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Germ cell mutagenesis in lacZ transgenic mice treated with methyl methanesulfonate
1Drug Safety Research Laboratory, Daiichi Pharmaceutical Co., Ltd., Tokyo, Japan.
Abstract:
Mutagenesis induced by methyl methanesulfonate (MMS), a germ cell mutagen, in the testis and the sperm isolated from epididymis and vas deferens have been investigated using lacZ transgenic mice (Muta Mouse). Male Muta Mice were injected intraperitoneally with MMS at a dose of 80 mg/kg, a potent dominant lethal dose. Animals were killed on days 3 and 7 (Experiment 1) or days 10 and 14 (Experiment 2) after the treatment. Mutant frequencies (MFs) in the testis, sperm and spleen (Experiment 2 only) were analyzed by the positive selection system using E. coli C (GalE-) strain and phenyl beta-D-galactoside. The spontaneous MFs in the testis and sperm were 2.0-3.1 x 10(-5). No induction of mutation in the testis or sperm of the MMS-treated groups was observed at any sampling point. In the spleen, the spontaneous MF was approximately twice as high as that in the germ cells although the MF at each sampling point was almost the same as the spontaneous MF. MMS is known as a potent clastogen from the results of the dominant lethal assay and the micronucleus assay. The reason for the discrepancy between the results of these assays and the present results may have been insensitivity of the in vitro packaging to large deletion due to the failure to rescue the large deleted gene. It is suggested that the transgenic mouse assay using the in vitro packaging can not replace the dominant lethal assay in the case of MMS.
Insights
Methyl methanesulfonate (MMS) did not induce mutations in mouse germ cells, despite being a known mutagen. The transgenic mouse assay may be insensitive to MMS-induced large deletions.
Area of Science:
- Toxicology
- Genetics
- Molecular Biology
Background:
- Methyl methanesulfonate (MMS) is a known germ cell mutagen and potent clastogen.
- Assessing mutagenicity in germ cells is crucial for understanding heritable genetic damage.
Purpose of the Study:
- To investigate MMS-induced mutagenesis in the testis and sperm of Muta Mice.
- To evaluate the sensitivity of the lacZ transgenic mouse assay for detecting MMS-induced germ cell mutations.
Main Methods:
- Male Muta Mice were administered a potent dominant lethal dose of MMS (80 mg/kg).
- Mutant frequencies (MFs) in testis, sperm, and spleen were analyzed using a positive selection system.
- Analyses were conducted at various time points post-treatment (days 3, 7, 10, and 14).
Main Results:
- No significant induction of mutations was observed in the testis or sperm of MMS-treated mice.
- Spleen MFs were approximately twice as high as spontaneous MFs in germ cells but showed no induction.
- Spontaneous MFs in testis and sperm ranged from 2.0-3.1 x 10(-5).
Conclusions:
- The transgenic mouse assay using in vitro packaging may be insensitive to large deletions induced by MMS.
- This assay cannot replace the dominant lethal assay for evaluating MMS mutagenicity.
- Further investigation into assay limitations for specific mutagens like MMS is warranted.