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Mutation assays in male germ cells from transgenic mice: overview of study and conclusions
J Ashby1, N J Gorelick, M D Shelby
1Zeneca Central Toxicology Laboratory, Macclesfield, Cheshire, UK.
Abstract:
Three confirmed mouse germ cell mutagens, ethyl nitrosourea (ENU), isopropyl methanesulphonate (iPMS) and methyl methanesulphonate (MMS), have been evaluated for their activity as mutagens to the germ cell DNA of two strains of transgenic mice (lac I, Big Blue and LacZ, Muta Mouse). Both testicular DNA and epididymal sperm DNA were evaluated. A range of sampling times was studied, from 3 days post-dosing to 100 days post-dosing. ENU and iPMS were mutagenic to both testicular DNA and epididymal sperm DNA. Mutant frequencies were higher for both chemicals in DNA recovered from testicular tissue than in epididymal sperm DNA. Likewise, mutant frequencies were higher for both DNA samples at the later sampling times. MMS was not mutagenic under any condition of test. A good level of qualitative agreement in test results was seen for the two assays and for the same assays conducted in different laboratories. The level of quantitative agreement was not as high, but was, nonetheless, generally good. Recommendations for the future conduct of transgenic rodent germ cell mutation assays are made. The test data are discussed within the context of the larger question of how such assays should be integrated into the chemical hazard assessment process.
Insights
Ethyl nitrosourea (ENU) and isopropyl methanesulphonate (iPMS) are mutagenic to mouse germ cell DNA, with higher mutation frequencies found in testicular tissue and at later sampling times. Methyl methanesulphonate (MMS) showed no mutagenic activity in this study.
Area of Science:
- Toxicology
- Genetics
- Molecular Biology
Background:
- Transgenic rodent models are crucial for evaluating chemical mutagenicity.
- Assessing germ cell mutagenicity is vital for understanding heritable genetic damage.
Purpose of the Study:
- To evaluate the mutagenic activity of ethyl nitrosourea (ENU), isopropyl methanesulphonate (iPMS), and methyl methanesulphonate (MMS) in the germ cell DNA of Big Blue (lac I) and Muta Mouse (LacZ) transgenic mice.
- To compare mutagenic responses in testicular DNA versus epididymal sperm DNA.
- To determine the impact of sampling time on mutagenicity detection.
Main Methods:
- Administration of ENU, iPMS, and MMS to transgenic mice.
- Analysis of mutant frequencies in testicular and epididymal sperm DNA at various time points post-dosing (3 to 100 days).
- Utilized two transgenic mouse strains: Big Blue (lac I) and Muta Mouse (LacZ).
Main Results:
- ENU and iPMS demonstrated mutagenic activity in both testicular DNA and epididymal sperm DNA.
- Mutant frequencies were higher in testicular DNA compared to epididymal sperm DNA for both ENU and iPMS.
- Higher mutant frequencies were observed at later sampling times (post-dosing).
- MMS did not exhibit mutagenic activity under the tested conditions.
Conclusions:
- ENU and iPMS are effective germ cell mutagens in the tested transgenic mouse models.
- Testicular DNA and later sampling times provide more sensitive detection of germ cell mutations.
- MMS is not mutagenic to mouse germ cells under these experimental conditions.
- Recommendations are provided for optimizing transgenic rodent germ cell mutation assays for chemical hazard assessment.