Fig. 3. Time-lapse confocal microscopy of living bristle cells shows barbed-end loss from actin filaments. (a) Actin bundles decorated with GFP-moesin from a single bristle-cell extension were visualized over a 90-minute period. Images were taken at 30-minute intervals (0, 30, 60 and 90 minutes) and are displayed from left to right. These images were aligned using a constellation of fluorescent irregularities on the bundles. The position of one of these bright spots is adjacent to the asterisk (^*). Bristle orientation is indicated in the rightmost panel. The top region of these images is characterized by gaps in eight bundles that do not appear to widen during this time course. The upper and lower boundaries of one of these gaps are indicated by the closely spaced arrows for each time point. The bottom region of these images — near the bristle base — is characterized by widening gaps in eight bundles. The upper and lower boundaries of two of these gaps are indicated by the pair of arrows (left side of image) and the pair of double-headed arrows (right side of image). Note that the lower boundaries of these gaps, defined by the barbed ends of the modules below, are moving away from the fixed upper boundaries. (b and c) The rate of barbed-end module shortening was determined as described in the text by measuring the length of five well defined gaps in the upper region of the bristle (b) and in the lower region of the bristle (c). A least-squares fit for each lengthening gap generates a line with a slope representing the rate of module shortening. All modules in the five non-widening gaps (b) showed negligible shortening: average rate of 0.08±0.05 (SEM) µm/hour. All modules in the five widening gaps (c) showed similar shortening rates: average rate of 1.10±0.04 (SEM) µm/hour.