3D shape changes and traction stresses of a chemotaxing wild-type D. discoideum cell expressing lifeact-GFP migrating on a highly adhesive substratum. The substrate on which the cell is migrating was additionally coated with poly-L-Lys. Cells were transformed to generate lines expressing Lifeact (Abp140-GFP) to define the cell’s 3D shape. Z stacks of each time-lapse sequence of the chemotaxing cell were acquired every 12 s on a spinning disk confocal microscope (DMIRE2 [Leica]; CSU10 [Yokogawa]) controlled by Slidebook software (3I). Calculation of the traction stresses was performed using MATLAB and an inverted light microscope (TE300; Nikon) controlled by MetaMorph software (Molecular Devices). The 3D cell shape is shown in gray and the rendering of the shape as well as the generation of this video was performed using the IMARIS software (Bitplane). Notice that the cell is initially in the SK mode, forming numerous, weak, transient TAs while its body is barely in contact with the substrate. When the cell starts to adhere more and the movement slows, the cell begins exerting stresses of considerably higher magnitude all around its periphery and becomes progressively more rounded, essentially getting stuck. The movie corresponds to Fig. S1 (E and F) and is accelerated 60× real time.
