Figure 4.

Lamellar Stresses Are Increased and Redistributed during CIL

(A) Kymographs of lamellar recoil upon laser abscission of the actin network in freely moving and colliding cells. Dotted rectangle highlights the width of the ablation region.

(B) Quantification of recoil rate over time and initial recoil rate upon laser abscission. Error bars represent SEM. ^∗∗p < 0.01.

(C) Quantification of lamellae strain over time upon laser abscission and modeled forces assuming that the actin network behaves elastically over short time scales. The elastic and dissipative mechanical properties in the lamellae are modeled by an exponential decay of the strain that is overlaid onto the constant retrograde flow. Note that zero strain represents the end of the exponential decay. Assuming mechanical properties similar to previously published lamellae we can estimate the tension. Inset: Sketch illustrating the mechanical model of an elastic and dissipative element. The strain u is calculated by the ratio Δl /l. Error bars represent SEM. ^∗∗p < 0.01.

(D) Hemocyte velocities in freely moving and colliding cells 60 s after laser abscission with respect to the ablation site (red arrow). Magenta arrow is the average direction of the population. Note that after mock ablation there was a significant forward movement of cells, while ablation of the fiber during cell collision led to a significant rearward movement. ^∗p < 0.05.

(E) Localization of actin network stress during cell collision. Top panels: a time-lapse series of a hemocyte containing labeled F-actin undergoing a collision (adapted from Figure 2A). Bottom panels: modeled intracellular actin stresses. Note that stresses were only measured for regions of the lamella that persisted for a 40-s period as deformation history is required in the analysis. Arrows highlight region of lamellae overlap. Dotted line highlights the redistribution of stresses around the cell body and asterisks the regions of high stress that colocalize with the actin fiber.

(F) Kymograph of lamellar stresses over the region that colocalized with the actin fiber. Note the redistribution of stress from the back of the network to the front.

(G) Kymograph of the instantaneous changes in actin flow direction in the region colocalizing with the actin fiber.

(H) Quantification of the mean change in flow direction of the actin network in three regions corresponding to the back, middle, and front of the actin fiber. Note that the changes initially increase in the rear of the network.

See also Movie S4.