title: Nature of anaphase laggards and micronuclei in female cytokinesis-blocked lymphocytes.
abstract: 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.
authors.affiliation: 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.
authors.forename: Ghita C-M
authors.initials: GC
authors.lastname: Falck
authors.forename: Julia
authors.initials: J
authors.lastname: Catalán
authors.forename: Hannu
authors.initials: H
authors.lastname: Norppa
mesh_terms: D000705:Anaphase / Q000235:genetics*; D002455:Cell Division; D002478:Cells, Cultured; D002869:Chromosome Aberrations; D003571:Cytochalasin B / Q000633:toxicity*; D005260:Female; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008214:Lymphocytes / Q000187:drug effects*; D015162:Micronucleus Tests; D008870:Microtubules / Q000502:physiology*; D008875:Middle Aged; D008941:Spindle Apparatus / Q000502:physiology; D014960:X Chromosome / Q000235:genetics
chemical_list: D003571:Cytochalasin B