Desmosome

Overview


A desmosome, also known as macula adherens (Latin: 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 30nm). Desmosomes are also found in muscle tissue where they bind muscles cells to one another.

Structure
They 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 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.

On the cytoplasmic side of the plasma membrane is a disk-like structure (attachment plaque) composed of very dense materials.

The main desmosomal linking proteins, desmoplakins and plakoglobins, bind to the intracellular domain of cadherins and form a connecting bridge to the cytoskeleton.

Blistering diseases
If the desmosomes 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 are 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.