Induction Of Mutations In Mice Research Articles

The effects of extremely low frequency magnetic fields on mutation induction in mice

The growing human exposure to extremely low frequency (ELF) magnetic fields has raised a considerable concern regarding their genotoxic effects. The aim of this study was to evaluate the in vivo effects of ELF magnetic fields irradiation on mutation induction in the germline and somatic tissues of male mice. Seven week old BALB/c×CBA/Ca F1 hybrid males were exposed to 10, 100 or 300μT of 50Hz magnetic fields for 2 or 15h. Using single-molecule PCR, the frequency of mutation at the mouse Expanded Simple Tandem Repeat (ESTR) locus Ms6-hm was established in sperm and blood samples of exposed and matched sham-treated males. ESTR mutation frequency was also established in sperm and blood samples taken from male mice exposed to 1Gy of acute X-rays. The frequency of ESTR mutation in DNA samples extracted from blood of mice exposed to magnetic fields did not significantly differ from that in sham-treated controls. However, there was a marginally significant increase in mutation frequency in sperm but this was not dose-dependent. In contrast, acute exposure X-rays led to significant increases in mutation frequency in sperm and blood of exposed males. The results of our study suggest that, within the range of doses analyzed here, the in vivo mutagenic effects of ELF magnetic fields are likely to be minor if not negligible.

Stage-specificity of spontaneous mutation at a tandem repeat DNA locus in the mouse germline

Mouse expanded simple tandem repeat (ESTR) loci are the most unstable loci in the mouse genome. Despite the fact that over the last decade these loci have been extensively used for studying germline mutation induction in mice, to date little is known about the mechanisms underlying spontaneous and induced ESTR mutation. Here we used flow cytometry and single-molecule PCR to compare the frequency of ESTR mutation in four flow-sorted fractions of the mouse male germ cells – spermatogonia, spermatocytes I, round and elongated spermatids. The frequency and the spectrum of ESTR mutation did not significantly differ between different stages of mouse spermatogenesis. Considering these data and the results of other publications, we propose that spontaneous ESTR mutation is mostly attributed to replication slippage in spermatogonia and these loci may be regarded as a class of expanded microsatellites.

Germline mutation induction at mouse and human tandem repeat DNA loci.

The ability to predict the genetic consequences for humans of exposure to ionising radiation has certainly been one of the most important goals of human genetics in the past fifty years. However, despite numerous experimental studies, little is known about the effects of radiation exposure on germline mutation in humans. For example, data collected in Hiroshima and Nagasaki during the past 40 years on children of atomic bomb survivors using standard monitoring systems have not provided evidence of any statistically signifycant differences in mutation rate between exposed and control families (Neel at al., 1990). Similarly, a survey of survivors treated with radiotherapy showed that the occurrence of genetic diseases in their offspring was similar to that in control families (Byrne et al, 1998). For this reason, germline mutation induction in mice still remains the main source of experimental data used to evaluate the genetic risk of human exposure to ionising radiation (UNCEAR, 1993; Sankaranarayanan and Chakraborty, 2000).

Comparison of induction of hprt mutations by 1,3-butadiene and/or its metabolites 1,2-epoxybutene and 1,2,3,4-diepoxybutane in lymphocytes from spleen of adult male mice and rats in vivo

Induction of hprt mutations by 1,3-butadiene (BD) and its metabolites 1,2-epoxybutene (EB) and 1,2,3,4-diepoxybutane (DEB) was studied in lymphocytes from spleens of 6- to 14-week-old mice and 10- to 11-week-old rats. For unknown reasons, results from experiments with mice that received inhalation exposure to BD were quite variable. In the first experiment, mice were exposed for 5 days to 200, 500 or 1300 ppm and this resulted in a statistically significant, dose-dependent, induction of mutations. When the experiment was repeated and an extra expression time for mutations was included, it was not possible to detect induction of mutations. In a third experiment, a 6-day exposure to 500 ppm was mutagenic when mice with zero mutants were not excluded from the statistical analysis of the data. The monofunctional metabolite EB appeared to be mutagenic in mice (3×33 and 3×100 mg/kg), but not in rats (3×33 and 100 mg/kg or 30 days drinking water with 0.1, 0.3 or 1.0 mM EB). Contrary to expectations, there was no induction of mutations in mice and rats exposed to the bifunctional metabolite DEB (mice, 3×7, 21, 3×14, or 42 mg/kg; rats, 20 or 40 mg/kg or 30 days drinking water with 0.3 or 1 mM DEB), although in our earlier studies with mice and rats, DEB treatment significantly enhanced frequencies of micronuclei in splenocytes and in early spermatids of mice and rats. Some of these results differ from findings reported by other investigators. It is now becoming evident that these differences are, to a large extent, due to differences in age of the animals at the time of treatment. For example, the mutagenic potency of BD, EB and DEB was stronger in preweanling mice or 4-week-old mice than in 8- to 12-week-old adult mice.

Induction of hprt Mutations in Mice after Exposure to Fission-Spectrum Neutrons or 60 Co Gamma Rays

The effects of exposure to fission-spectrum neutrons and 60Co gamma rays on mutation induction in B6CF1 mice were investigated. Mutation induction was measured at the hypoxanthine-phosphoribosyl-transferase (hprt) locus in splenic lymphocytes at 56 days after whole-body irradiation. Lymphocytes were cultured 12-16 days in round-bottomed, 96-microwell plates in the presence of 5 x 10(4) feeder cells (syngeneic lymphocytes irradiated with 50 Gy gamma rays). The selective agent used as 6-thioguanine at a concentration of 2.5 micrograms/ml. Animals were exposed to either single doses of neutrons (1.5 Gy) or photons (7.5 Gy) or fractionated doses delivered over 2 weeks of neutrons (0.25 Gy x 6, total 1.5 Gy) or photons (1.5 Gy x 6, total 9.0 Gy). The frequency of hprt mutant induction by fission-spectrum neutrons delivered in a 1.5-Gy single dose compared to a 7.5-Gy single dose of 60Co photons was approximately the same, i.e., 5.98 x 10(-5) +/- 1.51 x 10(-5) (SE) vs. 5.56 x 10(-5) +/- 3.09 x 10(-5) (SE), respectively (Student's two-tailed t test, P = 0.8997). Multiple doses of neutrons gave rise to slightly higher mutant frequencies compared to photons even though the ratio of total doses of neutrons to photons was increased from 5 to 6, i.e., 8.71 x 10(-5) +/- 5.39 x 10(-5) (SE), total dose 1.5 Gy, vs 2.30 x 10(-5) +/- 9.07 x 10(-6) (SE), total dose 9.0 Gy, respectively (Student's two-tailed t test, P = 0.3330). These results suggest that the relative differences in magnitude in radiation-induced genotoxic effects between fission-spectrum neutrons and 60Co gamma rays increase when the comparisons are made between fractionated rather than single-dose exposure regimens.

Comments on Commentary by D. Billen

Billen (1) proposes that the spontaneous to DNA due primarily to the thermodynamic instability arising from storage in the living genome at 37?C can be used to determine a negligible for ionizing radiations. The concept of DNA instability is, I believe, of great relevance to radiobiology, but logically it leads to a rather different conclusion, namely that however small the dose and however low the dose rate there is a finite chance that a biological effect will be caused. The concept of negligible does not belong in the domain of the physicochemical properties of DNA but in the domain of the acceptability of risk, a sociopolitical issue. My argument is as follows. I agree with Billen (1) that about 100 events occur in the genome of the diploid mammalian cell per minute and that cells have evolved efficient repair processes to enable them to cope with this rate of induction. The nature of these sites in double-stranded DNA, the repository of the genetic information, is base loss, base damage, and single-strand breaks, i.e., single-strand damage. While this is being continually produced it must be equally continually being repaired; i.e., there is a dynamic equilibrium between degradation and repair in the living cell. Even at this rate of formation the distances between the transitory lesions are enormous, and so the generation of double-strand due to the coincidence of single-strand sites in opposing strands is indistinguishable from zero. Cells do generate double-strand breaks; however, this is not primarily but rather part of their normal functioning and a controlled process. Radiation induces both singleand double-strand and DNA-protein crosslinks (2). I think, as does Billen, that provided the single-strand is not induced at a rate comparable to the rate of induction of spontaneous single-strand then the continually active repair processes will satisfactorily repair both the radiation-induced and the spontaneous damage. This is then irrelevant to biological effect. However, the double-strand (mainly breaks) and the DNA-protein crosslinks caused by radiation will not necessarily be repaired effectively, and it is these lesions that can constitute relevant damage and lead to biological effects at low dose rates. Thus I would predict that at low dose rates, radiation-induced biological effects would be directly proportional to dose and invariant with dose rate. At dose rates where the ate of induced single-strand was comparable with that ue to spontaneous I would predict a transition to a dependence of effect on dose rate due to the disruption of the dynamic equilibrium between DNA degradation and repair and the consequent build-up of unrepaired of both spontaneous and radiolytic origin. Indeed, such a transition is exactly what is observed for the induction of specific locus mutations in mice when males are irradiated at the spermatogonial stage (to be published elsewhere). At dose rates of 0.015 Gy/min (a singlestrand induction rate of about one-third that due to spontaneous damage) a transition is observed; below this rate mutation frequency is invariant with dose rate, and above this rate it increases sharply with increasing dose rate. Viewed in this way I believe the concept of DNA instability is of considerable value to radiobiology and radiological protection in the following ways:

Induction of mutations in males of the fish Oryzias latipes at a specific locus after γ-irradiation

We have studied frequencies of mutations induced at the b locus of the fish, Medaka Oryzias latipes, after γ-irradiation. Homozygotes for the b locus have colorless melanophores whose phenotypic expression can be distinguished from that of the wild type. An advantage of the use of oviparous fish for detection of skin color mutations is that the mutant phenotype can be confirmed as early as 1.5 days after fertilization because of the transparent egg membrane of the embryo. Wild-type ( B/ B) male fish were exposed to 4.75 or 9.5 Gy of 137Cs γ-rays at a dose of 0.95 Gy/min and then mated witht the female testers ( b/ b). A total of 77 761 F 1 offspring were examined for mutation and other abnormalities. In the control, we had 1 mutant among 22 068 offspring, resulting in a mutation rate of 4.53 × 10 −5/locus/gamete. However, this mutant embryo died before hatching. Therefore, in an attempt to present specific-locus mutation frequencies in the fish, the frequencies of color mutants that survived more than 4 days after hatching were used as frequencies of viable mutants; (number of viable color mutants)/(number of hatched fry that survived more than 4 days after hatching). In the 4.75 Gy-irradiated group the viable mutant frequencies were 45.0 × 10 −5, 69.7 × 10 −5 and 0/locus/gamete, while exposure to 9.5 Gy resulted in mutation rates of 217 × 10 −5, 130 × 10 −5 and 8.06 × 10 −5, respectively, for sperm, spermatids and spermatogonia. In comparison with viable color mutant frequencies those of the total color mutants, which include such mutants as ones that died before hatching (defined as number of total color mutants/number of fertilized eggs minus number of early deaths), were considerably higher. For sperm, spermatids, and spermatogonia after exposure to 4.75 Gy, the frequencies were 1180 × 10 −5, 629 × 10 −5 and 9.90 × 10 −5/locus/gamete, respectively, and in 9.5-Gy-irradiated fish, the frequencies were 1940 × 10 −5, 953 × 10 −5 and 55.5 × 10 −5. Although our data are incomplete, the present results were compared with mutation induction in mice. We concluded that the frequencies of viable color mutants in the fish can be compared with those in mice.

Induced dominant lethality in mice by phosphorus-32.

DESPITE much work on the induction of mutations in mice by ionizing radiations1 and chemicals2–6, the possible mutagenic effects of internally administered radioisotopes have received little attention (see, however, ref. 7). Any genetic effects of radioisotopes are important from the point of view both of the hazards of radioactive fallout and of the use of certain isotopes in human medicine. We present here the results of preliminary observations of the effects of phosphorus-32 in work concerned with the evaluation of genetic hazards of certain important radio-nuclides in mice. Phosphorus-32 is known to produce mutations in Drosophila8 and in micro-organisms9.

HIGH EFFECTIVENESS OF CHRONIC NEUTRON EXPROSURES FOR THE INDUCTION OF SPECIFIC LOCUS MUTATIONS IN MICE.

MAMMALIAN radiation genetics has been largely concerned with the effects of X- and γ-irradiation, about which much has been learned in recent years. Surprisingly little work has been done with neutrons, although it is known that fast neutrons of modal energy around 1 MeV are about six times as effective as acute X-irradiation for the induction of dominant lethal mutations in mouse spermatozoa, whether the neutron dose is administered at high or at low intensity1,2. For the assessment of human hazards from high linear energy transfer radiation, it is particularly important to investigate the effectiveness of chronic neutron exposures with respect to the induction of point mutations in immature germ-cells of mammals. An experiment of this type, using the specific locus method, is now in progress and has revealed a surprisingly high yield of mutations following fast neutron irradiation of mouse spermatogonia.

Induction of mutations in mice by chronic gamma irradiation; interim report.

Estimation of the genetic hazard of ionizing radiations to man calls for ecological and genetic study of human populations and experimental work on other mammals. An interim report is given of a long-term experiment intended to check the linearity of the mutation-rate/radiation-dose law at seven specified loci in the mouse, using low accumulated γ-ray doses.

Comparison of X-Ray-Induced Mutation Rates in Drosophila and Mice

Previous articleNext article No AccessComparison of X-Ray-Induced Mutation Rates in Drosophila and MiceW. L. RussellW. L. Russell Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 90, Number 850Jan. - Feb., 1956Supplement: Comparison of X-Ray-Induced Mutation Rates in Drosophila and Mice Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/281910 Views: 8Total views on this site Citations: 28Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:Edward J. Calabrese, Paul B. 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