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Adherens junctions provide strong mechanical attachments between adjacent cells through linkage of cytoplasmic face with cytoskeleton.
Identify the characteristics of adherens junctions in epithelial tissues
Adherens junctions are involved in a number of critical functions, including providing additional structural support. For example, they hold cardiac muscle cells tightly together as the heart expands and contracts.
Adherens junctions are built primarily from cadherins, whose extracellular segments bind to each other and whose intracellular segments bind to catenins. Catenins are connected to actin filaments.
Adherens junctions may serve as a regulatory module to maintain the actin contractile ring with which it is associated in microscopic studies.
Adherens junctions (or zonula adherens, intermediate junction, or "belt desmosome") are protein complexes that occur at cell–cell junctions in epithelial tissues. They are usually more basal than tight junctions. An adherens junction is defined as a cell junction whose cytoplasmic face is linked to the actin cytoskeleton. They can appear as bands encircling the cell (zonula adherens) or as spots of attachment to the extracellular matrix (adhesion plaques). A similar cell junction in non-epithelial cells is the fascia adherens. It is structurally the same, but appears in ribbon-like patterns that do not completely encircle the cells. One example is in cardiomyocytes.
Adherens junctions are composed of the following proteins :
cadherins. The cadherins are a family of transmembrane proteins that form homodimers in a calcium-dependent manner with other cadherin molecules on adjacent cells.
p120 (sometimes called delta catenin) binds the juxtamembrane region of the cadherin.
β-catenin or gamma-catenin (plakoglobin) binds the catenin-binding region of the cadherin.
α-catenin binds the cadherin indirectly via β-catenin or plakoglobin and links the actin cytoskeleton with cadherin.
Adherens junctions were, for many years, thought to share the characteristic of anchor cells through their cytoplasmic actin filaments. The accepted model has been that adherens junctions serve as a bridge connecting the actin cytoskeleton of neighboring cells through direct interaction. However, scientists have not been able to isolate the quaternary complex of cadherin-βcatenin-αcatenin-actin in vitro. Recent data (2005) demonstrate that membrane associated actin is several fold less stable compared to components of the adherens junctional complex. Additionally, it was found that monomeric α-catenin preferentially binds to the cadherin junction complex through β-catenin. Dimeric α-catenin preferentially binds to actin and suppresses Arp2/3 complex-mediated actin branching, thus acting as a molecular switch to regulate actin polymerization. Adherens junctions may serve as a regulatory module to maintain the actin contractile ring with which it is associated in microscopic studies.
Cadherins are the major transmembrane proteins, Adherens junctions are found in all tissues of the body, Adherens junctions link to the actin cytoskeleton, or Adherens junctions are more basal than tight junctons