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Detection of the two germ cell mutagens ENU and iPMS using the LacZ/transgenic mouse mutation assay
1Division of Toxicology and Cancer Risk Factors, German Cancer Research Center, Heidelberg, Germany.
Abstract:
We have investigated the mutagenic effects of ENU, a potent mutagen in mouse spermatagonia, and of the two postmeiotic germ cell mutagens MMS and iPMS in germ cells, using a transgenic mouse mutation assay (lacZ/Muta Mouse, positive selection system). The test compounds were administered to 6-week-old animals by a single intraperitoneal injection. Seminiferous tubule germ cells were isolated from the testes after an expression time of 52 days and genomic DNA was extracted to examine induced mutations in the lacZ target gene. The spontaneous mutant frequencies observed in the control animals (n = 7) ranged from 3.5 to 17.9 x 10(-5) (mean value 9.5 +/- 5.3 x 10(-5). ENU (150 mg/kg; n = 8) induced a 6.9-fold increase over controls, iPMS (100 mg/kg; n = 7) a 2.4-fold increase, and no effect at all was found following MMS treatment (80 mg/kg; n = 8). The study demonstrates that the transgenic mouse mutation assay is able to detect the germ cell mutagens ENU and iPMS in the target tissue. The critical steps of the assay, however, seem to be dosing and sampling time. In contrast, MMS has failed to induce germ cell mutations in seminiferous tubules of transgenic mice at the tested dose and after an expression period of 52 days.
Insights
The transgenic mouse mutation assay effectively detected mutagenic effects of ethylnitrosourea (ENU) and isopropyl methanesulfonate (iPMS) in germ cells. However, methyl methanesulfonate (MMS) did not show mutagenic effects under the tested conditions.
Area of Science:
- Toxicology
- Genetics
- Molecular Biology
Background:
- Mutagenic effects of chemical agents on germ cells are crucial for understanding heritable genetic damage.
- Transgenic mouse models offer sensitive systems for evaluating mutagenicity.
- Ethylnitrosourea (ENU), methyl methanesulfonate (MMS), and isopropyl methanesulfonate (iPMS) are known mutagens with varying effects on different cell types.
Purpose of the Study:
- To assess the mutagenic potential of ENU, MMS, and iPMS in mouse germ cells using a transgenic mutation assay.
- To evaluate the efficacy of the lacZ/Muta Mouse system in detecting germ cell mutagens.
- To determine the influence of dosing and sampling time on mutation detection.
Main Methods:
- Administration of ENU, MMS, and iPMS to 6-week-old transgenic mice via intraperitoneal injection.
- Isolation of seminiferous tubule germ cells after a 52-day expression period.
- Genomic DNA extraction and analysis of induced mutations in the lacZ target gene using a positive selection system.
Main Results:
- ENU induced a 6.9-fold increase in mutant frequencies compared to controls.
- iPMS showed a 2.4-fold increase in mutant frequencies.
- MMS did not induce a significant increase in germ cell mutations at the tested dose and time point.
- Spontaneous mutant frequencies in control mice ranged from 3.5 to 17.9 x 10(-5).
Conclusions:
- The transgenic mouse mutation assay successfully identified ENU and iPMS as germ cell mutagens.
- MMS failed to demonstrate mutagenicity in mouse seminiferous tubules under the experimental conditions.
- Dosing and sampling time are critical factors for the sensitivity of the transgenic mutation assay.