Video time-lapse study of mitosis in binucleate V79 cells: chromosome segregation and cleavage.

Binucleate V79 Chinese hamster cells were video time-lapse recorded during mitosis. The general pattern found was: formation of one integrated metaphase plate, most often in a tetra- or tripolar spindle, prolonged prometaphase/metaphase, and normal duration of anaphase and contraction of cleavage furrows. Cleavage, however, often showed partial regression. Reversal of cleavage usually occurred late and then was not clearly separable from fusion of daughter cells. Reversal/fusion was more common the more furrows were initiated in late anaphase. This suggests that a final part of cleavage, or establishment of daughter cell integrity, is hampered by the preceding complex chromosome/spindle arrangements in the binucleate cells. Lagging of chromosomes in anaphase and formation of micronuclei were found to be frequent events. The nuclei formed from cells with a tetra- or tripolar spindle were often uneven in size, suggesting that the cells have difficulties in distributing the chromosomes in an organized way between many poles. A comparison with previous studies of binucleate mitoses in other cell lines shows major similarities in the mitotic performance. It is suggested that induction of binucleate cells should be included as a relevant end point when screening novel compounds for toxicity and aneuploidy.