title: Rejoining of isochromatid breaks induced by heavy ions in G2-phase normal human fibroblasts.
abstract: We reported previously that exposure of normal human fibroblasts in G2 phase of the cell cycle to high-LET radiation produces a much higher frequency of isochromatid breaks than exposure to gamma rays. We concluded that an increase in the production of isochromatid breaks is a signature of initial high-LET radiation-induced G2-phase damage. In this paper, we report the repair kinetics of isochromatid breaks induced by high-LET radiation in normal G2-phase human fibroblasts. Exponentially growing human fibroblasts (AG1522) were irradiated with gamma rays or energetic carbon (290 MeV/nucleon), silicon (490 MeV/nucleon), or iron (200 MeV/nucleon) ions. Prematurely condensed chromosomes were induced by calyculin A after different postirradiation incubation times ranging from 0 to 600 min. Chromosomes were stained with Giemsa, and aberrations were scored in cells at G2 phase. G2-phase fragments, the result of the induction of isochromatid breaks, decreased quickly with incubation time. The curve for the kinetics of the rejoining of chromatid-type breaks showed a slight upward curvature with time after exposure to 440 keV/microm iron particles, probably due to isochromatid-isochromatid break rejoining. The formation of chromatid exchanges after exposure to high-LET radiation therefore appears to be underestimated, because isochromatid-isochromatid exchanges cannot be detected. Increased induction of isochromatid breaks and rejoining of isochromatid breaks affect the overall kinetics of chromatid-type break rejoining after exposure to high-LET radiation.
authors.affiliation: NASA Lyndon B. Johnson Space Center, Radiation Biophysics Laboratory, Houston, Texas 77058, USA. tkawata@ems.jsc.nasa.gov
authors.forename: T
authors.initials: T
authors.lastname: Kawata
authors.forename: M
authors.initials: M
authors.lastname: Durante
authors.forename: Y
authors.initials: Y
authors.lastname: Furusawa
authors.forename: K
authors.initials: K
authors.lastname: George
authors.forename: H
authors.initials: H
authors.lastname: Ito
authors.forename: H
authors.initials: H
authors.lastname: Wu
authors.forename: F A
authors.initials: FA
authors.lastname: Cucinotta
mesh_terms: D002478:Cells, Cultured; D002842:Chromatids / Q000378:metabolism* / Q000528:radiation effects; D004260:DNA Repair / Q000502:physiology*; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology / Q000528:radiation effects*; D016195:G2 Phase / Q000235:genetics*; D020450:Heavy Ions / Q000009:adverse effects*; D006801:Humans; D007621:Karyotyping