POS - Cell Migration

Question 1

What do the following GTPase proteins control?

a. cdc42
b. Rac
c. Rho

Answer 1

a. Filopodia
b. Lamellipodial Ruffling
c. Acting bundles (stress fibres), focal complexes and myosin activation

Question 2

What are the four main elements of cell motility?

Answer 2

1. Gel-sol transition
2. Lamellipodial extension
3. Actin-myosin interactions
4. Focal contacts

Question 3

Briefly describe the normal cytoskeletal arrangement in the cytoplasm and what happens during the gel-sol transition.

Answer 3

Normally actin filamints are crosslinked by filamin which can bind at a variety of angles. This allows slow deformation of the cytoplasm but stops it being pulled apart with sudden force. Gelsolin can cleave the actin filaments and the occupy the site they just cleaved (called capping) which prevents the filaments re-forming. This results in the cytoplasm becoming more fluid.

Question 4

What is meant by thixotropic?

Answer 4

Fluid under an applied stress, but resistant to sudden pulls.

Question 5

How is actin related peptide involved in the formation of Y-branched actin filaments?

Answer 5

ARP can bind to the sides of actin filaments.

Question 6

What molecule(s) sequester actin monomers?

Answer 6

Thymosin-beta4 initilally, this then transfers the actin to profilin, forming profilactin. The actin is ready to polymerise as it has ATP.

Question 7

What is the role of PIP2?

Answer 7

It binds profilin in the profilactin complex therefore releasing actin monomers. It also activates WASp/Scar protein. This binds to ARP.

Question 8

How is elongation terminated:

a. at the leading edge,
b. at the - end?

Answer 8

a. Capping protein

b. Actin depolymerisation factor (ADF)

Question 9

What molecule generates the force needed to move the cell?

Answer 9

Myosins