Molecular basis of the core structure of tight junctions

The morphological feature of tight junctions (TJs) fits well with their functions. The core of TJs is a fibril-like proteinaceous structure within the lipid bilayer, the so-called TJ strands. TJ strands in apposing plasma membranes associate with each other to eliminate the intercellular space. A network of paired TJ strands generates a continuous belt that circum-scribes each cell to establish the diffusion barrier to the solutes in the paracellular pathway throughout the cellular sheet. Identification and characterization of TJ-associated proteins during the last two decades has unveiled the nature of TJ strands and how they are spatially organized. The interplay between integral membrane proteins, claudins, and cytoplasmic plaque proteins, ZO-1/ZO-2, is critical for TJ formation and function. Tight junctions (TJs) are fascinating struc-tures in terms of their function and morphology. In 1963, using ultrathin-section electron microscopy, Farquhar and Palade described the fine structure of TJs together with adherens junctions (AJs) and desmosomes at the most luminal side of the lateral membran