Chemical and radiation induced late dominant lethal effects in mice.

Although theoretically expected, experimental data to date have not shown dominant lethal expression to occur throughout the developmental period. Specifically, late post-implantation effects have not been demonstrated. We routinely use an experimental technique in which parental females mated to mutagenically treated males are allowed to give birth and wean their litter, and their uterine horns are then inspected for uterine scars indicative of live and dead embryos. In a number of experiments in which males were mutagenically treated with either chemicals or X-irradiation, a discrepancy was observed between the number of live embryos as determined by the scar technique and the number of live observed at birth, suggesting the possibility of embryonic losses at a late stage in development. Initial analyses showed that mutagenic treatment increased the percentage of these late losses. These differences were statistically significant in 2 of 3 analyses. Factors affecting statistical significance and an understanding of dominant lethal mutations are discussed.     

Studies on the mutagenic effect of contraceptive drugs. I. Induction of dominant lethal mutations in female mice

30 adult virgin female mice (2 strains) received either high or low doses of Anovlar or Lyndiol oral contraceptives and were tested for induction of dominant lethal mutations. The pregnant mice were dissected on Day 14 of pregnancy and total implantations, early deaths, late deaths, and corpora lutea were counted in each pregnancy. A significant reduction in fertile mating (p .025) was found in 1 strain of those who received the high dose of Lyndiol (10 times that of the low dose, which is physiologically equivalent to the human dose). This dose also increased the number of dead implants in both strains which resulted in higher estimates of dominant lethal mutations. It is concluded that when Lyndiol and Anovlar were given at the physiological dose level to control ovulation in mice, the frequency of dominant lethal mutations was not increased above the control level.     

Caffeine concentrations in mice plasma and testicular tissue and the effect of caffeine on the dominant lethal test.

Large groups of male Swiss mice received per os on average 100 mg caffeine per kg body weight per day for 1 or 8 weeks. The dominant lethal test was designed to achieve maximum sensitivity in order to detect any possible mutagenic effect. No mutagenic induction of dominant lethals, pre-implantation egg loss or depression of the fertility of females, caused by caffeine at the dose levels administered were observed. The half life of caffeine, which was between 2.5 and 3 h, was similar in plasma and testicular tissue. It was concluded that caffeine did not accumulate in the testicular tissue of mice. The maximum concentration of caffeine found was below 10 microgram/g testicular tissue, which is about a 100 times lower than concentrations that cause chromosome aberrations in cultured mammalian cells.     

Ethylene dibromide: negative results with the mouse dominant lethal assay and the electrophoretic specific-locus test.

Ethylene dibromide (1,2-dibromoethane; EDB) was tested for the induction of dominant lethal and electrophoretically-detectable specific-locus mutations in the germ cells of DBA/2J male mice. Males were treated with a single intraperitoneal injection of 100 mg/kg EDB and mated to two C57BL/6J females. In the dominant lethal assay, matings were carried out to measure the effect of EDB on meiotic and postmeiotic stages; germ cells representing spermatogonial stem cells were analyzed in the electrophoretic specific-locus test. Neither of these germ cell tests produced any evidence that EDB is a germ cell mutagen. It appears from these data and those reported in the literature that EDB, a genotoxic carcinogen that affects male fertility in some mammalian species, is not mutagenic in the germ cells of the male mouse.     

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.     

Organ-specific effects of DNA methylation by alkylating agents in the inbred Swiss mouse.

Young adult inbred Swiss mice given single or repeated equitoxic doses of N-methyl-N-nitrosourea (MNUA) or methyl methanesulphonate (MMS) develop thymomas and pulmonary adenomas only following MNUA in spite of nearly identical overall alkylation of DNA of tumour target tissues by both agents due mainly to the biologically ineffective product 7-methylguanine. The main difference in DNA alkylation was the production of O6-methylguinine, a known pre-mutagenic product, by MNUA in amounts 10 or more times as large as following MMS. This supports the possibility that somatic mutations are a part of the process of carcinogenesis.     

The effects of radiation and alkylating agents on chromatin degradation in normal and tumour lymphoid cells.

The dynamic of chromatin degradation was studied in thymocytes and LS/BL tumour cells. In permeabilised LS/BL cells, the rate of DNA degradation induced by endogenous calcium and magnesium-dependent endonuclease was approx. 25 times slower than in thymocytes. In LS/BL cells irradiation does not induce chromatin degradation. The alkylating agent TS 160 induced chromatin degradation in both LS/BL lymphosarcoma cells and thymocytes.     

Unscheduled DNA synthesis in spermatogenic cells of mice treated in vivo with the indirect alkylating agents cyclophosphamide and mitomen

Cyclophosphamide (CPA) and mitomen (DMO) are chemical mutagens that require metabolic activation to produce their biological effect. We have used an in vivo UDS assay in various meiotic and postmeiotic germ-cell stages of male mice to study DNA repair after treatment with these chemicals. EMS, a compound requiring no metabolic activation, was also used for comparative purposes.CPA and DMO induced UDS in meiotic through early-to-midspermatid stages, but no UDS was detected in late spermatids and mature sperm. While EMS produced a maximum UDS response in the germ cells immediately after treatment, CPA and DMO did not produce a maximum response until ～0.5 to 1 h after injection. This delay is attributed to the time required for CPA and DMO to be enzymatically vonverted active alkylating metabolites.Unlike the results found with EMS, mutation frequencies (dominant lethals, translocations, specific-locus mutations) following CPA treatment are not noticeably reduced in germ-cell stages in which UDS occurred. In the case of DMO, mutations are induced only in mature spermatozoa, and these germ-cell stages represent only a fraction of those in which no UDS is detected. The results with CPA and DMO thus still leave unclear the relationship between DNA repair and the differential spermatogenic response of mice to genetic damage.     

Genetic recombination in Coprinus: III. Inlluence of gamma-irradiation and temperature treatments on meiotic recombination

Non-lethal doses of gamma-irradiation (5 krad) increased meiotic recombination in Coprinus lagopus when treatments were given at the beginning of karyogamy. The division stage at this time was judged to be late leptotene and the duration of the sensitive period was assessed to be 3–4 h. In C. lagopus the radiation-sensitive stage is distinct from the cold-sensitive stage (pachytene). The additive effect of irradiation at early karyogamy followed by cold treatment in pachytene suggested that the two factors influenced different steps in the recombination process. On the other hand, irradiation followed by heat treatment did not significantly alter recombination frequency as compared to single treatments. It was surmised that radiation and high temperature act on the same factor(s) or at the same steps to bring about a similar net result. It was suggested that irradiation at leptotene may cause single-strand breaks in DNA which eventually participate in exchange.     

Biochemical studies on the lethal effects of solar and artificial ultraviolet radiation on Staphylococcus aureus

The effects of UV-B radiation generated in the laboratory and as a component of sunlight on the viability and particular biochemical activities of the bacterium Staphylococcus aureus have been examined. UV-B radiation progressively inhibits protein synthesis (assayed as ³H-alanine incorporation) and kills cells. Cell respiration, and RNA and DNA synthesis (³H-uridine and ³H-thymidine incorporation) were not greatly affected by UV-B irradiation. The OH and ¹O₂-free radical scavengers protected cells against killing and inhibition of protein synthesis by UV-B, suggesting that such radicals mediate the effects of UV-B on this organism. A similar protective effect using a ferric ion chelator suggests an important role for metallic ions in UV-B lethality.Abbreviations VIS, UV-A, UV-B, UV-C radiation in the bands 400–750 nm, 315–400 nm, 280–315 nm, 200–280 nm respectively - DBCO diazabicyclooctane - OFR oxygen free radical - OH, ¹O₂, O _inf2 ^sup- hydroxyl free radical, singlet oxygen, superoxide radical respectively     

Reversion of the 8-azaguanine resistant phenotype of variant Chinese hamster cells treated with alkylating agents and 5-brono-2'-deoxyuridine.

From cultures of V79 Chinese hamster cells, 10 independent clones of 8-azaguanine resistant cells were isolated and subcultured. Cells from all ten clones were resistant to 1 mg/ml levels of 8-azaguanine (8-AzG), contained less than 3% of the wild type levels of the enzyme, hypoxanthine guanine phosphoribosyl transferase (HGPRT), and were unable to grow in HAT medium. The ten clones were classified according to the conditions under which they reverted to the wild type phenotype. Clones in classes I and II reverted spontaneously with frequencies of 40-10(-5) and about 3-10(-5) respectively, and the reversion frequency was independent of the density of cells of all but one of the clones in the culture medium used. Class II clones evinced increased reversion frequencies with ethyl methanesulfonate (EMS) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), and to a lesser extent with 5-bromo-2'-deoxyuridine (budR), suggesting that these clones contained point mutations in a locus which controls HGPRT activity. The processes of reversion and toxicity appeared to be associated. Class III clones did not revert spontaneously or with BUdR and MNNG, but did revert with EMS. The reversion frequency of class I clones was not increased after treatment with EMS, MNNG or BUdR.     

Oral antioxidants counteract the negative effects of female aging on oocyte quantity and quality in the mouse

This study aims to compare the effect of early and late onset administration of oral antioxidants on number and quality of oocytes retrieved from aged mice after exogenous ovarian stimulation. Control hybrid females were fed a standard diet supplemented or not supplemented with pharmacological doses of vitamins C and E either from the first day of weaning or from the age of 32 weeks until they were autopsied at the age 40-42, 50-52, or 57-62 weeks after exogenous ovarian stimulation. Analysis of chromosomal distribution, DNA organization and cellular morphology was performed in ovulated cumulus-enclosed and -free oocytes, ovarian non-germinal vesicle oocytes enclosed by or free of mucous cumulus cells and in vitro-matured ovarian germinal-vesicle oocytes. Both early and late onset administration of oral antioxidants counteracted the negative effects of female aging on number of ovarian oocytes and total percentage of oocytes retrieved from oviducts and ovaries exhibiting a normal distribution of chromosomes in the metaphase-II plate and/or morphological traits of apoptosis. Although both early and late onset administration of oral antioxidants can counteract the negative effects of female aging on number and quality of oocytes, transference of these results to human beings should be made with caution because of the potential side effects of high doses of vitamins on reproductive function as well as many other undesirable systemic disorders.     

Mutation and nuclear stage in Schizosaccharomyces pombe I. An experimental approach to the role of recombination in mutation induction

A reverse mutation system using G1 and G2 cells of Schizosaccharomyces pombe is described. In order to enable the system to deal with the problem of mutation dependence on recombination, tests were performed on (i) the homogeneity of cell populations with respect to nuclear stage; (ii) the fate of cells during post-irradiation incubation; (iii) the colony-forming ability of G1 and G2 revertants, and (iv) cell viability on the mutation plates. On the basis of the results, it is thought that, using this system, information can be obtained on the role of recombinational events in the process of mutation induction.     

Mutagenesis studies on cultured mammalian cells. The sensitivity of the asparagine-requiring phenotype to several chemical agents.

The effect of several chemical agents on the mutation frequency from asparagine dependence to asparagine independence has been studied in Jensen sarcoma cells. It was found that ethylmethanesulfonate brought about a dramatic exponential increase, while nitrosoguanidine was not lighly effective as a mutagen, causing only a modest increase in mutation frequency, and quinacrine HCl was ineffective. The results presented here are compared with those obtained in other systems and with our previous work on the effects of UV on mutation induction in the asparagine system. They suggest that the basis of the asparagine requirement of mammalian cell lines resides in a specific genetic alteration in nuclear DNA which is corrected by the mutagenic action of the agents tested here.     

The effects of plasma-derived extracellular vesicles on cumulus expansion and oocyte maturation in mice

Cumulus cell expansion is required for the ovulation of a fertilizable oocyte. Extracellular vesicles (EVs) are bilayer-lipid membrane vesicles that may be found in a variety of bodily fluids and play an important role in biological processes. This study aimed to examine the effects of plasma-derived EVs on cumulus expansion and in vitro maturation (IVM) of the oocyte. EVswere isolated using ultracentrifugation from the plasma of female mice. The morphology and size of EVs were analyzed by transmission electron microscopy (TEM) and dynamic light scattering (DLS). Western blotting allowed us to identify CD63, CD81, CD9, and HSP70 protein markers of EVs; the expression of the genes related to cumulus cell expansion, including hyaluronan synthase 2 (Has2) and prostaglandinendoperoxide synthase 2 (Ptgs2), were assessed using real-time polymerase chain reaction. Plasma-derived EVs labeled with Dil dye were successfully incorporated with cumulus cells during IVM. Plasma-derived EVs significantly induced cumulus expansion and maturation of oocytes. The percentage of oocytes that reached the MII stage was significantly greater in the EVs treatment group compared with other groups. Although treatment with epidermal growth factor (EGF) significantly increased cumulus expansion in cumulus-oocyte complexes (COCs), the impact was less than that seen with plasma-derived EVs. Furthermore, EVs generated from plasma substantially enhanced Has2 and Ptgs2 mRNA expression in the cumulus-oocyte complex. This research indicates that EVs derived from plasma are capable of promoting cumulus expansion and oocyte maturation.