Lecture 7 Flashcards
Cell membrane
The cell membrane opposes actin polymerization in migrating cells.
Cell area
Remains constant over time.
cell aspect ratio
Correlates with actin enrichment at the leading edge.
An actin/membrane
model for cell shape
Actin polymerization pushes the cell membrane from
within, generating membrane tension which, in turn,
exerts an opposing force on the actin network.
- Membrane tension is the same at all points along the
perimeter of the cell.
- Actin density is graded: there are more actin filaments
in the at the center of the leading edge.
- In the center of the leading edge, where actin density is
highest, the force exerted by the membrane per
filament is low and actin rapidly polymerizes.
- As actin filament density gradually decreases towards
the cell sides, the force per filament caused by
membrane tension increases until polymerization stalls
at the far sides of the cell.
inhibiting actin polymerization
reduces cell aspect ratio
Adding membrane
increases cell aspect ratio
Adhesions
Link the actin network to the EC matrix.
Myosin II
contracts the actin network
Molecular clutch model
Adhesions oppose myosin-driven inward flow.
Polymerising actin filaments slide inward (clutch engaged); actin polymerisation drives production - clutch disengaged.
Actin network in the cell rear
flows inward (retracting edge).
Myosin localisation
correlates with actin flow patterns
Myosin localises at the read end of the cell.
Myosin contraction
Is necessary for inward actin flow at the rear.
General model for motile shape determination
How should reducing cell-substrate
adhesion strength affect cell area?
Cell area should decrease
How should reducing cell-substrate
adhesion strength affect cell aspect ratio?
Aspect ratio should decrease
