Movie 1

Three cells of different sizes responding to changing positions of a micropipette filled with the chemoattractant. The cells are labeled for activated Ras (red) and express GFPPTEN (green). The left panels display bright-field DIC images, the right panels confocal crosssections though the cell at a plane 1.5 μm beyond the substrate surface. The middle cell exemplifies that large cells may respond almost as fast as small ones: when the micropipette is moved from the right to the left at 235.44 s and 514.08 s, the first protrusions with activated Ras which are formed at the previous tail become detectable at 252.72 s and 529.20 s, respectively. In particular the large cell entering from top responds with a broad front, which is sub-divided into sections occupied with activated Ras and interspersed with PTEN-decorated zones. The same cells are shown in Figure 1A; the 170-s image of the Movie corresponding to the 0-s frame in the Figure. Frame-to-frame interval 2.16 s.