Cell Polarity Flashcards
What is the apical domain?
The domain which faces the outside, often facing a lumen
What is the basolateral domain?
The domain which has contact with the basement membrane
How is immunofluorescence used to visualise polarity?
- Using an antibody to find where a protein is in the cell and a secondary antibody to visualise
- Can observe the apical and basolateral domain
- Can also see the lateral domain which is the bit in the middle where the junctions come together
- Tight junctions surround the cell
What are tight junctions?
- Provide a diffusion barrier to prevent ions from travelling across the epithelium
What is the difference between junction composition in vertebrates and invertebrates?
vertebrates = tight junction is above adherens
invertebrates and insects = adherens junction is above the tight junction
What are the two main routes to generate diversity?
- Polar mother cells divide to generate daughters that have inherited different components
- Daughters could be equal at birth but then become different by exposure to different environmental signals
What did Hamburger and Hamilton find?
Distinct cytoplasmic domains are differentially partioned to leech descendants and differences were reflected in cell lineages
Why were C.elegans worms good for cell lineage experiments?
Because they have a defined number of cells
What were the par genes found to do?
Play a key role in asymmetric division
In C.elegans asymetric division is what produces all the precursor cells in the embryo
What happens in Par mutants?
- There is a partioning defective and can lead to very similar daughter cells or in the worst cases, daughter cells which are completely identical
What does aPKC do?
- Protein kinase which localizes to the apical membrane and interacts with other polarity proteins to organize the cytoskeleton and maintain cell shape.
- ensures the unequal distribution of cellular components to daughter cells with different fates.
How does fertilisation effect cell symmetry?
- Sperm entry point defines the posterior pole and the axis of polarity
- Sperm delivers a microtubule organising centre into what will become the posterior pole, Can recruit some of the Par proteins (which have kinasing ability)
How is polarity established in the embryo?
- Symmetry breaking (sperm entry)
- Microtubule organising centre
- Recruitment of the Par proteins, segregation to either side, includes spindle fibres
- Mitosis
How is polarity established using Par proteins?
- ## Kinases which are present at the apical side phosphorylate components that are meant to go to the basolateral side
Which Par proteins go where?
- Par 1 and 2 at posterior
- Par3/6/aPKC at anterior
- Par5 maintains boundary
Why are epithelial cells good at blocking out pathogens from the bloodstream?
Tight epithelium through tight junctions
What does trafficking mean?
Regulated secretion of a particular component i.e. insulin into bloodstream or Igg to the baby in the uterus to their bloodstream
What allows differential secretion?
The composition of cell surface receptors
What process ensures transporters are in the right place during glucose absorption?
Vesicle trafficking
What is vesicle trafficking?
Movement of membrane-bound vesicles within a cell facilitating the transport of various substances
What is the role of ParM in bacteria?
- ParM forms polarised actin filaments
- It interacts with ParR which associates with the plasmid
- Moves the plasmids to either side as the actin filament extends
What can tumours do in regards to polarity?
- Cause cells to lose polarity causing the tumour to become malignant
- Most cancers are epithelial in origin- loss of apical and basal polarity can lead to the disorganisation of epithelial layers
What are amotl proteins?
- Scaffold proteins (regulators of key signalling pathways)
- Interact with components of junctions and actin
- Link actin cytoskeleton to junctions
- Overexpression of amotl proteins in cancer cells as soon as polarity is effected
- Important protein in cancer progression
