Zonula Adherens

Classical and desmosomal cadherins are constituents of different types of intercellular junctions. E-cadherin, the classical cadherin of epithelial cells, is part of the adherens junction (zonula adherens), which is attached to a belt of actin via the catenins. As the name says, desmosomal cadherins are part of the desmosomes, which are rivet-like structures that make focal connections between cells. Desmosomes are characterized by a... 

Muller H, Wieschaus E 1996 armadillo, bazooka, and stardust are critical for early stages in formation of the zonula adherens and maintenance of the polarized blastoderm epithelium in Drosophila. J Cell Biol 134 149-163... 

Figure 6 An electron micrograph of intercellular junctions between two human colon Caco-2 cells in culture. D, desmosome LS, lateral space mv, microvilli ZA, zonula adherens ZO, zonula occludens (i.e., tight junction). Bar equals 200 nm.

The tight junction is a component of the junctional complexes which join cells. Immediately basolateral to the tight junction is the zonula adherens (Figs. 6 and 7). Because the zonula adherens and the gap junctions are focal contact regions, they do not impact transport by the paracellular pathway. All of these junctions are specialized regions of the lateral cell membrane which demarcate the lateral space. In certain types of cells the lateral space is rather narrow and... 

The columnar, cuboidal basal cells are 18-20 xm in height and 8-10 iim in diameter. They form a monolayer adhered to a basement membrane by hemidesmosomes which are linked to anchoring fibrils of collagen type VII. At the lateral borders, basal cells are extensively interdigitated and joined together in places only by junctional complexes (zonula adherens), desmosomes, and gap junctions. 

This physiological barrier exists to provide protection from the entry of toxins, bacteria, and viruses from the apical side to the basolateral side, and it allows the passage of selective molecules and cells. The intercellular junctions can be divided into three different regions (1) tight junctions zonula occludens), (2) adherens junctions (zonula adherens), and (3) desmosomes. The intercellular junctions form an 80-nm-long tortuous path between the two adjacent cells that runs the entire lateral side of the cell, as discovered by transmission electron microscopic studies.4... 

Figure 2.2. The intercellular junction is mediated by proteins at different levels (1) tight junction (zonula occludens), (2) adherens junction zonula adherens), and (3) desmosomes.

Although cadherins do not exclusively cluster, the formation of adherens junctions is important for several tissue functions [18]. In epithelial tissues cadherins mediate zonula adherens junctions, which partition the cell membrane into apical and basolateral surfaces. In neuronal cells they mechanically stabilize synaptic junctions by mediating adhesion between the presynaptic and postsynaptic cells. In cardiac myocytes they establish intercalated discs, which both stabilize gap junctional coupling and transmit contractile forces. 

Alveolar epithelial cells (AECs) are connected with each other by various epithelial cell-cell contacts (i.e., tight junctions, adherens junctions and others). These contacts comprise several groups of proteins, such as occludin, zonula occludens (ZO-1, -2, -3), claudins, tricellulin, E-cadherin and intercellular adhesion molecule-1 (ICAM-1) [13-15], Their regulation and interplay, which has influence on epithelial barrier properties, however, is largely unknown to date. 

Careful observation at the borders of the enterocytes reveals a close juxtaposition of the membranes of adjacent epithelial cells, identified as zonulae occludens, located at the apical neck of the epithelial cells [168], The zonulae occludens is composed of apical complex the tight junctions and more basal structure underneath, the adherens junctions (also referred to as intermediate junctions) [169,170]. The adherens junctions are linked to the actomyosin ring at the cell circumference. This actin cytoskeleton, which forms a perijunctional area at the apical neck of the epithelial cells, is the cause for their polarized nature (Figure 1.12). The classical functions of tight junctions are the regulation of paracellular permeability and the restriction of apical basolateral intramembrane diffusion of lipids (cell polarity housekeeping). 

Kevil CG, Okayama N, Trocha SD, et al. Expression of zonula occludens and adherens junctional proteins in human venous and arterial endothelial cells role of occludin in endothelial solute barriers. Microcirculation 1998 5 197-210. 

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