Fig. 2. Cell and fibronectin fibril dynamics in a day 2 FRC culture. Time-lapse image series showing the dynamic motion of fibrils A and B from Fig. 1. Corresponding images are shown for the cells (viewed by DIC) and fibronectin (FN) fibrils. Merged images in which the fibronectin fibrils are pseudocolored red are shown on the right. The blue, green and red circles are the outlines of nuclei on individual cells that show significant movement during the 19 hour period. The motion paths (trajectories) of these cells are indicated below the image series. Arrows in the fibronectin images indicate two fibrils (A and B) that appear joined at 0 hours, but gradually pull apart until they are separated by 16 hours. Corresponding arrows on the merged pictures indicate that these fibrils lie on cellular processes and become separated upon retraction of these processes. A movie corresponding to these still images is available as Movie 2 in supplementary material. Bar, 50 µm.