Description of various types of intercellular junctions, their location and significance with examples and Multiple choice questions (MCQs)

1. Intercellular Junctions
13 January 2017
Resource Faculty: Dr. Ashish Shrestha
Dr. Vinay Marla
Prepared By:
Raman Dhungel
BDS 2014 , BPKIHS
1 ©RAMAN 2016

2. Objectives:
We shall be discussing:
about different types of intercellular junctions
about the location of these junctions
about the proteins and structural molecules
involved
about clinical abnormalities
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3. Contents:
 Introduction to intercellular junctions
Classification
Functions
Proteins involved
Clinical significance
Summary & MCQs
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4. What are intercellular junctions?
points of contact between the plasma membranes of
adjacent cells.
consist of multi-protein complexes that provide
contact between neighboring cells or between a cell
and the extracellular matrix.
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5. Composition:
Typically consist of three components:
a transmembrane adhesive protein,
a cytoplasmic adapter protein,&
a cytoskeletal filament.
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6. Functions of intercellular junctions:
Cell junctions may :
- Form fluid-tight seal between cells.
- Anchor cells together or to extracellular materials.
- Allow ions/molecules to pass from cell to another cell
within a tissue.
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7. Classification:
1. Occluding Junctions (Zonula occludens)
2. Adhesive/Anchoring Junctions
a) Cell-to-cell
◦ i) Zonula adherens
◦ ii) Macula adherens (Desmosome)
b) Cell-matrix
◦ i) Focal adhesions
◦ ii) Hemidesmosome
3. Communicating (Gap) Junctions
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9. Occluding/Tight junctions
closely associated areas of two cells whose membranes
join together forming a virtually impermeable barrier to
fluid.
control the passage of material through the intercellular
spaces (e.g., from the interstitium to the lumen of a gland).
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10. Occluding/Tight junctions
Most abundantly seen
in apices of epithelial
cells
Found only in
vertebrates
Can modify to form
leaky junctions
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11. Anchoring junctions(cell to cell)
-provide strength to the cell by mechanical attachment.
Two types on the lateral cell surface:
 zonula adherens ,which interacts with the network of actin
filaments inside the cell; and
 macula adherens or desmosome, which interacts with
intermediate filaments.
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12. Structure of
zonula adherens
Actin filaments of adjacent
cells are attached to the
E-cadherin–catenin
complex by -actinin and
vinculin.The E-cadherin–
catenin complex interacts
with identical molecules
embedded in the plasma
membrane of the adjacent
cell.
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13. Structure of
Desmosome
Intracellular attachment
plaque anchored with
intermediate filaments
are seen. The extracellular
portions of desmocollins
and desmogleins from
opposing cells interact
with each other in the
localized area of the
desmosome, forming the
cadherin “zipper.”
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14. Anchoring junctions (Cell to ECM)
Focal adhesions - anchor actin filaments of the cytoskeleton
into the basement membrane (e.g. between a leucocyte and a
vessel wall) &
Hemidesmosomes (hemi, Gk.- half) anchor intermediate
filaments of the cytoskeleton into the basement membrane.
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15. Focal Adhesion
On the cytoplasmic
side, the arrangement of
different actin-binding
proteins are seen. These
proteins interact with
transmembrane protein
integrin , the extracellular
domains of which bind to
proteins of the extracellular
matrix (e.g., fibronectin).
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16. Hemidesmosomes:
Hemidesmosomes look like half-
desmosomes that attach cells to
the underlying basement
membrane.
Rather than using desmogleins,
hemidesmosomes use
desmopenetrin cell adhesion
proteins,which are members of
Integrin family.
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17. Gap junctions:
clusters of intercellular channels that allow direct diffusion
of ions and small molecules between adjacent cells.
intercellular space narrows from 25 nm to 3 nm.
first discovered in myocardium and nerves between
adjacent cells because of their properties of electrical
transmission
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18. Structure of a gap
junction:
-gap junction between adjoining
cells showing the structural
components of the membrane
that form channels(connexons)
-formed by a circular array of
six subunits, dumbbell-shaped
transmembrane
proteins(connexins)
- connexons, have a central
opening of about 2 nm in
diameter.
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19. Clinical Significance:
Cell – cell and cell – matrix junctions have important
role in differentiation, development & function of
normal cells, tissues and organs.
However, function may be altered by genetic
abnormalities of junctional or cytoskeletal proteins, or
by autoimmune disease.
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20. Clinical Significance:
Mutation of gene of desmosome, hemidesmosome and
intermediate filament protein :
i. Epidermolysis bullosa
ii.Blistering skin disorder
Mutation of gene of extracellular matrix proteins:
i. Pemphigus vulgaris
ii.Pemphigus foliaceous
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21. Pemphigus Vulgaris
- an autoimmune
disease
-antibodies against
proteins
Blistering disease of
oral mucosa:
antibodies against
desmoglein-3 &
Skin: antibodies
against desmoglein-1
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22. Clinical significance:
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Mutation in the gene encoding connexin-26 (Cx26)
-congenital deafness.
Cx46 and Cx50 gene mutations- congenital
cataracts
bullous pemphigoid- presence of autoantibodies to
collagen XVII (BP180) and BP230.

23. Clinical Significance:
Mutation of connexins may also cause:
Demyelinating disease (Charcot-Marie Tooth)
 Oculodentodigital dysplasia –ODD syndrome
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24. Summary:
1. Occluding Junctions (Zonula occludens)
2. Adhesive/Anchoring Junctions
a) Cell-to-cell
◦ i) Zonula adherens
◦ ii) Macula adherens (Desmosome)
b) Cell-matrix
◦ i) Focal adhesions
◦ ii) Hemidesmosome
3. Communicating (Gap) Junctions
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25. 13 January 2017 ©RAMAN 201625
@ZAMIn

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27. MCQ
1. Junction that prevents two cell compartments from
mixing is:
A. gap junction
B. desmosomes
C. tight junction
D. cell junction
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28. MCQ
2. Pore- like connections between adjacent cells is an
example of
A. cell junction
B. desmosomes
C. tight junction
D. gap junction
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29. MCQ
3. Which of the following is a cell adhesion molecule
A. Lysin
B. Myosin
C. Integrin
D. Keratin
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30. MCQ
4. Tight junctions:
A. are essential for metabolic coupling
B. don’t occur in vertebrates
C. have the closest approach of two plasma
membranes of any junction
D. surround connexons
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31. MCQ
5. Hemi desmosome differs from spot desmosome in
that hemi desmosome:
A. connects cell to cell
B. connects extracellular matrix to extracellular
matrix
C. connects cell to extracellular matrix
D. has tonofilament , made up of intermediate
filament
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32. 13 January 2017
References:
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