Movie 2

Merged confocal images of a large cell labeled for activated Ras (red) and expressing PTEN-GFP (green). The left panels are focused on the substrate-attached cell surface, the right panels display cross-sections through the cell bodies at a plane 1.5 μm beyond the substrate-attached surface. The cell re-orientates twice, showing various responses to reversal of the attractant gradient. In the periods of the 51.60-s to 94.60-s frames and of the 172.00 to 268.75-s frames the previous tail, now exposed to the source of attractant, retracts rather than protrudes toward the micropipette. In the 174.15-s to 180.60-s period, a thin protrusion emanating at the right border of the frame is seen in the left panel to turn into the direction of the gradient, with activated Ras at its tip. In the 184.90-s to 245.10-s frames, the formation of protrusions progresses at the bottom part of the cell from the previous front (opposite to the actual micropipette position) toward the newly established front. Frame-to-frame interval 2.15 s.