Microtubules in a constitutively active Rac1(Q61L)-expressing PtK1 cell. Microtubules are subjected to continuous retrograde flow away from the cell edge, but many plus ends undergo net growth and remain close to the edge. The cell was microinjected with X-rhodamine-conjugated tubulin and an EGFP-Rac1(Q61L) expression plasmid, and was 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. 2 of associated paper (J Cell Biol, 161:845-851, 2003).
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