI tract and parts of the nephron (proximal and distal tubules and collecting duct) form apical interlocking bands of tight junctions. b Squamous epithelia, such as in the lung, Bowman’s capsule and thin segments of the nephron, have interspaced TJs without regard to cell polarity. c Simple squamous endothelia of blood vessels, blood-brain barrier, and lymphatic vessels have irregularly spaced TJs that vary greatly in number based on tissue and vascular segment specific microenvironments