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Mutagenic efficiency on proliferating vs. quiescent cell populations
290 per metaphase was 10.7 and 10.8 resp. and 7.1 in control. At stronger concentrations very few or no mitoses were observed. A direct damageing effect of rubratoxin B on chromosomes was expressed b y breaks, exchanges, ring chromosomes as well as some c-mitotic pictures. A correlation between the chromosome aberrations and the SCE rate was observed. The effect of 1-h exposure in inducing SCE was compared with results of treatment with aflatoxin B1. The induction of SCE by aflatoxin B at concentrations of 10 and 20/~g/ml is much higher: 21.6 and 23.3 resp.
Vergara, R., Istituto di Mutagenesi e Differenziamento, CNR, Pisa (Italy)
Mutagenic efficiency on proliferating vs. quiescent cell populations Previous studies (R. Vergara and M. Terzi, Cell Biol. Int. Rep., 4 (1980) 303) have shown that the number of 6-thioguanine-resistant mutants induced by mutagenic treatment in V 7 9 C h i n e s e hamster cell lines is not the same if the cell population is kept quiescent by L-histidinol block. This applied to mutagenesis with 4-nitroquinoline-l-oxide (4NQO) that acts preferentially on quiescent cells whereas no difference was found in the 2 types of physiological states when N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was used as mutagen. However, as the induction level was much greater in the case of MNNG we thought it interesting to repeat this t y p e of experiment using higher doses of 4NQO and lower doses of MNNG. A somewhat greater induction in quiescent cell populations was found at small doses of MNNG, b u t the difference was rather small if compared with the action of 4NQO that exhibited a remarkably greater effect on quiescent cells at all tested concentrations.
Knaap, A.G.A.C. a, and J.W.I.M. Simons b, a National Institute of Public Health, Bilthoven, and b Department of Radiation Genetics and Chemical Mutagenesis, State University of Leiden, Wassenaarseweg 72, Leiden (The Netherlands)
Induction of reverse mutations at the H G P R T locus in L 5 1 7 8 Y mouse lymphoma cells Point mutations, possibly capable for reversion, were induced with the mismatching agent 6-hydroxyaminopurine. Reconstruction experiments in which a small number of wild-type cells were mixed with different numbers of mutant cells indicated that cell densities of up to 106 cells/ml can be used for the selection of revertant cells. Reverse mutation was induced by ENU treatment and optimal expression of induced mutants was obtained 2 days after treatment. The dose--response relationship for induction of reverse mutations proved to be bell-shaped with a maximum mutant frequency of 3.3 × 10 -s. The estimate of the spontaneous reversion frequency per cell generation, based on 3 spontaneous mutants, is a b o u t 1.5 × 10 -9.
Vergara, R., Istituto di Mutagenesi e Differenziamento, CNR, Pisa (Italy)
Mutagenic efficiency on proliferating vs. quiescent cell populations Previous studies (R. Vergara and M. Terzi, Cell Biol. Int. Rep., 4 (1980) 303) have shown that the number of 6-thioguanine-resistant mutants induced by mutagenic treatment in V 7 9 C h i n e s e hamster cell lines is not the same if the cell population is kept quiescent by L-histidinol block. This applied to mutagenesis with 4-nitroquinoline-l-oxide (4NQO) that acts preferentially on quiescent cells whereas no difference was found in the 2 types of physiological states when N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was used as mutagen. However, as the induction level was much greater in the case of MNNG we thought it interesting to repeat this t y p e of experiment using higher doses of 4NQO and lower doses of MNNG. A somewhat greater induction in quiescent cell populations was found at small doses of MNNG, b u t the difference was rather small if compared with the action of 4NQO that exhibited a remarkably greater effect on quiescent cells at all tested concentrations.
Knaap, A.G.A.C. a, and J.W.I.M. Simons b, a National Institute of Public Health, Bilthoven, and b Department of Radiation Genetics and Chemical Mutagenesis, State University of Leiden, Wassenaarseweg 72, Leiden (The Netherlands)
Induction of reverse mutations at the H G P R T locus in L 5 1 7 8 Y mouse lymphoma cells Point mutations, possibly capable for reversion, were induced with the mismatching agent 6-hydroxyaminopurine. Reconstruction experiments in which a small number of wild-type cells were mixed with different numbers of mutant cells indicated that cell densities of up to 106 cells/ml can be used for the selection of revertant cells. Reverse mutation was induced by ENU treatment and optimal expression of induced mutants was obtained 2 days after treatment. The dose--response relationship for induction of reverse mutations proved to be bell-shaped with a maximum mutant frequency of 3.3 × 10 -s. The estimate of the spontaneous reversion frequency per cell generation, based on 3 spontaneous mutants, is a b o u t 1.5 × 10 -9.