Figure 3. Motility of unstimulated cells.

(a) Three 10-hour trajectories of Dictyostelium cells moving in the absence of external stimuli. (Reprinted with permission from Ref. ²⁵.)(b) Confocal images showing typical extensions of pseudopods in unstimulated Dictyostelium cells. Images are at 8 s intervals. In a Y-split, the existing pseudopod splits in two, of which one is eventually retracted. In a one-way-split, a new protrusion is made at the base of an existing pseudopod. De novo pseudopods are those that appear where no recent pseudopod activity has been observed. The outlines below show the direction of the growing pseudopod superimposed on the outline of the earliest image. (c) A 14-minute trajectory of a moving cell with the coloured arrows depicting the direction of the different types of pseudopodia. (Panels (b) and (c) reprinted with permission from Ref. ²⁶.) (d) Pseudopod splits observed in a microfluidic chamber (left) and simulations of an excitable system driving cell protrusions (right). The cell outlines are approximately 2 (left) and 2.5 (right) seconds apart. (Reprinted with permission from Ref. ³⁰.)