The multiple endpoint mammalian mutagenesis approach developed in our institute screens in the same animal for recessive specific-locus alleles at 7 loci, approximately 30 loci coding for dominant-cataract mutations, 23 loci controlling protein-charge changes and 12 loci for enzyme-activity alterations. Experiments to screen for the approximately 70 loci in the same offspring of treated male mice were performed with ethylnitrosourea (ENU), procarbazine and X-ray exposure. Mutations were recovered for each genetic endpoint in all treatment groups where a sufficient number of offspring was scored. ENU treatment is highly effective in inducing mutations to all genetic endpoints. The mutations were confirmed by breeding tests. The mutation rates to specific-locus and enzyme-activity alleles were both higher than the mutation rates to either dominant-cataract or protein-charge alleles. The advantages and possibilities of the multiple endpoint approach are discussed in detail.

Animals↗

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Dominant cataract and recessive specific locus mutations in offspring of X-irradiated male mice.

Male mice were X-irradiated with 3.0 + 3.0 Gy or 5.1 + 5.1 Gy (fractionation interval 24 h). The offspring were screened for dominant cataract and recessive specific locus mutations. In the 3.0 + 3.0-Gy spermatogonial treatment group, 3 dominant cataract mutations were confirmed in 15 551 offspring examined and 29 specific locus mutations were recovered in 18 139 offspring. In the post-spermatogonial treatment group, 1 dominant cataract mutation was obtained in 1120 offspring and 1 recessive specific locus mutation was recovered in 1127 offspring. The induced mutation rate per locus, per gamete, per Gy calculated for recessive specific locus mutations is 2.0 X 10(-5) in post-spermatogonial stages and 3.7 X 10(-5) in spermatogonia. For dominant cataract mutations, assuming 30 loci, the induced mutation rate is 5.0 X 10(-6) in the post-spermatogonial stages and 1.1 X 10(-6) in spermatogonia. In the 5.1 + 5.1-Gy spermatogonial treatment group, 3 dominant cataract mutations were obtained in 11 205 offspring, whereas in 13 201 offspring 27 recessive specific locus mutations were detected in the spermatogonial group. In the post-spermatogonial treatment group no dominant cataract mutation was observed in 425 offspring and 2 recessive specific locus mutations were detected in 445 offspring. The induced mutation rate per locus, gamete and Gy in spermatogonia for recessive specific locus mutations is 2.8 X 10(-5) and for dominant cataract mutations 0.9 X 10(-6). In post-spermatogonial stages, the mutation rate for recessive specific locus alleles is 6.2 X 10(-5). In the concurrent untreated control group, in 11 036 offspring no dominant cataract mutation and in 23 518 offspring no recessive specific locus mutation was observed. Litter size and the number of carriers at weaning have been determined in the confirmation crosses of the obtained dominant cataract mutants as indicators of viability and penetrance effects. Two mutants had a statistically significantly reduced litter size and one mutant had a statistically significantly reduced penetrance.

Animals↗

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Induction of specific-locus and dominant lethal mutations in male mice by 1-methyl-1-nitrosourea (MNU).

1-Methyl-1-nitrosourea (MNU) induced specific-locus mutations in mice in all spermatogenic stages except spermatozoa. After intraperitoneal injection of 70 mg/kg body weight of MNU a high yield of specific-locus mutations was observed in spermatids (21.8 x 10(-5) mutations per locus per gamete). The highest mutational yield was induced in differentiating spermatogonia. In 1594 offspring we observed 5 specific-locus mutants (44.8 x 10(-5) mutations per locus per gamete). In addition, 2 mosaics were recovered, which gave a combined mutation rate of 62.7 x 10(-5). In As spermatogonia the mutation rate was 3.9 x 10(-5). The same dose of 70 mg/kg of MNU induced dominant lethal mutations 5-48 days post treatment, mainly due to post-implantation loss in spermatids and spermatocytes. It is interesting to compare the induction pattern of mutations by MNU with methyl methanesulfonate (MMS), ethyl methanesulfonate (EMS) and ethylnitrosourea (ENU). Based on the different spermatogenic response of the induction of specific-locus mutations we can characterize the 4 mutagens in the following way: EMS = MMS not equal to MNU not equal to ENU.

Alleles↗

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Mutagenicity testing of vincristine sulfate in germ cells of male mice.

Vincristine sulfate (VCR) affects the fertilization ability of all germ-cell stages in male mice. The reduced fertilization ability leads to a pseudo-dominant-lethal effect and sterile matings. The frequency of these effects is dose-dependent. The frequency of specific-locus mutations was not increased by VCR in male mice following 2 mg/kg bw treatment.

Animals↗