title: Higher frequency of chromosome aberrations in late-arising first-division metaphases than in early-arising metaphases after exposure of human lymphocytes to X-rays in G0.
abstract: OBJECTIVE
  To determine whether metaphases arising at different times after mitogen stimulation of G0 lymphocytes differ in frequencies of X-ray-induced chromosome aberrations.
  
  
  METHODS
  Human G0 lymphocytes from peripheral blood exposed to 0, 1.5 or 3.0 Gy X-rays were stimulated to divide with the mitogen phytohaemagglutinin (PHA). First-division metaphases were distinguished from second and third divisions by chromatid labelling with 5-bromodeoxvuridine (BUdR) and staining with Giemsa or DAPI. Cultures harvested 48, 70 and 94 h after mitogen stimulation were analysed for unstable aberrations on Giemsa-stained slides and for stable and unstable aberrations by fluorescence in situ hvbridization (FISH) with painting probes for chromosomes 1, 2 and 4.
  
  
  RESULTS
  Frequencies of aberrations declined at the later culture periods, as expected on the basis of unstable aberrations being lost in mitotic division. Whe n scoring was restricted to firstdivision metaphases, however, aberration frequencies were higher in 94-h cultures than in 48-h cultures.
  
  
  CONCLUSIONS
  Frequencies of radiation-induced chromosome aberrations in first-division metaphases increase with culture time after mitogen stimulation. Possible explanations for this finding are a delay of damaged cells in mitogenic response or progression through divisions and heterogeneity among lymphocytes in culture kinetics and radiosensitivity. The data argue against the common assumption that all first-division cells are equivalent as indicators of radiation-induced chromosome aberrations.
authors.affiliation: Department of Biology, College of the Holy Cross, Worcester, MA 01610, USA. ghoffmann@holycross.edu
authors.forename: G R
authors.initials: GR
authors.lastname: Hoffmann
authors.forename: A M
authors.initials: AM
authors.lastname: Sayer
authors.forename: L G
authors.initials: LG
authors.lastname: Littlefield
mesh_terms: D002869:Chromosome Aberrations / Q000528:radiation effects*; D005260:Female; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D066298:In Vitro Techniques; D008214:Lymphocytes / Q000166:cytology* / Q000528:radiation effects*; D008677:Metaphase / Q000235:genetics* / Q000528:radiation effects*; D011836:Radiation Tolerance; D016192:Resting Phase, Cell Cycle / Q000235:genetics / Q000528:radiation effects