Polarity, Asymmetry and Plane of Division

Question 1

Describe polarity in B. subtilise

Answer 1

I) DIVIVA/PopZ landmarks form at concave membrane curvature of old pole, in tetramers
2) PAR localises ORI to pole
3) Via PAR, Par-parS is nucleated and associated with Smc; chromosomes condense and Smc translocated to old pole
4) membrane curvature, DNA exclusion
5) DIVIVA recruited to new pole by PAR-ORI; anchored
6) MinD binds MinC
7) FtsZ localisation inhibited

Question 2

cdc42

Answer 2

• prenylated @ C-terminus; PM-association
• exocytic vesicle fusion
• actin stabilisation

Question 3

actin patch formation

Answer 3

• cdc24 = GEF
• PAK-Bem1-cdc24 recrute cytoskeleton elements (such as type V myosin) for vesicle delivery and localised growth
• this can be tracked with CRIB reporters
• important at the Neurospora hyphal apex

Question 4

Schmooing

Answer 4

• MAPK activates TFs such as calcium-dependent FAR1, which prevents cdc proteolysis, and polarises cdc42

Question 5

asymmetric Ash1 mRNA localisation requires

Answer 5

• cdc42 polarisation
• MyoIV mediates preferential RNA localisation
• stem-loop £D structure
• if you clone a hairpin into the 3’ UTR of an ectopic tractable mRNA, you can visualise asymmetry

Question 6

PAR mutants

Answer 6

1) sperm entry localises PAR-2 to posterior pole
2) domain spreads via actinomyosin contractile optical flow
3) PAR2/3 reciprocal inhibition
4) cdc42/PAR6/PKC forms at anterior pole
5) tension results in symmetric division

Question 7

First ACD in C. elegans

Answer 7

1) spindle is composed of sperm-derived centrioles
2) male and female pronuclei migrate to posterior
3) central nuclear centrosome complex rotates
4) astral microtubules pulled by polarised dyenin
5) NE breakdown
6) posterior spindle displacement for asymmetric anaphase B
7) cytokinetic cleavage furrow is positioned by asters and midzone; bisects mitotic spindle

Question 8

asters

Answer 8

• negative regulators of ECT2 Rho-GDP
• prevent polar accumulation and posterior contagion
• sperm-derived centrioles

Question 9

midzone

Answer 9

• positive regulator of ECT2
• recruits equatorial myosin, formin and contractile actin scaffold into alignment
• promote cortical furrowing and contractile ring construction

Question 10

equatorial contractivity

Answer 10

increases tension

Question 11

orchestrated division will require

Answer 11

intercellular signalling

Question 12

cadherin-based adhesion

Answer 12

• focuses TCJ tensile force to determine spindle orientation

Question 13

Plant division

Answer 13

• Errera’s rule
• Lowest energy configuration
• 90 degree boundary
• error prone selection of competing division planes

Question 14

Fucus

Answer 14

• polar division is important in the asymmetric thallus and rhizoid (which anchors the developing zygote); observed via laser microsurgery and patch clamping
• affected by exogenous and endogenous cues (calcium buffer blocks fertilisation)