Cell-Cell interactions Flashcards
Name the 4 main categories of signalling and any sub-categories that are included
- Cytoplasmic connections between cells
- Cell-to-cell signals
- Cell-matrix
- Free diffusion of chemical signals between cells
- Adjacent cells (paracrine/ synaptic)
- Distant cells (endocrine)
Whats a juxtacrine signal?
Cell-to-cell contacts at the plasma membrane
Tell me about juxtacrine signals
- Have to have physical contact between cells
- signalling occurs at all cell-cell contact centres
In cell-cell contact, what happens at speciaised regions on the membrane and at non-specialised regions on the membrane ?
Specialised regions on the membrane
- Signalling and tissue organisation and behaviour
Non-specialised regions on the membrane
- Signalling and movement/ migration
What can cells have specialised regions for?
Cell-cell signals (desmosomes-tight junctions etc) in some cases
Name the cell adhesion molecules
Label which are the specialised contact cells
Label which are the non-specialised contact cells
Label which experience Homophilic interactions
Label which experience heterophilic interactions
What are the subtypes of cell-cell specialised junctions and their sub-sub types
1. cell-cell contacts at organised junctions
- tight junctions (vertebrates)
- Septate junctions (invertebrates)
2. Anchoring junctions
- Adherence junctions-adhering protein’s present (actin attachment sites)
- Desmosomes (intermediate filament attachment sites e.g. Keratin)
3. Communicating junctions
- Gap junctions
- Electrical synapses
Label the junctions of the epithelial cell
Whats a Functional syncytia?
Fused cells with multiple nuclei with intercellular cytoplasmic connections
What size molecules can diffuse through the limited size cytoplasmic pores ?
<1000 Da
What does the plasmodesmata between cells allow?
Electrical coupling from one cell to the other
The cell-cell gap junctions are made of what?
Homo and heteromeric made of connexin 4 pass proteins- 14 family members present either in singla gap junctions or in groups of thousands (e.g. cardiac intercalated discs)
Is the pores in cell-cell gap junctions regulatable ?
yes
What are the different types of connecting forms in cell-cell gap junctions ?
Can gap junctions be concentrated together?
yes
Tell me about the regulation of gap junctions?
The channels close at high Ca2+ concentrations and low pH, allowing regulation of the coupling of cells (stops apoptosis of one cell affecting those connected via gap junctions)
is phosphorylation reversable and regulated?
yes
Where does histidine and aspartate phosphorylation occur?
In plants and prokaryotes
What does phosphorylation cause a conformational change in?
Many enzymes and receptors causing activation or deactivation
What does the addition of a phosphate to a weakly polar R group such as serine/ threonine cause?
Turns a hydrophobic region into a hydrophilic/ charged region
what does conformational change allow?
substrate binding to occur at these regions
What two things can happen in cell signalling ?
- Either a cell surface receptor is a kinase which is activated by binding to its ligand
- A signal at the cell surface causes transmembrane proteins to cluster and bring binding parterns including kinase and their substrates together
What are kinase receptors activated by?
binding its ligand, dimerisation and autophosphorylation
what do kinase receptors produce?
An amplifying signalling cascade
What do non-kinase receptors lack?
catalytic domains
How do non-kinase receptors signal?
By clustering bringing binding partners e.g. kinases and their substrates together
What do tight junctions seperate?
Seperation of a lumen about an epithelium
Whats the main role of tight junctions?
Tight junctions also compartmentalise the membrane as well as the surrounding of the cells
This means that concentrations can be different in the apical and basolateral membrane
What transmembrane proteins can be found in tight junctions?
What do they form?
- Occludin
- Claudin
These form bands at the apex of the epithelial cells
They interact to form an impermeable seal
Act as signalling centres
Form homophilic interactions
Tell me the functions of the tight junctions ?
- Restricting apical/basolateral intramembrane diffusion
- Regulating signal cascades (PKA)
- Regulating gene expressions (transcription and mRNA processing) (ZONAB)
- Gating paracellular permeability
How do tight junctions maintain osmotic variance across epithelia?
By producing impermeable bonds between cells which limits the paracellular permeability
Name 2 anchoring junctions which strengthen links between cells ?
What do they both contain?
How do they vary?
Anchoring junctions
- Actin cytoskeleton (adherence junctions)
- Intermediate filaments (desmosomes)
Both contains members of the cadherin family
Variability:
- steaks or punctuate in non-epithelia
- belt desmosome- needed for formation of the tight junctions
Label this cell
What does the presence of Ca2+ cause in anchoring junctions?
dimerization of cadherins
What binding is present in anchoring junctions?
The binding is homophilic
How many cadherin repeats form a dimer in a cell?
5
Name the different cadherin’s in different junctions and examples of each?
And where they are found
- Classical Cadherins: E (epithelial) , N(Neuronal), P (placental) and VE (vascular endothelia) cadherins found in adherens junctions
- Atypical Cadherins: Desmoglein, Desmocollin found in desmosomes
How can Ca2+ be removed?
using EDTA
Cadherins also act as signalling centres concentrating kinases and their substrates, give an example
PI3 kinase
Anchoring junctions links
What do beta-catenin regulate?
Cell division
Tell me the role of PI3 Kinase?
drives cell growth
proliferation
differentiation
motility
survival
Tell me the role of Beta-catenin ?
cell proliferation
stem cell fates
Tell me about cell sorting importance in early formation of CNS- in vivo
What does too much N cadherin mean?
Neuronal tube can’t close which can lead to spina bifida and problems in brain formation
Where was the notch gene first described?
What did it show?
in the fly
It showed genetic inheritance is carried on chromosomes
Whats the ligand in the notch called?
delta
Tell me the steps to Notch signaling ?
1= Protease in golgi
2= Extracellular plasma membrane bound enzyme e.g. TACE
3= Intracellular membrane bound enzyme e.g. Gamma-secretase
What does Notch signaling regulate?
cell division
cell fate
proliferation
Lateral inhibition in fly’s
Tell me about Notch expression in;
Notch, ligands and receptor?
- induces and responds to notch
- Notch signaling inhibits cell division and induces differentiation
Tell me about notch expression in Notch and ligand?
- can induce a signal but doesn’t respond to one
Loss of notch ligand in skin cell remains in dividing state and results in what?
Hyperproliferation of cells and tumour formation
What are selectins?
A type of Lectin (sugar binding proteins)
Transmembrane proteins
Tell me types of Selectins and when they are expressed?
E (activated endothelia) and P (activated endothelia and platlets) selectin expressed by vein endothelial cells in inflammation
How do selectins work?
By binding to sugars on cell membranes and can cause cell attachmemnt to tissues
