X-ray induced translocations in bone marrow cells of scid and wild type mice detected by fluorescence in situ hybridization using mouse chromosome specific DNA libraries

Lack of genomic instability in bone marrow cells of SCID mice exposed whole-body to low-dose radiation

It is clear that high-dose radiation is harmful. However, despite extensive research, assessment of potential health-risks associated with exposure to low-dose radiation (at doses below or equal to 0.1 Gy) is still challenging. Recently, we reported that 0.05 Gy of 137Cs gamma rays (the existing limit for radiation-exposure in the workplace) was incapable of inducing significant in vivo genomic instability (measured by the presence of late-occurring chromosomal damage at 6 months post-irradiation) in bone marrow (BM) cells of two mouse strains, one with constitutively high and one with intermediate levels of the repair enzyme DNA-dependent protein-kinase catalytic-subunit (DNA-PKcs). In this study, we present evidence for a lack of genomic instability in BM cells of the severely combined-immunodeficiency (SCID/J) mouse (which has an extremely low-level of DNA-PKcs activity) exposed whole-body to low-dose radiation (0.05 Gy). Together with our previous report, the data indicate that low-dose radiation (0.05 Gy) is incapable of inducing genomic instability in vivo (regardless of the levels of DNA-PKcs activity of the exposed mice), yet higher doses of radiation (0.1 and 1 Gy) do induce genomic instability in mice with intermediate and extremely low-levels of DNA-PKcs activity (indicating an important role of DNA-PKcs in DNA repair).

Telomere alterations and genomic instability in long-term cultures of normal human fibroblasts irradiated with X rays and protons

Telomeres are the end of linear chromosomes, responsible for chromosome stability and cell viability. It is well known that radiations are able to induce chromosome instability but it has not yet been investigated whether telomere structure is affected by the radiation exposure and if radiations with different quality act in a different way on telomeres. The effect of radiations with different quality on telomere structure and chromosome instability was analysed in human primary fibroblasts exposed to X rays or low-energy protons (28.5 keV μm(-1)). Telomere length was evaluated at different harvesting times from 24 h up to 360 h (15 days), whereas chromosome instability was evaluated in terms of sister chromatid exchanges (SCEs) (48 h from irradiation) and chromosome painting (360 h from irradiation). Results indicated a delayed telomere lengthening 360 h after X-ray treatment, whereas protons were able to induce such a lengthening shortly from irradiation as well as at longer harvesting times. Data obtained from chromosome instability analysis indicated an increase of SCE frequency only after proton irradiation, but, on the contrary, at the longer harvesting time chromosome painting analysis displayed a higher frequency of aberrations after X-ray treatment, suggesting a role of selective process against highly damaged cells.

Involvement of G2-dependent DNA double-strand break repair in the formation of ultraviolet light B-induced chromosomal aberrations

Wortmannin, an inhibitor of DNA double-strand break (DSB) repair added 19 h before harvest enhanced the incidence of ultraviolet light B (UVB)-induced chromatid aberrations in Chinese hamster V79 cells. Posttreatment with wortmannin for last 3 h of culture also enhanced the yield of breakage-type chromatid aberrations and suppressed the yield of exchange-type chromatid aberrations almost completely. Thus, the inhibition of DSB repair in the G2 phase stimulated the breakage-type aberration formation, while suppressing the exchange-type aberration formation. We propose the model of UVB-induced chromatid-type aberration formation which might be fully related to G2-dependent DSB repair pathway.

Persistence of radiation-induced translocations in rat peripheral blood determined by chromosome painting

In this article, we address the issue of persistence of chromosome exchanges following acute in vitro exposure of rat peripheral blood to 137Cs. Irradiation occurred 24 hr after culture initiation, and metaphase chromosomes were prepared 2, 3, 4, and 5 days later. Chromosomes 1, 2, and 4 were painted in unique colors and scored for structural aberrations. Dicentric chromosomes and acentric fragments diminished rapidly with time, as expected. Translocations exhibited greater persistence, but still showed a reduction in frequency, reaching a plateau of approximately 65 and 55% of their initial values, 4 days after exposure to 1 and 2 Gy, respectively. An exponentially declining model was fit to the combined dicentric, acentric fragment, and translocation frequencies, which showed that all three aberration types declined at equivalent rates. The frequencies of dicentrics and fragments declined to a plateau of zero, while translocations reached a plateau at frequencies significantly greater than zero. The decline in translocations with time is inconsistent with prevailing theoretical expectations, but is consistent with a model where some translocations are fully stable (persistent) and some are unstable (not persistent) through cell division. These results may have implications for radiation biodosimetry in humans.