Desmosome

desmosomes

Cell adhesion in desmosomes

A desmosome, also known as macula adherens or macula adherentes (Latin for adhering spot), is a cell structure specialized for cell-to-cell adhesion. A type of junctional complex, they are localized spot-like adhesions randomly arranged on the lateral sides of plasma membranes.

Desmosomes help to resist shearing forces and are found in simple and stratified squamous epithelium. The intercellular space is very wide (about 30 nm). Desmosomes are also found in muscle tissue where they bind muscles cells to one another.

Structure

Desmosomes are molecular complexes of cell adhesion proteins and linking proteins that attach the cell surface adhesion proteins to intracellular keratin cytoskeletal filaments.

The cell adhesion proteins of the desmosome, desmoglein and desmocollin, are members of the cadherin family of cell adhesion molecules. They are transmembrane proteins that bridge the space between adjacent epithelial cells by way of homophilic binding of their extracellular domains to other desmosomal cadherins on the adjacent cell. Both have five extracellular domains, and have calcium-binding motifs.

The extracellular domain of the desmosome is called the Extracellular Core Domain (ECD) or the Desmoglea, and is bisected by an electron-dense midline where the desmoglein and desmocollin proteins bind to each other. These proteins can bind in a W, S, or λ manner.

On the cytoplasmic side of the plasma membrane, there are two dense structures called the Outer Dense Plaque (ODP) and the Inner Dense Plaque (IDP). These are spanned by the Desmoplakin protein.^[1] The Outer Dense Plaque is where the cytoplasmic domains of the cadherins attach to desmoplakin via plakoglobin and plakophillin. The Inner Dense Plaque is where desmoplakin attaches to the intermediate filaments of the cell.

Desmosomes function like rivets.

Blistering diseases

If the blank connecting adjacent epithelial cells of the skin are not functioning correctly, layers of the skin can pull apart and allow abnormal movements of fluid within the skin, resulting in blisters and other tissue damage. Blistering diseases such as Pemphigus vulgaris can be due to genetic defects in desmosomal proteins or due to an autoimmune response. These patients are often found to have antibodies that bind to the desmosomal cadherins and disrupt the desmosomes.

Hemidesmosomes

When visualized by electron microscopy, hemidesmosomes similar in appearance to desmosomes. Rather than linking two cells, hemidesmosomes attach one cell to the extracellular matrix. Rather than using cadherins, hemidesmosomes use integrin cell adhesion proteins. Hemidesmosomes are asymmetrical and are found in epithelial cells connecting the basal face to other cells.

References

1. ^ Bornslaeger EA, Corcoran CM, Stappenbeck TS, Green KJ (August 1996). "Breaking the connection: displacement of the desmosomal plaque protein desmoplakin from cell-cell interfaces disrupts anchorage of intermediate filament bundles and alters intercellular junction assembly". J. Cell Biol. 134 (4): 985–1001. PMID 8769422. PMC: 2120955. http://www.jcb.org/cgi/pmidlookup?view=long&pmid=8769422. 

• Green KJ and Jones JC. (1996). "Desmosomes and hemidesmosomes: structure and function of molecular components". The FASEB Journal 10 (8): 871–81.  Full text online
• Desmosomes Connect Intermediate Filaments from Cell to Cell in Molecular Biology of the Cell by Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts and Peter Walter (2002) Published by Garland Science. ISBN 0-8153-4072-9

External links

• MedEd at Loyola Histo/practical/epithelium/hp1-13.html
• Histology at BU 20502loa - "Ultrastructure of the Cell: microvillous border, Junctional Complex of absorptive epithelium"
• Histology at BU 20604loa - "Ultrastructure of the Cell: microvillous border and Junctional Complex, desmosomes and zonula adherens"
• Histology at BU 22502loa - "Ultrastructure of the Cell: cardiac muscle, intercalated disk"