摘要:

AbstractIn recognition of the need for a more comprehensive data base for genetic risk assessment of human exposure to mutagenic agents in the environment, a model system was developed for specific‐locus studies in Neurospora crassa. This lower eukaryotic organism permits the utilization of microbial techniques for recovery of large numbers of specific‐locus mutations at two closely linked loci as well as their subsequent genetic analysis. In particular, this assay makes possible exploratory experiments with different environmental mutagens to obtain data on a wide variety of experimental conditions. Such data make it possible to study induction kinetics and mutational spectra in a manner that is not as yet feasible in higher eukaryotic organisms. Theadenine‐3 (ad‐3)specific‐locus assay was modeled after the 2–gene, morphological specific‐locus assay in thedilute‐short‐earregion of the mouse, and it also detects forward‐mutations at two closely linked loci, namely,ad‐3Aandad‐3B.Becausead‐3mutations are recovered by a direct method, based on the accumulation of a reddish‐purple pigment in the vacuoles of the mycelium rather than their requirement for adenine, this system is both a morphological and biochemical specific‐locus assay. The use of thead‐3assay system in experiments with different environmental mutagens has provided precise dose‐response curves not only for inactivation, but also the overall induction ofad‐3mutations. Genetic characterization of thesead‐3mutations by a series of 3 rapid and simple genetic tests permits the identification of 18 subclasses of gene/point mutations, and 12 subclasses of multilocus deletion mutations. These subclasses also include 3 different classes of multiple‐locus mutations with separate sites of recessive lethal damage either in the immediately adjacent regions or elsewhere in the genome. In summary, this specific‐locus assay provides a capability that is unique among eukaryotic organisms for the recovery and analysis of genetic damage at 2 cl

ISSN:0893-6692    

DOI:10.1002/em.2850200402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractData from experiments on the induction of specific‐locus mutations in model systems are utilized in genetic risk assessment to estimate potential adverse effects in the human population. In such assessments with radiation or chemical mutagens, the following information is required: (1) spontaneous and induced forward‐mutation frequencies, (2) dose‐response curves for the overall induction of specific‐locus mutations, (3) genetic characterization of spontaneous and induced mutations, and (4) dose‐response curves for the different genotypic classes. Specific‐locus assays in most eukaryote assay systems provide only portions of the information required for genetic risk assessment. In recognition of the need for a more comprehensive data base, a model system was developed for specific‐locus studies in Neurospora crassa. Theadenine‐3(ad‐3) specific‐locus assay was modeled after the 2 gene, morphological specific‐locus assay in thedilute‐short‐earregion of the mouse, and it detects forward‐mutations at two closely linked loci:ad‐3Aandad‐3B. Thead‐3assay system has provided precise dose‐response curves not only for inactivation, but also the overall induction ofad‐3mutations. The utilization of this assay in experiments with radiation or chemical mutagens has provided a data base on the induction and genetic characterization of specific‐locus mutations that is unique among eukaryotic organisms. In this assay, gene/point mutations, multilocus deletion mutations, and 3 different classes of multiple‐locus mutations can be identified. The latter consist of specific‐locus mutations associated with recessive lethal mutations located either closely linked to thead‐3region or elsewhere in the genome. The overall data base on the heterozygous effects of X‐ray‐inducedad‐3mutations demonstrates that such effects are allele specific, genotype specific, and locus specific. There are probably a variety of mechanisms by which the heterozygous effects of individual allelic mutations at different genetic loci can be affected. In conclusion, unless the frequencies of all of the different classes of induced specific‐locus mutations are determined, and utilized in genetic risk assessment exercises, the risk of human exposure to environmental mutagens

ISSN:0893-6692    

DOI:10.1002/em.2850200403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractMechanisms for Dominance:AdhHeterodimer Formation in Heterozygotes Between ENU or X‐ray Induced Null Alleles and Normal Alleles inDrosophila melanogasterTo study mechanisms for dominance of phenotype, eight ENU‐ and four X‐ray‐induced mutations at the alcohol dehydrogenase (Adh) locus were analyzed for partial dominance in their interaction with normal alleles. All ENU and one of the X‐ray mutations were single base substitutions; the other three X‐ray mutations were 9–21 base deletions. All but one of the 12 mutant alleles were selected for this study because they produced detectable mutant polypeptides, but seven of the 11 producing a peptide could not form dimers with the normal peptide and the enzyme activity of heterozygotes was about half that of normal homozygotes. Four mutations formed dimers with a decreased catalytic efficiency and two of these were near the limit of detectability; these two also inhibited the formation of normal homodimers. The mutant alleles therefore show multiple mechanisms leading to partial enzyme expression in heterozygotes and a wide range of dominance ranging from almost complete recessive to nearly dominant. All amino acid changes in mutant peptides that form dimers are located between amino acids 182 and 194, so this region is not critical for dimerization. It may, however, be an important surface domain for catalyzation. © 1992 W

ISSN:0893-6692    

DOI:10.1002/em.2850200404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractIn some biological systems ionizing radiation appears to induce large deletions and rearrangements, while in others point mutations predominate the mutational spectrum. Moreover, while the point mutations are often randomly distributed, some systems exhibit “hot spots.” Retroviral shuttle vectors are particularly useful for investigating the basis of these differences since the genetic target can be conveniently analyzed in a variety of host backgrounds and genomic locations. We have studied the mutational specificity of X‐rays in a Chinese hamster ovary cell line (CHO) containing a stably integrated retroviral shuttle vector, carrying the CHO aprt cDNA as the genetic target. Cells were irradiated with 7 Gy using a 180 kVp X‐ray source. The predominant mutation (87% of all APRT mutants), as determined by Southern analysis, was the complete deletion of the shuttle vector construct. In addition, 23 APRT mutants, carrying an apparently intact shuttle vector, were characterized at the sequence level: 5 were transitions, 9 were transversions, 3 were small deletions or insertions, 4 were frameshifts, and 2 were small rearrangements. Although the type and the location of the point mutations character ized appeared largely random, small deletions, insertions, and frameshifts were frequently associated with direct sequence repeats. © 1992 Wiley

ISSN:0893-6692    

DOI:10.1002/em.2850200405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractAn alkaline unwinding assay was used to quantitate the induction of DNA strand breaks (DNA SB) in the livers of rats and mice treated in vivo, in rodent hepatocytes in primary culture, and in CCRF‐CEM cells, a human lymphoblastic leukemia cell line, following treatment with tri‐ (TCA), di‐ (DCA), and mono‐ (MCA) chloroacetic acid and their corresponding aldehydes, tri‐ (chloral hydrate, CH), di‐ (DCAA) and mono‐ (CAA) chloroacetaldehyde. None of the chloroacetic acids induced DNA SB in the livers of rats at 4 hr following a single administration of 1–10 mmole/kg. TCA (10 mmole/kg) and DCA (5 and 10 mmole/kg) did produce a small amount of strand breakage in mice (7% at 4 hr) but not at 1 hr. N‐nitrosodiethylamine (DENA), an established alkylating agent and a rodent hepatocarcinogen, produced DNA SB in the livers of both species. TCA, DCA, and MCA also failed to induce DNA strand breaks in splenocytes and epithelial cells derived from the stomach and duodenum of mice treated in vivo. None of the three chloroacetaldehydes induced DNA SB in either mouse or rat liver. The continuous exposure of mice to 5 g/L DCA in the drinking water for 7 and 14 days did not induce appreciable hepatic DNA SB (<10% at 14 days), although peroxisome proliferation, as evidenced by an increased cyanide‐insensitive palmitoyl CoA oxi‐dase (PCO) activity, was stimulated to 490% (7 days) and 652% (14 days) of control. Under this protocol, DENA (0.1 g/L) produced DNA damage after both 7 days (73% of control) and 14 days (57% of control). Similarly, long‐term exposure of rats (30 weeks) to 2 g/L DCA in the drinking water, a level that increased PCO activity to 364% of the control value, exhibited no DNA damage. Both the chloroacetic acids and the chloroacetaldehydes were ineffective in inducing DNA SB in cultured rat and mouse hepatocytes at concentrations below those that yielded cytotoxicity. The chloroacetic acids were also ineffective in the CCRF‐CEM cells. However, two of the chloroaldehydes, DCAA and CAA, did induce DNA SB in the CCRF‐CEM cells at concentrations that did not decrease the cell viability after 2 hr of treatment. Prior incubation of DCAA and CAA with a rat S9 liver homogenate eliminated much of the DNA damaging activity. These studies provide further evidence that the chloroacetic acids lack genotoxic activity not only in rodent liver, a tissue in that they induce tumors, but in a variety of other roden tissues and cultured cell types. Two of the chloroacetaldehydes, DCAA and CAA, are direct acting DNA damaging agents in CCRF‐CEM cells, but not in liver or splenocytes in vivo or in cultured hepatocytes. CH showed no activity in any system investi

ISSN:0893-6692    

DOI:10.1002/em.2850200406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractTwo photoproducts, derived from UV‐irradiation of the amino acid L‐tryptophan and with highAh(TCDD) receptor binding affinity, were tested for genotoxic and antimutagenic effects. The two indolo[3,2‐b]carbazole derivatives, with the molecular weights of 284 and 312, respectively, were tested inSaccharomyces cerevisiaestrain D7 for mitotic gene conversion and reverse mutation and in strain RS112 for sister chromatid conversion and gene conversion. No significant (P>0.05) genotoxic effects were found in strain D7, while strain RS112 showed a small but significant increase in the frequency of sister chromatid conversions. In Chinese hamster ovary (CHO) cells the two compounds induced a statistically significant but less than twofold increase in the frequency of sister chromatid exchanges (SCE). No mutations were detected when the compounds were tested inSalmonella typhimuriumstrains TA98 and TA100. However, both 284 and 312 acted as antimutagens on strain TA100+S9 in the presence of benzo(a)pyrene. The decrease in mutagenicity by the most potent compound 284 was 20 revertants/nmol. This effect could be explained by an inhibitory effect on the cytochrome P450‐dependent ethoxyresorufin O‐deethylase (EROD) activity as seen in rat hepatocytes. The two compounds were also tested with hamster cells expressing rat cytochrome [P‐450IA]. The results support the conclusion that this cytochrome P‐450 isozyme is inhibited by the tryptophan photoproducts. Similar results were also seen with two other high affinityAhreceptor ligands the quinazolinocarboline alkaloids rutaecarpine and dehydrorutaecarpine. © 1992 W

ISSN:0893-6692    

DOI:10.1002/em.2850200407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe SOS chromotest is a simple short‐term genotoxicity assay measuring the induction of genesfiAinEscherichia coliK‐12. The recent availability of SOS tester strains with additional mutations in DNA repair or protection systems allows testing of DNA damaging compounds for genotoxic specificity.E. coliPQ300 differs from the standard SOS tester strain PQ37 in that it contains an additional mutation in geneoxyRthat renders it more sensitive to oxidative genotoxins. The generation of reactive oxygen intermediates (ROI) by hydroperoxides (H2O2, t‐butyl hydroperoxide, cumene hydroperoxide), γ‐radiation, glucose oxidase, and xanthine oxidase resulted in a more vigorous SOS response in strain PQ300 compared to strain PQ37. PQ300 was also more sensitive than PQ37 for the detection of reducing agents such as ascorbic acid, cysteine, and glutathione, which also alter the redox status of the bacterial cells. However, intercalating agents (adriamycin, bleomycin, and mitomycin C) and the UV‐and radiomimetic compound 4‐nitroquinoline‐1‐oxide whose DNA damaging potential are known also to involve ROI did not show significant differences between strains PQ37 and PQ300. It is concluded that theoxyR‐deficient strain PQ300 is useful for detecting certain classes of genotoxins that change the oxidative/antioxidative balance of tester bacteria in the SOS chromotest. © 1

ISSN:0893-6692    

DOI:10.1002/em.2850200408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractStudies of the mutagenicity and antimutagenicity of hispidulin and hortensin, the flavonoids fromMillingtonia hortensisL. (Bignoniaceae), were performed using the liquid preincubation method of theSalmonella/microsome test. At the highest dose tested, 100 μg/plate, both compounds showed no mutagenicity and no cytotoxicity towardS. typhimuriumstrains TA98 and TA100 either in the presence or absence of S9 mix. However, these substances were antimutagens toward 2–aminoanthracene, aflatoxin Bl (in TA98), and dimethylnitrosamine (in TA100); but neither substance inhibited the direct mutagenic activity of 2‐(2‐furyl)‐3‐(5‐nitro‐2‐furyl) acrylamide nor that of sodium azide in strains TA98 and TA100, respectively. © 199

ISSN:0893-6692    

DOI:10.1002/em.2850200409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractA prototype cigarette that heats tobacco (test cigarette), developed by R.J. Reynolds Tobacco Company, has yielded consistently negative results in several in vivo and in vitro genetic toxicology tests. The objective of the present study was to evaluate the potential of cigarette smoke condensate (CSC) from the test cigarette to induce DNA adducts in mouse tissues and compare the results with those obtained with CSC from a reference tobacco‐burning cigarette (1R4F). CD‐I mice were skin‐painted with CSC from reference and test cigarettes three times a week for 4 weeks. The highest mass of CSC applied was 180 mg “tar” per week per animal for both reference and test cigarette. DNA adducts were analyzed in skin and lung tissues using the32P‐postlabeling method with the P1, nuclease modification. Distinct diagonal radioactive zones (DRZ) were observed in the DNA from both skin and lung tissues of animals dosed with reference CSC, whereas no corresponding DRZ were observed from the DNA of animals closed with either test CSC or acetone (solvent control). The relative adduct labeling (RAL) values of skin and lung DNA from reference CSC‐treated animals were significantly greater than those of the test CSC‐treated animals. The RAL values of the test CSC‐treated animals were no greater than those of solvent controls. The negative results in DNA adduct assays with test CSC are consistent with all previous results of in vivo and in vitro genetic toxicology testing on this cigarette and provide additional evidence that smoke condensate from the test cigarette is not genotoxic. © 19

ISSN:0893-6692    

DOI:10.1002/em.2850200410

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

ISSN:0893-6692    

DOI:10.1002/em.2850200411

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY