Microtubules in a control PtK1 cell at the edge of an epithelial cell island. Few pioneer microtubules rapidly grow into forming protrusions. The cell was microinjected with X-rhodamine-conjugated tubulin and observed by fluorescence microscopy. Epifluorescence image series were acquired on an inverted microscope (model TE300; Nikon) equipped with electronically controlled shutters, filter wheels, and a 14-bit cooled CCD camera (Orca II; Hamamatsu Corporation) controlled by MetaMorph® software (Universal Imaging Corp.) at 5-s intervals using a 60/1.4 NA Plan Apo objective lens (Nikon). Images were taken every 5 s and are played back at 15 frames/s. For still images, see Fig. 1 of associated manuscript (J Cell Biol, 161:845-851, 2003).