Everything about Hemidesmosome totally explained
Hemidesmosomes (HD) are very small stud- or rivet-like structures on the inner basal surface of
keratinocytes in the
epidermis of skin. They are similar in form to
desmosomes when visualized by electron microscopy. While desmosomes link two cells together, 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.
The HD comprises two rivet-like
plaques (the inner and outer plaques), together with the anchoring
fibrils and anchoring
filaments 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
cytosolic 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.
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