Nature of anaphase laggards and micronuclei in female cytokinesis-blocked lymphocytes

• Published in: Mutagenesis 2002-03, Vol.17 (2), p.111-117
• Main Authors: Falck, Ghita C.-M., Catalán, Julia, Norppa, Hannu
• Format: Article
• Language: English
• Subjects: Anaphase - genetics; Biological and medical sciences; Cell Division; Cells, Cultured; Chromosome Aberrations; Cytochalasin B - toxicity; Female; General aspects. Methods; Humans; In Situ Hybridization, Fluorescence; Lymphocytes - drug effects; Medical sciences; Micronucleus Tests; Microtubules - physiology; Middle Aged; Spindle Apparatus - physiology; Toxicology; X Chromosome - genetics
• ISSN: 0267-8357; 1464-3804; 1464-3804
• DOI: 10.1093/mutage/17.2.111

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.