L9 - Polarity 2

Question 1

What are the 2 main routes to diversity in cell fate decisions? (2)

Answer 1

1) Intrinsic mechanism – mother cell becomes polarised and divides where the daughter cells are inherited asymmetrically
2) Extrinsic mechanism – daughter cells are equal at birth but then exposed to different external environmental factors

Question 2

What are the important step to developing cell polarity and cell fate decisions? (3)

Answer 2

1) Establishment of an axis or polarity and marking a site that is recognised by factors inside the cell
2) Mitotic spindle is positioned along the axis
3) Cell fate determinants are often distributed differentially to daughter cells

Question 3

What forms the core of cell polarity networks in many animals?

Answer 3

PAR proteins

Question 4

What genes cause asymmetric divisions

Answer 4

PAR genes

Question 5

What causes symmetry to break on fertilisation?

Answer 5

-Caused by the sperm delivering a microtubule organizing centre (MTOC), this site becomes the posterior pole so defines the axis of polarity

Question 6

What keeps cell in place in fertilisation steps?

Answer 6

PAR proteins

Question 7

What sets up the forces acting on mitotic spindle? (2)

Answer 7

-Interactions between microtubules and the cortex
-LGL (lethal giant larva) allows a greater pulling force on the spindle and sets up the cell division plane to be asymmetric

Question 8

When is polarity established in drosophila?

Answer 8

-Polarity is established when the cell is still in the neuroectoderm layer

Question 9

What are 3 activities required for cell movement? (3)

Answer 9

1) Protrusion – pushing out of plasma membrane in front of cell
(Lamellipodium is a common way for protrusion to happen)
2) Attachment – actin cytoskeleton inside the cell is attached via interacting proteins across plasma membrane to substratum
3) Traction – bulk of cell body is drawn forward through process of contraction

Question 10

How is cell polarity established in cell migration? (3)

Answer 10

-Signals converge on Rho small GTPases
-Rac is essential for structure of actin filaments
-Cdc42 activation results in a lot of actin filaments

Question 11

What is chemotaxis?

Answer 11

This is the movement of cells towards or away from a signal such as a diffusible chemical

Question 12

How is chemotaxis used in cell migration?

Answer 12

-Peptides bind to GPCR and triggers intracellular activation of heterotrimeric G protein. This leads to activation of Rac GTPase leading to lamellipodial protrusion in the direction of peptide gradient

Question 13

What is Epithelial Mesenchymal Transition (EMT)?

Answer 13

-Involves conversion of epithelial apical-based polarity axis into a migration axis with front-near polarity