The effect of cystamine on the outcome of dominant lethal mutations and reciprocal translocations in sex cells of mice subjected to gamma-irradiation in different doses]

Protective effect of cystamine (150 mg/kg) against genetic damages induced by gamma-irradiation in germ cells of male mice of CBA strain (at doses of 100, 300, 600 r) was studied. The application of cystamine decreased the frequency of dominant lethal mutations induced by radiation in sperms, spermatids and spermatocytes. The degree of the protective effect of cystamine depended on a radiation dose. The protective effect of cystamine was the highest at the radiation dose of 300 r. It was negligible at the radiation dose of 100 r and was completely absent at the dose of 600 r. Cystamine did not affect the rate of induced reciprocal translocations in the spermatogonia at all the radiation doses used.     

Temperature-sensitive autosomal dominant lethal mutations in Drosophila melanogaster induced by ethylmethane sulfonate

Cold- and heat-sensitive dominant autosome and recessive sex-linked lethals were scored using C(1)RM, y; vg bw; e ss tester stock. The frequencies of heat-sensitive mutations were 1.43, 0.30, 0.07% and of cold-sensitive ones were 0.39, 0.16 and 0.09% in the 1-st, 2-nd and 3-rd chromosomes, respectively. For the first time, dominant cold-sensitive lethals were obtained in chromosome 3. The data from genetic analysis point to the fact that penetrance of such mutations strongly depends on the genetic background. That may be the reason, why they were not obtained using some of the balancer-3 chromosomes. Also, "cryptic" dominant autosome mutants were found which were not conditional but only revealed in the F2 generation. Their possible origin as gonado-somatic mosaics is discussed.     

Frequency of dominant lethal mutations induced by combined exposure to incorporated 137Cs and external gamma-irradiation in mice

The genetic effect of combined exposure to incorporated 137Cs and external gamma-irradiation was studied in germ cells of male mice. The activity of incorporated 137Cs was 3.7 x 10(4) Bq/g. The dose of external gamma-irradiation was 1.5 Gy. In the case of combined exposure, mice were treated with a cesium solution immediately after irradiation. The genetic effect was estimated by the frequency of dominant lethal mutations (DLM) induced at different stages of spermatogenesis. Upon combined exposure to external and internal irradiation, the frequency of DLM in premeiotic cells significantly exceeded the total frequency of DLM induced by separate exposure to external and internal irradiation; i.e., a marked synergistic interaction of external and internal irradiation was observed.     

Evaluation of effects of gamma-irradiation at low doses on repair and meiotic recombination mutants of Drosophila melanogaster

A comparative study of the effects of gene mutations mus209, mus309, mei-41 and rad54 of Drosophila melanogaster on the sensitivity to low-level exposure of different duration was carried out. Taken into account was the survival rate at different stages of ontogeny, female fecundity, the frequency of dominant lethal mutations (DLM) and the DNA damage. mei-41 and rad-54 mutants were most sensitive to the action of low dose radiation (80 mGy) in terms of survival and DLM. However, at the level of DNA damage, an increased radiosensitivity is observed only at larger doses of low intensity irradiation. Based on these observations, we can conclude about the importance of repair and its genes in the formation of the effect of low level doses of ionizing radiation in Drosophila.     

The influence of dominant lethal mutations on litter size and body weight and the consequent impact on transgenerational carcinogenesis

The reported untreated mouse control data from the Oak Ridge National Laboratory assessment of dominant damage (ADD) experiments demonstrate a strong negative correlation between body weight at 4, 5, 7, 9, and 11 weeks of age and number in litter at 3 weeks of age. Independently from the above finding, mother mice are also shown to differ substantially as to the mean weights of their litters. Much literature suggests that, as a general rule, (a) heavier mice are more likely to develop spontaneous and induced tumors earlier and (b) caloric restriction decreases body weights and tumor incidences and increases longevity. The above findings make it likely that many experiments that have been interpreted to demonstrate radiation-induced transgenerational carcinogenesis have instead merely illustrated a confounding effect of extensive induced dominant lethality. That is, because of induced dominant lethality, experimental groups contain heavier mice or rats, which accordingly develop more spontaneous tumors at a faster rate than control groups, with the increased tumor rates having nothing to do with induction of dominant tumor mutations. Our findings prompt suggestions as to possible modifications in the analysis and experimental design of such experiments.     

Comparative investigations on the chemical induction of point mutations and dominant lethal mutations in mice

Summary A selection of mono- and polyfunctional alkylating agents as well as a folic acid antagonist and an acridine derivate were tested with the host-mediated assay, and as far as not known from the literature, with the dominant lethal test for mutagenic activity in mice. In the host-mediated assay system the indicator organisms Salmonella typhimurium G46 His ^–, Serratia marcescens a 13 His ^– and a 21 Leu ^– were used as back mutation systems and E. coli 343 as a forward mutation system. We found indications that polyfunctional alkylating agents induce dominant lethal mutations to a larger extent, whereas monofunctional alkylating agents revealed more mutagenic activity on the molecular level. No definite mutagenicity could be observed for amethopterine, which is mutagenic in cytogenetic investigations. Trypaflavin which is known to be mutagenic in the dominant lethal test, did not induce point mutations in our indicator strains. We conclude that the spectra of mutations, which can be recognized by these two methods, overlap only partially.Parts of this paper were presented on the 4th International Congress of Human Genetics, Paris, Sept. 1971.This work was sponsored by the Deutsche Forschungsgesellschaft.Essential results of this paper are part of the doctorate thesis of W. Buselmaier.     

Demonstration of dominant lethal mutations in early mouse embryogenesis

Male mice of C57Bl/6Y strain were injected intraperitoneally with 2.5 and 5 mg/kg doses of thioTEPA. Males were mated to tetrahybrid CBWA females during the second week after the treatment. Embryonic mortality was studied by two methods: by standard dominant lethal method on the 15-17th day of pregnancy and cytologically on the 4th day. The rate of fertilization was not affected by thioTEPA. After treatment with 2.5 mg/kg of thioTEPA the frequency of induced dominant lethals was 89.8%; preimplantation losses were 78,5% in treated and 13,8% in control group. The cytological analysis revealed that preimplantation embryonic death is equal to 63,9%. The death of embryos before implantation occurred at 2-20 blastomere stages. After treatment with 5 mg/kg of thioTEPA all embryos died before implantation at 2-16 blastomere stages. It was demonstrated that dominant lethal method gave more complete estimation of dominant lethal frequency, and that cytological analysis is the correct estimation of preimplantation death. Thus the methods used supplement each other.     

Increment kinetics of recessive lethal mutations and dominant lethals in offspring of Drosophila melanogaster on storage of methyl-methanesulfonate-treated sperm in females

The frequencies of sex-linked recessive lethal mutations in F1 males after feeding adult male Drosophila melanogaster with 0.25 and 0.5 mM methyl methanesulfonate (MMS) orally for 24 h increased approximately linearly with storage of the treated spermatozoa in females, whereas the number of hits of dominant lethals in the sperm after feeding 0.3 and 0.5 mM MMS increased approximately with the square of the storage time. Chromosome losses and mosaics in F1 males also increased with the dose of MMS to males, but their yields were too low to be analyzed quantitatively, only indicating a slight increase of chromosome loses and a slight decrease of mosaics with the time of storage of sperm. Maternal non-disjunctions (or chromosome losses), detected in F1 males, decreased with the dose of MMS to spermatozoa and their yield decreased with the time of storage of sperm of both MMS-treated and the control groups. A unitary model is proposed to explain the effect of storage on the dominant lethals and recessive lethal mutations.     

The effect of sexual harassment on lethal mutation rate in female Drosophila melanogaster

The rate by which new mutations are introduced into a population may have far-reaching implications for processes at the population level. Theory assumes that all individuals within a population have the same mutation rate, but this assumption may not be true. Compared with individuals in high condition, those in poor condition may have fewer resources available to invest in DNA repair, resulting in elevated mutation rates. Alternatively, environmentally induced stress can result in increased investment in DNA repair at the expense of reproduction. Here, we directly test whether sexual harassment by males, known to reduce female condition, affects female capacity to alleviate DNA damage in Drosophila melanogaster fruitflies. Female gametes can repair double-strand DNA breaks in sperm, which allows manipulating mutation rate independently from female condition. We show that male harassment strongly not only reduces female fecundity, but also reduces the yield of dominant lethal mutations, supporting the hypothesis that stressed organisms invest relatively more in repair mechanisms. We discuss our results in the light of previous research and suggest that social effects such as density and courtship can play an important and underappreciated role in mediating condition-dependent mutation rate.     

The influence of lethal mutations on the quantification of radiation transformation frequencies

Transformation frequencies for gamma irradiated C3H 10T1/2 cells have been analysed, taking account of the occurrence of lethal mutations in these cells. Lethal mutations already noted by these authors in primary thyroid and established CHO K1 cells occur at high levels in C3H 10T1/2 cells and lead, therefore, to considerable underestimates of transformation frequency, particularly at high doses where this is expressed on a per surviving cell basis. The results may help to provide an explanation for the dose response plateau which is seen when these cells are irradiated and transformed foci per surviving cell are scored.     

Biological effect of low doses of alkylating agents in drosophila studies

The low dose (0.05-0.1 mM) influence of alkylating agents on germ cell survival and male fertility, the level of embryonic and postembryonic lethality as well as the sex-linked recessive lethal (SLRL) frequency induced by high alkylating agent doses was studied in Drosophila melanogaster. The pretreatment of adult males with low doses of methyl and ethyl methanesulfonate (MMS and EMS) did not change or even enhanced EMS cytotoxicity and mutagenicity in both mature sperm and premeiotic cells. On the contrary, the low EMS dose pretreatment of larvae protected them against higher mutagen doses increasing male fertility, decreasing embryonic and postembryonic lethality in F1, and leading to three-fold reduction in the SLRL frequency in F2. The adaptive response was dependent on the Drosophila developmental stage exposed to challenge mutagen doses, since the protection was maximal in larvae and practically absent when the high dose was administered to adult males. The adaptive response observed does not seem to be associated with DNA repair, but it is rather due to other protective mechanisms.     

Distribution of MR-induced sex-linked recessive lethal mutations in Drosophila melanogaster

In the ‘doubling-dose’ method currently used in genetic risk evaluation, two principle assumptions are made and these are: (1) there is proportionality between spontaneous and induced mutations and (2) the lesions that lead to spontaneous and induced mutations are essentially similar. The studies reported in this paper were directed at examining the validity of these two assumptions in Drosophila. An analysis was made of the distribution of sex-linked recessive lethals induced by MR, one of the well-studied mutator systems in Drosophila.

Appropriate genetic complementation tests with 15 defined X-chromosome duplications showed that MR-induced lethals occurred at many sites along the X-chromosome (in contrast to the known locus specificity of MR-induced visible-mutations); some, but not all these sites at which recessive lethals arose in the MR-system are the same as those known to be hot-spots for X-ray-induced lethals. With in situ hybridization we were able to demonstrate that a majority of MR-induced lethals is associated with a particular mobile DNA sequence, the P-element, i.e. they arose as a result of transposition.

The differences between the profiles of MR-induced and X-ray-induced recessive lethals, and the nature of MR-induced and X-ray-induced mutations, thus raise questions about the validity of the assumptions involved in the use of the ‘doubling-dose’ method.     

Comparison of radiation-and chemically-induced dominant lethal mutations in male mice

Ionizing radiation-induced dominant lethal mutations in all spermatogenic stages. After irradiation of male mice with 200 R the yield of induced mutations in early spermatids was twice the yield in spermatozoa, late spermatids, and spermatocytes. After irradiation with 400 R or 800 R the spermatocytes were the most sensitive stage for the induction of dominant lethal mutations. The frequency of radiation-induced dominant lethal mutations in postspermatogonial stages was dose-dependent. The yield of dominant lethal mutations in spermatogonia was independent of the dose.