cell polarity in yeast Flashcards
what are the 4 stages in generating cell polarity?
- marking the site
- decoding the site
- establishing the site
- maintaining the site
what stain is used to follow budding events?
calcofluor- binds chitin
what do cells with axial gene mutants show in haploid cells?
bipolar budding
how were genes involved in bud site selection identified?
identified the genes that allowed recovery of cells with random budding pattern to be recovered to normal phenotype
genes for axial budding
BUD 10,3,4 and septins
what do these axial budding proteins do
mark the mother bud neck during one cycle as the site for budding of the next cycle
bipolar budding genes
BUD8,9 AND RAX2 and actin cytoskeleton
where does bud8 mark?
distal end of cell
where does bud9 mark?
proximal end of cell- adjacent to bud scar
what do double bud8bud9 cells do in diploids?
bud randomly
what is the role of rax2p?
is present at both poles and maintains bipolar budding over multiple generations
what genes are required for both patterns?
bud1, 2 and 5
what is the role of these genes required for both patterns?
decode the axial/bipolar marks and signal to machinery involved in generating the polarity axis
what do mutations in bud 1,2,5 cause?
random budding
bud 1 is a GTPase and is activated by what?
bud5
bud1 GAP is what?
bud2
how did they identify polarity establishment genes?
found that many mutants blocked in signalling and could not advance cell cycle. cdc42,24,43 mutants could not direct their growth to form a new bud
at restrictive temp what can ts cdc42 mutants not do?
establish polairty
bud1 recruits what protein?
cdc24- the GEF for cdc42. so cdc42 activated and polarity established
where is cdc42 lolcalised in G1 and S and G2
bud tip
where is cdc42 localised in G2/M?
around whole bud
where is cdc42 localised in late anaphase/telophase
bud neck
what regulates spatial and temporal control of the cell cycle?
cdc28 (G1 cyclin-GDK)
how does cdc28 regulate availability of cdc42s GEF?
cdc28 phosphorylates Far1 so it is broken down. cdc24 can then be released from nucleus to cytosol and is recruited by bud1 so it can activate cdc42
how does cdc28 regulate cdc42s GAP?
inhibits the Rga2/Bem3/Bem2 complex- the GAP
cdc28 promotes accumulation of what complex?
Boi1/Boi2/Bem1/ced24 complex- GEF. the cdc42 can recruit its own GEFto amplify signal. allows budding even without landmark proteins- but random
cdc42 effectors
Ste20, septins, gic1/2, sec3, polarisome/formins/actin cables
why is the polarisome important?
links Rho-GTPase signalling to actin filament assembly and localisation of formin proteins Bni1 and Bnr1 whcih drive actin cable assembly
what are septins
landmark proteins with Gtp binding domain and coiled coil region
what septins form a ring at the mother neck in vivo
cdc3,10,11,12
what is the purpose of the septin ring in cytokinesis?
forms a boundary between mother and bud to limit material exchange
why is rho1 important?
ensures that cell wall machinery is active at sites of growth
how is endocytosis involved in maintaining the site?
membrane proteins are removed by endocytosis and recycled or degraded. proteins dissociate from membrane and relocalise through secretory vesicle association
