Radiation-induced germline mutations detected by a direct comparison of parents and first-generation offspring DNA sequences containing SNPs

Identification of candidate genes for an early-maturing soybean mutant by genome resequencing analysis

Flowering is indicative of the transition from vegetative to reproductive phase, a critical event in the life cycle of plants. In this study, we performed whole genome resequencing by Illumina HiSeq to identify changes in flowering genes using an early-flowering phenotype of soybean mutant line Josaengserori (JS) derived from Korean landrace, Seoritae (SR), and we obtained mapped reads of 131,769,690 and 167,669,640 bp in JS and SR, respectively. From the whole genome sequencing results between JS and SR, we identified 332,821 polymorphic SNPs and 65,178 indels, respectively. Among these, 30 flowering genes were in SNPs and 25 were in indels. Among 30 flowering genes detected in SNPs, Glyma02g33040, Glyma06g22650, Glyma10g36600, Glyma13g01290, Glyma14g10530, Glyma16g01980, Glyma17g11040, Glyma18g53690, and Glyma20g29300 were non-synonymous substitutions between JS and SR. Changes in Glyma10g36600 (GI), Glya02g33040 (AGL18), Glyma17g11040 (TOC1), and Glyma14g10530 (ELF3) in JS affected the expression of GmFT2a and resulted in early flowering. These results provide insight into the regulatory pathways of flowering in soybean mutants and help to improve our knowledge of soybean mutation breeding.

In vivo radioadaptive response: a review of studies relevant to radiation-induced cancer risk

Radioadaptive response (RAR) describes phenomena where small conditioning doses of ionizing radiation (IR) reduce detrimental effects of subsequent higher IR doses. Current radiation protection regulations do not include RAR because of the large variability in expression among individuals and uncertainties of the mechanism. However, RAR should be regarded as an indispensable factor for estimation and control of individual IR sensitivity. In this article, RAR studies relevant to individual cancer risk are reviewed. Using various stains of mice, carcinogenic RAR has been demonstrated. Consistently much in vivo evidence for RAR with end points of DNA and chromosome damage is reported. Most in vivo RAR studies revealed efficient induction of RAR by chronic or repeated low-dose priming irradiation. Chronic IR-induced RAR was observed also in human individuals after environmental, occupational, and nuclear accident radiation exposure. These observations may be associated with an intrinsically distinct feature of in vivo experimental systems that mainly consist of nonproliferating mature cells. Alternatively, induction of RAR by gap junction-mediated bystander effects suggests that multicellular systems comprising densely communicating cells may be capable of responding to long-lasting low-dose-rate priming irradiation. Regulation by endocrine factors is also a plausible mechanism for RAR at an individual level. Emerging evidence suggests that glucocorticoids, known as stress hormones, participate in in vivo RAR induction following long-term low-dose-rate exposure to IR.

Molecular analysis of point mutations in a barley genome exposed to MNU and gamma rays

We present studies aimed at determining the types and frequencies of mutations induced in the barley genome after treatment with chemical (N-methyl-N-nitrosourea, MNU) and physical (gamma rays) mutagens. We created M(2) populations of a doubled haploid line and used them for the analysis of mutations in targeted DNA sequences and over an entire barley genome using TILLING (Targeting Induced Local Lesions in Genomes) and AFLP (Amplified Fragment Length Polymorphism) technique, respectively. Based on the TILLING analysis of the total DNA sequence of 4,537,117bp in the MNU population, the average mutation density was estimated as 1/504kb. Only one nucleotide change was found after an analysis of 3,207,444bp derived from the highest dose of gamma rays applied. MNU was clearly a more efficient mutagen than gamma rays in inducing point mutations in barley. The majority (63.6%) of the MNU-induced nucleotide changes were transitions, with a similar number of G>A and C>T substitutions. The similar share of G>A and C>T transitions indicates a lack of bias in the repair of O(6)-methylguanine lesions between DNA strands. There was, however, a strong specificity of the nucleotide surrounding the O(6)-meG at the -1 position. Purines formed 81% of nucleotides observed at the -1 site. Scanning the barley genome with AFLP markers revealed ca. a three times higher level of AFLP polymorphism in MNU-treated as compared to the gamma-irradiated population. In order to check whether AFLP markers can really scan the whole barley genome for mutagen-induced polymorphism, 114 different AFLP products, were cloned and sequenced. 94% of bands were heterogenic, with some bands containing up to 8 different amplicons. The polymorphic AFLP products were characterised in terms of their similarity to the records deposited in a GenBank database. The types of sequences present in the polymorphic bands reflected the organisation of the barley genome.

The effect of low-dose exposure on germline microsatellite mutation rates in humans accidentally exposed to caesium-137 in Goiânia

A serious radiological accident occurred in 1987 in Goiânia, Brazil, which lead to extensive human and environmental contamination as a result of ionising radiation (IR) from caesium-137. Among the exposed were those in direct contact with caesium-137, their relatives, neighbours, liquidators and health personnel involved in the handling of the radioactive material and the clean-up of the radioactive sites. The exposed group consisted of 10 two-generation families, totalling 34 people. For each exposed family, at least one of the progenitors was directly exposed to very low doses of γ-IR. The control group consisted of 215 non-irradiated families, composed of a father, mother and child, all of them from Goiânia, Brazil. Genomic DNA was purified using 100 μl of whole blood. The amplification reactions were prepared according to PowerPlex® 16, following the manufacturer's instructions. Genetic profiles were obtained from a single polymerase chain reaction amplification. The exposed group had only one germline mutation of a paternal origin in the 'locus' D8S1179 and the observed mutation presented a gain of only one repeat unit. In the control group, 11 mutations were observed and the mutational events were distributed in five loci D16S539, D3S1358, FGA, Penta E and D21S11. The mutation rates for the exposed and control groups were 0.006 and 0.002, respectively. There was no statistically significant difference (P = 0.09) between the mutation rate of the exposed and control groups. In conclusion, the quantification of mutational events in short tandem repeats can provide a useful system for detecting induced mutations in a relatively small population.

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 (5Gy, 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 < or = 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 < or = 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.