Mutagenesis, Vol. 17, No. 2, 111-117,
March 2002
© 2002 UK Environmental Mutagen Society/Oxford University Press
Nature of anaphase laggards and micronuclei in female cytokinesis-blocked lymphocytes
1 Laboratory of Molecular and Cellular Toxicology, Department of Industrial Hygiene and Toxicology, Finnish Institute of Occupational Health, Topeliuksenkatu 41 a A, FIN-00250 Helsinki, Finland and 2 Department of Anatomy, Embryology and Genetics, University of Zaragoza, Zaragoza, Spain
We used pancentromeric fluorescence in situ hybridization and X chromosome painting to characterize late anaphase aberrations in cultured (72 h) female lymphocytes in the presence of cytochalasin B (Cyt-B). Aberrant cells, mostly containing laggards, were very common (34.5%) among multipolar anaphases but fewer (5.4%) among bipolar anaphases. Characterization of the laggards showed that 75% were autosomes, 15% autosomal fragments and 10% X chromosomes in bipolar divisions; similar figures were obtained in multipolar cells. The X chromosome lagged behind more often than would be expected by chance (1/23), representing 12 and 7% of all lagging chromosomes in bipolar and multipolar divisions, respectively. Bipolar divisions contained more lagging autosomes but fewer lagging fragments and X chromosomes with Cyt-B than without it. Comparison of the frequencies of anaphase laggards and interphase micronuclei (MN) showed that lagging autosomes seldom form MN in bipolar divisions, 11% being micronucleated without Cyt-B and 8% with Cyt-B. In multipolar divisions, autosome laggards produced MN more often (35%) and were mainly responsible for the excessive MN frequency of multinucleate cells. Lagging acentric fragments frequently formed MN, with a higher efficiency in the presence of Cyt-B (65% bipolar, 58% multipolar) than in its absence (41%). X chromosome laggards were very easily micronucleated, half of them forming MN in untreated cells and seemingly all after Cyt-B treatment. Our findings suggest that most autosome laggards are merely delayed in their poleward movement, eventually being engulfed by the nucleus. Lagging fragments and X chromosomes are probably detached from the spindle and, therefore, preferentially form MN. X laggards are particularly efficiently micronucleated in Cyt-B-treated cells, perhaps because they stay further away from the poles in round cytokinesis-blocked anaphases than in normally elongated non-blocked anaphases.
3 To whom correspondence should be addressed. Tel: +358 9 47472336; Fax: +358 9 47472110; Email: hannu.norppa{at}occuphealth.fi
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