Polarised growth in yeast

Question 1

What is the difference between cell proliferation and cell growth?

Answer 1

Cell proliferations leads to an increase in the number of cells.
Cell growth is an increase in the size of an individual cell

Question 2

How is yeast cell cycle and growth different to human cell cycle and growth?

Answer 2

In yeast the nucleus stays in tact until cytokinesis, whereas in MAN it breaks open

Question 3

Define cell polarity

Answer 3

cell polarity means regions of the cell have distinct compositions and thereby have different capabilities and functions
(cell symmetry can be broken by organisation of proteins and lipids inside the cell and on the cell surface)

Question 4

What are the four critical steps in polarisations leading to budding yeast?

Answer 4

1. mark the site
2. decoding the site
3. establishing the site
4. maintaining the site

Question 5

What is the difference between axial and bipolar division?

Answer 5

Axial division occur in haploid cells, and the bud neck forms at the same pole as the birth scars
Bipolar division occurs at the opposite pole to the birth scar in the daughter cell and at either pole in the mother cell. (diploid cells)

Question 6

What step is axial and bipolar division related to?

Answer 6

marking the site for bud development

Question 7

What genes were identified to be important in axial division?

Answer 7

BUD10, BUD3 and BUD4

Question 8

What genes were identified to be important in bipolar division?

Answer 8

BUD8, BUD9 and RAX2

Question 9

How do these marking the site genes act in relation to eachother?

Answer 9

cannot function without all gene products present

Question 10

What is the phenotype of bud10-, bud3- or bud4- mutants?

Answer 10

In haploid cells, axial budding is lost and it becomes bipolar.
In diploid cells there are no affects

Question 11

What is the phenotype of bud8- mutants?

Answer 11

Mutants cannot bud at the distal pole - all buds form at the birth scar (ie axial)

Question 12

What is the phenotype of bud9- mutants?

Answer 12

Cannot bud at proximal pole - all buds at distal pole.

Question 13

What is the phenotype of bud8-/bud9- double mutant?

Answer 13

No pattern, random budding in diploid cells , and axial budding as haploid (WT)

Question 14

What can the proteins discovered through studies of axial and bipolar budding be thought of as?

Answer 14

Landmark proteins

Question 15

What set of genes interact with the landmark proteins?

Answer 15

BUD1, BUD2 and BUD5

Question 16

How can you describe the signaling pathway that transmits the landmark signal?

Answer 16

Modular, requires every step (ie every gene product) in order to be functional

Question 17

What type of product does BUD1 encode?

Answer 17

Ras related GTPase

Question 18

What type of product does BUD2 encode?

Answer 18

GAP

Question 19

What type of product does BUD5 encode?

Answer 19

GEF

Question 20

How does the landmark protein interact with the signaling module?

Answer 20

Landmark protein (eg BUD8) recruits BUD5 to convert BUD1-GDP to BUD1-GTP

Question 21

What family of proteins are prominent in polarity establishment leading to the set up of polarity axis in the budding/mother cell?

Answer 21

Rho-GTPases

Question 22

What is the most important Rho-GTPase in yeast?

Answer 22

CDC42

Question 23

What is the GEF to CDC42?

Answer 23

CDC24

Question 24

What is the phenotype of cdc42ts mutants at 37 degrees?

Answer 24

Isotropic growth and no axis of polarity established
Fail to bud and fail to polarise actin cytoskeleton. Only patches no actin cables.
Fail to form septin ring

Question 25

How does cdc24 interact with cdc42?

Answer 25

cdc24 binds to the active site of BUD1 and activates it allowing it to replace GDP with GTP

Question 26

How is cdc42 under temporal control by the cell cycle as well as spatial control from the landmark signaling cascade?

Answer 26

G1 cyclin CDK = cdc28. Cdc28 activates CDC42 via many pathways. FAR-1 sequesters cdc42 in the nucleus, and cdc28 phosphorylates FAR-1 allowing the release of cdc42 into the cytosol

Question 27

When does bud initiation occur in relation to the cell cycle?

Answer 27

Bud initiation takes place in late G1 phase, only happens once every cell cycle

Question 28

What is the GAP for cdc42?

Answer 28

BEM3

Question 29

What are some important effectors for polarised growth from activating cdc42?

Answer 29

Septins Gic1/2 Formins, polarisome, actin cables Sec3

Question 30

What is the polarisome?

Answer 30

A complex of proteins localised to the incipient (newly growing) bud site and tip of the newly growing bud

Question 31

What does the polarisome seem to be important for?

Answer 31

Seems to be important in linking cdc42 signaling to actin cable assembly, and for localising formin proteins Bni1 and Bnr1, important for driving actin assembly

Question 32

What is the function of actin cables in the actin cytoskeleton of yeast?

Answer 32

delivery of vesicles to the site of polarised growth

Question 33

What is the function of actin cortical patches in the actin cytoskeleton in yeast?

Answer 33

endocytosis

Question 34

What is the function of the contractile actomyosin ring in the actin cytoskeleton in yeast?

Answer 34

Septum formation

Question 35

What are septins?

Answer 35

Type of cytoskeletal element involved in cell polarity and cytokinesis - structurally related proteins containing a GTP binding domain

Question 36

In yeast, which septins associate in vivo to form a ring at the mother bud neck (and in vitro will associate to form filaments)?

Answer 36

cdc3, cdc10, cdc11 and cdc12

Question 37

What will the phenotype be of a protein mutant at the late stage polarity 'maintaining the site' be?

Answer 37

There will be formation of a bud, but all processes following the formation will be jeffed up

Question 38

What are the three most critical processes at the maintaining the site stage of bud polarity?

Answer 38

- targeting vesicles to the actively growing site - polarised membrane growth - synthesis and directed deposition of new cell wall

Question 39

What is RHO1 essential for in maintaining the site of polarity?

Answer 39

Important for ensuring the cell wall machinery is at the site of bud growth

Question 40

What is the phenotype of rho1- mutant?

Answer 40

arrest cell cycle and lyse as small buds