AbstractWhen primary baby mouse skin (BMS) cultures were subcultured for 48 hours into media containing 10−6to 10−7M colchicine or demecolcine, the number of altered cell foci appearing after 3–4 weeks' maintenance at 36°C was substantially enhanced over drug‐free controls. This applied whether or not the primary cultures had been irradiated with white fluorescent light. The additional presence of cytochalasin D and 12‐O‐tetradecanoyl‐phorbol‐l3‐acetate (TPA) sometimes improved and sometimes partly suppressed the enhancing effect of the antitubulin drugs, and these drugs were omitted for reproducible focus enhancement. The enhancement depended on passage through DNA synthesis in presence of colchicine, which did not prevent concurrent or subsequent DNA synthesis but induced a substantial proportion (>33) to replicate in the tetraploid (4n to 8n) chromosome configuration. Another effect was to induce widespread asymmetric nuclear division, allowing the potential for chromosome loss. All these effects occurred within the first one or few cell cycles after removal of the antitubulin drugs. The results suggest that the generation of tetraploidy perhaps followed by chromosome loss may be an important factor in the rapid induction of altered cell foci. Pre‐existing DNA damage is anot
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