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Nikjoo H, Rahmanian S, Taleei R. Modelling DNA damage-repair and beyond. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2024; 190:1-18. [PMID: 38754703 DOI: 10.1016/j.pbiomolbio.2024.05.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Revised: 03/27/2024] [Accepted: 05/10/2024] [Indexed: 05/18/2024]
Abstract
The paper presents a review of mechanistic modelling studies of DNA damage and DNA repair, and consequences to follow in mammalian cell nucleus. We hypothesize DNA deletions are consequences of repair of double strand breaks leading to the modifications of genome that play crucial role in long term development of genetic inheritance and diseases. The aim of the paper is to review formation mechanisms underlying naturally occurring DNA deletions in the human genome and their potential relevance for bridging the gap between induced DNA double strand breaks and deletions in damaged human genome from endogenous and exogenous events. The model of the cell nucleus presented enables simulation of DNA damage at molecular level identifying the spectrum of damage induced in all chromosomal territories and loops. Our mechanistic modelling of DNA repair for double stand breaks (DSB), single strand breaks (SSB) and base damage (BD), shows the complexity of DNA damage is responsible for the longer repair times and the reason for the biphasic feature of mammalian cells repair curves. In the absence of experimentally determined data, the mechanistic model of repair predicts the in vivo rate constants for the proteins involved in the repair of DSB, SSB, and of BD.
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Affiliation(s)
- Hooshang Nikjoo
- Department of Physiology, Anatomy and Genetics (DPAG), Oxford University, Oxford, OX1 3PT, UK.
| | | | - Reza Taleei
- Medical Physics Division, Department of Radiation Oncology Sidney Kimmel Medical College at Thomas Jefferson University, Philadelphia, PA, 19107, USA.
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Alexandrov ID, Alexandrova MV. The dose-, LET-, and gene-dependent patterns of DNA changes underlying the point mutations in spermatozoa of Drosophila melanogaster. I. Autosomal gene black. Mutat Res 2021; 823:111755. [PMID: 34217017 DOI: 10.1016/j.mrfmmm.2021.111755] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Revised: 04/23/2021] [Accepted: 05/24/2021] [Indexed: 11/26/2022]
Abstract
Sequence analysis of 7 spontaneous, 27 γ-ray- and 20 neutron/neutron+γ-ray-induced black (b) point mutants was carried out. All these mutants were isolated as non-mosaic transmissible recessive visibles in the progeny of irradiated males from the wild-type high-inbred laboratory D32 strain of Drosophila melanogaster. Among spontaneous mutants, there were two (28.5 %) mutants with copia insertion in intron 1 and exon 2, three (42.8 %) with replacement of b+D32 paternal sequence with maternal b1 sequence (gene conversion), one (14.3 %) with 142-bp-long insertion in exon 2, and one (14.3 %) with a short deletion and two single-base substitutions in exon 3. Among γ-ray-induced mutants, there were 1 (3.7 %) with copia insertion in intron 2, 6 (22.2 %) with gene conversion, and the remaining 20 (74.1 %) mutants had 37 different small-scale DNA changes. There were 20 (54.1 %) single- or double-base substitutions, 7 (18.9 %) frameshifts (indels), 9 (24.3 %) extended deletions or insertions, and 1(2.7 %) mutant with a short insertion instead of a short deletion. Remarkably, clusters of independent small-scale changes inside the gene or within one DNA helical turn were recovered. The spectrum of DNA changes in 20 neutron/ neutron+γ-ray-induced mutants was drastically different from that induced by γ-rays in that 18 (90.0 %) mutants had the b1sequence. In addition, 2 (10.0 %) with gene conversion had 600- or 19-bp-long deletion in exon 3 and 1 (5.0 %) mutant with a short insertion instead of a short deletion. Analysis of all 27 mutants with gene conversion events shows that 20 (74.1 %) had full b1 sequence whereas 7 others (25.9 %) contained a partial b1 sequence. These data are the first experimental evidence for gene conversion in the early stages of animal embryogenesis in the first diploid cleavage nucleus after male and female pronuclei have united. The gene conversion, frameshifts (indels), and deletions between short repeats were considered as products of a relevant DNA repair pathways described in the literature. As the first step, the gametic doubling doses for phenotypic black point mutations and for intragenic base substitution mutations in mature sperm cells irradiated by 40 Gy of γ-rays were estimated as 5.8 and 1.2 Gy, respectively, showing that doubling dose for mutations at the molecular level is about 5 times lower than that at the phenotypic level.
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Affiliation(s)
- I D Alexandrov
- Dzhelepov Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, 141980, Dubna, Moscow Region, Russia.
| | - M V Alexandrova
- Dzhelepov Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, 141980, Dubna, Moscow Region, Russia
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Affiliation(s)
- Nori Nakamura
- Department of Molecular Biosciences, RERF, Hiroshima, Japan
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Small de novo CNVs as biomarkers of parental exposure to low doses of ionizing radiation of caesium-137. Sci Rep 2018; 8:5914. [PMID: 29651024 PMCID: PMC5897394 DOI: 10.1038/s41598-018-23813-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2017] [Accepted: 03/20/2018] [Indexed: 12/21/2022] Open
Abstract
The radiological accident in Goiania in 1987 caused a trail of human contamination, animal, plant and environmental by a radionuclide. Exposure to ionizing radiation results in different types of DNA lesions. The mutagenic effects of ionizing radiation on the germline are special concern because they can endures for several generations, leading to an increase in the rate of mutations in children of irradiated parents. Thus, to evaluate the biological mechanisms of ionizing radiation in somatic and germline cells, with consequent determination of the rate mutations, is extremely important for the estimation of genetic risks. Recently it was established that Chromosomal Microarray Analysis is an important tool for detecting wide spectra of gains or losses in the human genome. Here we present the results of the effect of accidental exposure to low doses of ionizing radiation on the formation of CNVs in the progeny of a human population accidentally exposed to Caesium-137 during the radiological accident in Goiânia, Brazil.
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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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Ohno T, Kakinuma S, Kato S, Tsujii H, Shimada Y. Risk of second cancers after radiotherapy for cervical cancer. Expert Rev Anticancer Ther 2014; 6:49-57. [PMID: 16375644 DOI: 10.1586/14737140.6.1.49] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Radiotherapy for cervical cancer has both beneficial and detrimental effects: improvement of patient survival and potential induction of a second cancer among long-term survivors. Large epidemiological studies have demonstrated small, but significant, increases of second cancers with radiotherapy compared with the general population. The risk of second cancer has been characterized by organ sites, dose, time since radiotherapy and age at the time of radiotherapy. Analyses of genetic susceptibility and molecular carcinogenesis can be used to develop more appropriate strategies for radiation therapy for cervical cancers.
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Affiliation(s)
- Tatsuya Ohno
- Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Chiba, Japan.
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Sankaranarayanan K, Taleei R, Rahmanian S, Nikjoo H. Ionizing radiation and genetic risks. XVII. Formation mechanisms underlying naturally occurring DNA deletions in the human genome and their potential relevance for bridging the gap between induced DNA double-strand breaks and deletions in irradiated germ cells. Mutat Res 2013; 753:114-130. [PMID: 23948232 DOI: 10.1016/j.mrrev.2013.07.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2013] [Revised: 06/27/2013] [Accepted: 07/22/2013] [Indexed: 12/21/2022]
Abstract
While much is known about radiation-induced DNA double-strand breaks (DSBs) and their repair, the question of how deletions of different sizes arise as a result of the processing of DSBs by the cell's repair systems has not been fully answered. In order to bridge this gap between DSBs and deletions, we critically reviewed published data on mechanisms pertaining to: (a) repair of DNA DSBs (from basic studies in this area); (b) formation of naturally occurring structural variation (SV) - especially of deletions - in the human genome (from genomic studies) and (c) radiation-induced mutations and structural chromosomal aberrations in mammalian somatic cells (from radiation mutagenesis and radiation cytogenetic studies). The specific aim was to assess the relative importance of the postulated mechanisms in generating deletions in the human genome and examine whether empirical data on radiation-induced deletions in mouse germ cells are consistent with predictions of these mechanisms. The mechanisms include (a) NHEJ, a DSB repair process that does not require any homology and which functions in all stages of the cell cycle (and is of particular relevance in G0/G1); (b) MMEJ, also a DSB repair process but which requires microhomology and which presumably functions in all cell cycle stages; (c) NAHR, a recombination-based DSB repair mechanism which operates in prophase I of meiosis in germ cells; (d) MMBIR, a microhomology-mediated, replication-based mechanism which operates in the S phase of the cell cycle, and (e) strand slippage during replication (involved in the origin of small insertions and deletions (INDELs). Our analysis permits the inference that, between them, these five mechanisms can explain nearly all naturally occurring deletions of different sizes identified in the human genome, NAHR and MMBIR being potentially more versatile in this regard. With respect to radiation-induced deletions, the basic studies suggest that those arising as a result of the operation of NHEJ/MMEJ processes, as currently formulated, are expected to be relatively small. However, data on induced mutations in mouse spermatogonial stem cells (irradiation in G0/G1 phase of the cell cycle and DSB repair presumed to be via NHEJ predominantly) show that most are associated with deletions of different sizes, some in the megabase range. There is thus a 'discrepancy' between what the basic studies suggest and the empirical observations in mutagenesis studies. This discrepancy, however, is only an apparent but not a real one. It can be resolved by considering the issue of deletions in the broader context of and in conjunction with the organization of chromatin in chromosomes and nuclear architecture, the conceptual framework for which already exists in studies carried out during the past fifteen years or so. In this paper, we specifically hypothesize that repair of DSBs induced in chromatin loops may offer a basis to explain the induction of deletions of different sizes and suggest an approach to test the hypothesis. We emphasize that the bridging of the gap between induced DSB and resulting deletions of different sizes is critical for current efforts in computational modeling of genetic risks.
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Affiliation(s)
- Krishnaswami Sankaranarayanan
- Radiation Biophysics Group, Department of Oncology-Pathology, Karolinska Instituet, Box 260, Stockholm SE 17176, Sweden
| | - Reza Taleei
- Radiation Biophysics Group, Department of Oncology-Pathology, Karolinska Instituet, Box 260, Stockholm SE 17176, Sweden
| | - Shirin Rahmanian
- Radiation Biophysics Group, Department of Oncology-Pathology, Karolinska Instituet, Box 260, Stockholm SE 17176, Sweden
| | - Hooshang Nikjoo
- Radiation Biophysics Group, Department of Oncology-Pathology, Karolinska Instituet, Box 260, Stockholm SE 17176, Sweden.
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Radiation induced COX-2 expression and mutagenesis at non-targeted lung tissues of gpt delta transgenic mice. Br J Cancer 2012; 108:91-8. [PMID: 23321513 PMCID: PMC3553512 DOI: 10.1038/bjc.2012.498] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
BACKGROUND Although radiation-induced bystander effects have been confirmed using a variety of endpoints, the mechanism(s) underlying these effects are not well understood, especially for in vivo study. METHODS A 1-cm(2) area (1 cm × 1 cm) in the lower abdominal region of gpt delta transgenic mice was irradiated with 5 Gy of 300 keV X-rays, and changes in out-of-field lung and liver were observed. RESULTS Compared with sham-treated controls, the Spi(-) mutation frequency increased 2.4-fold in non-targeted lung tissues at 24 h after partial body irradiation (PBIR). Consistent with dramatic Cyclooxygenase 2 (COX-2) induction in the non-targeted bronchial epithelial cells, increasing levels of prostaglandin, together with 8-hydroxydeoxyguanosine, in the out-of-field lung tissues were observed after PBIR. In addition, DNA double-strand breaks and apoptosis were induced in bystander lung tissues after PBIR. CONCLUSION The PBIR induces DNA damage and mutagenesis in non-targeted lung tissues, especially in bronchial epithelial cells, and COX-2 has an essential role in bystander mutagenesis.
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Sankaranarayanan K, Nikjoo H. Ionising radiation and genetic risks. XVI. A genome-based framework for risk estimation in the light of recent advances in genome research. Int J Radiat Biol 2010; 87:161-78. [DOI: 10.3109/09553002.2010.518214] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Elespuru RK, Sankaranarayanan K. New approaches to assessing the effects of mutagenic agents on the integrity of the human genome. Mutat Res 2007; 616:83-9. [PMID: 17174354 DOI: 10.1016/j.mrfmmm.2006.11.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Heritable genetic alterations, although individually rare, have a substantial collective health impact. Approximately 20% of these are new mutations of unknown cause. Assessment of the effect of exposures to DNA damaging agents, i.e. mutagenic chemicals and radiations, on the integrity of the human genome and on the occurrence of genetic disease remains a daunting challenge. Recent insights may explain why previous examination of human exposures to ionizing radiation, as in Hiroshima and Nagasaki, failed to reveal heritable genetic effects. New opportunities to assess the heritable genetic damaging effects of environmental mutagens are afforded by: (1) integration of knowledge on the molecular nature of genetic disorders and the molecular effects of mutagens; (2) the development of more practical assays for germline mutagenesis; (3) the likely use of population-based genetic screening in personalized medicine.
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Affiliation(s)
- R K Elespuru
- Division of Biology, Office of Science and Engineering Laboratories, Center for Devices and Radiological Health, Food and Drug Administration, Silver Spring, MD 20993, The Netherlands.
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Bourguignon MH, Gisone PA, Perez MR, Michelin S, Dubner D, Giorgio MD, Carosella ED. Genetic and epigenetic features in radiation sensitivity. Eur J Nucl Med Mol Imaging 2005; 32:229-46. [PMID: 15657757 DOI: 10.1007/s00259-004-1730-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Recent progress especially in the field of gene identification and expression has attracted greater attention to genetic and epigenetic susceptibility to cancer, possibly enhanced by ionising radiation. It has been proposed that the occurrence and severity of the adverse reactions to radiation therapy are also influenced by such genetic susceptibility. This issue is especially important for radiation therapists since hypersensitive patients may suffer from adverse effects in normal tissues following standard radiation therapy, while normally sensitive patients could receive higher doses of radiation offering a better likelihood of cure for malignant tumours. This paper, the first of two parts, reviews the main mechanisms involved in cell response to ionising radiation. DNA repair machinery and cell signalling pathways are considered and their role in radiosensitivity is analysed. The implication of non-targeted and delayed effects in radiosensitivity is also discussed.
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Affiliation(s)
- Michel H Bourguignon
- Direction Générale de la Sûreté Nucléaire et de la Radioprotection (DGSNR), 6 Place du Colonel Bourgoin, 75572, Paris Cedex 12, France.
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McBratney BM, Margaryan E, Ma W, Urban Z, Lozanoff S. Frontonasal dysplasia in 3H1 Br/Br mice. THE ANATOMICAL RECORD. PART A, DISCOVERIES IN MOLECULAR, CELLULAR, AND EVOLUTIONARY BIOLOGY 2003; 271:291-302. [PMID: 12629672 DOI: 10.1002/ar.a.10034] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The adult Brachyrrhine (3H1 Br/+) mouse displays severe midfacial retrognathia, with a "pugnose" external appearance, but information concerning craniofacial morphology of the homozygote (3H1 Br/Br) mutant is lacking. This study characterized craniofacial phenotype and genotypic features of the homozygous condition. Segregation analysis was performed by phenotypic scoring of offspring from 3H1 Br/+ reciprocal matings. Whole-mount staining was undertaken to determine the presence or absence of cranial base structures in newborn and adult mice, while features of cranial base chondrification were examined using light microscopy and type II collagen immunohistochemistry. Karyotype analysis was performed to determine whether gross chromosomal aberrations were present. Finally, microsatellite mapping analysis was undertaken to provide further resolution of the Br locus. Results showed that Br was inherited as an autosomal semidominant feature. 3H1 Br/Br mice consistently lacked a presphenoid (with its lateral projections, including a preoptic root, postoptic root, and lesser wing). Karyotyping did not reveal major gross aberrations; however, microsatellite analysis localized Br to distal mouse chromosome 17 in the vicinity of D17Mit155. These results indicated that 3H1 Br/Br mice show characteristic features of frontonasal dysplasia, including median facial clefting and bifid cranium, as well sphenoidal malformations. Furthermore, this mutant should serve as a useful model for examining mechanisms of frontonasal dysplasia.
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Sankaranarayanan K. Ionizing radiation and genetic risks. X. The potential "disease phenotypes" of radiation-induced genetic damage in humans: perspectives from human molecular biology and radiation genetics. Mutat Res 1999; 429:45-83. [PMID: 10434024 DOI: 10.1016/s0027-5107(99)00100-1] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Estimates of genetic risks of radiation exposure of humans are traditionally expressed as expected increases in the frequencies of genetic diseases (single-gene, chromosomal and multifactorial) over and above those of naturally-occurring ones in the population. An important assumption in expressing risks in this manner is that gonadal radiation exposures can cause an increase in the frequency of mutations and that this would result in an increase in the frequency of genetic diseases under study. However, despite compelling evidence for radiation-induced mutations in experimental systems, no increases in the frequencies of genetic diseases of concern or other adverse effects (i.e., those which are not formally classified as genetic diseases), have been found in human studies involving parents who have sustained radiation exposures. The known differences between spontaneous mutations that underlie naturally-occurring single-gene diseases and radiation-induced mutations studied in experimental systems now permit us to address and resolve these issues to some extent. The fact that spontaneous mutations (among which are point mutations and DNA deletions generally restricted to the gene) originate through a number of different mechanisms and that the latter are intimately related to the DNA organization of the genes, are now well-documented. Further, spontaneous mutations include those that cause diseases through loss of function as well as gain of function of genes. In contrast, most radiation-induced mutations studied in experimental systems (although identified through the phenotypes of the marker genes) are predominantly multigene deletions which cause loss of function; the recoverability of an induced deletion in a livebirth seems dependent on whether the gene and the genomic region in which it is located can tolerate heterozygosity for the deletion and yet be compatible with viability. In retrospect, the successful mutation test systems (such as the mouse specific locus test) used in radiation studies have involved genes which are non-essential for survival and are also located in genomic regions, likewise non-essential for survival. In contrast, most of the human genes at which induced mutations have been looked for, do not seem to have these attributes. The inference therefore is that the failure to find induced germline mutations in humans is not due to the resistance of human genes to induced mutations but due to the structural and functional constraints associated with their recoverability in livebirths. Since the risk of inducible genetic diseases in humans is estimated using rates of "recovered" mutations in mice, there is a need to introduce appropriate correction factors to bridge the gap between these rates and the rates at which mutations causing diseases are potentially recoverable in humans. Since the whole genome is the "target" for radiation-induced genetic damage, the failure to find increases in the frequencies of specific single-gene diseases of societal concern does not imply that there are no genetic risks of radiation exposures: the problem lies in delineating the phenotypes of recoverable genetic damage that are recognizable in livebirths. Data from studies of naturally-occurring microdeletion syndromes in humans and those from mouse radiation studies are instructive in this regard. They (i) support the view that growth retardation, mental retardation and multisystem developmental abnormalities are likely to be among the quantitatively more important adverse effects of radiation-induced genetic damage than mutations in a few selected genes and (ii) underscore the need to expand the focus in risk estimation from known genetic diseases (as has been the case thus far) to include these induced adverse developmental effects although most of these are not formally classified as "genetic diseases". (ABSTRACT TRUNCATED)
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Affiliation(s)
- K Sankaranarayanan
- MGC, Department of Radiation Genetics and Chemical Mutagenesis, Leiden University Medical Centre, Sylvius Laboratories, Wassenaarseweg 72, 2333 AL, Leiden, Netherlands.
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Sykes PJ, Hooker AM, Morley AA. Inversion due to intrachromosomal recombination produced by carcinogens in a transgenic mouse model. Mutat Res 1999; 427:1-9. [PMID: 10354496 DOI: 10.1016/s0027-5107(99)00084-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Somatic intrachromosomal recombination (SICR) can result in inversions and deletions in the DNA. pKZ1 mice possess an Escherichia coli (E. coli) lacZ transgene which is only expressed after a DNA inversion involving the transgene occurs. The E. coli beta-galactosidase protein can then be detected in frozen tissue sections using a chromogenic substrate. Therefore, pKZ1 mice can be used to detect SICR inversion events in vivo in different tissues. We have tested the pKZ1 mouse for its potential as a general mutagenesis model for detecting SICR in spleen in response to carcinogens which have widely different mechanisms of genotoxicity. Animals were given a single exposure of carcinogen and spleen cells were examined 3 days later for inversion events by histochemical staining of tissue sections. Mitomycin C, X-irradiation, etoposide and methylene chloride caused significant induction of inversion events in spleen tissue, ranging from 1.6- to 4.2-fold induction with the doses used here. This is the first time that inversion events induced by these carcinogens have been specifically studied in vivo in a mouse model and the findings expand the repertoire of mutation events known to be caused by these agents. We suggest that the pKZ1 mouse can be used as a general mutagenesis model for detection of SICR events and is likely to be a useful model for studying the mechanism of SICR in response to DNA damaging agents.
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Affiliation(s)
- P J Sykes
- Department of Haematology and Genetic Pathology, Flinders University of South Australia and Flinders Medical Centre, Bedford Park, SA 5042, Australia.
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Abstract
The lens plays an essential role for proper eye development. Mouse mutants affecting lens development are excellent models for corresponding human disorders. Moreover, using mutations in particular genes the process of eye and lens development can be dissected into distinct steps. Therefore, three mouse mutants will be described in detail and discussed affecting three essential stages: formation of the lens vesicle, initiation of secondary lens fiber cell formation, and terminal differentiation of the secondary fiber cells. The mutant aphakia (ak) has been characterized by bilaterally apakic eyes [Varnum and Stevens (1968) J. Hered. 59, 147-150], and the corresponding gene was mapped to chromosome 19 [Varnum and Stevens (1975) Mouse News Letters 53, 35]. Recent investigations in our laboratory refined the linkage 0.6 +/- 0.3 N cm proximal to the microsatellite marker D19Mit10. The linked gene Pax2, responsible for proper development of the posterior part of the eye and the optic nerve, was excluded as candidate gene by sequence analysis. Histological analysis of the homozygous ak mutants revealed a persisting lens stalk and subsequently the formation of lens rudiments. The lens defects led to irregular iris development and retinal folding. Congenital aphakia is known as a rare human anomaly. Besides a corneal dystrophy (CDTB), no corresponding disease is localized at the homologous region of human chromosome 10q23. The Cat3 mutations are characterized by vacuolated lenses caused by alterations in the beginning of secondary lens fiber cell differentiation at embryonic day 12.5. Secondary malformations develop at the cornea and the iris, but the retina remains unaffected. Two mutant alleles of the Cat3 locus have been mapped to mouse chromosome 10 very close to the microsatellite markers D10Mit41 and D10Mit95 (less than 0.3 cM). Since Cat3 is mapped to a position, which is homologous to human chromosome 12q21-24, the disorder cornea plana congenita can be considered as a candidate disease. The series of Cat2 mutations have been mapped close to the locus encoding the gamma-crystallin gene cluster Cryg [Löster et al. (1994) Genomics 23, 240-242]. The Cat2nop mutation is characterized by a deletion of 11 bp and an insertion of 4 bp in the 3rd exon of Crygh leading to a truncated gamma B-crystallin. The defect in the Crygh gene is causative for the stop of lens fiber cell differentiation from embryonic day 15.5 onward. Besides the lens, no further ocular tissue is affected. The Cat2 mouse mutants are interesting models for human cataracts caused by mutations in the gamma-crystallin genes at human chromosome 2q32-35. The ak, Cat3 and Cat2 mutants are discussed in the context of other mutants affecting early eye and lens development. Additionally, human congenital cataracts are discussed, which have been characterized similar to the mouse models. The overview of the three types of mutants demonstrates that genes, which affect the early eye development, e.g. at the lens vesicle stage, have consequences for the development of the whole eye. In contrast, if the mutation influences later steps of lens differentiation, the consequences are restricted to the lens only. These data indicate a decreasing effect of the lens for the regulation of eye development during embryogenesis.
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Affiliation(s)
- J Graw
- GSF-National Research Center for Environment and Health, Institute of Mammalian Genetics, Neuherberg, Germany
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16
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Klopp N, Favor J, Löster J, Lutz RB, Neuhäuser-Klaus A, Prescott A, Pretsch W, Quinlan RA, Sandilands A, Vrensen GF, Graw J. Three murine cataract mutants (Cat2) are defective in different gamma-crystallin genes. Genomics 1998; 52:152-8. [PMID: 9782080 DOI: 10.1006/geno.1998.5417] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A number of murine cataract mutations have been localized to chromosome 1 close to the gamma-crystallin gene cluster (Cryg) (Everett et al., 1994, Genomics 20: 429-434; Löster et al., 1994, Genomics 23: 240-242). Based on the size of the mapping or allelism tests they have not been shown to be genetically distinct and have been assigned to locus symbol Cat2. Here we assign three mutations to the respective gamma-crystallin gene. Using a systematic candidate gene approach to analyze the entire Cryg cluster, an A-->G transition was found in exon 2 of Cryga for the ENU-436 mutation and is designated Cryga1Neu. The mutant allele Crygbnop (formerly Cat2(nop)) is caused by a replacement of 11 bp by 4 bp in the third exon of Crygb, while a C-->G transversion in exon 3 of Cryge has been found for the Cryget (formerly Cat2(t)) mutation. For the mutation Cryga1Neu, an Asp-->Gly exchange is deduced, whereas the mutations Crygbnop and Cryget lead to the formation of in-frame stop codons and give rise to truncated proteins of 144 and 143 amino acids, respectively. The effects of the mutations upon gamma-crystallin structure are likely to be quite different. The Cryga1Neu mutation is expected to affect the link between Greek-key motifs 2 and 3, whereas both Crygbnop and Cryget mutations are supposed to truncate the fourth Greek-key motif. All three mutations are predicted to alter protein folding of the gamma-crystallins and result in lens cataract, but the phenotype for each is quite distinctive.
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Affiliation(s)
- N Klopp
- Institute of Mammalian Genetics, GSF-National Research Center for Environment and Health, Neuherberg, D-85764, Germany
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Friedman JM. One fewer worry for survivors of childhood cancer. Am J Hum Genet 1998; 62:25-6. [PMID: 9443886 PMCID: PMC1376817 DOI: 10.1086/301693] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
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18
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de Serres FJ, Webber BB. Quantitative and qualitative comparisons of spontaneous and radiation-induced specific-locus mutation in the ad-3 region of heterokaryon 12 of Neurospora crassa. Mutat Res 1997; 375:37-52. [PMID: 9129678 DOI: 10.1016/s0027-5107(96)00253-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The data from forward-mutation experiments to obtain specific-locus mutations at two closely linked loci in the adenine-3 (ad-3) region of heterokaryon 12 (H-12) of Neurospora crassa have been used to determine the relative frequencies and mutational spectra of ad-3 mutants occurring spontaneously and those induced by 7 different radiation treatments. Previous studies have demonstrated that specific-locus mutants at these two loci result from 5 major genotypic classes, namely two classes of gene/point mutations (ad-3AR and ad-3BR), and 3 classes of multilocus deletion mutations ([ad-3A]IR, [ad-3B]IR and [ad-3A ad-3B]IR). Two different approaches were used to compare spontaneous mutation in the ad-3 region with that induced by 7 different radiation treatments (UV, 32P, 447 MeV protons, 85Sr, 250 kVp X-rays, 39 MeV helium ions, and 101 MeV carbon ions). These comparisons included X2-tests on the numbers of ad-3 mutants resulting in the following two sets of ratios: (1) gene/point mutations and multilocus deletion mutations; and (2) complementing and non-complementing ad-3BR mutants. Combination of the data from these two methods of comparison has demonstrated that each of the 7 radiation treatments induced a spectrum of ad-3 mutants that is statistically different from the spontaneous spectrum. In addition, these same two methods of comparison have been used to compare the mutagenic effects of each of the 7 radiation treatments with each other. Combination of the data from these two methods of comparison demonstrated that the majority of radiation-induced specific-locus mutations: (90.5% (19/21 of the pairwise combinations)) are qualitatively different from each other. We conclude that the mechanisms by which various radiations modify DNA tend to exhibit fundamental differences from each other and from the processes involved in spontaneous mutation.
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Affiliation(s)
- F J de Serres
- Laboratory of Toxicology, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709-2233, USA.
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de Serres FJ, Malling HV, Brockman HE, Ong TM. Quantitative and qualitative comparison of spontaneous and chemical-induced specific-locus mutation in the ad-3 region of heterokaryon 12 of Neurospora crassa. Mutat Res 1997; 375:53-72. [PMID: 9129679 DOI: 10.1016/s0027-5107(96)00254-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The data from forward-mutation experiments to obtain specific-locus mutations at two closely linked loci in the adenine-3 (ad-3) region of heterokaryon 12 (H-12) of Neurospora crassa have been tabulated to determine the relative frequencies and mutational spectra of ad-3 mutants occurring spontaneously and those induced by 22 different chemical treatments. Previous studies have demonstrated that specific-locus mutations at these two loci result from 5 major genotypic classes, namely two classes of gene/point mutations (ad-3AR and ad-3BR), and 3 classes of multilocus deletion mutations ([ad-3A]IR, [ad-3B]IR and [ad-3A ad-3B]IR). In addition, prior studies have demonstrated that some chemical mutagens induced ad-3 mutants exclusively, or almost exclusively, by gene/point mutation and other chemical mutagens by gene/point mutation and multilocus deletion mutation. In the latter cases, there was wide variation in the percentages of ad-3 mutants in these 5 major genotypic classes. Two comparative methods of analysis that also were used to compare spontaneous and chemical-induced ad-3 mutational spectra included X2-tests on the numbers of ad-3 mutants resulting in the following two sets of ratios: (1) gene/point mutations and multilocus deletion mutations; and (2) complementing and non-complementing ad-3BR, mutants. Combination of the p-values from X2-tests for these two methods of comparison demonstrated that all 22 chemicals induce a spectrum of ad-3 mutants that is qualitatively different from that occurring spontaneously. In addition, these same two methods of comparison have been used to compare the mutagenic effects of each of the 22 chemical treatments with each other. Combination of the data from these two methods of comparison has demonstrated that 93.1% (215/231) of the pairwise combinations of these 22 chemicals were different from each other. The implication of these experimental data on the induction of specific-locus mutations in somatic cells of Neurospora for genetic risk assessment exercises is discussed.
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Affiliation(s)
- F J de Serres
- Laboratory of Toxicology, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709-2233, USA.
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20
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Ishikawa Y, Hyodo-Taguchi Y. Heritable malformations in the progeny of the male medaka (Oryzias latipes) irradiated with X-rays. Mutat Res 1997; 389:149-55. [PMID: 9093378 DOI: 10.1016/s1383-5718(96)00141-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Heritable malformations were examined in the progeny of X-irradiated male medaka (Oryzias latipes) by three-generation crosses. Two X-irradiated male fish were pair-mated with non-irradiated females to produce F1 founders, and each F1 fish was pair-mated with a non-irradiated fish to produce F2 progeny. For detection of recessive mutations, pair-matings between F2 siblings were performed for each F1 family. Morphogenesis of the embryos of each generation was observed using a stereomicroscope, throughout the entire period of embryonic development. In the F1 embryos, the frequencies of dominant lethals and malformations were increased by the X-irradiation. Two out of 30 F1 pairs produced a number of malformed and lethal F2 embryos, indicating inheritance of high rates of the dominant lethals in the two F1 families. Moreover, F2 sib-pairs offspring of which exibited high rates of dominant lethals were found in 10 out of 28 F1 families. Recessive lethal mutations, which were associated with a particular phenotype, were found in 2 out of the 28 F1 families. These results indicate that the heritable malformations induced by X-irradiation can be studied in the medaka.
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Affiliation(s)
- Y Ishikawa
- Division of Biology, National Institute of Radiological Sciences, Chiba, Japan
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Sankaranarayanan K. Environmental chemical mutagens and genetic risks: lessons from radiation genetics. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 1996; 28:65-70. [PMID: 8844986 DOI: 10.1002/(sici)1098-2280(1996)28:2<65::aid-em1>3.0.co;2-d] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Affiliation(s)
- K Sankaranarayanan
- Department of Radiation Genetics and Chemical Mutagenesis, Sylvius Laboratories, Leiden University, The Netherlands
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Sankaranarayanan K, Yasuda N, Chakraborty R, Tusnady G, Czeizel A. Ionizing radiation and genetic risks. V. Multifactorial diseases: A review of epidemiological and genetic aspects of congenital abnormalities in man and of models on maintenance of quantitative traits in populations. ACTA ACUST UNITED AC 1994. [DOI: 10.1016/0165-1110(94)90009-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Giometti CS, Tollaksen SL, Grahn D. Altered protein expression detected in the F1 offspring of male mice exposed to fission neutrons. Mutat Res 1994; 320:75-85. [PMID: 7506389 DOI: 10.1016/0165-1218(94)90061-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Liver protein expression in F1 offspring arising from spermatogonia exposed to 60 cGy of fission spectrum neutrons from the JANUS reactor was compared to that in offspring from unexposed spermatogonia by using two-dimensional electrophoresis (2DE). Approximately 100 protein spots in 2DE patterns from 167 control offspring and 530 offspring from irradiated sires were monitored for quantitative decreases of 50%, indicative of mutation events causing the loss of one normal copy of a structural gene. Reproducible abnormalities were found only in 3 patterns, all from the offspring of neutron-irradiated sires. Two of the three patterns were from littermates (brother and sister) and both showed an approximately 70% decrease in the amount of liver protein MSN188. The third pattern was from a male mouse sired by a different male and showed an approximately 50% decrease in the abundance of protein MSN94. The decreased abundance of MSN188 and MSN94 was assumed to be due to mutation events referred to as NEUT1 and NEUT2, respectively. Sibling crosses between the 2 mice showing the NEUT1 trait produced offspring with control, decreased and undetectable levels of MSN188 in a ratio of 0.25:0.5:0.25. Test crosses between the F1 offspring expressing the NEUT2 trait back to C57BL/6JANL mice produced offspring expressing normal or decreased amounts of MSN94 in a ratio of 0.5:0.5. Inbreeding of individuals expressing decreased amounts of MSN94 produced mice expressing control, decreased amounts, or no detectable amount of that protein in a ratio of 0.25:0.5:0.25. These results indicate that the decreased abundance of MSN188 or MSN94 originally detected in the F1 offspring is due to a genetically transmissible event. Unlike the heritable protein changes observed previously in the F1 offspring of sires exposed to N-ethyl-N-nitrosourea in which a protein variant was produced, both the NEUT1 and NEUT2 mutation events appear to prevent the production of any protein product. These 2 mutations may thus represent mutation lesions other than point mutations (e.g., deletions or translocations) detectable as quantitative changes in protein expression in the F1 generation.
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Affiliation(s)
- C S Giometti
- Biological and Medical Research Division, Argonne National Laboratory, IL 60439
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25
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Favor J. International Commission for Protection Against Environmental Mutagens and Carcinogens. Working paper no. 4. Spontaneous mutations in germ cells of the mouse: estimates of mutation frequencies and a molecular characterization of mutagenic events. Mutat Res 1994; 304:107-18. [PMID: 7506351 DOI: 10.1016/0027-5107(94)90321-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Affiliation(s)
- J Favor
- GSF-Institut für Säugetiergenetik, Oberschleissheim, Germany
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Sankaranarayanan K. International Commission for Protection Against Environmental Mutagens and Carcinogens. Working paper no. 6. Estimation of genetic risks of exposure to chemical mutagens: relevance of data on spontaneous mutations and of experience with ionizing radiation. Mutat Res 1994; 304:139-58. [PMID: 7506354 DOI: 10.1016/0027-5107(94)90323-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
This paper examines the impact of advances in knowledge on the molecular biology of human Mendelian diseases on the estimation of genetic risks of exposure to ionizing radiation and to chemical mutagens. More specifically, it addresses the question of whether and to what extent naturally occurring Mendelian diseases can be used as a baseline for efforts in this area. Data on the molecular nature and mechanisms of origin of spontaneous mutations underlying naturally occurring Mendelian diseases and on radiation-induced mutations in experimental systems suggest that for ionizing radiation, naturally occurring Mendelian diseases may not constitute an entirely adequate frame of reference and that current risk estimates for this class of diseases are conservative; these estimates however provide a margin of safety in formulating radiation protection guidelines. Currently available data on mechanisms and specificities of action of chemical mutagens, molecular dosimetry, repair of chemically induced adducts in the DNA, adduct-mutation relationships etc., permit the tentative conclusion that naturally occurring Mendelian diseases may provide a better baseline for genetic risk estimation for chemical mutagens than for ionizing radiation. With both ionizing radiation and chemical mutagens, the question of which Mendelian diseases are potentially inducible will become answerable in the near future when more molecular data on human genetic diseases become available. It is therefore essential that risk estimators keep abreast of advances in human genetics and integrate these into their conceptual framework. However, induced Mendelian diseases (especially the dominant ones which are of more immediate concern) are likely to represent a very small fraction of the adverse genetic effects of induced mutations. More attention therefore needs to be devoted to studies on the heterozygous effects of induced mutations.
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Affiliation(s)
- K Sankaranarayanan
- MGC Department of Radiation Genetics and Chemical Mutagenesis, Sylvius Laboratories, State University of Leiden, The Netherlands
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Sankaranarayanan K. Ionizing radiation and genetic risks. I. Epidemiological, population genetic, biochemical and molecular aspects of Mendelian diseases. Mutat Res 1991; 258:3-49. [PMID: 2023599 DOI: 10.1016/0165-1110(91)90027-s] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
This paper reviews the currently available information on naturally occurring Mendelian diseases in man; it is aimed at providing a background and framework for discussion of experimental data on radiation-induced mutations (papers II and III) and for the estimation of the risk of Mendelian disease in human populations exposed to ionizing radiation (paper IV). Current consensus estimates indicate that a total of about 125 per 10(4) livebirths are directly affected by one or another naturally occurring Mendelian disease (autosomal dominants, 95/10(4); X-linked ones, 5/10(4); and autosomal recessives, 25/10(4). These estimates are conservative and take into account conditions which are very rare and for which prevalence estimates are unavailable. Most, although not all, of the recognized "common" dominants have onset in adult ages while most sex-linked and autosomal recessives have onset at birth or in childhood. Autosomal dominant and X-linked diseases (i.e., the responsible mutant alleles) presumed to be maintained in the population due to a balance between mutation and selection are the ones which may be expected to increase in frequency as a result of radiation exposures. Viewed from this standpoint, the above assumption seems safe only for a small proportion of such diseases; for the remainder, there is no easy way to discriminate between different mechanisms that may be responsible or to rigorously exclude some in favor of some others. Mutations in genes that code for enzymic proteins are more often recessive in contrast to those that code for non-enzymic proteins, which are more often dominant. At the molecular level, with recessives, a wide variety of changes is possible and these include specific types of point mutations, small and large intragenic deletions, multilocus deletions and rearrangements. In the case of dominants, however, the kinds of recoverable point mutations and deletion-type changes are less extensive because of functional constraints. The mutational potential of genes varies, depending on the gene, its size, sequence content and arrangement, location and its normal functions, and can be grouped into three groups: those in which only point mutations have been found to occur, those in which only deletions or other gross changes have been recovered and those in which both kinds of changes are known. Molecular data are available for about 75 Mendelian conditions and these suggest that in approximately 50% of them, the changes categorized to date are point mutations and in the remainder, intragenic deletions or other gross changes; there does not seem to be any fundamental difference between dominants and recessives with respect to the underlying molecular defect.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- K Sankaranarayanan
- MGC Department of Radiation Genetics and Chemical Mutagenesis, Sylvius Laboratories, State University of Leiden, The Netherlands
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Sankaranarayanan K. Ionizing radiation and genetic risks. IV. Current methods, estimates of risk of Mendelian disease, human data and lessons from biochemical and molecular studies of mutations. Mutat Res 1991; 258:99-122. [PMID: 2023602 DOI: 10.1016/0165-1110(91)90030-y] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
This paper is aimed at a synthesis of conclusions and concepts from the first three papers of this series and an inquiry of their relevance to the estimation of the risk of autosomal dominant and X-linked diseases in man, due to exposure to ionizing radiation. For a population under conditions of continuous irradiation, the doubling-dose method (DD method) enables the prediction of the excess risk of dominant and X-linked diseases at equilibrium. Per unit dose, this quantity is the product of the natural prevalence of these diseases (assumed to be 10,000/10(6) livebirths) and the reciprocal of the DD. The DD currently used is 1 Gy and is based primarily on data on the induction of recessive specific-locus mutations in male mice. The estimate of risk to the first generation is derived from that at equilibrium; the figure is about 15% of the equilibrium value (i.e., 15 cases/10(6) livebirths/cGy). With the direct method, the first-generation risk of dominant disease is estimated using data on the induction of dominant skeletal and cataract mutations in male mice and a number of correction factors. The estimates are about 10-20 cases and 0-9 cases, respectively, for irradiation of males and females, per 10(6) livebirths/cGy. In the Japanese studies, no significant adverse genetic effects, attributable to exposure of the parents to the atomic bombs, could be demonstrated with respect to any of the endpoints used. Most of the latter are clinically and socially relevant but mutationally insensitive. On the basis of these data, Neel and colleagues have estimated that the gametic DD for genetic effects of radiation in man is at least about 4-5 times the 1 Gy value thus far used. The concepts, assumptions, and the data-base used with the DD method have been re-examined. Arguments are advanced to support the thesis that ionizing radiation is probably not very efficient in inducing the very specific molecular changes that are known to underlie spontaneous mutations which cause naturally occurring dominant genetic diseases. It is suggested that (i) the DD estimate of 1 Gy that is used to estimate risk for autosomal dominant and X-linked diseases is conservative and (ii) the 1% prevalence figure for these diseases that is used for this purpose may be too high. If these suggestions are correct, then the estimate of risk for the dominant and X-linked diseases may need to be revised downwards.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- K Sankaranarayanan
- MGC Department of Radiation Genetics and Chemical Mutagenesis, Sylvius Laboratories, State University of Leiden, The Netherlands
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Sankaranarayanan K. Ionizing radiation and genetic risks. III. Nature of spontaneous and radiation-induced mutations in mammalian in vitro systems and mechanisms of induction of mutations by radiation. Mutat Res 1991; 258:75-97. [PMID: 2023601 DOI: 10.1016/0165-1110(91)90029-u] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
This paper (1) presents an analysis of published data on the molecular nature of spontaneously arising and radiation-induced mutations in mammalian somatic cell systems and (2) examines whether the molecular nature and mechanisms of origin of radiation-induced mutations, in mammalian in vivo and in vitro systems, as currently understood, are consistent with expectations based on the biophysical and microdosimetric properties of ionizing radiation. Depending on the test system (CHO cells, human T lymphocytes and human lymphoid cell line TK6), 80-97% of spontaneous HPRT mutations show normal Southern patterns; the remainder is due to gross changes, predominantly partial (intragenic) deletions. Total gene deletions at the HPRT locus are rare except in the TK6 cell line. At the APRT locus in CHO cells, 80-97% of spontaneous mutations are due to base-pair changes, the remainder being, mostly, partial deletions. The latter can extend upstream in the 5' direction but not beyond the APRT gene in the 3' direction. At the human HLA-A locus (T lymphocytes), the percentage of mutations with normal Southern patterns is lower than that for HPRT, and in the range of 50-60%. At the HLA-A locus, mitotic recombination contributes substantially to the mutation spectrum (approximately 30% of mutations recovered) and this is likely to be true of the TK locus in the TK6 cell line as well. With a few exceptions, most of the radiation-induced mutations show altered Southern patterns and are consistent with their being deletions and/or other gross changes (HPRT, 70-90% (CHO); 50-85% (TK6); 50-75% (T lymphocytes); TK, 60-80% (TK6); HLA-A, 80% (T lymphocytes); DHFR, 100% (CHO]. The exceptions are APRT mutations in CHO cells (16-20% of mutants with deletions or other changes) and HPRT mutations in T lymphocytes from A-bomb survivors (15-25%); the latter finding is consistent with the occurrence of in vivo selection against HPRT mutant cells. In cases of HPRT intragenic deletions analyzed (CHO cells and V79 Chinese hamster cells), there is evidence for a non-random distribution of breakpoints. The spontaneous mutation frequencies vary widely, from about 0.04/10(6) cells (sickle cell mutations at the human HBB locus) to 30.8/10(6) cells (HLA-A mutations in T lymphocytes) and are dependent on the locus, the system employed and a number of other factors. Those for the other loci fall between these limits.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- K Sankaranarayanan
- MGC Department of Radiation Genetics and Chemical Mutagenesis, Sylvius Laboratories, State University of Leiden, The Netherlands
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