Induction of specific-locus mutations in male mice by ethyl methanesulfonate (EMS)

Using a sequential mating procedure, the induction of specific-locus mutations by ethyl methanesulfonate (EMS) was reinvestigated in male mice. Doses of 175 mg/kg b.w. and 250 mg/kg b.w. of EMS induce gene mutations in the mating intervals 5-8 and 9-12 days post treatment. However, only the frequency of dominant lethal mutations increases with the dose, not the frequency of specific-locus mutations. This observation implies that with a higher dose of EMS a larger fraction of mutagenized spermatozoa and spermatids are selectively eliminated, leading to underestimation of the specific-locus mutation yield at high doses. EMS does not induce specific-locus mutations in spermatogonia.     

Induction of specific-locus and dominant lethal mutations in male mice by busulfan

The chemotherapeutic agent busulfan was tested for the induction of dominant lethal and specific-locus mutations in male mice. A dose of 5 mg/kg b.w. of busulfan induces dominant lethal mutations in spermatozoa. A dose of 20 mg/kg b.w. induces dominant lethal mutations in spermatozoa and spermatids. A total of 83,196 offspring were scored in the specific-locus experiments. Busulfan-induced specific-locus mutations were recovered in spermatozoa and spermatids, but not in spermatogonia. The sensitivity patterns for the induction of dominant lethal and specific-locus mutations by busulfan in germ cells of male mice are similar but not identical.     

Induction of specific-locus and dominant-lethal mutations by cyclophosphamide and combined cyclophosphamide-radiation treatment in male mice

Cyclophosphamide is the most widely used antineoplastic agent. It is also used to condition patients for bone-marrow transplantations. Because of the general interest of this compound we initiated a systematic study of the induction of dominant-lethal and specific-locus mutations in male mice. In addition, we investigated the induction of specific-locus mutations by the combined treatment of cyclophosphamide and ionizing radiation.A dose of 40 mg/kg bw of cyclophosphamide caused dominant-lethal mutations in male mice only in the 1st and 2nd week after treatment. A dose of 120 mg/kg induced dominant-lethal mutations in the mating intervals 1–21 days posttreatment. No dominant lethal mutations were observed after the 3rd week. The same differential spermatogenic response was observed for the induction of specific-locus mutations. Cyclophosphamide induced recessive mutations exclusively in spermatozoa and spermatids. No mutations were recovered from treated spermatocytes and spermatogonia. In contrast to cyclophosphamide, radiation induces specific-locus mutations in all germ-cell stages.The pretreatment with cyclophosphamide 24 h before radiation enhanced the frequency of specific-locus mutations in spermatogonia. The distribution of the observed mutations among the 7 loci and their viability supports the hypothesis that these mutations were induced by radiation rather than by cyclophosphamide. The compound causes an immediate inhibition of DNA and RNA synthesis in spermatogonia. The inhibition very likely interferes with the repair process. The disturbance of the repair process is probably the cause of the synergistic effect for the induction of specific-locus mutations in spermatogonia of mice after pretreatment with cyclophosphamide 24 h before irradiation.     

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 × 10⁻⁵ mutations per locus per gamete). The highest mutational yield was induced in differentiating spermatogonia. In 1954 offspring we observed 5 specific-locus mutants (44.8 × 10⁻ mutations per locus per gamete). In addition, 2 mosaics were recovered, which gave a combined mutation rate of 62.7 × 10⁻⁵. In A_s spermatogonia the mutation rate was 3.9 × 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 ≠ MNU ≠ ENU.     

Induction of specific-locus and dominant-lethal mutations in male mice by diethyl sulfate (DES)

Diethyl sulfate (DES), a monofunctional alkylating agent, induces mutations and chromosomal aberrations in many different organisms and cell systems, including dominant-lethal mutations in male mice. However, until now it could not be demonstrated that DES induces specific-locus mutations in mice. This observation would contradict the close correlation observed between the induction of dominant-lethal mutations and specific-locus mutations in mice with other chemicals. DES induces dominant-lethal and specific-locus mutations in spermatozoa and late spermatids of mice. The mutation frequency for dominant-lethal mutations is dose-dependent, while for specific-locus mutations it is independent of the dose. In the mating interval 5-8 days post-treatment the mutation frequency for 200 mg/kg DES is 17.0 X 10(-5) and for 300 mg/kg 7.5 X 10(-5) mutations per locus. The dose-dependent increase of dominant-lethal mutations probably reduced the chance of recovering specific-locus mutations. The importance of these findings for mutagenicity testing is discussed.     

Induction of specific-locus and dominant lethal mutations in male mice by ifosfamide (Holoxan)

Ifosfamide induced dominant lethal mutations in spermatozoa of mice at doses of 200 and 300 mg/kg and in spermatids and spermatocytes at 600 mg/kg. The highest dose also induced specific-locus mutations in post-spermatogonial germ-cell stages of mice but not in spermatogonial stem cells. The nature of the induced mutations suggests they are intergenic. The spermatogenic specificity of ifosfamide in mouse germ cells is similar to that of the structurally related cytostatic drugs cyclophosphamide and trofosfamide. Due to the post-spermatogonial germ cell specificity of ifosfamide, the genetic risk is limited to a few weeks after exposure.     

The frequency of dominant cataract and recessive specific-locus mutations and mutation mosaics in F1 mice derived from post-spermatogonial treatment with ethylnitrosourea

The frequency of dominant cataract and recessive specific-locus mutations and mutation mosaics was determined in F1 mice derived from post-spermatogonial germ-cell stage treatment with 2 X 80, 160 or 250 mg/kg ethylnitrosourea. A total of 5 dominant cataract mutations, 3 dominant cataract mutation mosaics, 1 specific-locus mutation and 9 specific-locus mutation mosaics were recovered in 15,542 screened F1 offspring. Results indicate that ethylnitrosourea treatment increases the mutation rate of dominant cataract and recessive specific-locus alleles in post-spermatogonial germ-cell stages of the mouse and that the mutations occur mainly as mosaics. Genetic confirmation of newly induced mutations occurring as mosaics is more problematical for induced recessive alleles than for induced dominant alleles and should be considered when evaluating such mutagenicity results.     

Methylation of DNA and protamine by methyl methanesulfonate in the germ cells of male mice

The molecular dosimetry of methyl methanesulfonate (MMS) in the germ cells of male mice has been investigated. The mice were injected i.p. with 100 mg/kg of [3H]MMS and methylations per sperm head, per deoxynucleotide, and per unit of protamine were then determined over a 3-week period. The methylations per sperm head paralleled the dominant lethal frequency curve for MMS, reaching a maximum of between 22 and 26 million methylations per vas sperm head 8-11 days after treatment. Methylation of sperm DNA was greatest at 4 h (the earliest time point studied) after treatment, with 16.6 methylations/10(5) deoxynucleotides. DNA methylation gradually decreased during the subsequent 3-week period. The methylation of germ-cell DNA did not increase in the stages most sensitive to MMS (late spermatids leads to early spermatozoa) and was not correlated with the dominant lethal frequency curve for MMS. However, methylation of protamine did increase in the germ-cell stages most sensitive to MMS, and showed an excellent correlation with the incidence of dominant lethals produced by MMS in the different germ-cell stages. The pattern of alkylation produced by MMS in the developing germ-cell stages of the mouse is similar to that found for EMS. However, for equimolar exposures, MMS alkylates the germ cells 5-7 times more than does EMS. Hydrolyzed samples of protamine from [3H]MMS-exposed animals were subjected to thin-layer chromatography and amino acid analysis. Both procedures showed that most of the labeled material recovered from the hydrolysates co-chromatographed with authentic standards of S-methyl-L-cysteine. The amino acid analyses showed an average of approximately 80% of the labeled material eluting with S-methyl-L-cysteine. The mechanism of action of both MMS and EMS on the developing germ cells appears to be similar. The occurrence of S-methyl-L-cysteine as the major reaction product in sperm protamine after MMS exposure supports our initial model of how dominant lethals are induced in mouse germ cells by these chemicals: Alkylation of cysteine sulfhydryl groups contained in mouse-sperm protamine blocks normal disulfide-bond formation, preventing proper chromatin condensation in the sperm nucleus. Subsequent stresses produced in the chromatin structure eventually lead to chromosome breakage, with resultant dominant lethality.     

Chlornaphazine and chlorambucil induce dominant lethal mutations in male mice

Two antineoplastic agents, chlornaphazine (CN) and chlorambucil (CHL), were tested for the induction of dominant lethal mutations in male mice. Both compounds are nitrogen mustard derivatives and have been shown to be genotoxic in a variety of organisms. CN was administered intraperitoneally to DBA/2J male mice at a dosage of 0, 500, 1000, or 1500 mg/kg body weight (bw). Immediately following treatment, each male was mated at 4-day intervals to two virgin C57BL/6J females. CHL was administered intraperitoneally to C3H/HeJ and DBA/2J males at a dosage of 0, 2.5, or 5.0 mg/kg bw. These males were mated at weekly intervals to two virgin T-stock females. CN and CHL clearly induced dominant lethal mutations. CN induced dominant lethal effects in all post-meiotic germ-cell stages of treated DBA males, with a clear dose-response relationship. The results with CHL-treated DBA males indicated that all post-meiotic germ-cell stages, except late-spermatids, were affected by CHL treatment, while in C3H males, CHL induced dominant lethal effects in all post-meiotic germ-cell stages. A dose-response relationship was also observed with CHL in C3H male mice. In the present experiments, regardless of the agent or the mouse strain used, spermatids appeared to be the germ-cell stage most sensitive to dominant lethal induction.     

The use of alkaline elution procedures to measure DNA damage in spermiogenic stages of mice exposed to methyl methanesulfonate

The ability of methyl methanesulfonate (MMS) to induce DNA breakage in spermiogenic stages of the mouse was studied using an alkaline elution technique. At daily intervals over a 3-week period following i.p. injection of 50 mg MMS/kg, mature spermatozoa were recovered from treated (3H-labeled) and control (14C-labeled) animals, lysed together on polycarbonate filters, and eluted with a high pH (12.2) buffer. Elution of germ-cell DNA from MMS-treated animals was found to increase in stages in which genetic damage from MMS is greatest. In general, the pattern of DNA elution from treated, spermiogenic stages paralleled the pattern of sensitivity to dominant lethals, specific-locus mutations and heritable translocations found by other investigators. It also paralleled the pattern of sperm-head methylation and protamine methylation measured in an earlier study (Sega and Owens, 1983). At 9 days post treatment (sperm sampled were in mid-to late-spermatid stages at the time of MMS exposure) the elution of sperm DNA did not change significantly over a pH range of 11.6-12.8, suggesting that, at the time of assay, DNA breaks were already present in the sperm. Because of the parallelism found between increased sperm DNA elution and increased genetic damage after mutagen treatment, alkaline elution may prove useful in monitoring potential genetic damage in human sperm.     

Bleomycin, unlike other male-mouse mutagens, is most effective in spermatogonia, inducing primarily deletions

Dominant-lethal tests [P.D. Sudman, J.C. Rutledge, J.B. Bishop, W.M. Generoso, Bleomycin: female-specific dominant lethal effects in mice, Mutat. Res. 296 (1992) 205-217] had suggested that Bleomycin sulfate (Blenoxane), BLM, might be a female-specific mutagen. While confirming that BLM is indeed a powerful inducer of dominant-lethal mutations in females that fails to induce such mutations in postspermatogonial stages of males, we have shown in a specific-locus test that BLM is, in fact, mutagenic in males. This mutagenicity, however, is restricted to spermatogonia (stem-cell and differentiating stages), for which the specific-locus mutation rate differed significantly (P<0.008) from the historical control rate. In treated groups, dominant mutations, also, originated only in spermatogonia. With regard to mutation frequencies, this germ-cell-stage pattern is different from that for radiation and for any other chemical studied to date, except ethylnitrosourea (ENU). However, the nature of the spermatogonial specific-locus mutations differentiates BLM from ENU as well, because BLM induced primarily (or, perhaps, exclusively) multilocus deletions. Heretofore, no chemical that induced specific-locus mutations in spermatogonia did not also induce specific-locus as well as dominant-lethal mutations in postspermatogonial stages, making the dominant lethal test, up till now, predictive of male mutagenicity in general. The BLM results now demonstrate that there are chemicals that can induce specific-locus mutations in spermatogonia without testing positive in postspermatogonial stages. Thus, BLM, while not female-specific, is unique, (a) in its germ-cell-stage specificity in males, and (b) in inducing a type of mutation (deletions) that is atypical for the responding germ-cell stages (spermatogonia).     

Procarbazine-induced specific-locus mutations in male mice.

Procarbazine is used in drug-combination treatment of Hodgkin's disease. The specific locus method was used to test and confirm the ability of procarbazine to induce gene mutations in pre- and post-meiotic germ cells of male mice. The lowest dose of procarbazine that significantly increased the mutation frequency in As spermatogonia over the control frequency was 400 mg/kg (P = 0.003). The corresponding dose for the post-spermatogonial germ-cell stages was 600 mg/kg (P = 0.009). The dose--response was linear for the point estimates of the mutation frequencies after treatment of As spermatogonia with 0, 200, 400 and 600 mg/kg. The point estimate of the mutation frequency at the 800 mg/kg level was one-third of that expected from a linear extrapolation. Variation in mutation rates among the 7 loci between the lowest (a locus) and the highest (p locus) was 12-fold. Only 24% of procarbazine-induced specific locus mutations in As spermatogonia were lethal in the homozygous condition. From the mutation spectra and the viability tests, it is concluded that procarbazine-induced mutations may be mainly due to base-pair changes. Procarbazine-induced specific-locus mutations fulfilled the criteria for the estimation of the doubling dose, the dose necessary to induce as many mutations as occur spontaneously. The doubling dose of procarbazine in As spermatogonia of mice was 114 mg/kg. The therapeutic dose for procarbazine is about 215 mg/kg. If man and mouse were equally sensitive, this dose would induce 1.9 times as many mutations as arise spontaneously. From the incidence of patients with Hodgkin's disease (1 : 42 000) the calculated population dose of procarbazine is 5.12 micrograms/kg. Assuming equal sensitivity between the sexes we can calculate, for an estimated number of 30 000 genes, the induction of about 22 mutations per million children due to procarbazine treatment. The same number of induced mutations can be calculated if the risk of patients is used for the estimation of the genetic hazard.     

Induction of specific-locus mutations in male germ cells of the mouse by acrylamide monomer

Acrylamide monomer (AA), injected into male mice at the maximum tolerated dose of 5 x 50 mg/kg (24-h intervals), significantly increased the specific-locus mutation rate in certain poststem-cell stages of spermatogenesis, but not in spermatogonial stem cells. Germ-cell stages in which the treatment induced dominant lethals--namely, exposed spermatozoa and late spermatids (number of surviving offspring only 3% and 27%, respectively, of those in concurrent controls)--jointly yielded the highest frequency of specific-locus mutations. AA thus conforms to Pattern 1 in our earlier classification of chemicals according to the spermatogenic stage at which they elicit maximum response (Russell et al., 1990). No specific-locus mutations were observed among 17,112 offspring derived from exposed spermatogonial stem cells, a result which rules out (at the 5% significance level) an induced mutation rate greater than 2.3 times the historical control rate. A sustained high productivity in matings made for several months following week 3 indicates that there is no significant spermatogonial killing and that cell selection is presumably not the explanation for the negative result. On the basis of genetic and/or cytogenetic evidence, the mutations induced postmeiotically by AA were 'large lesions' (multi-locus), while one of 2 recovered from exposure of differentiating spermatogonia is probably a small lesion. An earlier survey of mammalian mutagenesis results led us to conclude that, regardless of the classification of a chemical according to the stage at which it elicits its maximum response, the nature of mutations is determined by the germ-cell stage in which they are induced (Russell et al., 1990). The AA results on lesion size and on distribution of mutations among the loci fit the general pattern.     

Dominant cataract and recessive specific-locus mutations detected in offspring of procarbazine-treated male mice

The induction of dominant cataract mutations by procarbazine was studied concomitantly with the induction of specific-locus mutations in treated male mice. The most effective dose in the specific-locus test, 600 mg/kg of procarbazine, and a fractionated dose of 5 X 200 mg/kg were used. The frequencies of dominant cataract mutations were higher, but not significantly different from the historical control. The ratio between the number of recovered specific-locus and dominant cataract mutations was in accordance with that found in our experiments with gamma-rays (Ehling et al., 1982; Kratochvilova, 1981) or in experiments with ethylnitrosourea (Favor, 1986). A total of 3 dominant cataract mutations were recovered in the offspring of procarbazine-treated spermatogonial stem cells. Two mutations had complete penetrance while the third exhibited a reduced penetrance of approximately 70%. The viability and fertility of the heterozygotes of all 3 mutations were not affected. Only 1 mutation was shown to be viable as a homozygote.     

Induction of specific-locus mutations in female mice by 1-ethyl-1-nitrosourea and procarbazine

Using the specific-locus method, the ability of 1-ethyl-1-nitrosourea (ENU) and procarbazine hydrochloride (procarbazine) to induce gene mutations in mouse oocytes was tested and confirmed. The sensitive stage for the induction of mutations in oocytes with 160 mg/kg of ENU is 2-4 weeks post treatment. The induced mutation frequency in this mating interval was 5.1 X 10(-7) mutations/locus/gamete/mg/kg. The induction of mutations by procarbazine occurred 8-33 weeks after treatment. The induced mutation frequency in this mating interval for the 400 mg/kg group was 0.4 X 10(-7) mutations/locus/gamete/mg/kg. One third of the induced mutations was lethal in homozygous condition in both experiments. ENU and procarbazine have a lower mutational response in oocytes than in stem-cell spermatogonia.     

Mutagenicity of Ascaris chymotrypsin inhibitor in germ cells of mice

Chymotrypsin inhibitor isolated from Ascaris suum (ACHI) was tested for the induction of dominant lethal mutations in male mice. Dominant lethal effects of ACHI for the main stages of germ cell development were analyzed by mating at specific time points after dosing. Two groups of adult BALB/c males received 24 or 40 mg per kilogram body weight (BW) per day intraperitoneal (IP) injection of ACHI in sterile phosphate-buffered saline (PBS) for five consecutive days (subacute exposure). Males from a third group were administered single IP injections of ACHI—60 mg/kg BW (acute exposure). The control group received concurrent injections of PBS for five successive days. After the last dose, each male was mated with two untreated females. For fractionated examination with regard to successive germ cell stages (spermatozoa, spermatids, spermatocytes, spermatogonia), every second week, two other untreated virgin females were placed with each male for mating. The uteri of the females were inspected on the 15th day of gestation, and preimplantation loss and postimplantation loss determined from dominant lethal parameters. Exposure of mice germ cells to ACHI did not impair mating activity of males. Fertility index was reduced (P < 0.05) only for females mated at the third week with males exposed to the highest dose of ACHI. In the females bred to ACHI-treated males, significant (P < 0.05) increase in preimplantation loss was observed at postinjection weeks 1 (reflecting exposure to spermatozoa after single treatment and to spermatozoa or late spermatids after subacute dosing) and 3 (reflecting exposure to mid and early spermatids for acute dosing and to mid and early spermatids or late spermatocytes following acute treatment), regardless of dose and length of exposure to the inhibitor. At the 60-mg/kg-BW group, a significant increase of this parameter was also noted at week 5 (reflecting exposure to early spermatocytes). During mating days 15–21, a significant (P < 0.05) increase in postimplantation loss and dominant lethal effects were observed for all doses of ACHI. Acute ACHI exposure 5 weeks prior to mating resulted in dominant lethal effects in early spermatocytes. These preliminary data suggest that ACHI induces dominant lethal mutations at postmeiotic and meiotic stages of spermatogenesis, but spermatids are the most sensitive cell stage to the effect of ACHI. These results show that ACHI may be one of the factors causing disturbances in spermatogenesis leading to a reduction of host reproductive success.     

Studies on chemically induced dominant lethality. I. The cytogenetic basis of MMS-induced dominant lethality in post-meiotic male germ cells.

Young adult male mice were injected intravenously with doses of methyl methanesulfonate(MMS) ranging from 25 to 100 mg/kg body weight. These males were serially mated to superovulated females from day 1 post injection to day 23 post injection. The morning after mating (about 4-6 h post-copulation) the females were sacrificed and ova flushed from the ampulla. The ova were cultured, in the presence of colchicine, for 26 h and metaphase preparations made of the first cleavage division. Chromosome analysis was done and the types, and extent, of chromosome aberrations correlated to previously published dominant lethal data at the same MMS doses and time intervals. The types of aberrations seen were predominantly double fragments (presumably isochromatid deletions), chromatid interchanges, and some chromatid deletions, as well as shattering effect on the male complement at the highest dose and the time of peak sensitivity to dominant lethal induction. When the frequency of cells containing a cytologically visible aberration is compared to the total dominant lethal data an excellent correlation is obtained. Furthermore, the frequency of highly damaged cells, agrees very well with estimated frequencies of preimplantation loss. These data strongly suggest that chromosome aberrations seen at the first cleavage stage are the basis of MMS-induced dominant lethality.     

Genomic analysis of gamma-ray-induced germ-cell mutations at the b locus recovered from the medaka specific-locus test.

To study how gamma-ray-induced germ-cell mutations are fixed at the early embryonic stage of the next generation, genomic alterations in the b locus mutants (colorless melanophores) detected during development in the medaka specific-locus test (SLT) were analyzed. First, nine anonymous DNA markers linked to the b locus were cloned and mapped into the region extending about 47cM surrounding the b locus. Next, losses of paternal alleles of these DNA markers were examined in each of the 51 gamma-ray-induced b locus mutants obtained after irradiation of sperm or spermatids. In these mutants, 47 were dominant lethals, three were semi-viable and one was viable. All the mutants examined had large deletions surrounding the b locus. One viable mutant had an interstitial deletion, while all the semi-viable and dominant lethal ones appeared to have terminal deletions. Deletions extending about 20-35cM were the most frequently observed in 18 of the 51 mutants examined. The largest one extended more than 40cM. These results suggest that most of the gamma-ray induced germ cell mutations recovered as total specific-locus mutants were accompanied by large genomic deletions, which eventually led the mutant embryos to dominant lethality.     

Somatic cell mutagenicity in Drosophila melanogaster in comparison with genetic damage in early germ-cell stages

With the intention of assessing the general performance, sensitivity and the underlying mechanisms of somatic cell mutagenicity assays in Drosophila, a study was undertaken to compare the effectiveness of 5 procarcinogens and 4 direct-acting agents in the white/white-coral eye mosaic assay (SMART) with their activity in early (premeiotic) male and female germ-cell stages, after exposure of Drosophila larvae. The outcome indicated a lack of agreement in the results from recessive lethal assays (SLRL) in comparison with the somatic mutation and recombination test (SMART). The procarcinogens 2-naphthylamine (NA), 3-methylcholanthrene (MC), 9,10-dimethylanthracene (DA) and 7,12-dimethylbenz[a]anthracene (DMBA), and the direct-acting mutagens bleomycin (BM), methyl methanesulfonate (MMS) and ethyl methanesulfonate (EMS), were quite efficient in producing somatic recombination and mutations in white/white-coral larvae, as opposed to only weak effects in early germ-cell stages. 2-Acetylaminofluorene (2AAF) showed marginal effects in both germ cells and somatic tissue after exposure of female larvae, but was inactive in testis. The discrepancy in mutational response between somatic cells and premeiotic germ cells is most impressive for MMS and BM. There is sufficient evidence for attributing a good sized proportion of the encountered variation to efficient error-free DNA repair of premutational damage and to segregational elimination during meiosis of deleterious mutations: (1) The efficient point mutagen ENU was the but one agent producing high levels of viable genetic alterations in early germ cells and in somatic cells. A similar behaviour was previously described for diethylnitrosamine, which ethylates DNA in the same fashion as ENU. (2) In early germ-cell stages of mei-9L1 male larvae, MMS induced multiple mutations (putative clusters) at a low dose differing by a factor 20-40 from those needed to produce an equivalent response in repair-competent strains. This is consistent with the concept of an active excision repair in premeiotic cells. (3) In the case of EMS, next to DNA repair, germinal selection seems to restrict the realization of EMS-induced genetic damage in premeiotic cells. (4) Bleomycin-induced chromosome aberrations caused high mortality rates in males (hemizygous for an X-chromosome) but not in females. MMS and BM, agents known to show preference for chromosome aberration induction, produced 3-6-fold higher rates of somatic mutational events (SME) in female genotypes as compared with the other sex.(ABSTRACT TRUNCATED AT 400 WORDS)     

Induction of specific-locus and dominant lethal mutations in male mice by chlormethine

Chlormethine (WHO), a nitrogen mustard (2,2'-dichloro-N-methyldiethylamine), induces dominant lethal and specific-locus mutations in spermatozoa and spermatids of mice.