Cell Polarity

Question 1

What is the apical domain?

Answer 1

The domain which faces the outside, often facing a lumen

Question 2

What is the basolateral domain?

Answer 2

The domain which has contact with the basement membrane

Question 3

How is immunofluorescence used to visualise polarity?

Answer 3

• 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

Question 4

What are tight junctions?

Answer 4

• Provide a diffusion barrier to prevent ions from travelling across the epithelium

Question 5

What is the difference between junction composition in vertebrates and invertebrates?

Answer 5

vertebrates = tight junction is above adherens
invertebrates and insects = adherens junction is above the tight junction

Question 6

What are the two main routes to generate diversity?

Answer 6

1. Polar mother cells divide to generate daughters that have inherited different components
2. Daughters could be equal at birth but then become different by exposure to different environmental signals

Question 7

What did Hamburger and Hamilton find?

Answer 7

Distinct cytoplasmic domains are differentially partioned to leech descendants and differences were reflected in cell lineages

Question 8

Why were C.elegans worms good for cell lineage experiments?

Answer 8

Because they have a defined number of cells

Question 9

What were the par genes found to do?

Answer 9

Play a key role in asymmetric division
In C.elegans asymetric division is what produces all the precursor cells in the embryo

Question 10

What happens in Par mutants?

Answer 10

• There is a partioning defective and can lead to very similar daughter cells or in the worst cases, daughter cells which are completely identical

Question 11

What does aPKC do?

Answer 11

• 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.

Question 12

How does fertilisation effect cell symmetry?

Answer 12

• 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)

Question 13

How is polarity established in the embryo?

Answer 13

1. Symmetry breaking (sperm entry)
2. Microtubule organising centre
3. Recruitment of the Par proteins, segregation to either side, includes spindle fibres
4. Mitosis

Question 14

How is polarity established using Par proteins?

Answer 14

• ## Kinases which are present at the apical side phosphorylate components that are meant to go to the basolateral side

Question 15

Which Par proteins go where?

Answer 15

• Par 1 and 2 at posterior
• Par3/6/aPKC at anterior
• Par5 maintains boundary

Question 16

Why are epithelial cells good at blocking out pathogens from the bloodstream?

Answer 16

Tight epithelium through tight junctions

Question 17

What does trafficking mean?

Answer 17

Regulated secretion of a particular component i.e. insulin into bloodstream or Igg to the baby in the uterus to their bloodstream

Question 18

What allows differential secretion?

Answer 18

The composition of cell surface receptors

Question 19

What process ensures transporters are in the right place during glucose absorption?

Answer 19

Vesicle trafficking

Question 20

What is vesicle trafficking?

Answer 20

Movement of membrane-bound vesicles within a cell facilitating the transport of various substances

Question 21

What is the role of ParM in bacteria?

Answer 21

• 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

Question 22

What can tumours do in regards to polarity?

Answer 22

• 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

Question 23

What are amotl proteins?

Answer 23

• 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