cell polarity Flashcards
why is cell polarity important for the function of the cell
regions of the cell will require different proteins for different functions
why is budding yeast a good example for cell polarity (3)
unicellular
the genome is known and annotated
obvious internal and external signals of polarity
how do haploid and diploid cells bud, in terms of location off the cell surface
haploid= axial pattern- directly adjacent to eac
Diploid= bipolar pattern- at either side of the poles
3 genes involved in both axial and bipolar budding
BUD1, BUD2, BUD5
the budding genes involved in both axial and bipolar budding, what are their function
they decode the axial and bipolar marks and SIGNAL the machinery involved in generating the polarity axis
what does a mutation in the BUD1, BUD2 and BUD5 genes result in
random budding pattern in both haploid and diploid cells
what cycle do the BUD1/2/5 genes function in
GTPase cycle
what proteins are very important for polarity establishment (family and certain protein)
- Rho-GTPases
- Cdc42
what type of sensitivity mutant is Cdc42
temperature sensitive
24 degrees= polarisation= bud, grow and divide
37 degrees= isotropic growth- no axis of polarity
how does Cdc24 activate Cdc42 as the GEF in a GTPase cycle
Cdc24 will bind to an activated gene, the BUD1 gene. This allows the activation of Cdc42
The activation of Cdc42 results in?
polarity site to become established
what are the Cdc42, 24 and 43 proteins part of and involved in
polarity site to be established
Rho-GTPases
the Ste2 and Ste3 receptors bind to alpha-factor and a-factor repectively, what cells secrete these pheromones
MATa
MAT(alpha)
what type of receptors are Ste2 and Ste3, and why is it importaant for the functionality of the cell
G-protein coupled receptors= signalling cascade
part of the marking of the site of budding (before decoding and establishment)
what is the output of WT (wild-type) PAR proteins in the cell polarity network
mutual antagonism
establishment of opposing and complementary membrane domains that define a cell’s axis of polarity§
where was this PAR protein network first found in
C.elegans
example of polarisation in C.elegans after the entry of sperm into the oocyte
Position of entry defines the posterior region
then it will divide asymmetrically along the anterior/posterior axis
larger anterior cell and smaller posterior
different cell fates
=anterior= ectoderm
posterior= meso-/ endoderm germline
mutation in the PAR gene in C.elegans
The divide of the regions- anterior and posterior- become less pronounced, leading to possible identical cells
longer name for PAR genes
partitioning defective
after fertilisation, the sperm has delivered a key structure to the posterior section of the cell, essential for polarisation of the cell. what is this structure
MTOC, microtubule organising centre
what does the MTOC do in the posterior regions of the cell
generates microtubules
microtubules recruit Par1 and Par 2
Role of Par1 and Par2 in the posterior domain of the cell?
antagonises the anterior Par proteins
-leading to the accumulation of the ‘anterior Par proteins’ at the anterior cortical domain
antagonisation of anterior Par proteins allows the generation of pole definition, what are the anterior Par proteins
Par3/ Par6/ aPKC
What is key in the definition of the poles
Phosphorylation
what causes the asymmetrical spindle placement (HINT- due to sperm etc.)
Formed microtubules pulling on the anterior cortex causes the shift towards the posterior end
in Drosophila, what is the name of the CNS progenitor cells that push through the ectoderm
Neuroblasts
Neuroblasts divide multiple times asymmetrically, what is the name of this daughter cell and what 2 cells will rise from this cell
the daughter cell of the neuroblast= ganglion mother cell (as it divides to produce daughter cells too)
-neuron and glial cell
during and after delamination of neuroblast, what polarity proteins are found in the stalk and apical region of the cell
Cdc42, Par3 and Par6
in the Ganglion mother cell (GMC), factors are transported in the basal direction. 2 factors called Prospero and Stauffen, what do they do in the GMC
regulate expression of specific genes in the GMC
when the GMC divides asymmetrically different fates due to these determinants
3 main activities involved in movement of cells=
Protrusion
Attachment
Traction
- pushing out of the plasma membrane in front of cell
- actin cytoskeleton inside the cell is attached via proteins across the membrane to substratum
- Bulk of the cell body is drawn forward, by contraction
2 types of protrusion
filopodia and lamellipodia
microspikes or sheet-like broad structures
role of Cdc42, Rho and Rac in movement of cells and cell polarity establishment
Cdc42- isotropic growth= filopodia everywhere
Rac- essential for small actin filaments
Rho- stress fibres, cell migration
signals triggering cell migration converge on what GTPases
Rho small GTPases
