week 3 - Cell polarity Flashcards
What are the 4 steps needed for cell polarity to develop in eukaryotes?
- Marking the site
- Decoding the site
- Establishing the site
- Maintaining the site.
What does budding yeast need to generate in order to grow and divide.
It must first have polarity.
In yeast cells - How can the birth scars that mark the sites of previous cell seperations be viewed?
staining with the fluorescent dye ‘calcofluor’ as it binds to chitin in yeast.
The position of the new bud depends on whether the cell is haploid or diploid.
in what patten do haploid and diploid cells bud in?
Haploid cells - bud in AXIAL pattern:
- mother and daughter cells form buds immediately adjacent to the previous site of cell separation.
Diploid cells - but in BIPOLAR pattern:
- mother and daughter bud at the poles of their ellipsoidal cells.
In the axial budding pattern, there are certain genes which have products that mark the mother bud neck in one cycle, as a marked site in the next cycle. (BUD10, BUD3, BUD4 and the septins.)
What happens if there is a mutation in these genes?
in mutants they now take up the biploar pattern and grow at opposite ends of the cell.
Mutations in these do not have defects in diploid cells.
BUD8, BUD9, RAX2 and components of the actin cytoskeleton are involved in the bipolar yeast budding pattern. what do they do?
What happens if these genes are mutated?
They mark the ends of the diploid cells.
If these are mutated, the biplar pattern is disrupted.
However, mutations in these genes, do not affect haploid cells as they continue to have an axial budding pattern.
There are some genes which are required for both axial and bipolar budding (BUD1, BUD2, BUD5).
These genes DEcode the axial and bipolar marks and signal to the machinery involved in generating the polarity axis.
What happens if there is a mutation in these genes?
Mutations in these genes cause a random budding pattern in both haploid and diploid cells.
so those genes are needed signal to the polarity establishment machinery the position of the bud site cortical landmarks.
1) What is the purpose of the polarity establishment machinery?
2)What are the important proteins involved in polarity establishment?
1) it is involved in generating the polarity axis and for polarisation of the cell cytoskeleton and other components.
2) The family of Rho-GTPases: which has Cdc42
How does Cdc function to establish cell polarity?
The binding partner for Cdc42 is Cdc24 (a GEF) and several GAPs.
When Bud1 is active, Cdc24 binds to the active form of Bud1 at sites marked for budding.
Cdc24 can then activate Cdc42 to allow the polarity site to become established.
What is Cdc42?
it is a small GTPase of the Rho Family.
it is regulated through cycles of activation and inactivation by its binding partners Cdc24 (a GEF) and several GAPs.
How do haploid cells mate in budding yeast?
Explain how MATa and MAT alpha cells secrete pheromones.
- Haploid cells can polarise and redirect their growth to mate. Different cell types sectrete pheromotes which gives the budding yeast projections - so response is chemotropic.
MATa secretes a-factor and MAT alpha secretes alpha factor.
MATa has receptors which bind alpha factor and MAT alpha has receptors which binds a-factor. These causes the downstream cell response.
What is Candidiasis and Candidaemia?
the fungus candida albicans is often benign but commonly causes mucosal disease.
- if it becomes invasive - there is substantial morbidity and can cause life threatening bloodstream infections.
Studies in budding yeast have greatly added to our knowledge of pathways involved in polarity development in the human pathogen Candida albicans.
what is central to the virulence of Candidiasis?
its ability to grow in yeast and in hyphal form.
