Minisatellite Mutation Rate Research Articles

Germline minisatellite mutations in workers occupationally exposed to radiation at the Sellafield nuclear facility

Germline minisatellite mutation rates were investigated in male workers occupationally exposed to radiation at the Sellafield nuclear facility. DNA samples from 160 families with 255 offspring were analysed for mutations at eight hypervariable minisatellite loci (B6.7, CEB1, CEB15, CEB25, CEB36, MS1, MS31, MS32) by Southern hybridisation. No significant difference was observed between the paternal mutation rate of 5.0% (37 mutations in 736 alleles) for control fathers with a mean preconceptional testicular dose of 9 mSv and that of 5.8% (66 in 1137 alleles) for exposed fathers with a mean preconceptional testicular dose of 194 mSv. Subgrouping the exposed fathers into two dose groups with means of 111 mSv and 274 mSv revealed paternal mutation rates of 6.0% (32 mutations in 536 alleles) and 5.7% (34 mutations in 601 alleles), respectively, neither of which was significantly different in comparisons with the rate for the control fathers. Maternal mutation rates of 1.6% (12 mutations in 742 alleles) for the partners of control fathers and 1.7% (19 mutations in 1133 alleles) for partners of exposed fathers were not significantly different. This study provides evidence that paternal preconceptional occupational radiation exposure does not increase the germline minisatellite mutation rate and therefore refutes suggestions that such exposure could result in a destabilisation of the germline that can be passed on to future generations.

On the genetic effects of low-dose radiation

There is a discrepancy between the reportedly significant elevation in a minisatellite DNA mutation rate in the children of parents, who had been exposed to radiation from the Chernobyl accident, and absence of significant inherited genetic effects found among the offspring of atomic bomb survivors. At the same time, average doses received by the residents of the contaminated areas, where the studies of the children of exposed parents were performed, had been comparable to those from the natural radiation background. Several publications exaggerating medical consequences of elevated radiation background were discussed earlier. The following flaws can be found in such papers: interpretation of spontaneous conditions as radiation-induced, indication of radioactivity or dose levels without confrontation with the natural radiation background, conclusions about incidence increase of certain conditions without an adequate comparison with a control. In conclusion, arguments in favor of inapplicability of the linear non-threshold theory to the radiation doses, comparable to those from the natural radiation background, are discussed here.

Does Cancer Treatment in Childhood Induce Transgenerational Genetic Damage?

Does Cancer Treatment in Childhood Induce Transgenerational Genetic Damage?

Germline minisatellite mutations in survivors of childhood and young adult cancer treated with radiation

Purpose: To investigate minisatellite germline mutation rates in survivors of childhood and young adult cancer who received radiotherapy.Materials and methods: DNA samples from 100 families, where one parent was a cancer survivor, were analysed for mutations at eight hypervariable minisatellite loci (B6.7, CEB1, CEB15, CEB25, CEB36, MS1, MS31, MS32) by Southern hybridisation.Results: No significant difference was observed between the paternal mutation rate of 5.6% in exposed fathers with a mean preconceptional testicular dose of 1.23 Gy (56 mutations in 998 informative alleles) and that of 5.8% in unexposed fathers (17 in 295 informative alleles). Subgrouping the exposed fathers into dose groups of <0.10 Gy, 0.10–0.99 Gy, 1.00–1.99 Gy, ≥2.00 Gy revealed no significant differences in paternal mutation rate in comparison with the unexposed fathers. Maternal mutation rates of 1.6% in cancer survivor mothers with a mean preconceptional ovarian dose of 0.58 Gy (five mutations in 304 informative alleles) and 2.1% in unexposed mothers (21 in 987 informative alleles) were not significantly different. There were no differences in minisatellite mutation rates associated with treatment with chemotherapeutic agents.Conclusions: This study provides evidence that preconception radiotherapy for childhood or early adulthood cancer does not increase the germline minisatellite mutation rate.

Sexual selection does not influence minisatellite mutation rate

BackgroundMoller and Cuervo report a significant trend between minisatellite mutation rate and the frequency of extra-pair copulations in birds. This is interpreted as evidence that the high rate of evolution demanded by sexual selection has itself selected for a higher mutation rate in species where selection is strongest. However, there are good a priori reasons for believing that their method of calculating minisatellite mutation rates will be highly error prone and a poor surrogate measure of the evolutionary rate of genes. I therefore attempted to replicate their results using both their data and an independent data set based on papers they failed to locate.ResultsI find that Moller and Cuervo's data set contains numerous errors that act somewhat to strengthen their key regression. More importantly, data from uncited papers fail to replicate their reported trend and one species in particular, Vireo olivaceus, is apparently deliberately omitted, yet its inclusion removes significance from the original correlation. Over the small number of cases were comparisons can be made, mutation rate estimates do not differ between species but do vary significantly depending on the laboratory/operator.ConclusionThere appears to be no clear relationship between minisatellite mutation rate and EPC rate in birds. The previously reported trend can be attributed to data transcription errors and unfortunate data selection. My analysis highlights the importance of total methodological transparency when conducting meta-analyses.

Minisatellite mutation rates increase with extra-pair paternity among birds

BackgroundAmos [1] suggested recently that a previously reported positive relationship between minisatellite mutation rates and extra-pair paternity among species of birds [2] was confounded by transcription errors and selective inclusion of studies. Here we attempted to replicate the results reported by Amos [1], but also tested for the relationship by expanding the data base by including studies published after our original paper.ResultsWe were able to replicate the positive association between mutation rate and extra-pair paternity in birds, even after controlling statistically for the confounding effecs of mean number of bands scored, using 133 species, compared to 81 species in our first report [2]. We suggest that Amos [1] failed to reach a similar conclusion due to four different potential causes of bias. First, Amos [1] missed 15 studies from the literature that we were able to include. Second, he used estimates of mutation rates that were based on both within- and extra-pair offspring, although the latter will cause bias in estimates. Third, he made a number of transcription errors from the original publications for extra-pair paternity, mutation rates, number of novel bands, and mean number of bands scored per individual. Fourth, he included Vireo olivaceus although the mutation rate estimate was based on one single offspring!ConclusionThere was a positive association between mutation rates and extra-pair paternity in birds, accounting for an intermediate effect size that explained 5–11% of the variance; estimates that are bound to be conservative due to many different causes of noise in the data. This result was robust to statistical control for potentially confounding variables, highlighting that it is important to base comparative studies on all available evidence, and that it is crucial to critically transcribe data while simultaneously checking published estimates for their correctness.

New germline mutations in the hypervariable minisatellite CEB1 in the parents of children with leukaemia

Gardner and co-workers advanced the hypothesis that the Seascale leukaemia cluster could have been caused by new mutations in germ cells, induced by paternal preconceptional irradiation (PPI) exposure at the Sellafield nuclear installation. Since evidence has shown that PPI can increase the de novo germline mutation rate in hypervariable minisatellite loci, we investigated the hypothesis that sporadic childhood leukaemia might be associated with an increased parental germline minisatellite mutation rate. To test this hypothesis, we compared de novo germline mutation rates in the hypervariable minisatellite locus, CEB1, in family trios (both parents and their child) of children with leukaemia (n=135) compared with unaffected control families (n=124). The majority of case and control germline mutations were paternal (94%); the mean paternal germline mutation rates of children with leukaemia (0.083) and control children (0.156) were not significantly different (odds ratio, 95% confidence interval: 0.50, 0.23–1.08; P=0.11). There were no significant differences in case and control parental allele sizes, case and control germline mutation progenitor allele sizes (2.74 vs 2.54 kb; P=0.56), case and control mutant allele sizes (2.71 vs 2.67 kb; P=0.90), mutant allele size changes (0.13 vs 0.26 kb; P=0.10), or mutational spectra. Within the limitation of the number of families available for study, we conclude that childhood leukaemia is unlikely to be associated with increased germline minisatellite instability.

Minisatellite germline mutation rate in the Techa River population

Germline mutation at eight minisatellite loci has been studied among the irradiated families from the Techa River population and non-exposed families from the rural area of the Chelyabinsk and Kurgan Oblasts. The groups were matched by ethnicity, parental age, occupation and smoking habit. A statistically significant 1.7-fold increase in mutation rate was found in the germline of irradiated fathers, whereas maternal germline mutation rate in the exposed families was not elevated. Most of the minisatellite loci showed an elevated paternal mutation rate in the exposed group, indicating a generalised increase in minisatellite germline mutation rate in the Techa River population. These data suggest that the elevated minisatellite mutation rate can be attributed to radioactive exposure. The spectra of paternal mutation seen in the unexposed and exposed families were indistinguishable.

A pilot study examining germline minisatellite mutations in the offspring of Danish childhood and adolescent cancer survivors treated with radiotherapy

Purpose:To investigate germline mutation rate at eight minisatellite loci in 24 Danish families, where one parent is the survivor of childhood or adolescent cancer treated with radiotherapy.Materials and methods:Parents and offspring were profiled for eight hypervariable minisatellite loci (B6.7, CEB1, CEB15, CEB25, CEB36, MS1, MS31, MS32) by Southern blotting.Results:Seven paternal mutations were observed for 130 informative alleles in 18 offspring from 11 radiation-exposed fathers (mean preconceptional dose for offspring 0.29 Gy, range <0.01 – 1.2 Gy), compared to six mutations for 146 informative alleles in 21 offspring from 13 unexposed fathers. No statistically significant difference between the total paternal mutation rates was observed (5.4% for exposed fathers and 4.1% for unexposed fathers). Three maternal mutations were observed for 148 informative alleles in 21 offspring from 13 radiation-exposed mothers (mean preconceptional dose for offspring 0.71 Gy, range <0.01 – 9.2 Gy), compared to one mutation for 130 informative alleles in 18 offspring from 11 unexposed mothers. Again, no statistically significant difference was observed between the total maternal mutation rates (2.0% for exposed mothers and 0.8% for unexposed mothers).Conclusions:The data from this pilot study demonstrate no statistically significant increase in germline minisatellite mutation rate associated with radiotherapy for childhood and adolescent cancer.

Long-term genetic effects of radiation exposure.

To date, there has been little experimental knowledge on the genetic risks of human exposure to ionising radiation for humans. Recent data suggest that hypervariable tandem repeat minisatellite loci provide a useful and sensitive experimental approach for monitoring radiation-induced germline mutation in humans. Here, I review the results of studies on minisatellite mutation rates in human populations exposed to radioactive fallout after the Chernobyl accident and nuclear weapon tests in Kazakhstan.

Monitoring of radiation-induced germline mutation in humans.

Estimating the genetic hazards of radiation and other mutagens in humans depends on extrapolation from experimental systems. Recent data have shown that minisatellite loci provide a useful and sensitive experimental approach for monitoring radiation-induced mutation in humans. This review describes the progress made in validating this approach and presents the results of recent publications on the analysis of minisatellite mutation rates in the irradiated families.

Monitoring of radiation-induced germline mutation in humans.

Estimating the genetic hazards of radiation and other mutagens in humans depends on extrapolation from experimental systems. Recent data have shown that minisatellite loci provide a useful and sensitive experimental approach for monitoring radiation-induced mutation in humans. This review describes the progress made in validating this approach and presents the results of recent publications on the analysis of minisatellite mutation rates in the irradiated families.

Minisatellite DNA mutation rate in dandelions increases with leaf-tissue concentrations of Cr, Fe, Mn, and Ni

We have examined whether mutation rates at minisatellite DNA loci in dandelions (Taraxacum officinale Weber, sensu lato: Asteraceae) increase with increasing exposure to metal pollution. From 16 sites (Colorado to Pennsylvania, USA) covering a range of airborne particulate-matter exposures, soil metal concentrations, and leaf-tissue metal concentrations, we grew an average of 7.9 offspring from each of 10 parent plants, and we analyzed the parent-offspring transmission of 82,715 minisatellite DNA markers to 1,258 offspring for rates of mutation. The mean number of markers examined per individual (using six minisatellite probes) was 65.8. Detection of mutations is facilitated by agamospermous reproduction (clonal seed production) in dandelions. Across sites, the average single-event, parent-offspring marker transmission mutation rate was 0.0067, ranging from 0.002 to 0.015 (a 7.5-fold difference). No significant correlation was detected between site single-event mutation rates and either airborne particulate-matter or soil concentrations for any of the metals. However, across sites, mutation rates were significantly (p < 0.05) and positively correlated to increasing leaf-tissue concentrations of Cr, Fe, Mn, and Ni (Cd, Cu, Pb, and Zn exhibited no correlation). Multiple-regression analyses suggest that a model including three metals--in order of importance: Cr (p = 0.002), Fe (p = 0.02), and Ni (p = 0.005); overall, p = 0.001--may improve the ability to predict mutation rate relative to leaf metal concentrations in dandelions. Mutations at minisatellite DNA loci in sexually apomictic organisms may thus provide convenient biomarkers by which to assess the mutagen stressor risk in environments.

Molecular evolution of a plastid tandem repeat locus in an orchid lineage.

The molecular evolution of a chloroplast minisatellite locus in the Anacamptis palustris (Orchidaceae) lineage and haplotype variation in two Italian A. palustris populations were investigated. A phylogenetic analyses of the chloroplast tRNA(LEU) intron, where the minisatellite locus is located, revealed that a deletion in the ancestor of the A. palustris lineage led to the formation of two noncontiguous, complementary sequence motifs. We propose a model to explain the initial formation of the minisatellite repeat motif, starting with the two noncontiguous, complementary sequence motifs. A survey of minisatellite variation in four species of the A. palustris lineage revealed several haplotypes that differed not only in repeat number, but also in repeat organization. A haplotype network suggests that three different minisatellite loci evolved independently at the same position in the tRNA(LEU) intron. A secondary structure model revealed that the A. palustris minisatellite repeat forms a stem region of the tRNA(LEU) intron, which allows its notable expansion without negatively affecting splicing. Minisatellite variation was high in the two examined A. palustris populations where 20 haplotypes were detected, whereas no length variation was detected in a neighboring poly (A) microsatellite locus. We estimated a chloroplast minisatellite mutation rate of 3.2 x 10(-3) mutations per generation. Southern blot analyses did not find evidence for chloroplast heteroplasmy. Based on the analysis of the largest known, extant A. palustris population, a stepwise mutation model (SMM) was inferred.

Hereditary minisatellite mutations among the offspring of Estonian Chernobyl cleanup workers.

A single accidental event such as the fallout released from the Chernobyl reactor in 1986 can expose millions of people to non-natural environmental radiation. Ionizing radiation increases the frequency of germline mutations in experimental studies, but the genetic effects of radiation in humans remain largely undefined. To evaluate the hereditary effects of low radiation doses, we compared the minisatellite mutation rates of 155 children born to Estonian Chernobyl cleanup workers after the accident with those of their siblings born prior to it. All together, 94 de novo paternal minisatellite mutations were found at eight tested loci (52 and 42 mutants among children born after and before the accident, respectively). The minisatellite mutation rate was nonsignificantly increased among children born after the accident (0.042 compared to 0.036, OR 1.33, 95% CI 0.80-2.20). Furthermore, there was some indication of an increased mutation rate among offspring born after the accident to workers who had received doses of 20 cSv or above compared with their siblings born before the accident (OR 3.0, 95% CI 0.97-9.30). The mutation rate was not associated with the father's age (OR 1.04, 95% CI 0.94-1.15) or the sex of the child (OR 0.95, 95% CI 0.50-1.79). Our results are consistent with both no effect of radiation on minisatellite mutations and a slight increase at dose levels exceeding 20 cSv.

Evolution and population genetics of the H-ras minisatellite and cancer predisposition.

Case-control studies have implicated rare length H-ras minisatellite alleles in cancer risk. In Europeans, this locus has four common alleles, and a larger number of rare alleles; possession of a rare allele has been identified as a risk factor responsible for 5-10% of some cancers. This unusual model of predisposition has been controversial in case-control studies, but also makes characteristic predictions about the population genetics of the locus, which we examine in this study. Using minisatellite variant repeat ("MVR") mapping, and compound haplotypes composed of the minisatellite and surrounding substitutional polymorphisms, we have reconstructed the main steps in the evolution of this locus in human populations. MVR-calibrated measurements of allele length yield rare allele frequencies significantly higher than most previous studies, and show that most other analyses have not distinguished two common alleles of 84 and 85 repeat units. Alleles classified as "rare" in European populations predominate (70%) in the African sample studied. Small-pool PCR (SP-PCR) analysis on common alleles in sperm DNA gives an estimate for the germline minisatellite mutation rate of about 0.05% (95% confidence upper limit 0.15%). Overall, our results do not reflect a locus subject to frequent mutation and strong selection, and are difficult to reconcile with the proposed cancer predisposition. Restricted variation at this locus is most simply explained by low mutation rate, and although definitive case-control studies can only be performed using methods capable of reproducibly distinguishing rare and common alleles, our work suggests that most studies to date have not resolved alleles adequately.

Sexual selection, germline mutation rate and sperm competition

BackgroundAn important component of sexual selection arises because females obtain viability benefits for their offspring from their mate choice. Females choosing extra-pair fertilization generally favor males with exaggerated secondary sexual characters, and extra-pair paternity increases the variance in male reproductive success. Furthermore, females are assumed to benefit from 'good genes' from extra-pair sires. How additive genetic variance in such viability genes is maintained despite strong directional selection remains an evolutionary enigma. We propose that sexual selection is associated with elevated mutation rates, changing the balance between mutation and selection, thereby increasing variance in fitness and hence the benefits to be obtained from good genes sexual selection. Two hypotheses may account for such elevated mutation: (1) Increased sperm production associated with sperm competition may increase mutation rate. (2) Mutator alleles increase mutation rates that are revealed by the expression of condition-dependent secondary sexual characters used by choosy females during their mate choice. M Petrie has independently developed the idea that mutator alleles may account for the maintenance of genetic variation in viability despite strong directional selection.ResultsA comparative study of birds revealed a positive correlation between mutation rate at minisatellite loci and extra-pair paternity, but not between mutation rate and relative testes mass which is a measure of relative sperm production. Minisatellite mutation rates were not related to longevity, suggesting a meiotic rather than a mitotic origin of mutations.ConclusionWe found evidence of increased mutation rate in species with more intense sexual selection. Increased mutation was not associated with increased sperm production, and we suggest that species with intense sexual selection may maintain elevated mutation rates because sexual selection continuously benefits viability alleles expressed in condition-dependent characters. Sexual selection may increase mutational input, which in turn feeds back on sexual selection because of increased variance in viability traits.

Elevated Minisatellite Mutation Rate in the Post-Chernobyl Families from Ukraine

Germline mutation at eight human minisatellite loci has been studied among families from rural areas of the Kiev and Zhitomir regions of Ukraine, which were heavily contaminated by radionuclides after the Chernobyl accident. The control and exposed groups were composed of families containing children conceived before and after the Chernobyl accident, respectively. The groups were matched by ethnicity, maternal age, parental occupation, and smoking habits, and they differed only slightly by paternal age. A statistically significant 1.6-fold increase in mutation rate was found in the germline of exposed fathers, whereas the maternal germline mutation rate in the exposed families was not elevated. These data, together with the results of our previous analysis of the exposed families from Belarus, suggest that the elevated minisatellite mutation rate can be attributed to post-Chernobyl radioactive exposure. The mechanisms of mutation induction at human minisatellite loci are discussed.

Induction of minisatellite mutations in the mouse germline by low-dose chronic exposure to γ-radiation and fission neutrons

Germline mutation induction at mouse minisatellite loci by paternal low-dose (0.125–1 Gy) exposure to chronic (1.66×10 −4 Gy min −1) low-linear energy transfer (low-LET) γ-irradiation and high-LET fission neutrons (0.003 Gy min −1) was studied at pre-meiotic stages of spermatogenesis. Both types of radiation produced linear dose–response curves for mutation of the paternal allele. In contrast to previous results using higher doses, the pattern of induction of minisatellite mutation after chronic γ-irradiation was similar to acute (0.5 Gy min −1) exposure to X-rays, indicating that the elevated mutation rate was independent of the ability of the cell to repair damage induced immediately or over a period of up to100 h. Chronic exposure to fission neutrons was more effective than acute or chronic low-LET exposure (relative biological effectiveness, RBE=3.36). The data also provide strong support for the previous conclusion that increases in minisatellite mutation rate are not caused by radiation-induced DNA damage at minisatellite loci themselves, but rather from damage induced by ionising radiation elsewhere in the genome/cell.

Induced minisatellite germline mutations in herring gulls ( Larus argentatus) living near steel mills

Despite widespread industrial release of genotoxic contaminants, little is understood of their role in inducing germline mutations in natural populations. We used multilocus DNA fingerprinting to quantify germline minisatellite mutations in families of herring gulls ( Larus argentatus) in three nesting categories: (a) near cities with large steel mills operating coking ovens; (b) near cities without steel mills; and (c) in rural locations removed from point sources of contamination. Gulls nesting near integrated steel mills showed significantly higher mutation rates than gulls from rural locations (Fisher’s exact, P=0.0004); urban sites without steel mills fell midway between steel and rural sites (difference from rural; Fisher’s exact, P=0.19). Distance of the nesting location of herring gulls from the steel industries’ coking ovens was negatively correlated with minisatellite mutation rate demonstrating significant risk for induced germline mutations in cities with steel operations (Kendall Tau; τ=0.119; P<0.0001).