Some aspects of the detection of potential mutagenic agents in Drosophila

The rodent carcinogens 1,4-dioxane and thiourea induce meiotic non-disjunction in Drosophila melanogaster females

The ability of the rodent carcinogens 1,4-dioxane (DX) and thiourea (TU) to induce meiotic non-disjunction (ND) was assessed in 3- and 6-day-old Drosophila melanogaster females. The chemicals were administered orally and three 24 h and one 48 h broods were obtained after mating, to sample oocytes treated in increasingly earlier stages of development. The broods represent mainly mature oocytes (brood I), nearly mature oocytes (brood II), early oocytes (brood III) and very early oocytes (brood IV). The toxicity of DX increased with dose (1% (not toxic), 1.5, 2, 3, 3.5%) as well as a reduction in fecundity which was moderate. Induction of ND in mature oocytes was positive with 2, 3 and 3.5% concentrations and was not related to dose. In immature oocytes it was also positive though already at the lowest concentration tested (1%), suggesting a sensitivity higher than that of mature oocytes. TU at 0.10-10%, did not affect viability, but since fecundity was seriously impaired at high doses, ND was not assessed beyond the 1.5% concentration. TU also induced ND in mature and in immature oocytes; neither a threshold nor a dose effect was detected. The response of mature oocytes was lower than that of immature oocytes. TU induced increases of ND in the earliest cells tested in a more consistent fashion than DX. The data clearly show that both chemicals induced ND in mature oocytes and in the three subsets in which immature oocytes were fractionated. Though toxicity may play a significant unspecific role in the induction of chromosome malsegregation by DX and TU, the induction of ND at low doses, moderately toxic to the oocytes, suggests that the interaction with specific targets contributed to the results obtained.

Effect of hydroquinone on meiotic segregation in Drosophila melanogaster females

The induction of sex chromosomes meiotic nondisjunction (ND) by hydroquinone (HQ) given orally was investigated in Drosophila melanogaster 2-7, 8-22, 24, 48, 72 and 96 h-old females. ND was assessed by a system where exceptional females (XXY) and only 1/4 of the expected regular progeny are viable. Oocytes were treated at different stages of development. 4% HQ tested only in 72 h-old females induced ND in oocytes sampled in brood I (mostly mature oocytes at metaphase I). 6% HQ increased ND in brood I of 8-22 h-old females, while other broods, (including cells treated at early prophase) were also affected in older flies, the highest significance being attained in the 48 h-old series. Newly hatched females (2-7 h-old) were refractory to the treatment, though oocytes sampled in the first three subcultures are comparable to cells showing enhancement of ND in series run with older females. Toxicity of 2, 4 and 6% HQ increased with concentration and females' age: (a) 2% was not toxic; (b) 4% was toxic only to 72 h-old females; (c) 6% was increasingly toxic to females 24, 48 and 72 h-old. The results indicate that age plays a significant role on both chromosomal segregation and toxicity and suggest that in Drosophila HQ is metabolized to its reactive species. The lack of toxic and aneugenic effect in very young females could reflect a more efficient detoxification due to the known high specific activity of glutathione-S-transferase (GST) after eclosion. The decline in GST activity around day 2 of adult life coincides with the high effect of HQ in 48 h-old females.

Genetic damage induced by methylglyoxal and methylglyoxal plus X-rays in Drosophila melanogaster germinal cells

The effect of methylglyoxal (MG) and MG administered prior to X-irradiation was investigated in Drosophila melanogaster germinal cells using the sex-linked recessive lethal (s.l.r.l.), II-III autosomal translocation (AT) and X-chromosome nondisjunction (ND) tests. For the s.l.r.l. test the males were either injected with MG (0.5 M, 0.75 M or 1.7 M) or fed for 24 h (1 M) and two 24 h broods (A and B) were obtained. For the AT test the males were injected with MG 1.7 M and the same brooding scheme was followed. ND was tested in females fed on MG 1 M. The only effect observed after MG treatment was a significant increase on the yield of s.l.r.l. with MG 1.7 M. In the combined treatments MG was administered prior to irradiation with 20 Gy of X-rays and the induction of s.l.r.l. and AT was assessed. Pre-treatment with MG 0.75 M and 1.7 M enhanced the frequency of s.l.r.l. in cells sampled in brood B, consisting mainly of the rather hypoxic late spermatids. It is suggested that this radiosensitizing effect could be ascribed to a decrease in the level of glutathione due to the metabolization of MG.

Mutagenicity of 7,12-dimethylbenz[a]anthracene and some other aromatic mutagens in Drosophila melanogaster

The optimal conditions for mutagenesis studies with DMBA and some other aromatic carcinogens in Drosophila were investigated in detail. The results presented in this paper indicate the following. The mutagenic effectiveness of DMBA is dependent on the route of administration, injection being far more effective when compared with feeding. The choice of the solvent is a crucial experimental condition. DMBA, when dissolved in oil/DMF, is ineffective whereas a special fat emulsion of DMBA gives high mutation frequencies. There appears to be an extreme strain dependence in the mutagenicity of DMBA. Mutagenic effectiveness in strain Berlin-K was rather low, whereas Oregon-K and Karsnäs-60 proved to be very susceptible to DMBA. Under the conditions of test, DMBA did not induce loss of a ring-X chromosome and did not produce recessive lethal mutations in such a chromosome. DMBA did not produce 2-3 translocations to any significant extent. An increase in DMBA-induced recessive lethal mutations was found upon storage of treated sperm with an optimal storage time of 4-10 days. DMBA is efficient in the production of delayed recessive lethal mutations in strain Berlin-K. Twice as many lethals were recovered with the F3 generation as compared with those in F2. In strain Oregon-K, where the frequency of F2 lethals was much higher than in strain Berlin-K, the ratio of F3/F2 lethals was clearly lower. Enzyme induction with phenobarbital reduces the mutagenic effectiveness of DMBA. Whereas TMBA was not mutagenic in Berlin-K, considerable mutagenicity was observed in Oregon-K and Karsnäs-60. Injection of carcinogenic polycyclic aromatic hydrocarbons and aromatic amines, when dissolved in special fat emulsions, enhances the mutagenic effectiveness of some compounds (DMBA, TMBA, DA and AcO-AAF), but this procedure does not always solve the problems pertinent to these classes of promutagens in Drosophila.

Sensitivity of different strains of Drosophila melanogaster to endosulfan and malathion

Four Drosophila melanogaster populations, two of them (ER1 and ER2) previously selected for adult resistance to endosulfan, were examined for response to endosulfan and malathion treatment. Both insecticides were fed to larvae and adult males and females to test their toxic capacity. Our results show that malathion is more toxic than endosulfan, that adult males are more sensitive to both insecticides than females, and that resistance of ER1 and ER2 strains is restricted to the insecticide to which they had been exposed previously (endosulfan).

Evaluation of mutagenic effect of the fungicide fenaminosulf in Drosophila melanogaster

Fenaminosulf (p-dimethylaminobenzenediazo sodium sulfonate, CAS registry No. 140-56-7) which is an active ingredient in several commercial fungicides was reported to be mutagenic in Salmonella typhimurium (McCann et al., 1975), Bacillus subtilis (Kada et al., 1974) and shown to cause chromosome aberrations in plants (Zutshi and Kaul, 1975). Since fenaminosulf has structural similarity to the potent carcinogen, butter yellow (p-dimethylaminoazobenzene, CAS registry No. 60-11-7), the present studies were undertaken to evaluate the mutagenic potential of this fungicide in Drosophila melanogaster. Fenaminosulf administered at 10 mg/100 ml food medium failed to induce sex-linked recessive mutations in Drosophila. Since Drosophila has drug-metabolizing enzymes similar to those of mammals (Vogel, 1975), it is suggested that the lack of mutagenic activity of fenaminosulf could be due to the conversion of fenaminosulf to non-mutagenic derivatives in Drosophila.

Test systems for mutagenicity screening of environmental chemicals and their relevance for the evaluation of genetic hazards to man

Mutagenicity test systems play a dual role in public health: (1) to identify chemicals in our environment that are capable of causing genetic alterations and thus pose a threat of genetic damage to generations yet unborn and (2) as a faster screen (than many of the conventional carcinogenicity tests) to identify chemicals with carcinogenic potentials. In this paper the different mutagenicity test systems currently available are reviewed together with a discussion of their advantages and disadvantages. It is argued that our current data base does not permit a realistic quantitative assessment of genetic hazards ensuing from exposure to environmental chemicals and that only qualitative conclusions are possible. A framework which may be useful in the context of the latter is briefly outlined.

Biotransformation of xenobiotics in Drosophila melanogaster and its relevance for mutagenicity testing

Biotransformation of lipophilic xenobiotics may lead to formation of reactive intermediates which can give rise to irreversible toxic events such as carcinogenesis, mutagenesis, teratogenesis, and tissue necrosis. In recent years considerable attention has been paid to the problem of testing for these effects. Short-term mutagenicity tests have been shown to have value for predicting the occurrence of delayed toxic effects in mammals following administration of indirectly acting harmful xenobiotics. In any test system the capacity to bioactivate the compound under test is a necessary prerequisite, and in most short-term test assays this is provided for by adding a metabolic activation system generally consisting of the 9,000 g supernatant fraction of a rat liver homogenate supplied with cofactors. The fruitfly Drosophila melanogaster constitutes an organism well-suited for mutagenicity testing, and it was shown that a number of precarcinogens evoke mutagenic effects in this species. Thus Drosophila is apparently able to metabolize xenobiotics to reactive intermediates, which in turn induce mutagenicity. However, knowledge about the presence and characteristics of the xenobiotic-metabolizing enzymes involved is lacking. Since knowledge of these enzymes contributes to the evaluation and interpretation of observed mutagenic events, this paper described studies concerning some important xenobiotic-metabolizing enzymes of Drosophila. Files were homogenized and subcellular fractions were investigated with respect to enzymatic activities. It was possible to demonstrate cytochrome P-450 and some related mixed-function oxidase activities. Cytochrome b5, epoxide hydrolase, and glutathione S-transferase are also present, while preliminary experiments suggest the presence of UDP-glucosyltransferase and phosphotransferase activities. The enzymes which have been found are discussed with respect to their similarities with rat liver enzymes and their relevance for mutagenicity testing with Drosophila melanogaster.

Sensitivity of drosophila mutants to chemical carcinogens

7 single-mutant and five double-mutant strains of Drosophila melanogaster were tested for their relative sensitivity to the chemical carcinogens: 1-acetylaminofluorene, benzo(alpha)pyrene, N-methyl-N'-nitro-N-nitrosoguanidine, 4-nitro quinoline-1-oxide and aflatoxin B1. Among the single mutants, mei-9a, mei-41D5 and mus(1)104D1 are hypersensitive to all 5 chemicals, whereas mus(1)107D1 is hypersensitive only to 4-nitroquinoline-1-oxide and is slightly sensitive to benzo(alpha)pyrene. The mei-9a mei-41D5 double-mutant is the most sensitive of 5 tested double-mutants which carry the mei-9a allele. When treated with 0.025 mM benzo(alpha)pyrene this double-mutant produces significantly more sex-linked recessive lethals and dominant lethals than does the control. Analysis of double-mutants reveals that the mei-9+ product functions in a different repair pathway of methyl methanesulfonate-induced damage than do the normal products of the mus(1)103, mus(1)104 and mus(1)107 loci. Our findings suggest that the sensitivity of Drosophila repair-deficient mutants could be exploited in screening for potential mutagens and carcinogens.

The relation between reaction kinetics and mutagenic action of mono-functional alkylating agents in higher eukaryotic systems. I. Recessive lethal mutations and translocations in Drosophila

The relationship in Drosophila males between chemical reaction pattern of mono-functional alkylating agents (AA), described in terms of primary alkylation pattern with DNA and proteins as well as the Swain--Scott s factor, and their biological effectiveness were investigated. The agents chosen for comparative analysis were the nitrosamides ENU and MNU, the methanesulfonic esters iPMS, EMS and MMS, the dialkylsulfate DMS, and the nitrosamines DEN and DMN. Parameters of their biological activity were mortality (LC50) of treated adult males, induction in post-meiotic stages of X-chromosomal recessive lethal mutations and 2--3 translocations after either adult feeding or injection. Induced frequencies of recessive lethals, determined for each AA with a range of concentrations, served as biological dosimeter for interaction with target DNA in the germ line. The results are interpreted as indicating for these AA a causal connection between the pattern of primary alkylation of DNA and the quality of genetic damage observed. 1. The agent with the lowest s value, ENU, and its pendant DEN, failed to produce translocations at mutation frequencies that reached 44% for ENU. The highest chromosome-breaking activity was attributed to AA with high s, MMS and DMS. For MMS, the proportions of translocations (T) to mutations (M) approximately reached a 1 : 1 ratio in stored spermatozoa, at a recessive-lethal frequency of 14%. Ability to break chromosomes, as indicated by the T : M ratios, decreased in the sequence MMS greater than or equal to DMS, MNU greater than DMN greater than EMS greater than iPMS greater than ENU = DEN. 2. Nearly the reversed sequence in relative mutagenci effectivenss was obtained when the (directly acting) AA were arranged on the basis of their CM4/LC50 ratios (CM4, the exposure condition producing 4% recessive lethals after injection): ENU greater than EMS greater than iPMS, MNU greater than MMS = DMS. 3. Among the AA, EMS had a somewhat unique position, in that it was slightly less effective in the translocation test, and also less cytotoxic but more mutagenic in the recessive-lethal test than one would expect from its s value. This is taken as an indication of the influence on biological effectiveness of factors other than the s value, e.g. methylation versus ethylation and the lipid/water partition ratio. An example of the latter was also provided by DMS which, although having the same s as MMS, with its 5-fold higher lipid/water partition ratio, was more toxic than MMS. 4. For those AA that were clearly active in the translocation tests--MMS, DMS, MNU, DMN and EMS--delayed formation of exchanges was observed. Only in 17 out of 555 translocation tests with positive response translocations were already found in progeny from unstored spermatozoa. Consequently, it was concluded that performance of storage experiments in Drosophila is an absolute necessity for the detection of this type of rearrangement by AA. 5...

Vinyl chloride mutagenesis in Drosophila melanogaster

In inhalation experiments, Drosophila males were exposed to vinyl chloride at concentrations of 200, 850, 10,000 30,000 or 50,000 ppm for 2 days, and to 30 or 850 ppm for 17 days. VCM was mutagenic in the recessive-lethal test both after short-term and long-term exposures. The lowest effective concentration (LEC) was 850 ppm after 2 day exposure, and this value could be lowered to 30 ppm by prolonging the exposure time to 17 days. With the concentration levels tested, the mutation frequency increased with concentrations and reached a plateau at 10,000 ppm. This indicates a substrate saturation effect. In contrast with the recessive lethal assay, negative results were obtained when tests on dominant lethals, translocations, entire and partial sex-chromosome loss were carried out with VCM at 30,000 ppm for 2 days. This finding of a false negative seems a logical consequence of the observed saturation effect, and strengthens the concept that there exist two effective concentrations for point mutations vs the induction of chromosome breakage events. Vinyl chloride monomer provides another example to support our view that chromosome breakage is not a reliable measure of mutagenic activity.

Chromosomal damage by alcohol in vitro and in vivo

Alcohol has no damaging effects on human chromosomes in vitro. The chromosomes of alcoholics, however, show a significant elevation of aberrations. Alcohol inhibits cellular and cell free RNA synthesis. One possible reason for the mutagenic activity of alcohol in vivo may be an inhibition of cellular repair.

The capacity of Drosophila for detecting relevant genetic damage

For the detection and study of mutagenic agents, Drosophila offers many advantages. It is a higher organism with a short generation time that is cheap and easy to breed in large numbers. The simple genetic testing methods provide unequivocal answers about the whole spectrum of relevant genetic damage. A comparison of the detection capacity of assays sampling different kinds of genetic damage revealed that various substances are highly effective in inducing mutations, but do not produce chromosome breakage effects at all, or only at much higher concentrations than those required for mutation induction. Of the different assay systems available, the classical sex-linked recessive lethal test thus deserves priority, in view of its superior capacity to detect mutagens. Of practical importance is also its high sensitivity, because a large number of loci in one-fifth of the genome is tested for newly induced forward mutations, including small deletions. Drosophila is capable of carrying out the same metabolic activation reactions as the mammalian liver. An additional advantage, in this respect, is the capacity of Drosophila for detecting short-lived activation products, because intracellular activation occurs within the spermatids ans spermatocytes. These properties make the test for recessive sex-linked lethals a useful tool for verifying results obtained in the pre-screening of potential mutagens with fast microbial assay systems. In studies on non-disjunction, detailed genetic analysis of the induced changes is possible, and these may shed light on the mechanisms involved. A new adaptation of the bithorax transvection method by Mendelson permits the recovery of high yields of chromosome aberrations in a fast one-generation test.

Mutangenicity and toxicity of amitrole. I. Drosophila tests

Amitrole was highly toxic at early larval stages of Drosophila (LD50 is 40 ppm in medium). Toxicity of amitrole was also revealed by prolongation of development time even at 10 ppm. However, no mutagenic effects of amitrole were observed either in the sex chromosome non-disjunction test (females reared on medium containing amitrole at 10 ppm) or in the sex-linked recessive lethal test (males reared on medium containing amitrole at 10 ppm).

Charlotte Auerbach and chemical mutagenesis

A review is presented of the many conceptual contributions of Charlotte Auerbach to the development of the field of chemical mutagenesis during the past thirty years. The following aspects are discussed: (1) differences between the genetic effects of chemicals and X-rays; (2) mosaicism, delayed mutation and replicating instabilities; (3) mutation as a cellular process; (4) specificity; (5) dose-effect curves, and (6) correlation between different kinds of damage.