The inner blood retinal barrier and tight junction proteins. Three integral proteins form tight junction complexes: occludin, claudins and junctional adhesion molecules (JAMs) & endothelial cell-selective adhesion molecule (ESAM). Tricellulin is a recently discovered tightjunction protein that contributes to the structure and function of tricellular contacts of neighboring cells in many epithelial tissues Occludin and claudins are trans-membrane proteins, predicted to have four trans-membrane and two extra-cellular domains, which are the major structural components of tight junction strands. There are also a group of proteins named membrane-associated guanylate kinase homologs that are positioned on the cytoplasmic surface of junctional contacts. Zonula occludens (ZO) belongs to the MAGUKs family and is thought to interact with occlude.