Time evolution of the traction stresses and corresponding progressive emergence of a tension kymograph for a chemotaxing D. discoideum wild-type cell migrating on a highly adhesive substratum. The tension kymograph of a representative wild-type D. discoideum cell migrating on a substrate additionally coated with poly-L-Lys, shown on the left, is progressively built by adding the traction tension Tx at each instant of time while the instantaneous cell contour (black) moves upward with the centroid velocity V. Red and black lines indicate the position of the front and back cell edge. The inset in the top left shows the oscillations of the strain energy, Us(t) (blue line), and the current value of Us(t) (red circle). The graph on the right shows the instantaneous magnitude of the cellular traction stresses ∣ τ⃗ ∣ together with the instantaneous outline of the cell (black contour). Time-lapse sequences of the chemotaxing 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 tension and generation of the video images was performed using MATLAB (MathWorks). Playback rate is 40× real time (10 frames/s). The video refers to the cell shown Fig. 5 A but includes additional time points.
