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Uncontrolled nuclear division in murine cells abortively transformed by simian virus 40.

Cytochalasin B (CB) prevents cytoplasmic cleavage without directly affecting nuclear division. Secondary cultures of mouse embryo fibroblasts or 3T3 cells show controlled nuclear division when treated with CB: only binucleated cells are formed. Many CB-treated transformed cells show uncontrolled nuclear division and become highly multinucleated. When CB-treated normal cells are concurrently infected with high inputs of SV40, many of these cells become highly multinucleated. It is suggested that these highly multinucleated cells represent abortively transformed cells since the actual number of transforming units (focus-forming units) of simian virus 40 (SV40) is too low to account for the appearance of these cells. Also, if the CB treatment is begun 6 days after SV40 inoculation, the large increase in highly multinucleated cells is not observed. Most cells stably transformed by SV40 or adenovirus show uncontrolled nuclear division when treated with CB. However, 3T3 cells transformed by SV40 or adenovirus and analyzed shortly after transformation are an exception and show controlled nuclear division. This property of 3T3 cells is apparently overcome by high inputs of SV40 since abortively transformed cells become highly multinucleated.