Lecture 12: 14/11

Question 1

What different aspects would you use to quantitatively characterize cell motility? Which parameters influence movement and what is their effect?

Answer 1

Characterization Aspects:
- Velocity (rotational velocity in the case of a flagellum)
- Force
- Power
- Directionality

Parameters Impacting:
- Surrounding flow of fluid
- Chemical gradients
- Thermal gradients
- Viscosity & Shear within the area of movement
- Elasticity of surrounding fluid (Newtonian vs Non-Newtonian)
- Substrate stiffness
- Function of the cell
- ATP Availability

Question 2

How does adhesion impact motility?

Answer 2

• Differentiates it from spreading
• Coordination between adhesion and detachment
• Connecting cytoskeleton to environment via integrins

Question 3

What is the relationship between focal adhesion size and contractive stress?

Answer 3

Focal adhesion size and density increase with contractile stress making them stronger

Pull harder, stick stronger

Question 4

What conformations of integrin exist? How do they work?

Answer 4

• Closed and open
• As you pull on filamin more, it opens up more binding sites on the integrin

Question 5

What is the clutch hypothesis?

Answer 5

Clutch parses cytoskeletal work between forward and retograde flow

Actin polymerization gets partitioned into cell going forward and actin going backward

Based on the tension provided by the adhesion promoters

Question 6

What is the relationship between protrusion and myosin? What is the relationship between protrusion or retrograde?

Answer 6

Myosin shifts it to retrograde motion.

The protrusion rate and retrograde flow = constant, because actin polymerization is constant

Question 7

Does motility speed scale with adhesion strength?

Answer 7

Stronger adhesion strength is not necessarily better.

There is a biphasic relationship between cell speed and adhesion.

Question 8

How do soft vs stiff substrates impact cell movement? (Durotaxis)

Answer 8

softer materials - deformed more by cells - less spreading

stiffer materials - deformed less by cell - more spreading

Question 9

How do gradient substrates impact directionality?

Answer 9

Cells on gradient substrates move toward stiff (durotaxis), most crawling cells exhibit this behavior.

As it gets to stiffer materials, it wanders less.

Question 10

What makes persistence change with substrate rigidity?

Answer 10

Directly correlated with tension in the cellular system.

Persistence time (tau) regulates “directedness”

Question 11

How does movement change with geometry?

Answer 11

The optimal 1D line was 2.5um.

3D and 1D are more similar than 2D, tighter regulation between fwd and back.

Question 12

What does and slope of MSD vs tau >1 tell us?

Answer 12

Directed movement

slope describes the persistence of the direction

Question 13

What can we say is different between the dark blue (greater TGFB exposure) vs light blue cells (control) ?

Answer 13

Greater slope for cells which are exposed to TGFB (more meschencylmal), meaning greater directionality/persistence.

The y-axis describes the speed. The dark blue ones are also faster. Cells speed up during EMT. (Epi to Mesch Transition)

Question 14

Do cells move together or individually during EMT?

Answer 14

Velocity correlation function is used (large value = together, small value = individual)

Question 15

Do E or M cells move more correlated?

Answer 15

E: correlated
M: individual

Question 16

Compare the mutant vs wild type cells and how their loss modulus is impacted? How is their strain energy and speed impacted?

Answer 16

The loss modulus to K225E cells is shifted to a lower frequency compared to the wild type.

Increases the binding duration of the crosslinkers in this cell. Increasing cross-linker affinity. Mutant exposes another binding site.

Traction stress and strain energy for mutant increases. The speed decreases for the mutant. Thus, stronger cells are not necessarily faster.