Figure 6

Fig. 6. Sequential subtraction analysis of MT dynamics at steady-state. Fluorescently labeled MTs were imaged in living melanophores beginning 2 hrs after injection of labelled tubulin and 1 hr after stimulation of aggregation by addition of adrenalin. (A) Image of MTs from a time-lapse sequence used for analysis. (B) Differential image obtained by subtracting from the image in A the next image in the time-lapse series. Black segments and white segments represent MT growth and shortening, respectively, during the time interval. (C) Diagram extracted from the difference image by bit slicing, illustrating growth (green) and shortening (red) excursions. White boxes (1,2,3) indicate the regions from which data were compiled. Yellow spot shows estimated position of the cell center. The angular density of green segments and red segments decreases towards the cell center. The ratio between frequency of growth and shortening events in all boxes was nearly the same. (D) Distribution of active MT ends along the cell radius as determined by the number of growth or shortening events. Number of MTs indicated relative to number of shortening MTs at the cell margin (zone 1) set to 100. Data shown, averages for 6 cells (See text for details).