Tight junctions

Tight junctions are a type of cell junction that forms a continuous, impermeable barrier between adjacent cells in a tissue. They are crucial for maintaining the distinct internal environments of different tissues and organs in multicellular organisms.

Structure

Tight junctions are composed of a complex network of proteins that span the cell membrane. The primary components of tight junctions are claudins and occludin, which interact with each other and with other proteins to form a seal between cells. Other important proteins include junctional adhesion molecules (JAMs) and zonula occludens proteins (ZO-1, ZO-2, and ZO-3), which help to anchor the junction to the cytoskeleton.

Function

The primary function of tight junctions is to prevent the passage of molecules and ions through the space between cells. This is important for maintaining the homeostasis of tissues and organs, as it allows each to have a distinct internal environment. Tight junctions also play a role in maintaining cell polarity, as they separate the apical and basolateral surfaces of epithelial cells.

In addition to their barrier function, tight junctions are involved in signal transduction pathways that regulate cell proliferation, differentiation, and migration. They also play a role in the immune response, as they can regulate the passage of immune cells and antigens across epithelial barriers.

Clinical significance

Defects in tight junctions can lead to a variety of diseases. For example, mutations in claudin proteins have been linked to several genetic disorders, including hereditary deafness and hypomagnesemia. Altered tight junction function is also associated with many pathological conditions, such as inflammatory bowel disease, cancer, and infectious diseases.

See also

• Gap junction
• Adherens junction
• Desmosome