The non-targeted effects of human exposure to ionising radiation, including transgenerational instability manifesting in the children of irradiated parents, remains poorly understood. Employing a mouse model, we have analysed whether low-dose acute or low-dose-rate chronic paternal γ-irradiation can destabilise the genomes of their first-generation offspring. Using single-molecule PCR, the frequency of mutation at the mouse expanded simple tandem repeat (ESTR) locus Ms6-hm was established in DNA samples extracted from sperm of directly exposed BALB/c male mice, as well as from sperm and the brain of their first-generation offspring. For acute γ-irradiation from 10–100 cGy a linear dose-response for ESTR mutation induction was found in the germ line of directly exposed mice, with a doubling dose of 57 cGy. The mutagenicity of acute exposure to 100 cGy was more pronounced than that for chronic low-dose-rate irradiation. The analysis of transgenerational effects of paternal irradiation revealed that ESTR mutation frequencies were equally elevated in the germ line (sperm) and brain of the offspring of fathers exposed to 50 and 100 cGy of acute γ-rays. In contrast, neither paternal acute irradiation at lower doses (10–25 cGy), nor low-dose-rate exposure to 100 cGy affected stability of their offspring. Our data imply that the manifestation of transgenerational instability is triggered by a threshold dose of acute paternal irradiation. The results of our study also suggest that most doses of human exposure to ionising radiation, including radiotherapy regimens, may be unlikely to result in transgenerational instability in the offspring children of irradiated fathers.

Background: Accumulation of evidence about the epigenetic regulation of genome function suggests the necessity to explore new aspects of the genotoxic action of radiation on the human body. Methodology: A methylation-sensitive PCR assay was used to analyze promoter methylation of p16/CDKN2A, p14/ARF, RASSF1A and GSTP1 genes in blood leukocytes from 103 unirradiated volunteers and 104 irradiated subjects (83 Chernobyl Nuclear Power Plant liquidators and 21 nuclear specialists). Additionally, 21 families whose fathers were nuclear specialists were examined. Results: A significantly elevated frequency of individuals with abnormal methylation of p16/CDKN2A and GSTP1 genes was revealed in the exposed group compared to the control group (p = 0.0097 and p = 0.005, respectively). The occurrence of promoter methylation of RASSF1A gene significantly correlated with aging both in the control group (r = 0, 213; p = 0.006) and in the exposed individuals (r = 0, 212; p = 0,031). No methylated genes were found in the offspring of control families. Conclusion: Our study showed for the fist time that prolonged radiation exposure at low and medium doses is associated with hypermethylation of genes involved in the basic protective functions of cells; an effect that is persistent in blood leukocytes for significant periods after irradiation.

The aim of this work is the study hereditary effects of ionizing radiation on mice progeny, whose parents were irradiated on different stages of spermatogenesis. Male mice BALB/c strain were acute irradiated by γ-radiation at doses 1, 2 and 3 Gy on gamma-unit GYPOS (dose rate-4,5 Gy/min, source-Cs-137). For comparison of sensitivity of different stages of spermatogenesis males were crossed with females the same strain in two weeks (post meiotic stage) and in three months (pre meiotic stage) after an irradiation. The offspring in both cases contained in standard conditions and were killed in the 3-4 weeks of age. DNA was isolated from liver by using DNA Prep TM (IZOGEN Lab). Amplification was performed by using lyophilizated PCR-mix DNA Core TM (IZOGEN Lab) on thermocycler PT-48 (TDL Company). Products of amplification were separated in 1,5 % agaroze gel and visualized by ethydium bromide. For detection effects of irradiation was used RAPD-and ISSR-assays. Analysis of offspring patterns carried out on the basis of comparison with parental patterns, with the purpose of registration of new, "not parental" bands, as case of mutation. We are counting mutation frequency per animal in the group and processed these data statistically. Our results are show, that beginning at dose 1 Gy, mutation frequencies in irradiated offspring is significantly distinguished from the control group. At the same time, change of mutation frequencies is independent of increasing of the irradiation dose. The comparison of sensitivity different stages of spermatogenesis is indicated, that post-irradiated changes in RAPD-and ISSR-patterns of pre and post meiotic cells have similar character.

Study of the long-term and transgeneration effects after exposure of ionizing radiation, as manifestation of genomic instability, is very important for predication of emergency radiation situations' consequences. We were investigated exposure of γ-radiation in doze range 1 -6 Gy on example of amounts of the single-starnd DNA breaks (SSB) in the spleen lymphocytes (SL) of irradiated mice and changes in RAPD-and ISSR-patterns of their progeny. Male mice BALB/c strain were acute irradiated by γ-radiation at doses 1, 2, 3 and 6 Gy on gamma-unit GYPOS (dose rate-4,5 Gy/min, source-Cs-137). For the study of long-term effects, mice were killed in an 11 months after irradiation. The SSB-level was evaluated using the alkaline comet-assay as described by Singh et al. [1998] with additional exposure of the hydrogen peroxide. The DNA comets analyzed with a fluorescence microscope AxioPhote by using the method of visual estimation [Collins et al., 1995]. For study of transgeneration effects after irradiation and comparison of sensitivity of different stages of spermatogenesis males were crossed with females the same strain in two weeks (post meiotic stage) and in three months (pre meiotic stage) after an irradiation. The offspring in both cases contained in standard conditions and were killed in the 3-4 weeks of age. DNA was isolated from liver by using DNA Prep TM (IZOGEN Lab). Amplification was performed by using lyophilizated PCR-mix DNA Core TM (IZOGEN Lab) on thermocycler PT-48 (TDL Company). Products of amplification were separated in 1,5 % agaroze gel and visualized by ethydium bromide. For detection effects of irradiation was used RAPD-and ISSR-assays. Analysis of offspring patterns carried out on the basis of comparison with parental patterns, with the purpose of registration of new, "not parental" bands, as case of mutation. We are counting mutation frequency per animal in the group and processed these data statistically. Our results are show, that the SL of the animals irradiated dozes 1 -3 Gy were more resistance to H 2 O 2 exposure, but, beginning at dose 1 Gy, mutation frequencies in irradiated offspring is significantly distinguished from the control group. At the same time, change of mutation frequencies is independent of increasing of the irradiation dose. The comparison of sensitivity on different stages of spermatogenesis are indicated, that post-irradiated changes in RAPD-and ISSR-patterns of pre and post meiotic cells have similar character 120