Fig. 5

Qualitative model of collective EF-induced cell polarization and motility. (A) EF polarizes symmetric stationary single cell from the rear in minutes; a myosin/contraction, protrusion-independent, mechanism driving retraction of the future rear is responsible for the polarization. After the initial polarization, the robust lamellipodial protrusion starts and guides the rapidly moving cell to the cathode. The cell responds to EF reversal by a U-turn or repolarization to go to the new cathode. (B) When PI3K is inhibited, the initial polarization is the same because PI3K does not affect the myosin/contraction, protrusion-independent, mechanism. (C) When myosin is inhibited, EF can still polarize the cell, but the resulting motility and cell shape are relatively random and unsteady. (D, E) Inside the cohesive group, cells sense EF individually, polarizing in minutes much like single cells. We hypothesize that individual cells polarize from the rear and that the myosin/contraction mechanism is dominant for both initial polarization and stable motility. The only significant difference between the control and PI3K-inhibited groups is that protrusions in the leading and trailing cells in the former accelerate the front and slow the rear, while in the latter the regional differences in the group are muted. (F) When myosin is inhibited, the cells lose mutual cohesion. The combined effects of randomized motility of individual cells and frequent collisions with neighbors, resulting in transient contact inhibition of locomotion and pulling on each other, override the guiding effect of EF. (G) Keys for the notations.