Cell Junctions, Structure, Function, and Regulation
357
Core plaque
(a)
(b)
Central
dense
stratum
Inner dense
stratum
Plasma
membrane
Outer dense
stratum
DSC 1a
DSG 1
ECD
10
0
10
20
30
40
50 nm
PM
ODP
IDP
PKP
PG
DP
IF
Fig. 12
Ultrastructure of desmosomal junction.
(a) Electron micrograph showing the
ultrastructure of a desmosome. The core region
is the intercellular space between the plasma
membranes of adjacent cells. The plaque regions
contain proteins whose interactions serve to
anchor the desmosome to intermediate
Flaments. The electron micrograph was kindly
provided by Andrew Kowalczyk. (b) Schematic of
desmosomal components. The cytoplasmic tail
of desmocollins (Dsc) and desmoglein (Dsg)
bind to plakoglobin (PG), plakophilin (Pkp), and
the amino-terminus of desmoplakin (Dsp) in the
outer dense plaque (ODP). The C-terminus of
Dsp binds to the intermediate Flaments.
(Reprinted with permission from Leung, C.L.,
Green, K.J., Liem, R.K.H. (2002) Plakins: a family
of versatile cytolinker proteins,
Trends Cell Biol.
12
, 37–45).
with an outer dense plaque located next
to the plasma membrane, a translucent
middle region, and an inner dense plaque
bordering
the
cytoplasm.
Intermediate
flaments converge on the desmosome,
Forming loops that pass into the inner
dense plaque. The dense plaques are sites
containing a high density oF proteins that
serve to attach the desmosomal cadherins
to the intermediate flaments.
Desmosomes contain cadherins From
two Families – the desmocollins (Dsc) and
the desmogleins (Dsg), with Dsc having
three isoForms and Dsg having Four iso-
Forms. Dsg2 and Dsc2 are the most widely
distributed oF the desmosomal cadherins
Found in simple epithelia, the basal layer
oF epidermis, and in myocardium, all oF
which are tissues that require cell adhesive
strength For a highly resilient junction.
Indeed, in the myocardium these cad-
herins are localized to the intercalated
discs that connect adjacent cardiac my-
ocytes to one another. Dsg3 and Dsc3 are
localized to the basal and suprabasal lay-
ers oF epidermis and stratiFying epithelia.
Dsg1 and Dsc1 have the most limited dis-
tribution and are Found in the highly diFFer-
entiated upper layers oF the epidermis. The
importance oF desmosomes to the mainte-
nance oF skin integrity is demonstrated by
Pemphigus foliaceus
and
Pemphigus vulgaris
,
two autoimmune blistering diseases that
result From the generation oF antibodies to
Dsg1 or to Dsg3 respectively.
2.4.1
Extracellular Domain of Desmoglein
and Desmocollin
The structural organization oF the extra-
cellular domain oF desmosomal cadherins
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