Fig. 6. Time-lapse FRAP analysis of -SMA-EGFP stress fibers. Photobleached regions appear as dark bars and squares (*). FRAP analysis of cells in control conditions (A) was compared with that of SMA-FP-treated cells (B). In control conditions, bleached -SMA-EGFP stress fibers almost completely recovered their fluorescence within 30 minutes (see square). Bar-shaped bleached zones on individual stress fibers move at different rates during fluorescence recovery, as indicated by the transformation of the straight bleach zone into a zig-zag line (arrows). Lapsed time is indicated at the lower right corner of each image. Scale bars, 10 µm. See also videos in supplementary material. (C) The average rate of movement of bleached zones was quantified by measuring the mean distance of at least ten stress fibers in at least ten cells using Openlab software (2.3±0.2 mm/hour (n=51). In cells pre-treated for 15 minutes with SMA-FP, rates of movement were approximately fivefold slower than in non-treated cells, averaging 0.53±0.09 µm/hour (n=38). Bars represent s.e.m. (**P0.001 compared with control cells).