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Jack B. Bishop - One of the best experts on this subject based on the ideXlab platform.
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mouse bone marrow micronucleus test results do not predict the germ cell mutagenicity of n hydroxymethylacrylamide in the mouse Dominant Lethal assay
Environmental and Molecular Mutagenesis, 2003Co-Authors: Kristine L Witt, L.a. Hughes, Jack B. Bishop, Leo T Burka, Alfred F Mcfee, James M Mathews, Sherry L BlackAbstract:N-Hydroxymethylacrylamide (NHMA), a mouse carcinogen inactive in the Salmonella assay and mouse micronucleus (MN) assay, was tested for reproductive effects in a mouse continuous breeding study. In that study, increased embryonic deaths were observed after 13 weeks exposure of parental animals to NHMA via drinking water (highest dose, 360 ppm); the results indicated the possible induction of chromosome damage in germ cells of treated males. An additional mouse MN test was conducted using a 31-day treatment period to better match the dosing regimen used in the breeding study; the results were negative. Additional studies were conducted to explore the germ cell activity of NHMA. A male mouse Dominant Lethal study was conducted using a single intraperitoneal injection of 150 mg/kg NHMA; the results were negative. A follow-up study was conducted using fractionated dosing, 50 mg/kg/day for 5 days; again, no increase in Dominant Lethal mutations was observed. NHMA (180-720 ppm) was then administered to male mice in drinking water for 13 weeks, during which three sets of matings occurred. Two weeks after mating, females were killed and the uterine contents were analyzed. Large, dose-related increases in Dominant Lethal mutations were observed with increasing length of exposure. The magnitude of the increases stabilized after 8 weeks of treatment. However, the frequency of micronucleated peripheral blood erythrocytes was not elevated in mice treated for 13 weeks with NHMA in drinking water. Thus, NHMA appears to be unique in inducing genetic damage in germ cells but not somatic cells of male mice.
Susan E. Lewis - One of the best experts on this subject based on the ideXlab platform.
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Ethylene dibromide: negative results with the mouse Dominant Lethal assay and the electrophoretic specific-locus test.
Mutation research, 1992Co-Authors: Lois B. Barnett, D.p. Lovell, C.f. Felton, B.j. Gibson, Ronald R. Cobb, D.s. Sharpe, M.d. Shelby, Susan E. LewisAbstract:Abstract Ethylene dibromide (1,2-dibromoethane; EDB) was tested for the induction of Dominant Lethal and electrophoretically-detectable specific-locus mutations in the germ cells of DBA/2J male mice. Males were treated with a single intraperitoneal injection of 100 mg/kg EDB and mated to two C57BL/6J females. In the Dominant Lethal assay, matings were carried out to measure the effect of EDB on meiotic and postmeiotic stages; germ cells representing spermatogonial stem cells were analyzed in the electrophoretic specific-locus test. Neither of these germ cell tests produced any evidence that EDB is a germ cell mutagen. It appears from these data and those reported in the literature that EDB, a genotoxic carcinogen that affects male fertility in some mammalian species, is not mutagenic in the germ cells of the male mouse.
Boriana Marintcheva - One of the best experts on this subject based on the ideXlab platform.
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C-terminal Phenylalanine of Bacteriophage T7 Single-stranded DNA-binding Protein Is Essential for Strand Displacement Synthesis by T7 DNA Polymerase at a Nick in DNA
Journal of Biological Chemistry, 2009Co-Authors: Sharmistha Ghosh, Boriana Marintcheva, Masateru Takahashi, Charles C. RichardsonAbstract:Single-stranded DNA-binding protein (gp2.5), encoded by gene 2.5 of bacteriophage T7, plays an essential role in DNA replication. Not only does it remove impediments of secondary structure in the DNA, it also modulates the activities of the other replication proteins. The acidic C-terminal tail of gp2.5, bearing a C-terminal phenylalanine, physically and functionally interacts with the helicase and DNA polymerase. Deletion of the phenylalanine or substitution with a nonaromatic amino acid gives rise to a Dominant Lethal phenotype, and the altered gp2.5 has reduced affinity for T7 DNA polymerase. Suppressors of the Dominant Lethal phenotype have led to the identification of mutations in gene 5 that encodes the T7 DNA polymerase. The altered residues in the polymerase are solvent-exposed and lie in regions that are adjacent to the bound DNA. gp2.5 lacking the C-terminal phenylalanine has a lower affinity for gp5-thioredoxin relative to the wild-type gp2.5, and this affinity is partially restored by the suppressor mutations in DNA polymerase. gp2.5 enables T7 DNA polymerase to catalyze strand displacement DNA synthesis at a nick in DNA. The resulting 5'-single-stranded DNA tail provides a loading site for T7 DNA helicase. gp2.5 lacking the C-terminal phenylalanine does not support this event with wild-type DNA polymerase but does to a limited extent with T7 DNA polymerase harboring the suppressor mutations.
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mutations in the gene 5 dna polymerase of bacteriophage t7 suppress the Dominant Lethal phenotype of gene 2 5 ssdna binding protein lacking the c terminal phenylalanine
Molecular Microbiology, 2009Co-Authors: Boriana Marintcheva, Udi Qimron, Stanley Tabor, C RichardsonAbstract:Summary Gene 2.5 of bacteriophage T7 encodes a ssDNA binding protein (gp2.5) essential for DNA replication. The C-terminal phenylalanine of gp2.5 is critical for function and mutations in that position are Dominant Lethal. In order to identify gp2.5 interactions we designed a screen for suppressors of gp2.5 lacking the C-terminal phenylalanine. Screening for suppres- sors of Dominant Lethal mutations of essential genes is challenging as the phenotype prevents propaga- tion. We select for phage encoding a Dominant Lethal version of gene 2.5, whose viability is recovered via second-site suppressor mutation(s). Functional gp2.5 is expressed in trans for propagation of the unviable phage and allows suppression to occur via natural selection. The isolated intragenic sup- pressors support the critical role of the C-terminal phenylalanine. Extragenic suppressor mutations occur in several genes encoding enzymes of DNA metabolism. We have focused on the suppressor mutations in gene 5 encoding the T7 DNA poly- merase (gp5) as the gp5/gp2.5 interaction is well documented. The suppressor mutations in gene 5 are necessary and sufficient to suppress the Lethal phenotype of gp2.5 lacking the C-terminal phenyla- lanine. The affected residues map in proximity to aromatic residues and to residues in contact with DNA in the crystal structure of T7 DNA polymerase- thioredoxin.
Pankaj Taneja - One of the best experts on this subject based on the ideXlab platform.
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antimutagenic effect of black tea extract using rodent Dominant Lethal mutation assay
Toxicology, 2001Co-Authors: Yogeshwer Shukla, Pankaj TanejaAbstract:Abstract The antimutagenic effect of black tea extract has been evaluated with the ‘Dominant Lethal Assay’ in Swiss albino mice using benzo[ a ]pyrene [BaP] as a mutagen. BaP was given through the intraperitoneal (i.p.) route at a single dose of 100 mg/kg b.w. to male mice once only. The animals were given 1, 2 and 4% aqueous solution of black tea as sole source of drinking solution prior to BaP. The pregnant females were analyzed for living implants, pre- and post-implantation losses. The results revealed that during mating weeks, BaP caused a reduction in implants and an increase in pre- and post-implantation losses. The protective effect of tea solution on BaP-induced mutagenicity was observed. The number of living implants increased and dead implants decreased significantly in the animals kept on 2 and 4% tea solution. The increase in Dominant Lethal mutation rate by BaP was inhibited by black tea extract. Four percent tea solution alone did not produce Dominant Lethality, and reveals that it is non-toxic/non-mutagenic to sperm. Hence the study suggests that tea has a protective effect against BaP-induced genetic damage to germ cells in Swiss albino mice.
Toshie Kawano - One of the best experts on this subject based on the ideXlab platform.
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establishment of the Dominant Lethal test in the freshwater mollusk biomphalaria glabrata say 1818
Mutation Research-genetic Toxicology and Environmental Mutagenesis, 2003Co-Authors: Eliana Nakano, Liz Cristina Watanabe, Fernanda Pires Ohlweiler, Carlos Alberto De Braganca Pereira, Toshie KawanoAbstract:Mutagens in the environment may represent a long-term risk for ecosystems. The reproductive potential of populations can be affected by alterations in the fecundity and offspring viability caused by germ cell mutations. Despite the ecological relevance of these effects, there are few studies on germ cell mutagenicity in natural populations. Biomphalaria glabrata was chosen for this study because of the scarcity of data on freshwater invertebrates and the ecological importance of this group. The aim of this study was to establish a germ cell mutagenicity test in B. glabrata by using a similar approach to that used in the Dominant Lethal test in rodents. Mitomycin C was used as a direct mutagen and cyclophosphamide as a mutagen that requires metabolic activation. Wild-type snails were exposed for 10 days to three concentrations of each agent and crossed with non-exposed albino snails at the end of the treatment. The total frequencies of malformations were analyzed in the offspring of wild-type snails; among the offspring of albino snails, only the heterozygous wild-type embryos were analyzed for malformations. Both agents induced germ cell mutations. The analysis of the offspring of the wild-type snails showed an effect of the exposure up to approximately 5 days after the end of the treatment with cyclophosphamide; the effect of mitomycin C was observed until 45 days after the end of the exposure. There was an increase in the frequencies of malformations in the wild-type offspring of the non-exposed albino snails crossed with the wild-type snails exposed to both agents. The Dominant Lethal test in B. glabrata proposed in this work is easy to perform, efficient, specific and sensitive in the evaluation of germ cell mutations induced by reference mutagens. The possibility of expanding its use to environmental biomonitoring studies seems very promising and worth trying.