Time evolution of the traction stresses in the laboratory reference frame during D. discoideum wild-type random migration. A representative D. discoideum cell exhibiting random migration is depicted by the black contour, and the color map shows the instantaneous magnitude of the traction stresses in [Pa]. The time point displayed is shown as part of the title. The inset in the top right shows the oscillations of the axial forces (Fx, blue line) and of the lateral forces (Fy, green line). The cell forms multiple, dynamic, transient, and weak TAs. When the cell occasionally establishes a stronger TA, it often remains spatially stationary, and the ratio of axial to lateral forces increases (black arrows). Time-lapse sequences of the representative cell were acquired every 4 s on an inverted light microscope (TE300; Nikon) controlled by the MetaMorph software (Molecular Devices). Calculation of the traction stresses and generation of the video images were performed using MATLAB (MathWorks). Playback rate is 40× real time (10 frames/s).
