Incomplete chromosome exchanges are not fingerprints of high LET neutrons.
ABSTRACT 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.
SourceAvailable from: Mary N Mohankumar[Show abstract] [Hide abstract]
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: Energetic heavy ions pose a great health risk to astronauts in extended ISS and future lunar and Mars missions. High-LET heavy ions are particularly effective in causing various biological effects, including cell inactivation, genetic mutations, cataracts and cancer induction. Most of these biological endpoints are closely related to chromosomal damage, which can be utilized as a biomarker for radiation insults. Previously, we had studied lowand high-LET radiationinduced chromosome aberrations in human epithelial cells cultured in 2-dimension (2D) using the multicolor banding fluorescence in situ hybridization (mBAND) technique. However, it has been realized that the biological response to radiation insult in a 2D cellular environment in vitro can differ significantly from the response in 3-dimension (3D) or at the actual tissue level. In this study, we cultured human epithelial cells in 3D to provide a more suitable model for human tissue. Human mammary epithelial cells (CH184B5F5/M10) were grown in Matrigel to form 3D structures, and exposed to Fe-ions at NASA Space Radiation Laboratory (NSRL) at the Brookhaven National Laboratory or 137 Cs-gamma radiation source at the University of Texas MD Anderson Cancer Center. After exposure, cells were allowed to repair for 16hr before dissociation and subcultured at low density in 2D. G2 and metaphase chromosomes in the first cell cycle were collected using a chemical-induced premature chromosome condensation (PCC) technique, and chromosome aberrations were analyzed using mBAND technique. With this technique, individually painted chromosomal bands on one chromosome allowed the identification of interchromosomal aberrations (translocation to unpainted chromosomes) and intrachromosomal aberrations (inversions and deletions within a single painted chromosome). Our data indicate a significant difference of the chromosome aberration yield between 2D and 3D cell cultures for gamma exposures, but not for Fe ion exposures. Therefore, the RBE for chromosome aberrations obtained in a 2D model may not represent accurately the RBE for tissues.
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ABSTRACT: Telomeres are specialised nucleoproteic complexes localised at the physical ends of linear eukaryotic chromosomes that maintain their stability and integrity. In vertebrate chromosomes, the DNA component of telomeres is constituted by (TTAGGG)n repeats, which can be localised at the terminal regions of chromosomes (true telomeres) or at intrachromosomal sites (interstitial telomeric sequences or ITSs, located at the centromeric region or between the centromere and the telomere). In the past two decades, the use of molecular cytogenetic techniques has led to a new spectrum of spontaneous and clastogen-induced chromosomal aberrations being identified, involving telomeres and ITSs. Some aberrations involve the chromosome ends and, indirectly, the telomeric repeats located at the terminal regions of chromosomes (true telomeres). A second type of aberrations directly involves the telomeric sequences located at the chromosome ends. Finally, there is a third class of aberrations that specifically involves the ITSs. The aims of this review are to provide a detailed description of these aberrations and to summarise the available data regarding their induction by physical and chemical mutagens.Mutagenesis 08/2011; 27(1):1-15. DOI:10.1093/mutage/ger052 · 3.50 Impact Factor