title: Sister chromatid exchanges in ring chromosomes following X-irradiation of human lymphocytes.
abstract: OBJECTIVE
  To examine whether X-rays induce sister chromatid exchanges (SCE).
  
  
  METHODS
  Peripheral lymphocytes irradiated in vitro or in vivo were cultured and treated with okadaic acid to generate premature chromosome condensation (PCC). When identical spreads were analysed using conventional Giemsa staining and pan-centromeric fluorescence in situ hybridization painting, ring chromosomes were observed.
  
  
  RESULTS
  In PCC preparations, cells in the late G(2) phase and late M phase were observed. In late M phase cells, 17-20% of ring chromosomes lacked one chromatid (single-chromatid ring), irrespective of dose. Both the distribution patterns of centromeres in rings and intercentromere distances in dicentric rings indicate that a considerable number of single-chromatid rings might be formed by SCE occurring in a chromosome-type ring, thereby joining strands of two rings, followed by a transformation into one ring. These single-chromatid rings were less stable in vivo than chromosome-type rings.
  
  
  CONCLUSIONS
  Single-chromatid rings visualized clearly using PCC techniques indicate SCE in the respective rings. Contrary to the conventional SCE-detecting technique, this approach does not require the use of bromodeoxyuridine, which itself leads to SCE. Some of the observed SCE might be secondary products resulting from the repair of radiation-induced DNA damage, while others may be spontaneous.
authors.affiliation: Radiation Hazards Research Group National Institute of Radiological Sciences 4-9-1, Anagawa, Inage-ku, Chiba 263-8555 Japan.
authors.forename: R
authors.initials: R
authors.lastname: Kanda
authors.forename: Y
authors.initials: Y
authors.lastname: Yamagishi
authors.forename: I
authors.initials: I
authors.lastname: Hayata
mesh_terms: D002453:Cell Cycle / Q000528:radiation effects; D002478:Cells, Cultured; D002875:Chromosomes / Q000528:radiation effects* / Q000648:ultrastructure*; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008214:Lymphocytes / Q000473:pathology* / Q000528:radiation effects*; D011829:Radiation Dosage; D012303:Ring Chromosomes; D012854:Sister Chromatid Exchange / Q000528:radiation effects*; D014965:X-Rays