Tight junction

Tight junctions are a type of cell junction that forms a continuous, watertight seal around cells and serves as a barrier to prevent the leakage of ions and molecules through the space between cells. They are found in epithelial cells and endothelial cells, which line the surfaces and cavities of the body.

Structure

Tight junctions are composed of a complex network of proteins that link the cytoskeleton of adjacent cells. The primary proteins involved in the formation of tight junctions are claudins, occludin, and junctional adhesion molecule (JAM). These proteins interact with each other and with other cellular proteins to form the tight junction strand, a continuous, belt-like structure that encircles the cell.

Function

The primary function of tight junctions is to prevent the passage of molecules and ions through the intercellular space. They act as a barrier to the free diffusion of water and solutes between the apical and basolateral sides of the cell. This allows cells to maintain distinct internal environments and to regulate the movement of substances across the epithelial barrier.

Tight junctions also play a role in maintaining cell polarity by preventing the lateral diffusion of proteins and lipids between the apical and basolateral domains of the cell membrane. This is important for the proper functioning of epithelial and endothelial cells, which have distinct apical and basolateral functions.

Clinical significance

Alterations in the structure or function of tight junctions can lead to a variety of diseases. For example, mutations in the genes encoding tight junction proteins can cause hereditary deafness, renal disease, and skin disorders. In addition, the breakdown of tight junctions is a key feature of many inflammatory diseases, including inflammatory bowel disease and asthma.

Tight junctions are also a target for many pathogens. Some viruses and bacteria can disrupt tight junctions to gain entry into cells or to spread from cell to cell. This makes tight junctions a potential target for the development of new therapeutic strategies.

See also

• Gap junction
• Desmosome
• Hemidesmosome
• Adherens junction