Hemidesmosome
Encyclopedia
Hemidesmosomes are very small stud- or rivet-like structures on the inner basal surface of keratinocyte
s in the epidermis of skin. They are similar in form to desmosome
s when visualized by electron microscopy. While desmosomes link two cells together, hemidesmosomes attach one cell to the extracellular matrix. Rather than using desmoglein
s, hemidesmosomes use desmopenetrin cell adhesion proteins. Hemidesmosomes are asymmetrical and are found in epithelial cells connecting the basal face to other cells.
The HD comprises two rivet-like plaques (the inner and outer plaques), together with the anchoring fibrils and anchoring filament
s these are collectively termed the HD-stable adhesion complex or HD-anchoring filament complex.
Together, the HD-anchoring filament complex forms a continuous structural link between the basal keratinocyte keratin
intermediate filaments and the underlying basement membrane
zone (BMZ) and dermal components. Over the past decade, these structures have been shown to comprise a variety of some 10 or more molecular components.
An example configuration of a hemidesmosome might consist of cytosol
ic keratin, non-covalently bonded to a cytosolic plectin
plaque, which is bonded to a single-pass transmembrane
adhesion molecule such as the α6β4 integrin
. The integrin might then attach to one of many multi-adhesive proteins such as laminin
, resident within the extracellular matrix
, thereby forming one of many potential adhesions between cell and matrix.
Electron microscopic
analysis of the epidermal basement membrane zone (BMZ) reveals that it comprises a narrow and sometimes folded interface between the basal keratinocytes and the dermis
. At high power, several complex structures are observed within the epidermal BMZ. The epidermal BMZ shows small (< 0.5 micrometers), regularly spaced electron dense structures which are the hemidesmosomes. Thin, extracellular, electron-dense lines, parallel to the plasma membrane, subjacent to the outer plaque are visible in one third of HDs and are termed sub-basal dense plates (SBDPs).
Anchoring filaments traverse the lamina lucida space and appear to insert into the electron dense zone, the lamina densa. Beneath the lamina densa, loop-structured, cross-banded anchoring fibrils extend more than 300 nm beneath the basement membrane within the papillary dermis. The length of these loops may enable them to link or encircle dermal collagen
fibers or other components such as those of the elastic microfibril network.
Keratinocyte
Keratinocytes are the predominant cell type in the epidermis, the outermost layer of the human skin, constituting 95% of the cells found there. Those keratinocytes found in the basal layer of the skin are sometimes referred to as "basal cells" or "basal keratinocytes"...
s in the epidermis of skin. They are similar in form to desmosome
Desmosome
A desmosome , also known as macula adherens , is a cell structure specialized for cell-to-cell adhesion...
s when visualized by electron microscopy. While desmosomes link two cells together, hemidesmosomes attach one cell to the extracellular matrix. Rather than using desmoglein
Desmoglein
The desmogleins are a family of cadherins consisting of proteins DSG1, DSG2, DSG3, and DSG4. They play a role in the formation of desmosomes that join cells to one another....
s, hemidesmosomes use desmopenetrin cell adhesion proteins. Hemidesmosomes are asymmetrical and are found in epithelial cells connecting the basal face to other cells.
The HD comprises two rivet-like plaques (the inner and outer plaques), together with the anchoring fibrils and anchoring filament
Protein filament
In biology, a filament is a "long chain of proteins, such as those found in hair, muscle, or in flagella". They are often bundled together for strength and rigidity. Some cellular examples include:*Actin filaments*Microtubules*Intermediate filaments...
s these are collectively termed the HD-stable adhesion complex or HD-anchoring filament complex.
Together, the HD-anchoring filament complex forms a continuous structural link between the basal keratinocyte keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
intermediate filaments and the underlying basement membrane
Basement membrane
The basement membrane is a thin sheet of fibers that underlies the epithelium, which lines the cavities and surfaces of organs including skin, or the endothelium, which lines the interior surface of blood vessels.- Composition :...
zone (BMZ) and dermal components. Over the past decade, these structures have been shown to comprise a variety of some 10 or more molecular components.
An example configuration of a hemidesmosome might consist of cytosol
Cytosol
The cytosol or intracellular fluid is the liquid found inside cells, that is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondrion into compartments....
ic keratin, non-covalently bonded to a cytosolic plectin
Plectin
Plectin is a giant protein found in nearly all mammalian cells which acts as a link between the three main components of the cytoskeleton: actin microfilaments, microtubules and intermediate filaments. In addition plectin links the cytoskeleton to junctions found in the plasma membrane that...
plaque, which is bonded to a single-pass transmembrane
Transmembrane protein
A transmembrane protein is a protein that goes from one side of a membrane through to the other side of the membrane. Many TPs function as gateways or "loading docks" to deny or permit the transport of specific substances across the biological membrane, to get into the cell, or out of the cell as...
adhesion molecule such as the α6β4 integrin
Integrin
Integrins are receptors that mediate attachment between a cell and the tissues surrounding it, which may be other cells or the ECM. They also play a role in cell signaling and thereby regulate cellular shape, motility, and the cell cycle....
. The integrin might then attach to one of many multi-adhesive proteins such as laminin
Laminin
Laminins are major proteins in the basal lamina , a protein network foundation for most cells and organs...
, resident within the extracellular matrix
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
, thereby forming one of many potential adhesions between cell and matrix.
Electron microscopic
Electron microscope
An electron microscope is a type of microscope that uses a beam of electrons to illuminate the specimen and produce a magnified image. Electron microscopes have a greater resolving power than a light-powered optical microscope, because electrons have wavelengths about 100,000 times shorter than...
analysis of the epidermal basement membrane zone (BMZ) reveals that it comprises a narrow and sometimes folded interface between the basal keratinocytes and the dermis
Dermis
The dermis is a layer of skin between the epidermis and subcutaneous tissues, and is composed of two layers, the papillary and reticular dermis...
. At high power, several complex structures are observed within the epidermal BMZ. The epidermal BMZ shows small (< 0.5 micrometers), regularly spaced electron dense structures which are the hemidesmosomes. Thin, extracellular, electron-dense lines, parallel to the plasma membrane, subjacent to the outer plaque are visible in one third of HDs and are termed sub-basal dense plates (SBDPs).
Anchoring filaments traverse the lamina lucida space and appear to insert into the electron dense zone, the lamina densa. Beneath the lamina densa, loop-structured, cross-banded anchoring fibrils extend more than 300 nm beneath the basement membrane within the papillary dermis. The length of these loops may enable them to link or encircle dermal collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
fibers or other components such as those of the elastic microfibril network.
See also
- focal adhesionFocal adhesionIn cell biology, focal adhesions are specific types of large macromolecular assemblies through which both mechanical force and regulatory signals are transmitted. More precisely, they can be considered as sub-cellular macromolecules that mediate the regulatory effects In cell biology, focal...
- desmosomeDesmosomeA desmosome , also known as macula adherens , is a cell structure specialized for cell-to-cell adhesion...
- epidermolysis bullosaEpidermolysis bullosaEpidermolysis bullosa is an inherited connective tissue disease causing blisters in the skin and mucosal membranes, with an incidence of 1/50,000. Its severity ranges from mild to lethal. It is caused by a mutation in the keratin or collagen gene....
- junctional complex