Movie 1. Live imaging and fixation of cell in Fig.1. Video shows an NIH3T3 cell that was co-transfected
with L61Rac and Lifeact-GFP. Running time is in minutes and seconds. At the time points indicated, the
cell was injected with L61Rac and subsequently fixed. Squares 1 and 2 in final frame indicate regions
corresponding, respectively, to protruding (Fig. 1) and treadmilling lamellipodia (Fig S2).
Movie 2. z-scan of tomogram in Fig. 1 and derivation of model in Fig.2. Video shows a scan through the
tomogram stack corresponding to Fig. 1 from the dorsal to the ventral surface, returning to the dorsal
surface with superposition of the tracked model in Fig. 2. Black particles with a white halo in tomogram
scan are gold particles used for registration of tilt series. See text and legend to Fig. 2 for additional details.
Movie 3. Live imaging and fixation of cell in Fig. 3. Video shows a treadmilling lamellipodium of an
NIH3T3 cell that was co-transfected with L61Rac and Lifeact-GFP. Running time is in minutes and
seconds. At the time points indicated, the cell was injected with L61Rac and subsequently fixed. Square in
final frame indicates region corresponding to tomogram.
Movie 4. z-scan of tomogram and model corresponding to Fig. 3. First part of video shows scan through
tomogram stacks with selected branch junctions highlighted in red circles. This is followed by a
combination of the tomogram stacks with the positions of branch junctions in the stack superimposed as red
spots. Finally, the complete model of the tomogram is presented, first with the branch junctions, followed
by two filament subsets (blue lines) and finally the remaining actin network obtained by automatic tracking
(green lines).
Movie 5. Live cell imaging of wound formation and repair. Video shows B16 melanoma cell corresponding
to Fig. 4C that was co-transfected with ArpC5-GFP (left) and VASP-mCherry (right). The cell was
wounded twice during the sequence (time is in minutes and seconds).
Movie 6. Scan of tomogram of lamellipodium in an L61Rac transfected NIH3T3 cell cytoskeleton
embedded in vitreous ice, followed by the accompanying model in top and side view (Fig. S5). Not all actin
filaments were tracked.
Movie 7. 3D model of branch junction in Fig. 7 incorporating the Arp2/3 complex (see legend to Fig. 7 for
color coding).
Movie 8. Mathematical simulation of protrusion, corresponding to Fig. 8D. For details see Discussion and
legend to Fig. 8D. In the movie, capping protein appears in white, instead of blue and the uncapped filament
ends are marked with a black line.