Reorientation of laser-severed K-fiber. Laser-severed K-fibers in PtK2 cells expressing GFP–α-tubulin were analyzed by time-lapse confocal microscopy using a microscope (TE-2000E PFS; Nikon). Selected frames from this recording are shown in Fig. S1 C. 1-s intervals (599 s), 108-nm pixels, 100× NA 1.4 objective. Time in seconds. 0 corresponds to laser irradiation.