Fig. 1. Microtubule organisation in late-apoptotic HeLa cells. (A) Confocal image of apoptotic HeLa cells (6 hours anisomycin treatment) labelled with an anti-tubulin antibody (red) and DAPI (blue). Microtubules extend away from the body of the cell into chromatin-rich surface blebs. Bar, 10 µm. A Volocity 3-D reconstruction of the lower apoptotic cell is shown in supplementary material Movie 1. (B) Chromatin redistribution into surface blebs in apoptotic HeLa cells treated with anisomycin (Aniso, 6 hours) in the absence or presence of latrunculin A (Lat A) or nocodazole (NDZ). The proportion of apoptotic cells (cleaved PARP-positive, not shown) with condensed chromatin in surface blebs was then quantified after DAPI staining. Arrows in the images indicate chromatin-containing blebs. Bar, 10 µm. (C) Microtubules are required to maintain the dispersed status of condensed apoptotic chromatin. HeLa cells were induced into apoptosis by UV irradiation, incubated for 4 hours then for a further 40 minutes in the absence or presence of nocodazole, latrunculin A or blebbistatin (Blebb) (alone or in combination). Cells were fixed and assessed for compact or dispersed chromatin (cells defined as having dispersed chromatin contained three or more distinct, pyknotic pieces of peripheral chromatin, clearly distinguishable from the central mass; see example images). Values are mean ± s.e.m. Significant differences were observed where indicated, ^**P<0.001 and ^*P<0.01 using the Student's t-test.