Drosophila mutations at the mei-9 and mus(2)201 loci which block excision of thymine dimers also block induction of unscheduled DNA synthesis by methyl methanesulfonate, ethyl methanesulfonate, N-methyl-N-nitrosourea, UV light and X-rays

The mei-9 and mus(2)201 mutants of Drosophila melanogaster were identified as mutagen-sensitive mutants on the basis of larval hypersensitivity to methyl methanesulfonate and characterized as excision repair-deficient on the basis of a greatly reduced capacity to excise thymine dimers from cellular DNA. The high degree of larval cytotoxicity observed with a variety of other chemical and physical agents indicated that these mutants may be unable to excise other important classes of DNA adducts. We have measured the ability of the single mutants and the double mutant combination mei-9;mus(2)201 to perform the resynthesis step in excision repair by means of an autoradiographic analysis of unscheduled DNA synthesis (UDS) induced in a mixed population of primary cells in culture. The 3 strains exhibit no detectable UDS activity in response to applied doses of 1.5-6.0 mM methyl methanesulfonate, 1.0-4.5 mM N-methyl-N-nitrosourea or 10-40 J/m2 254-nm UV light, dose ranges in which control cells exhibit a strong dose-dependent UDS response. The mei-9 and mei-9;mus(2)201 mutants also have no detectable UDS response to X-ray doses of 300-1800 rad, whereas the mus(2)201 mutant exhibits a reduced, but dose-dependent, response over this range. These data correlate well with the degree of larval hypersensitivity of the strains and suggest that mutations at both loci block the excision repair of a wide variety of DNA damage prior to the resynthesis step.     

The offspring of irradiated parents, are they stable?

Mutation induction in directly exposed cells is currently regarded as the main component of the genetic risk of ionising radiation for humans. However, recent studies showing that exposure to ionising radiation results in elevated mutation rates detectable in the non-irradiated progeny of exposed cells challenge the existing paradigm in radiation biology. This review describes some recent data on radiation-induced genomic instability in vitro and mainly focuses on the in vivo phenomenon of transgenerational instability, where elevated mutation rates are detected in the non-exposed offspring of irradiated parents. The possible mechanisms and implications of transgenerational instability are also discussed.     

Mutations at the mei-41, mus(1)101, mus(1)103, mus(2)205 and mus(3)310 loci of Drosophila exhibit differential UDS responses with different DNA-damaging agents

5 mutagen-sensitive mutants of Drosophila melanogaster, reported to perform normal or only slightly reduced excision repair of UV damage, were examined by an unscheduled DNA synthesis (UDS) assay. This assay measures the ability of cultured primary cells, derived from each mutant, to perform the resynthesis step in the excision repair pathway, following damage to cellular DNA by direct-acting alkylating agents, UV or X-irradiation. 2 mutants, classified as completely or partially proficient for both excision and postreplication repair of UV damage, mus(1)103 and mus(2)205, were found to give positive UDS responses only for UV damage. These mutants exhibit no measurable UDS activity following DNA damage by several different alkylating agents and X-rays. 3 mutants, classified as having no defect in excision repair, but measurable defects in postreplication repair of UV damage, mei-41, mus(1)101, and mus(3)310 exhibit 3 different response patterns when tested with the battery of agents in the UDS assay. The mutant mei-41 exhibits a highly positive UDS response following damage by all agents, consistent with its prior classification as excision-repair-proficient, but postreplication-repair-deficient for UV damage. The mutant mus(1)101, however, exhibits a strong positive UDS response following only UV damage and appears to be blocked in the excision repair of damage produced by both alkylating agents and X-irradiation. Finally, mus(3)310 exhibits no UDS response to alkylation, X-ray or UV damage. This is not consistent with its previous classification. Results obtained with the quantitative in vitro UDS assay are entirely consistent with the results from two separate in vivo measures of excision repair deficiency following DNA damage, larval hypersensitivity to killing and hypermutability in the sex-linked recessive lethal test.     

Transgenerational transmission of radiation induced genomic instability

Stability of genome is one of the evolutionary important trait of cells. Various mutations (gene, chromosomal, genomic) as well as artificial manipulations with genomes (inbreeding, DNA transfection, introduction of Br-DU in DNA) cause the genetic instability. Ionizing radiation is known as the factor which induced instability of genome in late mitotic descendants of cells after in vitro and in vivo exposure. Radiation induced genetic instability can be transmitted through germline cells. On the cell level both types of radiation induced genomic instability are manifested in elevated frequency of mutations, chromosome aberrations, micronuclei, increased radiosensitivity, disappearance of adaptive response, changes in gene expression. In studies of 1970-1980 years clear evidences on the different morphological and functional injuries in tissues of irradiated organisms as well as in tissues of the progeny of exposed parents were obtained. On the organism level the instability of mitotic and of meiotic progeny of irradiated cells is resulted in increased risk of cancer and of other somatic diseases. It seems to be useful to review the earlier radiobiology literature where delayed and transgenerational effects of ionizing radiation on tissues and on organisms level were clearly shown in animals. For the estimation of pathogenic role of radiation induced genomic instability in humans, particularly in children of exposed parents the parallel study of the same human cohorts using clinical parameters and various characteristic of genomic instability seems to be very important.     

Postreplication repair-defective mutants of Drosophila melanogaster fall into two classes

Summary Primary cell cultures derived from embryos of a control stock of Drosophila melanogaster respond to ultraviolet light within the first hour after exposure with a decline in thymidine incorporation and a decline in the ability to form newly synthesized (nascent) DNA in long segments. Cells derived from two nonallelic excision-defective mutants (mei-9 and mus201) exhibit the same quantitative decline in both phenomena as do control cells. In contrast, cells from five nonallelic postreplication repair-defective mutants (mei-41, mus101, mus205, mus302 and mus310) respond to ultraviolet light by synthesizing nascent DNA in abnormally short segments. Two of these five mutants (mus302 and mus310) also exhibit unusually low thymidine incorporation levels after irradiation, whereas the other three mutants display the normal depression of incorporation.These results indicate that excision repair does not influence the amount or the length of nascent DNA synthesized in Drosophila cells within the first hour after exposure to ultraviolet light. Of the five mutations that diminish postreplication repair, only two reduce the ability of irradiated cells to synthesize normal amounts of DNA.Abbreviation used UV ultraviolet light — principal wavelength 254 nm     

Radiosensitive Drosophila lines. VIII. The effect of the mus (201)Gl gene of Drosophila melanogaster on the sensitivity of the flies to ultraviolet rays in the imago stage

The effect of UV-light on survival of adult flies of the mutant line mus(2) 201G1 sensitive to methyl methanesulfonate (MMS) was studied. One day old flies were irradiated by UV-light and the survival was determined depending on the UV dose, the genotype and the sex of irradiated flies. High sensitivity of mutant flies was shown in the imaginal stage when division of somatic cells was absent. Moreover, the differences in sensitivity to UV-light were observed depending on the sex of flies. We suggest that the mutation mus(2)201G1 blocking the excision repair affects undivisional cells of the imaginal stage of Drosophila melanogaster.     

Genetic study on the effects of the repair-deficient mutant females mei-9a, mei-41D5, mus101D1, mus104D1 and mus302D1 of Drosophila on spontaneous and X-ray-induced chromosome loss in the paternal genome

The repair-deficient mutants mei-9a, mei-41D5, mus101D1, mus104D1 and mus302D1 in Drosophila melanogaster were investigated regarding their effects on spontaneous and X-ray-induced chromosome loss in postmeiotic cells. Each mutant was incorporated singly into XC2, and the ring-X male provided with BSYy+. From matings of males carrying mus101D1, mus302D1 or mei-41D5, mutants identifying a caffeine-sensitive (CAS) postreplication-repair pathway, with corresponding mutant females, and non-mutant males to non-mutant females, overall frequencies of spontaneous partial loss and spontaneous complete loss were significantly increased in each mutant cross except for spontaneous complete loss with mus302 where an increase was noted only in brood 2. Similar findings were noted when males carrying the excision-repair mutant mei-9a were mated with mei-9a females. Males carrying the mutant mus104D1, identifying a caffeine-insensitive (CIS) postreplication-repair pathway, tested with mus104D1 females, produced results that were not significantly different from non-mutant controls. When males were given 3000 rad X-irradiation, frequencies of induced partial loss were significantly higher with mus101D1, mus302D1, mei-41D5 and mei91, and not significantly higher with mus101D1, mus302D1, mei41D5 and mei-9a, and not significantly different from controls with mus104D1. It was suggested that the functional CAS postreplication-repair pathway primarily promotes repair of breaks while an alternative pathway(s) not defined by mus104 promotes misrepair. Therefore, the significant increases in both spontaneous and induced partial loss with the excision-repair-deficient mutant mei-9a suggests the possibility that (a) the excision-repair-pathway may not function in misrepair and (b) the undefined misrepair pathway may be dominant pathway for postreplication repair in Drosophila since mei-9a females presumably have functional postreplication repair and misrepair capacity. The suggestion that the CAS postreplication-repair pathway and the excision-repair pathway function primarily in repair, and an undefined pathway in misrepair is in line with the finding that with mus104D1, no significant increase was found in spontaneous complete loss, but with mus101D1, mus302D1, mei-41D5 and mei-9a significant increases were observed. Results on induced complete loss, with the exception of those with mei-41D5, show a poor correlation with other classes of loss of each of the mutants. Possible explanations for this discrepancy are discussed.     

The influence of gamma-irradiation in low doses on the rate of dominant lethal mutations in drosophila melanogaster

The dose-rate effect of acute and chronic irradiation in the dose of 0.2 Gy in Drosophila melanogaster repair (mei-41, mus209 [Russian character: see text] mus309) and free radicals detoxication (sod) mutant strains was investigated. Was shown the lack of dose rate effect on the rate of dominant lethal mutations in mei-41, mus209 and sod. However in mus309, that has defect in the main Drosophila pathway of the DNA double strand breack repair, the increase of the mutation rate after chronic irradiation was observed (inverse dose-rate effect). The obtained results suggest the main role of DNA double strand breack repair in dose-rate effect formation in Drosophila.     

Identification of a Second Locus in DROSOPHILA MELANOGASTER Required for Excision Repair

The mus(2)201 locus in Drosophila is defined by two mutant alleles that render homozygous larvae hypersensitive to mutagens. Both alleles confer strong in vivo somatic sensitivity to treatment by methyl methanesulfonate, nitrogen mustard and ultraviolet radiation but only weak hypersensitivity to X-irradiation. Unlike the excision-defective mei-9 mutants identified in previous studies, the mus(2)201 mutants do not affect female fertility and do not appear to influence recombination proficiency or chromosome segregation in female meiocytes.—Three independent biochemical assays reveal that cell cultures derived from embryos homozygous for the mus(2)^D1 allele are devoid of detectable excision repair. 1. Such cells quantitatively retain pyrimidine dimers in their DNA for 24 hr following UV exposure. 2. No measurable unscheduled DNA synthesis is induced in mutant cultures by UV treatment. 3. Single-strand DNA breaks, which are associated with normal excision repair after treatment with either UV or N-acetoxy-N-acetyl-2-aminofluorene,* are much reduced in these cultures. Mutant cells possess a normal capacity for postreplication repair and the repair of single-strand breaks induced by X-rays.     

Trans-generational radiation-induced chromosomal instability in the female enhances the action of chemical mutagens

Genomic instability can be produced by ionising radiation, so-called radiation-induced genomic instability, and chemical mutagens. Radiation-induced genomic instability occurs in both germinal and somatic cells and also in the offspring of irradiated individuals, and it is characterised by genetic changes including chromosomal rearrangements. The majority of studies of trans-generational, radiation-induced genomic instability have been described in the male germ line, whereas the authors who have chosen the female as a model are scarce. The aim of this work is to find out the radiation-induced effects in the foetal offspring of X-ray-treated female rats and, at the same time, the possible impact of this radiation-induced genomic instability on the action of a chemical mutagen. In order to achieve both goals, the quantity and quality of chromosomal damage were analysed.

In order to detect trans-generational genomic instability, a total of 4806 metaphases from foetal tissues from the foetal offspring of X-irradiated female rats (5 Gy, acute dose) were analysed. The study's results showed that there is radiation-induced genomic instability: the number of aberrant metaphases and the breaks per total metaphases studied increased and were found to be statistically significant (p ≤ 0.05), with regard to the control group.

In order to identify how this trans-generational, radiation-induced chromosomal instability could influence the chromosomal behaviour of the offspring of irradiated rat females in front of a chemical agent (aphidicolin), a total of 2481 metaphases were studied. The observed results showed that there is an enhancement of the action of the chemical agent: chromosomal breaks per aberrant metaphases show significant differences (p ≤ 0.05) in the X-ray- and aphidicolin-treated group as regards the aphidicolin-treated group.

In conclusion, our findings indicate that there is trans-generational, radiation-induced chromosomal instability in the foetal cells from X-ray-treated female rats and that this RIGI enhances the chromosomal damage caused by the chemical agent aphidicolin.     

Induction of mutations in unirradiated X-chromosome of Drosophila melanogaster hybrids of repair deficient females mei-41 [D5] and mus209 [B1] and irradiated males M5

It has been analyzed the frequency of the recessive lethal mutations in the unirradiated X-chromosome of Drosophila. Females of wild type (CS) as well as of error-prone (mei-41) and error-free (mus209) mutant strains were used. In CS hybrids the increasing of the mutation rate (p < 0.05) was found. In muc209 hybrids the mutation rate was not affected. In mei-41 hybrids the tendency to decreasing of the mutation rate was found. The obtained results demonstrate the possible role of error-prone repair in the inducing of mutations in the unirradiated X-chromosome in the presence of irradiated homologue.     

A cell-cycle stage-related chromosomal X-ray hypersensitivity in larval neuroblasts of Drosophila mei-9 and mei-41 mutants suggesting defective DNA double-strand break repair

We have examined the chromosomal X-ray hypersensitivity in relation to the cell cycle in larval neuroblasts of the mutagen-sensitive and excision repair-defective mutant mei-9 and of the mutagen-sensitive and post-replication repair-defective mutant mei-41 of Drosophila melanogaster. When compared to wild-type cells, cells bearing the mei-9L1 allele produced unusually high levels in particular of chromatid deletions and to a lesser extent also of isochromatid deletions, but virtually no exchange aberrations. The chromosomal hypersensitivity is apparent at M1 when cells are irradiated in S or G2 but not when irradiated in G1. On the other hand, following irradiation cells bearing the mei-41D5 allele predominantly produce chromosome deletions. Also dicentric and chromatid exchange formation is enhanced with a moderate increase in chromatid deletions. The phases of major sensitivity are the S and G1. Mei-9 and mei-41 mutants have been classified to date as proficient in DNA double-strand break repair. The data presented in this paper revealed an S-independent clastogenic hypersensitivity of mei-9 and mei-41 cells. They are interpreted as indicative evidence for the presence of impaired DNA double-strand break repair. The cell-cycle-related difference in the ratio of chromatid- versus chromosome-type deletions in both mutants suggests repair defects at partially different phases of the cell cycle in mei-9 and mei-41 mutant cells.     

Transgenerational genomic instability in the first generation offspring of mice exposed to low-intensity red and near-infrared irradiation in vivo

Transgenerational genomic instability in the first generation offspring of mice exposed to lowintensity infrared laser (632.8 nm) and light-emitting-diode infrared irradiation (850 nm) was investigated in vivo. It was found that the level of spontaneous damage in bone marrow according to the micronucleus test, the level of reactive oxygen species in whole blood, and the mass index of lymphoid organs in all of the descendants of irradiated mice did not increase. After additional X-ray exposure of the progeny at a dose rate of 1.5 Gy, a decrease in the level of damage and the absence of an adaptive response were revealed upon testing according to “radiosensitivity” and the radiation-induced adaptive-response scheme (0.1 + 1.5 Gy), respectively, compared to the descendants of nonirradiated mice. The rate of tumor growth in the offspring of irradiated mice did not differ from that in the descendants of nonirradiated mice, although inhibition of the tumor growth rate was observed in their irradiated parents. The survival rate after irradiation at a dose rate of 6.5 Gy did not differ from both the parents and the control.

     

Damaging and protective cell signalling in the untargeted effects of ionizing radiation

The major adverse consequences of radiation exposures are attributed to DNA damage in irradiated cells that has not been correctly restored by metabolic repair processes. However, the dogma that genetic alterations are restricted to directly irradiated cells has been challenged by observations in which effects of ionizing radiation arise in non-irradiated cells. These, so called, untargeted effects are demonstrated in cells that are the descendants of irradiated cells either directly or via media transfer (radiation-induced genomic instability) or in cells that have communicated with irradiated cells (radiation-induced bystander effects). Radiation-induced genomic instability is characterized by a number of delayed responses including chromosomal abnormalities, gene mutations and cell death. Bystander effects include increases or decreases in damage-inducible and stress-related proteins, increases or decreases in reactive oxygen and nitrogen species, cell death or cell proliferation, cell differentiation, radioadaptation, induction of mutations and chromosome aberrations and chromosomal instability. The phenotypic expression of untargeted effects and the potential consequences of these effects in tissues reflect a balance between the type of bystander signals produced and the responses of cell populations to such signals, both of which may be significantly influenced by cell type and genotype. Thus, in addition to targeted effects of damage induced directly in cells by irradiation, a variety of untargeted effects may also make important short-term and long-term contributions to determining overall outcome after radiation exposures.     

Hypersensitivity of Drosophila mei-41 mutants to hydroxyurea is associated with reduced mitotic chromosome stability

6 mutant alleles of the mei-41 locus in Drosophila melanogaster are shown to cause hypersensitivity to hydroxyurea in larvae. The strength of that sensitivity is directly correlated with the influence of the mutant alleles on meiosis in that: alleles exhibiting a strong meiotic effect (mei-41D2, mei-41D5, mei-41D7) are highly sensitive; alleles with negligible meiotic effects (mei-41(104)D1, mei-41(104)D2) are moderately sensitive and an allele which expresses meiotic effects only under restricted conditions (mei-41D9) has an intermediate sensitivity. This sensitivity is not a general feature of strong postreplication repair-deficient mutants, because mutants with that phenotype from other loci do not exhibit sensitivity (mus(2)205A1, mus(3)302D1, mus(3)310D1). The observed lethality is not due to hypersensitivity of DNA synthesis in mei-41 larvae to hydroxyurea as assayed by tritiated thymidine incorporation. Lethality is, however, potentially attributable to an abnormal enhancement of chromosomal aberrations by hydroxyurea in mutant mei-41 larvae. Both in vivo and in vitro exposure of neuroblast cells to hydroxyurea results in an increase in 3 types of aberrations which is several fold higher in mei-41 tissue. Since hydroxyurea disrupts DNA synthesis, these results further implicate the mei-41 locus in DNA metabolism and provide an additional tool for an elucidation of its function. The possible existence of additional genes of this nature is suggested by a more modest sensitivity to hydroxyurea which has been detected in two stocks carrying mutagen-sensitive alleles of alternate genes.     

Genomic instability in the offspring of irradiated parents: Facts and interpretations

This review is devoted to genomic instability in the offspring of parents that were irradiated or treated with chemical mutagens. The evidence is presented, showing high frequency of cancer diseases and instability of the genome of somatic and germline cells in the offspring of radiation-exposed animals. Possible epigenetic mechanisms of these effects are considered, as well as their significance as components of genetic factors of radiation risk for humans.     

Genomic instability in the offspring of irradiated parents: facts and interpretations

This review is devoted to genomic instability in the offspring of parents that were irradiated or treated with chemical mutagens. The evidence is presented, showing high frequency of cancer diseases and instability of the genome of somatic and germline cells in the offspring of radiation-exposed animals. Possible epigenetic mechanisms of these effects are considered, as well as their significance as components of genetic factors of radiation risk for humans.     

The relationship between reaction kinetics and mutagenic action of monofunctional alkylating agents in higher eukaryotic systems. IV. The effects of the excision-defective mei-9L1 and mus(2)201D1 mutants on alkylation-induced genetic damage in Drosophila

Repair-defective mutants of Drosophila melanogaster which identify two major DNA excision repair loci have been examined for their effects on alkylation-induced mutagenesis using the sex-linked recessive lethal assay as a measure of genotoxic endpoint. The alkylating agents (AAs) chosen for comparative analysis were selected on the basis of their reaction kinetics with DNA and included MMS, EMS, MNU, DMN, ENU, DEN and ENNG. Repair-proficient males were treated with the AAs and mated with either excision-defective mei-9L1 or mus(2)201D1 females or appropriate excision-proficient control females. The results of the present work suggest that a qualitative and quantitative relationship exists between the nature and the extent of chemical modification of DNA and the induction of of genetic alterations. The presence of either excision-defective mutant can enhance the frequency of mutation (hypermutability) and this hypermutability can be correlated with the Swain-Scott constant S of specific AAs such that as the SN1 character of the DNA alkylation reaction increases, the difference in response between repair-deficient and repair-proficient females decreases. The order of hypermutability of AAs with mei-9L1 relative to mei-9+ is MMS greater than MNU greater than DMN = EMS greater than iPMS = ENU = DEN = ENNG. When the percentage of lethal mutations induced in mei-9L1 females are plotted against those determined for control females, straight lines of different slopes are obtained. These mei-9L1/mei-9+ indices are: MMS = 7.6, MNU = 5.4, DMN = 2.4, EMS = 2.4 and iPMS = ENU = DEN = ENNG = 1. An identical order of hypermutability with similar indices is obtained for the mus(2)201 mutants: MMS(7.3) greater than MNU (5.4) greater than EMS(2.0) greater than ENU(1.1). Thus, absence of excision repair function has a significant effect on mutation production by AAs efficient in alkylating N-atoms in DNA but no measurable influence on mutation production by AAs most efficient in alkylating O-atoms in DNA. The possible nature of these DNA adducts has been discussed in relation to repair of alkylated DNA. In another series of experiments, the effect on alkylation mutagenesis of mei-9L1 was studied in males, by comparing mutation induction in mei-9L1 males vs. activity in Berlin K (control). Although these experiments suggested the existence of DNA repair in postmeiotic cells during spermatogenesis, no quantitative comparisons could be made.(ABSTRACT TRUNCATED AT 400 WORDS)     

Studies on mutagen-sensitive strains of Drosophila melanogaster. II. Detection of qualitative differences between genetic damage induced by X-irradiation of mature spermatozoa in oxygenated and anoxic atmospheres through the use of the repair-deficient mutant mei-9a

Muller-5 males were irradiated with X-rays in nitrogen, in air or in oxygen (followed by nitrogen or oxygen post-treatments in the nitrogen and oxygen series) and were mated to females of a repair-proficient strain (mei+) or to those of a strain known to be deficient in excision repair of UV damage (in somatic cells). The latter strain, designated as mei-9a, is also known to be sensitive, in the larval stages, to the killing effects of UV, X-rays and to a number of chemical mutagens. The frequencies of sex-linked recessive lethals and autosomal translocations induced in the spermatozoa of males were determined and compared. The frequencies of sex-linked recessive lethals in the mei-9 control groups were consistently higher than in the mei+ groups. Irradiation in air or in nitrogen led to significantly higher yields of recessive lethals when the irradiated males were mated to mei-9 females, whereas, after irradiation in oxygen, the yields were similar with both kinds of female. No significant differences in the frequencies of reciprocal translocations were observed between the mei+ and mei-9 groups after irradiation of the males in nitrogen, in air or in oxygen. Likewise, no differential effects of the contrasting post-treatments (nitrogen versus oxygen), either for recessive lethals or for translocations, could be discerned. These results are considered to support the notion that the kinds of genetic damage induced in mature spermatozoa in air or in nitrogen are qualitatively similar (at least with respect to the component(s) that lead to the production of recessive lethal mutations), but clearly different when induced in an oxygen atmosphere. The enhanced yields of recessive lethals with mei-9 females (after irradiation of the males either in air or in nitrogen) has been interpreted on the assumption that the mei-9 mutant is also deficient for the repair of X-ray-induced, recessive lethal-generating premutational lesions. Possible reasons for the lack of differences between the mei+ and mei-9 groups with respect to translocation yields and for the absence of measurable differences in response between the contrasting post-treatments (after irradiation of the males in nitrogen) are discussed.     

The effects of maternal irradiation during adulthood on mutation induction and transgenerational instability in mice

The long-term genetic effects of maternal irradiation remain poorly understood. To establish the effects of radiation exposure on mutation induction in the germline of directly exposed females and the possibility of transgenerational effects in their non-exposed offspring, adult female BALB/c and CBA/Ca mice were given 1Gy of acute X-rays and mated with control males. The frequency of mutation at expanded simple tandem repeat (ESTR) loci in the germline of directly exposed females did not differ from that of controls. Using a single-molecule PCR approach, ESTR mutation frequency was also established for both germline and somatic tissues in the first-generation offspring of irradiated parents. While the frequency of ESTR mutation in the offspring of irradiated males was significantly elevated, maternal irradiation did not affect stability in their F(1) offspring. Considering these data and the results of our previous study, we propose that, in sharp contrast to paternal exposure to ionising radiation, the transgenerational effects of maternal high-dose acute irradiation are likely to be negligible.