28.5: Anchoring Junctions
Anchoring junctions are multiprotein complexes that help cells connect to other cells and the extracellular matrix. Anchoring junctions are present on the lateral and basal surfaces of cells, providing strong and flexible connections. Focal adhesions are often formed due to cell interactions with the ECM substrata, which initiate signal transduction via kinase cascades and other mechanisms. Together, they provide stability and tissue integrity. There are three types of anchoring junctions: desmosomes, hemidesmosomes, and adherens.
Desmosomes appear as dense, symmetrical, disc-shaped plaques on the cell membrane. Adhesion proteins called cadherins are involved in plaque formation. The distinctive appearance is due to structural proteins on the inner surface of the cell’s membrane.
Hemidesmosomes look like half a desmosome and link cells to the basal lamina. While similar in appearance to desmosomes, they include the adhesion proteins called integrins rather than cadherins. These connections are essential in holding cells together.
Adherens junctions use either cadherins or integrins depending on whether they link to other cells or the matrix. The junctions are characterized by the presence of the contractile protein actin located on the cytoplasmic surface of the cell membrane. The actin can connect isolated patches or form a belt-like structure inside the cell.
The three anchoring junctions influence the shape and folding of the epithelial tissue.
Adapted from section 4.2 Epithelial tissue- Anatomy and Physiology 2 e, Openstax