Tight junctions act as a semi-permeable barrier to the transport of ions, solutes, and water and are considered to function as a fence that divides apical and basolateral domains of plasma membranes. Tight junctions coordinate a variety of signaling and trafficking molecules regulating cell differentiation, proliferation, and polarity and contain a number of junctional proteins including Occludin, Claudins, junctional adhesion molecules (JAMs), as well as multiple scaffold proteins. Occludin, the first identified component of tight junction strands, is thought function as a signal transmitter in multiple signaling pathways and can associate with multiple kinases and phosphatases such as PI3-kinase and protein phosphatases 1 and 2A. At least two isoforms of OCLN are known to exist.
