Cell polarity

Question 1

Cell polarity

Answer 1

the organisation of proteins inside and at the surface if cells
regions of the cell have distinct protein compositions so it can have different capabilities, morphologies and functions

Question 2

How is cell polarity generated?

Answer 2

cell surface landmarks adapting common pathways for cytoskeleton assembly
protein transport/membrane trafficking

Question 3

What internal signals cause yeast to undergo significant morphological changes?

Answer 3

growth and division signals

Question 4

What external signals cause yeast to undergo significant morphological changes?

Answer 4

pheromones for mating
nutritional signals like those for cell elongation

Question 5

How can the budding events of yeast be followed?

Answer 5

staining cells with fluorescent dye called calcofluor which binds to component of yeast cell wall called chitin
allows sites of previous cell seperations to be seen as bright rings on cell walls

Question 6

What controls where the position of new buds will be?

Answer 6

whether the cell is haploid or diploid

Question 7

Haploid cell budding pattern

Answer 7

axial pattern
mother and daughter cells are constrained to form buds immediately adjacent to previous site of cell seperation

Question 8

Diploid cell budding pattern

Answer 8

bipolar pattern
mother and daughter cells bud at the poles of the ellipsoidal cells

Question 9

What genes have been identified in axial patterns?

Answer 9

BUD10
BUD3
BUD4
septins

Question 10

What affect does mutations in axial genes have on the patten of budding?

Answer 10

mostly bud with bipolar pattern

Question 11

What genes have been identified in bipolar patterns?

Answer 11

BUD8
BUD9
RAX2
components of actin cytoskeleton

Question 12

What genes are required for both bipolar and axial patterns?

Answer 12

BUD1
BUD2
BUD5

Question 13

What happens when BUD1,2 and 5 are mutated?

Answer 13

random budding pattern in haploid and diploid cells
all function together to signal to polarity establishment machinery the position of bud site landmarks

Question 14

What proteins are important in polarity establishment?

Answer 14

Rho GTPase family
in yeast most important is Cdc42 which is highly conserved

Question 15

Cdc42

Answer 15

small GTPase of the Rho family
regulated through cycles of activation and inactivation by binding partners Cdc24 and several GAPs

Question 16

How does Cdc24 act on Cdc42?

Answer 16

it is its GEF- binds to active form of BUD1 at sites marked for budding
Cdc24 binds BUD1 and then activates Cdc42 to allow polarity site to be established so cell components can be trafficked to bud

Question 17

How is cell polarity generated in order to mate?

Answer 17

haploid cells can polarise and redirect their growth axes in order to facilitate mating with partner
response is chemotropic due to pheromones being secreted by different cell types

Question 18

MATalpha cells and MATa cells

Answer 18

MATalpha- secrete alpha-factor, which binds to MATa cells
MATa- secrete a-factor, which binds to MATalpha cells

Question 19

How do daughter cells have different properties to mother cells?

Answer 19

myosins Myo2 and Myo4 are required for asymmetric inheritance of specific factors

Question 20

How is backward movement of organelles in daughter cells prevented?

Answer 20

cargo adaptors are degraded

Question 21

Why can’t yeast be used to understand intercellular interactions?

Answer 21

they are unicellular so can’t study growth of tissues and multicellular organisms

Question 22

Candida albicans

Answer 22

benign member of mucosal flora but can cuase mucosal disease and become invasive
frequently seen in AIDS patients, premature babies and terminally ill patients
fungus can leave bloodstream and penetrate cells/tissues

Question 23

How can candida albicans become pathogenic?

Answer 23

switch from yeast to hyphal form is stimulated at 37 degree by serum or neutral pH
hyphae are more adherent to mammalian cells and penetrate tissue
yeast cells taken up by macrophages can become filamentous and lyse it
yeast cells carried effectively in bloodstream promoting fungal dissemination in body

Question 24

What are the two main routes to diversity?

Answer 24

polar mother cells divide to generate daughters that have inherited different components
daughters equal at birth become different by exposure to different signals/environments

Question 25

Important steps in generating cell polarity and cell fate decisions

Answer 25

establishment of axis of polarity mitotic spindle being positioned on axis cell fate determinants being distributed differentially among daughter cells

Question 26

Par proteins

Answer 26

form the core of a cell polarity network in many animal cells and in many developmental contexts

Question 27

Asymmetric cell division in c.elegans

Answer 27

starts with entry of sperm into oocyte, position of this will define the posterior end of oocyte divides asymmetrically along anterior posterior axis to produce larger anterior and smaller posterior cell

Question 28

How does mutation in Par affect size and fate?

Answer 28

difference in cell size and fate between 2 daughter cells is less pronounces and can even be identical

Question 29

How is symmetry broken during fertilisation?

Answer 29

when sperm delivers microtubule organising cell which becomes posterior pole and defines axis of polarity

Question 30

How do the microtubules generated create the poles?

Answer 30

microtubules recruit Par 1/2 which antagonise anterior par proteins they accumulate at anterior cortical domain results in distinct localisations of par proteins

Question 31

Where do the different par proteins go?

Answer 31

1/2- posterior 3/6- anterior 5- maintains boundary

Question 32

How is the mitotic spindle organised?

Answer 32

interactions between microtubules and the cortex results in pulling forces which act on the mitotic spindle to be displaced toward the posterior end

Question 33

Neuroblast division in drosophila

Answer 33

progenitor cells in a specific region of the epithelial monolayer called the ventral neuroectoderm assymetric cell divisions give rise to small basal daughter cells called ganglion motor cells, and larger apical daughter cells

Question 34

Hwo do ganglion motor cells and apical daughter cells divide differently?

Answer 34

GMC- only once more into a neuron and a glia cell ADC- continue to divide asymmetrically

Question 35

When is polarity established in drosophila?

Answer 35

when cell is delaminating and still in neuroectoderm localise to apical region in fully delaminated nueroblasts polarity is independent of surrounding cells

Question 36

Drosophila cell fate determinants

Answer 36

transported in a basal direction to the ganglion mother cell includes prospero and staufen

Question 37

What are the three stages of cell migration?

Answer 37

protrusion attachment traction

Question 38

Protrusion

Answer 38

pushing out of the plasma membrane in front of the cell

Question 39

Attachment

Answer 39

the actin cytoskeleton inside the cell is attached via interacting proteins across the plasma membrane to the substratum

Question 40

Traction

Answer 40

the bulk of the cell body is drawn forward through a process of contraction

Question 41

What are the two different types of protrusion?

Answer 41

filopedia- dense core of bundled actin filaments uses Cdc42 lamallipodia- sheet like, broad structures uses Rac

Question 42

Chemotaxis

Answer 42

the movement of cells toward or away from a signal such as a diffusible chemical neutrophil moving to site of infection

Question 43

How do neutrophils use chemotaxis?

Answer 43

receptors on surface of neutrophils detect low levels of bacterial peptides peptides bind to GPCRs which triggers intracellular activation of G protein leads to activation of Rac GTPase leads to lamellipodial protrusion in direction of peptide gradient

Question 44

When is de novo polarity set up in drosophila?

Answer 44

during embryo cellularisation

Question 45

What are the effects of EMT?

Answer 45

loss of e cadherin assymetric activation of small Rho GTPases

Question 46

Cla4 + Ste20

Answer 46

PAK protein kinases links polarity to cell cycle

Question 47

Sec3

Answer 47

part of the exocyst complex ensures polarised trafficking

Question 48

Bni1

Answer 48

nucleate actin filaments maintians polarity of cytoskeleton