Incomplete chromosome exchanges are not fingerprints of high LET neutrons
MGC, Department of Radiation Genetics and Chemical Mutagenesis, Leiden University Medical Centre, Wassenaarseweg 72, 2333AL, Leiden, The Netherlands. Radiation Protection Dosimetry
(Impact Factor: 0.91).
02/2002; 99(1-4):215-6. DOI: 10.1093/oxfordjournals.rpd.a006765
A new fluorescence in situ hybridisation (FISH) technique combining whole chromosome specific DNA libraries with pan-centromeric DNA and telomeric PNA probes was introduced to investigate the induction of chromosome exchanges in human lymphocytes after exposure to low (4 Gy X rays) and high (1 Gy neutrons) linear energy transfer radiation. This combination of probes allowed accurate detection of exchange aberrations involving the painted chromosomes and an unambiguous discrimination between complete and incomplete exchanges, as well as terminal and interstitial deletions. Data obtained in the present study using combined FISH assay with telomeres detection showed no differences between two types of radiation regarding the induction of incomplete exchanges.
Available from: pasteur.ac.ir
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ABSTRACT: Fluorescence in situ hybridization (FISH) with a telomeric peptide nucleic acid (PNA) probe was employed to analyze the induction of incomplete chromosome elements (ICE, i.e., unjoined or "open" chromosome elements with telomeric signal at only one end) and excess acentric fragments (i.e., in excess of fragments resulting from the formation of dicentric and ring chromosomes) by the methylating agent streptozotocin (STZ) in a Chinese hamster embryo (CHE) cell line. CHE cells were treated with 0-4 mM STZ and chromosomal aberrations were analyzed in the first mitosis after treatment using the telomeric probe. Centric (incomplete chromosomes) and acentric (terminal fragments) ICE were the only unstable chromosome-type aberrations induced by STZ in CHE cells. The induction of these aberrations exhibited a curvilinear concentration-response relationship. About 40% of the metaphases present in cell cultures treated with STZ contained one or more pairs of ICE. In STZ-treated cells, ICE were always observed as pairs consisting of an incomplete chromosome and a terminal fragment. Moreover, all of the excess acentric fragments induced by STZ were of terminal type. These results indicate that chromosomal incompleteness is a very common event following exposure to STZ and suggest that all of the excess acentric fragments induced by STZ originate from terminal deletions.
Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 04/2005; 570(2):237-44. DOI:10.1016/j.mrfmmm.2004.11.008 · 3.68 Impact Factor
Available from: Mary N Mohankumar
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ABSTRACT: Low energy neutrons (< 1 MeV) are known to induce complex chromosome aberrations due to their high radiobiological effectiveness (RBE). These complex chromosome aberrations normally escape detection by conventional giemsa staining methods. Data on the RBE of low energy neutrons is required in order to estimate risks, provide protection measures for nuclear workers, air and space crew personnel and also assign realistic dose estimates among survivors of the atomic bombings at Hiroshima and Nagasaki. In the present study, lymphocytes from five healthy donors were irradiated in vitro with mono-energetic neutrons of energies 2.3, 1.0, 0.79, 0.57, 0.37 and 0.186 MeV, using the Hiroshima University Radiobiological Accelerator (HIRRAC). Cultures were stimulated and cells arrested at metaphase were hybridised with FISH probes and analysed for chromosome aberrations. Many metaphase spreads were found to contain complex chromosomal rearrangements involving 3 or more breaks in 2 or more chromosomes. A wide variety of aberrations including dicentrics, simple translocations, centric and acentric rings, insertions and chromatid type aberrations were observed. A significant number of acentric fragments were indicative of a greater failure to repair chromosomal damage induced by neutrons. Analysis of the various types of aberrations indicate that insertions appear to be produced in significant numbers by neutrons and can be used to determine the neutron energy of maximum LET. Observations made in the present study suggest that the I ratio (ratio of translocation to insertions) is a potential fingerprint for determining the RBE of low energy neurons and other high LET radiations. The present study also indicates that neutrons induce sister chromatid fusions in lymphocytes irradiated in G0 state.
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ABSTRACT: Confluent human fibroblast cells (AG1522) were irradiated with gamma rays, 490 MeV/nucleon silicon ions, or iron ions at either 200 or 500 MeV/nucleon. The cells were allowed to repair at 37 degrees C for 24 h after exposure, and a chemically induced premature chromosome condensation (PCC) technique was used to condense chromosomes in the G2 phase of the cell cycle. Incomplete and complex exchanges were analyzed in the irradiated samples. To verify that chromosomal breaks were truly unrejoined, chromosome aberrations were analyzed using a combination of whole-chromosome specific probes and probes specific for the telomere region of the chromosome. Results showed that the frequency of unrejoined chromosome breaks was higher after irradiation with the heavy ions of high LET, and consequently the ratio of incomplete to complete exchanges increased steadily with LET up to 440 keV/microm, the highest LET included in the present study. For samples exposed to 200 MeV/nucleon iron ions, chromosome aberrations were analyzed using the multicolor FISH (mFISH) technique, which allows identification of both complex and truly incomplete exchanges. Results of the mFISH study showed that 0.7 and 3 Gy iron ions produced similar ratios of complex to simple exchanges and incomplete to complete exchanges; these ratios were higher than those obtained after exposure to 6 Gy gamma rays. After 0.7 Gy of iron ions, most complex aberrations were found to involve three or four chromosomes, which is a likely indication of the maximum number of chromosome domains traversed by a single iron-ion track.
Radiation Research 11/2003; 160(4):418-24. DOI:10.1667/RR3061 · 2.91 Impact Factor
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