Overview spot desmosome (Macula
Pages with explanations are linked to the
text below the images if available! (Labelling is in German)
Spot desmosomes (Terminologia histologica: Maculae adhaerentes)
are spot-like very stable connections between cells. They
are present between epithelial cells, heart
muscle cells, arachnoidal cells and follicular dendritic cells. Spot
desmosomes are located beneath belt desmosomes
in junctional complexes
and in high concentration between the spine-like process connections of
the epithelial cells in stratified squamous epithelia.
The high traction stability of spot demosomes is caused by the "glue"
located in the intercellular space. The latter is formed by transmembrane
connecting proteins of the desmocollin- and desmoglein type
which from their anchoring sites in the cell
membrane reach into the intercellular cleft wich has a width
of 15-25 nm in these desmosome areas The endings of the mentioned
proteins from both cell membranes bind to each other in a way that a dense
intermediate line (mesophragm) is formed. Very electron-dense
plaques are attached to the inner side of the cell membrane. Desmocollin,
placoglobin and desmoglein are the major proteins encountered
in this other plaque region, i.e. directly at the cell
membrane. A less electron dense inner zone continues the plaque
in direction to the cytoplasm. It mainly consists of desmoplacin
and binds to intermediate filaments reaching
into the plaque which in epithelial ells are cytokeratins. These
tonofilaments belong to the cytoskeleton
and reach forward into the cytoplasm and
to neigbouring spot desmosomes. In this way loops reaching through many
neighboured desmosomes are formed that are also called 10F-desmosomes
since the attached intermediate filaments
are 10 nm thick.
Pemphigus vulgaris is a severe skin desease caused by autoantibodies
released from plasma cells against desmoglein
that impair formation of stable desmosomes.
The relatively few spot desmosomes encountered between smooth
muscle cells are smaller, have a reduced height and show less "glue"
material. They anchor intermediate filaments
of the desmin type in their plaques which have diametersof only
7 nm. For this reason these spot desmosomes are also called 7F desmosomes.
Desmin filaments are also encountered in the attachment
plaques which are typical for smooth muscle
cells. Other 7F desmosomes (with intermediate
filaments of the desmin type) are present between epithelial
cells of glands.
--> junctional complex,
contacts, cell membrane, epithelum
--> Electron microscopic atlas Overview
--> Homepage of the workshop
Some images were kindly provided by Prof. H. Wartenberg;
other images, page & copyright H. Jastrow.