Fig. 4 - Photobleaching of MTs in the course of centripetal motion of pigment aggregate in nascent fragment. Top panel illustrates the scheme of the experiment. Intact melanophores were injected with rhodamine-labeled tubulin subunits and 60 min later fragments were dissected and stimulated with adrenalin. When pigment aggregate formed and started to move to the center, MTs were photobleached with a laser microbeam focussed into a narrow zone and positioned perpendicular to the path of motion of the aggregate and between the aggregate and either the fragment's proximal (cut) (left pair) or distal (right pair) edge. Images of the bleached zone were obtained immediately after irradiation (middle pair of micrographs) and a few minutes later when the aggregate shifted to the fragment's center (bottom pair of micrographs). Numbers indicate time in s after irradiation. Bars, 5 mm.