著者

山田 雅巳

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.25, no.2, pp.87-92, 2003 (Released:2005-08-19)

参考文献数

8

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Gene disruption methods are useful to construct bacteria lacking a specific gene especially when a gene’s function is unknown. In the 1980s, complementation techniques were used as the first step in cloning a gene. With the advances made through genome projects, gene identification and cloning have allowed easier construction of deficient bacterial strains with cloned genes. In this report, I describe three methods of disrupting specific genes on chromosomes in a strain of interest, namely linear transformation, preligation and the ‘one-step’ method. Moreover, several genetic techniques which are necessary for conducting these methods are also reviewed.

著者

鈴木 孝昌

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.25, no.3, pp.181-185, 2003 (Released:2005-08-19)

参考文献数

5

被引用文献数

1

---

Has mutation research contributed sufficiently to the genetic risk assessment of chemicals? The answer may be “No”. Although it has contributed much to predict carcinogenicity, how much benefit has exposure prevention of those mutagens brought to public health? It is suggested that the proportion of human carcinogenesis related to environmental chemicals is less than 10%. The main causes for cancer are tobacco smoking, diet, and aging. As genetic toxicologists, we have become too satisfied with a qualitative evaluation of mutation assay results and try to detect as many “carcinogens” as possible. This approach ignores the quantitative evaluation, which is more important in risk assessment. Many “carcinogens”, especially socalled non-genotoxic carcinogens, do not cause cancer at the human exposure level. The “genotoxic non-carcinogens”, if they exist, may be more important because cancer is not the only toxicological outcome of genotoxicity. We should pay more attention to heritable genetic effects of chemicals. An increasing incidence of smoking among young women alerts us to investigate the genetic effects of smoking in their progeny.The paradigm shift from hazard identification to risk assessment is important in mutation research. In this regard, quantitative, mechanism-based, and humanized mutation assays are required.

著者

奥山 治美

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.25, no.2, pp.147-157, 2003 (Released:2005-08-19)

参考文献数

87

被引用文献数

2 4

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Substances causing persistent inflammation (asbestos, viruses and pathogens) are often carcinogenic even if they are not directly mutagenic. Reactive oxygen species from inflammatory cells injure DNA and are cell-proliferative leading to accelerated carcinogenesis. Lipid mediators in the linoleic acid (LA) cascade through arachidonic acid (n-6) and some cytokines form amplification cascades to stimulate these processes, whereas the fatty acids of n-3 type competitively suppress the LA cascade and carcinogenesis. This interpretation is consistent with the observations that (1) dietary oils with low n-6/n-3 ratios are suppressive compared with high-LA oils, (2) inhibitors of the LA cascade are suppressive, and (3) manipulations to knockout genes related to the LA cascade are suppressive for carcinogenesis. On the other hand, many kinds of genes are affected differently by the chain length and unsaturation of fatty acids regardless of the n-6 or n-3 type. Saturates, monounsaturates and LA up-regulate cholesterol synthesis leading to enhanced prenylation of oncogene products, cell-proliferation and carcinogenesis. Dietary cholesterol and high tissue cholesterol levels feedback suppress cholesterol synthesis and cell-proliferative stimuli, which partly accounts for epidemiological observations that cancer mortality is lower in the group with higher cholesterol level. For the cancers, the incidence of which is high in the US and has been increasing rapidly in Japan, reducing the intake of LA to half while maintaining those of n-3 fatty acids and animal fats at the levels of average Japanese is recommended.

著者

鈴木 啓司 児玉 靖司 渡邉 正己

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.27, no.2, pp.111-115, 2005 (Released:2005-12-26)

参考文献数

29

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Ionizing radiation induces genomic instability, which is transmitted through many generations after irradiation in the progeny of surviving cells. We have hypothesized that radiation-induced large deletion causes potentially unstable chromosome regions, which are involved in delayed induction of radiation-induced genomic instability. Using phosphorylation-specific antibodies against ATM and histone H2AX, whose phosphorylation is induced by DNA double strand breaks, we detected delayed induction of phosphorylated ATM and H2AX foci in the progeny of X-ray-surviving cells, which indicated delayed induction of DNA double strand breaks. Furthermore, we found delayed chromosomal instability in X chromosomes in clones which contain large deletion involving the HPRT loci. It is suggested that large deletion involving —Mb region causes unstable chromatin structure, and it results in delayed rearrangement of chromosomes involved. These findings provide the possibility that manifestation of radiation-induced genomic instability results from delayed DNA breaks, i.e., the breaks lead to delayed chromosome rearrangements, delayed cell death etc., many generations after irradiation.

著者

中村 宜督

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.26, no.3, pp.253-258, 2004 (Released:2005-12-24)

参考文献数

25

被引用文献数

1 1

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An important group of compounds that have a chemopreventive property is organosulfur compounds such as isothiocyanates. In the present study, we clarified the molecular mechanism underlying the relationship between benzyl isothiocyanate (BITC)-induced cell cycle arrest and apoptosis. The exposure of the cultured cells to BITC resulted in the inhibition of the G2/M progression that coincided with apoptosis induction. An experiment using phase-specific synchronized cells demonstrated that the G2/M phase-arrested cells are more sensitive to undergoing apoptotic stimulation by BITC than the cells in other phases. We identified phosphorylated Bcl-2 as a key molecule linking the p38 MAPK-dependent cell cycle arrest with JNK activation by BITC. We also found that BITC induced a cytotoxic effect more preferentially in the proliferating normal human colon epithelial cells than the quiescent cells. Moreover, down-regulation of p53 resulted in the enhancement of susceptibility to undergoing apoptotic stimulation by BITC. These findings suggested that p53 might play a negative regulating role in BITC-induced apoptosis. In conclusion, the results from this study provided biological evidence that BITC has a potential to induce apoptosis selectively in p53-mutated proliferating pre-cancerous cells.

著者

福島 昭治 鰐渕 英機 森村 圭一朗 魏 民

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.27, no.2, pp.75-79, 2005 (Released:2005-12-26)

参考文献数

11

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Until recently it has been generally considered that genotoxic carcinogens have no threshold in exerting their potential for cancer induction. However, the non-threshold theory can be challenged with regard to assessment of cancer risk to humans. In the present study we show that food-related genotoxic hepatocarcinogens, heterocyclic amines and N-nitroso compounds at low doses do not induce preneoplastic lesions and cancer-related markers in rat medium-term carcinogenicity bioassay. The results imply existence of a threshold, at least practical one, for carcinogenicities of genotoxic carcinogens.

著者

東海林 克彦

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.27, no.2, pp.121-124, 2005 (Released:2005-12-26)

参考文献数

7

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This article aims to introduce the outline of issue and phenomena of welfare of laboratory animals which is enacted in Law for Welfare and Proper Management of Animals, and to clarify the difference of conception and method between welfare of laboratory animals and experiment using laboratory animals, in anticipation of contributing to its improvement in practice.

著者

宮田 昌明 高野 泰樹 山添 康

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.26, no.3, pp.247-251, 2004 (Released:2005-12-24)

参考文献数

23

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Co-intake of grapefruit juice with drugs results in a substantial increase in oral drug bioavailability. In contrast, DNA damage in target organ induced by a food-derived carcinogen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), was reduced in rats by grapefruit juice intake. Aflatoxin B1-induced DNA damage was also suppressed in rats treated with grapefruit juice and an ethyl acetate extract of grapefruit juice. A significant decrease in hepatic CYP3A content, but not in CYP1A, CYP2C, glutathione S-transferase and microsomal epoxide hydrolase contents was observed in rats after grapefruit juice intake. No significant differences in the portal blood and liver concentrations of aflatoxin B1, nor in blood concentration of PhIP, were observed between control rats and rats ingesting grapefruit juice. Thus, grapefruit juice intake causes suppression of carcinogen-induced DNA damage at least in part through decreased metabolic activation in rat liver.

著者

祖父尼 俊雄 能美 健彦 太田 敏博 林 真

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.27, no.2, pp.61-73, 2005-07-31

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The concept of a "biological threshold" is attracting interest as an evaluation criterion for the mutagenic activity of DNA-targeting mutagens. In this context, the concept is defined as "a concentration of a chemical which does not produce any damage through its inability to perform the necessary biochemical reactions, even though present at the target in finite amount". To clarify whether this criterion is indeed applicable to DNA-targeting mutagens, we re-evaluated the reverse mutation assay data using DNA repair-deficient bacterial strains, such as S. typhimurium strains lacking the O^6-methylguanine DNA methyltransferase genes (ada_<ST> and ogt_<ST>), the nucleotide excision repair gene (uvrB) or the 8-hydroxyguanine DNA glycosylase gene (mutM_<ST>), and E. coli strains lacking the nucleotide excision repair gene (uvrA). Mutagenic responses of 20 test chemicals including alkylating and non-alkylating agents were compared between the repair-deficient and their wild-type strains. All the alkylating agents, such as MNNG, ENNG, EMS, ENU, DMN and DEN, exhibited more sensible mutagenic responses in strains YG7108 (Δada_<ST>, Δogt_<ST>) and YG7113 (same as YG7108 but containing the plasmid pKM101) than in the parental strains TA1535 and TA100 (same as TA1535 but containing the pKM101), respectively. Upon applying MNNG, YG7108 showed about 2-100 fold increase in the number of His^+ revertants above the spontaneous level over the range of 0.00025-0.25μg/plate, whereas TA1535 did not show any significant increase in the number of His^+ revertants over the same dose range. On TA1535, an increasing tendency of the number of revertants was observed at 0.5μg/plate or above. This indicates an approximate 2,000-fold difference at the mutagenic concentration level between the wild-type and the repair-deficient strains. Other alkylating agents also showed significant differences in mutagenic responses between YG7108 and TA1535, or between YG7113 and TA100 respectively, with some variations among test chemicals. On the other hand, non-alkylating agents, such as 4-NQO, AF-2, 2-NF and MX, did not show any differences in the dose-response relationships between YG7113 and TA100. When non-alkylating agents, such as 4-NQO, 2-NF and MX were applied to TA1535 (ΔuvrB), TA1538 (ΔuvrB) and WP2uvrA (ΔuvrA), clearly different mutagenic responses, i.e. about 30- to 60-fold, were observed between the repair-deficient and the parental strains (TA1975, TA1978 and WP2, respectively). 4-NQO showed different mutagenic responses between YG3002 (ΔmutM_<ST>) and TA1975 (about 10-fold), though the application of other oxidative agents such as hydrogen peroxide resulted in less than 10-fold differences. The present results indicate that the wild-type strains having normal repair capacity show no gene mutation induction at the concentrations at which gene mutations are clearly induced in the repair-deficient strains through DNA damage. Thus, the present results suggest the existence of a "biological threshold" below which no mutagenic response is induced by DNA-targeting mutagenic substances.

著者

中西 真

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.26, no.2, pp.117-121, 2004 (Released:2005-12-21)

参考文献数

11

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Chk1 is required for arrest of the mammalian cell cycle before mitosis in response to DNA damage or replication block. It is also implicated in regulation of cell cycle progression because it is essential for embryonic cell viability. With the use of mouse embryonic stem cells conditionally deficient in Chk1, we now show that this kinase is indispensable for the timing of mitotic initiation. Chk1 deficiency resulted in premature onset of mitosis through reduction of Cdc2 phosphorylation on Tyr15 as a result of increased Cdc25 activity and decreased Wee1 activity. Our results suggest that Chk1 regulates Cdc2 to establish proper timing of mitotic initiation during the mammalian embryonic cell cycle.

著者

菊池 康基

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.26, no.1, pp.51-57, 2004 (Released:2005-12-13)

参考文献数

63

著者

坂本,豊

出版者

日本環境変異原学会

雑誌

環境変異原研究

巻号頁・発行日

vol.20, no.3, 1998-10-31

著者

田辺 秀之

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.25, no.1, pp.11-22, 2003 (Released:2005-08-19)

参考文献数

97

被引用文献数

1 1

---

The individual chromosomes in animal and plant interphase cell nuclei are discretely highly compartmentalized called “chromosome territories” that are visualized by 3D-FISH techniques. The chromosome territories are mutually exclusive without mixing each other, formed in essential components of the higher order chromatin architecture. Here I reviewed historical aspects of studies on the chromosome territory and recent advancement of studies on the chromosome positioning in relation to nuclear architecture. Chromosome positioning in the interphase cell nuclei has been investigated with regard to the following two aspects : radial positioning or relative positioning. It has been generally considered that the former radial positioning of a given chromosome territory is correlated with its size, its gene-density, and replication timing, namely comprehended as non-random distribution. From a series of 3D-FISH studies on the primate and chicken cell nuclei, the topology of the radial positioning of human chromosomes 18 and 19 homologs shows highly evolutionarily conserved during the evolution, but its functional significance is still within the speculation. On the other hand, the relative positioning has much affects to the translocation frequencies between adjacent two chromosomes, that was experimentally indicated by the mouse lymphoma cell nuclei, but in human lymphocytes the majority of reports suggested the random organization without particular patterns except for some clusters formed between homologous chromosomes. In future studies higher order nuclear architecture in relation to chromosome territory will be more elucidated by 3D-FISH techniques combined with living cell (in vivo) approaches by means of visualizing various nuclear molecules.

著者

林 哲也

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.27, no.2, pp.117-118, 2005 (Released:2005-12-26)

参考文献数

5

著者

中川 宗洋

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.26, no.2, pp.3-4, 2004-09-30

著者

石館 基

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.21, no.1, pp.53-81, 1999

著者

祖父尼 俊雄 能美 健彦 太田 敏博 林 真

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.27, no.2, pp.61-73, 2005 (Released:2005-12-26)

参考文献数

23

被引用文献数

9 9 1

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The concept of a “biological threshold” is attracting interest as an evaluation criterion for the mutagenic activity of DNA-targeting mutagens. In this context, the concept is defined as “a concentration of a chemical which does not produce any damage through its inability to perform the necessary biochemical reactions, even though present at the target in finite amount”. To clarify whether this criterion is indeed applicable to DNA-targeting mutagens, we re-evaluated the reverse mutation assay data using DNA repair-deficient bacterial strains, such as S. typhimurium strains lacking the O6-methylguanine DNA methyltransferase genes (adaST and ogtST), the nucleotide excision repair gene (uvrB) or the 8-hydroxyguanine DNA glycosylase gene (mutMST), and E. coli strains lacking the nucleotide excision repair gene (uvrA). Mutagenic responses of 20 test chemicals including alkylating and non-alkylating agents were compared between the repair-deficient and their wild-type strains.All the alkylating agents, such as MNNG, ENNG, EMS, ENU, DMN and DEN, exhibited more sensible mutagenic responses in strains YG7108 (ΔadaST, ΔogtST) and YG7113 (same as YG7108 but containing the plasmid pKM101) than in the parental strains TA1535 and TA100 (same as TA1535 but containing the pKM101), respectively. Upon applying MNNG, YG7108 showed about 2-100 fold increase in the number of His+ revertants above the spontaneous level over the range of 0.00025-0.25 μg/plate, whereas TA1535 did not show any significant increase in the number of His+ revertants over the same dose range. On TA1535, an increasing tendency of the number of revertants was observed at 0.5 μg/plate or above. This indicates an approximate 2,000-fold difference at the mutagenic concentration level between the wild-type and the repairdeficient strains. Other alkylating agents also showed significant differences in mutagenic responses between YG7108 and TA1535, or between YG7113 and TA100 respectively, with some variations among test chemicals. On the other hand, non-alkylating agents, such as 4-NQO, AF-2, 2-NF and MX, did not show any differences in the dose-response relationships between YG7113 and TA100. When non-alkylating agents, such as 4-NQO, 2-NF and MX were applied to TA1535 (ΔuvrB), TA1538 (ΔuvrB) and WP2uvrA (ΔuvrA), clearly different mutagenic responses, i.e. about 30- to 60-fold, were observed between the repair-deficient and the parental strains (TA1975, TA1978 and WP2, respectively). 4-NQO showed different mutagenic responses between YG3002 (ΔmutMST) and TA1975 (about 10-fold), though the application of other oxidative agents such as hydrogen peroxide resulted in less than 10-fold differences. The present results indicate that the wild-type strains having normal repair capacity show no gene mutation induction at the concentrations at which gene mutations are clearly induced in the repair-deficient strains through DNA damage. Thus, the present results suggest the existence of a “biological threshold” below which no mutagenic response is induced by DNA-targeting mutagenic substances.

著者

及川 伸二 大西 志保 村田 真理子 平工 雄介 川西 正祐

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.26, no.2, pp.125-133, 2004 (Released:2005-12-21)

参考文献数

24

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Reactive oxygen species generated by environmental factors, such as radiation, UV and chemicals can cause sequence-specific DNA damage and play important roles in mutagenesis and carcinogenesis. We have investigated sequence specificity of oxidative stress-mediated DNA damage by using 32P-labeled DNA fragments obtained from the human c-Ha-ras-1, p53 and p16 genes. Free hydroxyl radicals cause DNA damage with no marked site specificity. Copper-hydroperoxo complex caused DNA damage at thymine, cytosine and guanine residues. 1O2 preferentially induces lesions at guanine residues. Benzoyloxyl radical specifically causes damage to the 5’-G in GG sequence; this sequence is easily oxidized because a large part of the highest occupied molecular orbital of this radical is distributed on this site.Recently, we demonstrated that BP-7,8-dione, a metabolite of carcinogenic benzo [a] pyrene (BP) , strongly damaged the G and C of the 5’-ACG-3’ sequence complementary to codon 273 of the p53 gene in the presence of NADH and Cu (II) . BP-7,8-dione also caused preferential double base lesion at 5’-TG-3’ sequences. Since clustered DNA damage is poorly repaired, it is speculated that induction of the double base lesions in DNA might lead to activation of proto-oncogene or inactivation of the tumor suppressor gene. Therefore, oxidative DNA damage induced by BP-7,8-dione, especially double base lesions, may participate in the expression of carcinogenicity of BP in addition to DNA adduct formation. Here, we discuss the mechanisms of sequence-specific DNA damage including clustered DNA damage in relation to mutagenesis and carcinogenesis.

著者

本間 正充

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.26, no.3, pp.285-286, 2004 (Released:2005-12-24)

参考文献数

5

著者

鈴木 啓司 児玉 靖司 渡邉 正己

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.27, no.2, pp.111-115, 2005-07-31

---

Ionizing radiation induces genomic instability, which is transmitted through many generations after irradiation in the progeny of surviving cells. We have hypothesized that radiation-induced large deletion causes potentially unstable chromosome regions, which are involved in delayed induction of radiation-induced genomic instability. Using phosphorylation-specific antibodies against ATM and histone H2AX, whose phosphorylation is induced by DNA double strand breaks, we detected delayed induction of phosphorylated ATM and H2AX foci in the progeny of X-ray-surviving cells, which indicated delayed induction of DNA double strand breaks. Furthermore, we found delayed chromosomal instability in X chromosomes in clones which contain large deletion involving the HPRT loci. It is suggested that large deletion involving ~Mb region causes unstable chromatin structure, and it results in delayed rearrangement of chromosomes involved. These findings provide the possibility that manifestation of radiation-induced genomic instability results from delayed DNA breaks, i.e., the breaks lead to delayed chromosome rearrangements, delayed cell death etc., many generations after irradiation.