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A rapid somatic genotoxicity assay in Drosophila melanogaster using multiple mutant mutagen-sensitive (mus) strains
D S Henderson1, T A Grigliatti
1Department of Zoology, University of British Columbia, Vancouver, Canada.
Abstract:
Mutagen-sensitive (mus) mutations in Drosophila melanogaster render developing flies hypersensitive to the lethal effects of DNA-damaging agents. In principle, multiply mutant mus strains might then serve as sensitive in vivo indicators of a wide range of mutagens and genotoxic carcinogens. As a first step to evaluate that potential we characterized interactions between mus mutations in eight double mutants containing combinations of the second chromosomal mutations mus201D1, mus205B1, mus208B1, mus210B1 and mus211B1. We found that (i) all double mutants are fully viable in the absence of mutagen exposure, (ii) mus205B1 is epistatic to any other mus mutation with respect to methyl methanesulfonate (MMS) sensitivity, and (iii) in double mutants carrying any combination of mus201D1, mus210B1 or mus211B1, MMS sensitivity is increased in a synergistic manner. Based on those results, and on mutagen cross-sensitivity data of single mutants generated in previous studies, we constructed two triple mutant mus strains for use as testers in a simple genotoxicity assay. That assay measures the survival of DNA repair-deficient mus homozygotes relative to their repair-proficient heterozygous siblings. Those two classes of fly are easily distinguished from one another by their phenotypic markers. In addition, the heterozygotes serve as a relatively mutagen-insensitive internal control in all test vials. One tester strain (mus208B1 mus210B1 mus211B2) identified 11 of 12 chemical carcinogens as genotoxic (benzo[a]pyrene, cyclophosphamide, 1,2,3,4-diepoxybutane, diethylnitrosamine, dimethylnitrosamine, ethyl methanesulfonate, formaldehyde, hexamethylphosphoramide, methyl methanesulfonate, methylnitrosourea and N-methyl-N'-nitro-N-nitrosoguanidine). Safrole and two noncarcinogens (benzo[e]pyrene and caprolactam) tested as nongenotoxic.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Mutagen-sensitive (mus) mutations in Drosophila melanogaster can identify genotoxic carcinogens. New triple mutant strains effectively detect DNA-damaging agents in a simple fly assay.
Area of Science:
- Genetics
- Toxicology
- Molecular Biology
Background:
- Mutagen-sensitive (mus) mutations confer hypersensitivity to DNA-damaging agents in Drosophila melanogaster.
- Multiply mutant mus strains hold potential as in vivo indicators for mutagens and genotoxic carcinogens.
Purpose of the Study:
- To characterize interactions between specific mus mutations to develop sensitive genotoxicity testing tools.
- To evaluate the efficacy of newly constructed triple mutant mus strains in a genotoxicity assay.
Main Methods:
- Characterization of eight double mutant combinations of second chromosomal mus mutations (mus201D1, mus205B1, mus208B1, mus210B1, mus211B1).
- Construction and testing of two triple mutant mus strains in a genotoxicity assay comparing survival of homozygotes (DNA repair-deficient) and heterozygotes (repair-proficient).
Main Results:
- All double mutants were viable without mutagen exposure.
- mus205B1 was epistatic to other mus mutations regarding methyl methanesulfonate (MMS) sensitivity.
- Synergistic increase in MMS sensitivity observed in double mutants with mus201D1, mus210B1, or mus211B1.
- One tester strain identified 11 of 12 chemical carcinogens as genotoxic, while two noncarcinogens tested negative.
Conclusions:
- Developed and validated triple mutant Drosophila melanogaster strains as effective tools for genotoxicity screening.
- The assay, utilizing repair-deficient homozygotes and repair-proficient heterozygotes, provides a sensitive measure of DNA-damaging agent effects.
- This approach offers a valuable in vivo system for identifying genotoxic compounds.