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Nakamura N. Why Genetic Effects of Radiation are Observed in Mice but not in Humans. Radiat Res 2017; 189:117-127. [PMID: 29261411 DOI: 10.1667/rr14947.1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Genetic effects from radiation have been observed in a number of species to date. However, observations in humans are nearly nonexistent. In this review, possible reasons for the paucity of positive observations in humans are discussed. Briefly, it appears likely that radiation sensitivity for the induction of mutations varies among different genes, and that the specific genes that were used in the past with the specific locus test utilizing millions of mice may have simply been very responsive to radiation. In support of this notion, recent studies targeting the whole genome to detect copy number variations (deletions and duplications) in offspring derived from irradiated spermatogonia indicated that the mutation induction rate per genome is surprisingly lower than what would have been expected from previous results with specific locus tests, even in the mouse. This finding leads us to speculate that the lack of evidence for the induction of germline mutations in humans is not due to any kind of species differences between humans and mice, but rather to the lack of highly responsive genes in humans, which could be used for effective mutation screening purposes. Examples of such responsive genes are the mouse coat color genes, but in human studies many more genes with higher response rates are required because the number of offspring examined and the radiation doses received are smaller than in mouse studies. Unfortunately, such genes have not yet been found in humans. These results suggest that radiation probably induces germline mutations in humans but that the mutation induction rate is likely to be much lower than has been estimated from past specific locus studies in mice. Whole genome sequencing studies will likely shed light on this point in the near future.
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Affiliation(s)
- Nori Nakamura
- Department of Molecular Biosciences, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815 Japan
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3
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Kodaira M, Asakawa JI, Nakamura N. Radiation-Induced Deletions in Mouse Spermatogonia are Usually Large (over 200 kb) and Contain Little Sequence Similarity at the Junctions. Radiat Res 2017; 187:722-731. [DOI: 10.1667/rr14660.1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
- Mieko Kodaira
- Department of Molecular Biosciences, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815, Japan
| | - Jun-ichi Asakawa
- Department of Molecular Biosciences, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815, Japan
| | - Nori Nakamura
- Department of Molecular Biosciences, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815, Japan
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Asakawa JI, Kodaira M, Miura A, Tsuji T, Nakamoto Y, Imanaka M, Kitamura J, Cullings H, Nishimura M, Shimada Y, Nakamura N. Genome-Wide Deletion Screening with the Array CGH Method in Mouse Offspring Derived from Irradiated Spermatogonia Indicates that Mutagenic Responses are Highly Variable among Genes. Radiat Res 2016; 186:568-576. [PMID: 27869554 DOI: 10.1667/rr14402.1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Until the end of the 20th century, mouse germ cell data on induced mutation rates, which were collected using classical genetic methods at preselected specific loci, provided the principal basis for estimates of genetic risks from radiation in humans. The work reported on here is an extension of earlier efforts in this area using molecular methods. It focuses on validating the use of array comparative genomic hybridization (array CGH) methods for identifying radiation-induced copy number variants (CNVs) and specifically for DNA deletions. The emphasis on deletions stems from the view that it constitutes the predominant type of radiation-induced genetic damage, which is relevant for estimating genetic risks in humans. In the current study, deletion mutations were screened in the genomes of F1 mice born to unirradiated or 4 Gy irradiated sires at the spermatogonia stage (100 offspring each). The array CGH analysis was performed using a "2M array" with over 2 million probes with a mean interprobe distance of approximately 1 kb. The results provide evidence of five molecularly-confirmed paternally-derived deletions in the irradiated group (5/100) and one in the controls (1/100). These data support a calculation, which estimates that the mutation rate is 1 × 10-2/Gy per genome for induced deletions; this is much lower than would be expected if one assumes that the specific locus rate of 1 × 10-5/locus per Gy (at 34 loci) is applicable to other genes in the genome. The low observed rate of induced deletions suggests that the effective number of genes/genomic regions at which recoverable deletions could be induced would be only approximately 1,000. This estimate is far lower than expected from the size of the mouse genome (>20,000 genes). Such a discrepancy between observation and expectation can occur if the genome contains numerous genes that are far less sensitive to radiation-induced deletions, if many deletion-bearing offspring are not viable or if the current method is substandard for detecting small deletions.
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Affiliation(s)
- Jun-Ichi Asakawa
- Department of aGenetics, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815, Japan
| | - Mieko Kodaira
- Department of aGenetics, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815, Japan
| | - Akiko Miura
- Department of aGenetics, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815, Japan
| | - Takahiro Tsuji
- Department of aGenetics, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815, Japan
| | - Yoshiko Nakamoto
- Department of aGenetics, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815, Japan
| | - Masaaki Imanaka
- Department of aGenetics, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815, Japan
| | - Jun Kitamura
- Department of aGenetics, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815, Japan
| | - Harry Cullings
- b Department of Statistics, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815, Japan
| | - Mayumi Nishimura
- c Radiobiology for Children's Health Program, Research Center for Radiation Protection, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan
| | - Yoshiya Shimada
- c Radiobiology for Children's Health Program, Research Center for Radiation Protection, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan
| | - Nori Nakamura
- Department of aGenetics, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815, Japan
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Asakawa JI, Kodaira M, Cullings HM, Katayama H, Nakamura N. The genetic risk in mice from radiation: an estimate of the mutation induction rate per genome. Radiat Res 2013; 179:293-303. [PMID: 23368417 DOI: 10.1667/rr3095.1] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Restriction Landmark Genome Scanning (RLGS) is a method that uses end-labeled (32)P NotI sites that are mostly associated with coding genes to visualizes thousands of DNA fragments as spots in two-dimensional autoradiograms. This approach allows direct detection of autosomal deletions as spots with half normal intensity. The method was applied to mouse offspring derived from spermatogonia exposed to 4 Gy of X rays. A genome-wide assessment of the mutation induction rate was estimated from the detected deletions. Examinations were made of 1,007 progeny (502 derived from control males and 505 from irradiated males) and 1,190 paternal and 1,240 maternal spots for each mouse. The results showed one deletion mutation in the unirradiated paternal genomes of 502 offspring (0.2%) and 5 deletions in the irradiated paternal genomes of 505 offspring (1%). The difference was marginally significant, with the deletion sizes ranged from 2-13 Mb. If the frequencies are taken at face value, the net increase was 0.8% after an exposure of 4 Gy, or 0.2% per Gy per individual if a linear dose response is assumed. Since the present RLGS analysis examined 1,190 NotI sites, while the mouse genome contains ∼25,000 genes, the genomic probability of any gene undergoing a deletion mutation would be 25× 0.2%, or 5% per Gy. Furthermore, since the present RLGS screened about 0.2% of the total genome, the probability of detecting a deletion anywhere in the total genome would be estimated to be 500 times 0.2% or 100% (i.e., 1 deletion per Gy). These results are discussed with reference to copy number variation in the human genome.
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Affiliation(s)
- Jun-ichi Asakawa
- Departments of Genetics, Radiation Effects Research Foundation, 5-2 Hijiyama Park, Minami-ku, Hiroshima 732-0815, Japan.
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Kodaira M, Ryo H, Kamada N, Furukawa K, Takahashi N, Nakajima H, Nomura T, Nakamura N. No Evidence of Increased Mutation Rates at Microsatellite Loci in Offspring of A-Bomb Survivors. Radiat Res 2010; 173:205-13. [DOI: 10.1667/rr1991.1] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
- M. Kodaira
- Departments of Genetics and, Radiation Effects Research Foundation, Hiroshima, Japan
| | - H. Ryo
- Department of Radiation Biology and Medical Genetics, Graduate School of Medicine, Osaka University, Osaka, Japan
| | - N. Kamada
- Departments of Statistics and, Radiation Effects Research Foundation, Hiroshima, Japan
| | - K. Furukawa
- Departments of Statistics and, Radiation Effects Research Foundation, Hiroshima, Japan
| | - N. Takahashi
- Departments of Genetics and, Radiation Effects Research Foundation, Hiroshima, Japan
| | - H. Nakajima
- Department of Radiation Biology and Medical Genetics, Graduate School of Medicine, Osaka University, Osaka, Japan
| | - T. Nomura
- Department of Radiation Biology and Medical Genetics, Graduate School of Medicine, Osaka University, Osaka, Japan
| | - N. Nakamura
- Departments of Chief Scientist, Radiation Effects Research Foundation, Hiroshima, Japan
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