Epithelium 2 Flashcards
Junctional complexes are found pretty much in every types of cells except…
blood cells
When referring to the apical portion of the cell domain, which part of the cell does it pertain to?
top
What are zonula occludens and where are they normally found in a cell?
tight junctions normally found near the apical portion of the lateral domain
Where are zonula adherens normally found in a cell?
immediately below zonula occludens
What are maculae adherens?
desosomes: spot connections between two cells (think of staples between two sheets of paper)
In what order will you find the junctional complexes in the epithelium?
zonula occludens (apical)
zonula adherens
macula adherens
What is another name for gap junction?
nexus
Where do you find hemidesmosomes?
in basal domain
What is the general blueprint for a junctional complex?
1) cytoskeletal elements (actin microfilaments or intermediate filaments)
2) intracellular anchor proteins
3) CAMs (aka transmembrane adhesion proteins)
What does intracellular anchor proteins anchor?
connects cytoskeletal component to CAMs
What are occludins and claudins and what do they do?
CAMs, they form tight connection with one another (ex. occludin from one cell connects to the occludin of the next cell, not occludin to claudin)
What does the baterium Helicobacter pylori do to zonula occludens?
disrupts occludins (tight junctions) in the stomach, making cells more susceptible to acidic injury
What does cholera toxins do to zonula occludens?
toxic to zonula occludens proteins (intracellular), dirsupts the junctional complex, leading to loss of fluids
Gene encoding for a specific claudin in renal epithelial cells results in what?
excessive loss of magnesium ions in urine
Which claudin protein is lost in brain cancers?
claudin 5
Which missing claudin protein can cause deafness?
claudin 9
Why is the ratio of claudins to occludins important?
ratio of claudins to occludins dictates the degree of permeability that exist in tight junctions.
If you want less permeability in tight junctions, which should be higher? Claudins or occludins?
high claudins and low occludins
What would the ratio of claudin to occludin be in the blood brain barrier?
high occludin and low claudin (low permeability)
What role do tight junctions play in establishing polarity within a cell?
tight junctions keep receptors at the apical domain because they can’t cross, this allows for establishment of polarity within the cell
What type of cytoskeletal elements will you find in macula adherens?
intermediate filaments (not actin)
What’s an example of CAM found in zonula adherens?
E-cadherin
What kind of CAMs can be found in macula adherens?
desmocollin and desmoglein
What causes Pemphigus?
the body produces antibodies against demogleins (important CAM found in desmosomes)
What are focal adhesions?
anchors cell to proteins of the ECM
What kind of CAMs can be found in focal adhesions?
integrin
What is hemidesmosome?
anchor basement domain of cell to underlying basal lamina
What transmembrane protein is involved in hemidesmosomes?
collagen type XVII
What is bullous pemphigoid?
body produces antibodies against collagen XVII, causes separation between the cell and basal lamina allowing fluid to build up in between
Based on the general blueprint for junctional complexes, what component does integrin represent?
CAM
What do nexus (gap junctions) do?
allow cells to communicate with each other
What transmembrane protein (CAM) can be found in nexus?
connexins
Describe the structure of connexon.
made up of 6 connexins
Why would disruptions in nexus cause cardiac arrhythmias?
cardiac muscles have to contract in unison, without gap junctions, the cells cannot communicate with each other
What other conditions can disruptions of nexus cause?
- female infertility
- neuropathy
- deafness
- congenital cataracts
What can cause loosening of junctional complexes?
mutation in cadherin, catenin, or integrin
Where are catenin and vinculin found?
intracellular proteins found in zonula adherens
What does loosening of junctional complexes provide for cancer cells?
the ability to become motile (one of the steps to become metaplasia)
What type of molecule is cadherin?
CAM
Loss of cadherin is found in what and why?
cancerous cells because junctional complexes have been disrupted
What does altered expression of integrin do?
allow cells to migrate to extracellular environment
