| Description |
Tight junctions are specialized regions of cell-cell contact that seal the paracellular space. TJ strands on adjacent cells are presumed to interact with each other to form a "molecular gasket" that prevents ions, water and other molecules from leaking between cells. In addition to this barrier function, the fence function of tight junctions plays an important role in maintaining epithelial cell polarity by blocking the diffusion of membrane proteins between apical (luminal) and basolateral cell surfaces. At one time, the only transmembrane protein known to be associated with tight junctions was occludin, a ~65kD protein with four transmembrane domains. Despite widespread expectation, a critical structural role for occludin in TJ strands was ruled out by the observation of apparently normal tight junctions formed between cells disrupted at both occludin alleles. Fortunately, a closer examination of isolated tight junctions uncovered two related ~22kD, four-transmembrane domain proteins
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