Radiation-induced chromosome aberrations in human euchromatic (17cen-p53) and heterochromatic (1cen-1q12) regions

Abstract

The constitutively heterochromatic 1q12 band and the primarily euchromatic 17cen-p53 region comprise a similar size in terms of percentage of the total human genome but have a completely distinguishable chromatin structure. The aim of this study is to unravel whether this structural difference has an impact on the formation and processing of radiation-induced chromosome aberrations. To do so, we have analysed the initial induction and the long-term persistence of radiation-induced (3 Gy gamma-rays) chromosomal aberrations with breakpoints in either the 1q12 band or the 17cen-p53 region in comparison with the behaviour of the overall genome. The fusigenic potential of euchromatic and heterochromatic ends was also compared. This time course experiment was performed in a human lymphoblastoid cell line with sampling times at 1, 3, 7, 14 and 56 days after irradiation. The outcome of this study, with 68 000 metaphases studied by multicolour FISH, with centromeric (1cen and 17cen), paracentric (1q12) and locus specific (p53 gene) probes, revealed: (i) a similar radiosensitivity of all regions analysed irrespective of their chromatin configuration; (ii) a possible enhanced fusigenic potential of heterochromatic chromosome ends; (iii) a rapid decline of 1q12 translocations; and (iv) a similar long-term behaviour of translocations involving 1q12 and 17cen-p53. The implications of these findings in biomonitoring studies are discussed.

γH2AX Foci Form Preferentially in Euchromatin after Ionising-Radiation

“…A considerable body of published work exists that compares the frequencies of radiation induced CAs originating in heterochromatin versus euchromatin, (see for example [36] and references within), but there is no consensus as to whether radiation induced CAs occur with higher or lower than expected frequencies in heterochromatin. Notably though, a recent study has shown no difference in the frequency of γ-radiation-induced chromosome breaks between the largest block of heterochromatin in the human genome (1cen-1q12) and a similarly sized euchromatic region [21]. On balance, it seems unlikely that the lack of γH2AX foci in heterochromatin could be fully accounted for by a lower sensitivity to DSB induction in these regions.…”

“…No consistent pattern emerges from the literature, possibly because of differences in the species or cell type used or the means by which CAs were examined. Notably though, when Puerto et al (2001) [21] compared the human constitutive heterochromatic 1cen-1q12 region with the similarly sized euchromatic 17cen-p53 region they found no difference in the initial number of γ-radiation induced chromosome breaks, leading to the conclusion that chromatin configuration does not affect radiosensitivity. Histone H2AX phosphorylation is a well established marker of DSBs, and in this study we have found that following ionising radiation, γH2AX foci, are under-represented in heterochromatin in mammalian cells.…”

Cell transcriptional state alters genomic patterns of DNA double-strand break repair in human astrocytes

“…γH2AX nuclear foci have been shown to co-localize with actively transcribing euchromatic regions in a variety of cell types, suggesting that more compact heterochromatic regions may be resistant to H2AX phosphorylation 32–34 . To elucidate the relationship between chromatin state and DSB repair in NHAs, irradiated scratch-edge fetal NHAs were co-stained with antibodies against γH2AX and either di-/trimethyl-lysine-4-histone H3 (H3K4Me2/3) to detect euchromatin, or di-/trimethyl-lysine-9-histone H3 (H3K9Me2/3) to detect heterochromatin 35 .…”

“…However, the mechanistic link between activation, differentiation state and oncogenesis is unclear. As DSBs are known to occur preferentially in open versus closed chromatin domains in a variety of cell types 32–34 , one possible unifying explanation is that changes in the transcriptional state of the cell shift loci between domains, thereby altering their susceptibility to breakage, spatial proximity to other susceptible loci and accessibility to DNA repair machinery. Sensitization to transformation may arise from a pro-neoplastic set of genomic alterations that occurs with greater probability in certain epigenetic states.…”

Effect of DMSO on radiation-induced chromosome aberrations analysed by FISH

“…Fluorescence in situ hybridisation allows us to study the involvement of each human chromosome in radiation-induced aberrations. Whereas some studies support a DNA content proportionality (Matsukoa et al, 1994;Gebhart et al, 1996), other studies have pointed out that some other factors like the chromosome gene content could also be relevant Surralles et al, 1997;Puerto et al, 2001). In a previous study by Cigarran et al (1998), the different involvement of human chromosomes in radiationinduced aberrations showed a better correlation when the surface area of spherical territories of each chromosome in the interphase nuclei was considered.…”