Induction Of Dominant Lethals Research Articles

Mutagenicity tests with trypaflavin and hexamethylenetetramine in mammals in vivo and in vitro

In our experiments we first tested the ability of different concentrations of trypaflavine and hexamethylenetetramine to induce dominant lethal mutations by injecting the compounds intraperitoneally or orally into male mice. Only for high dosages the induction of dominant lethals could be ascertained (50 mg trypaflavine per kg body weight and 25000 mg/kg hexamethylenetetramine). No specific sensitivity of single stages of the cycle of spermatogenesis was observed. It could be demonstrated by fluorescence microscopy that trypaflavine invades the male germ cells. Further indications for the weak mutagenicity of this compound we received cytogenetically by finding some chromosome aberrations and increased rates of univalents in diakinesis. In vitro investigations with hexamethylenetetramine in high final concentrations used in the mice experiments induced cell death, depression of mitosis and clumping of chromosomal material in blood cells as well as in HeLa cell cultures. Lower concentrations tested on HeLa cells were found to induce a number of chromosomal aberrations, but in a certain dosage, only (1×10-3M). No chromosome changes could be recognized in blood or HeLa cell mitosis when hexamethylenetetramine was given in final concentrations 1×10-4M and lower. A comparison of the used concentrations of the test substances and their mutagenic efficiency with the usual therapeutic dosages give rise to assume that the genetic risk for man is low for both drugs.

The effect of dose-rate on the yield of translocations and dominant lethals following spermatogonial irradiation of mice

1. F1 (CSH♀ × 101♂) male mice were given 1200 r. 60Co Υ-irradiation over welve weeks and mated twelve weeks after the end of irradiation. The incidences of foetal and neonatal lethality and of semi-sterility in their offspring were compared with those in controls.2. Embryonic survival to 15 days in the irradiated series was 98·2% that of controls, while the incidence of semi-sterility was 0·9% compared with nil in the controls. Neither of these differences is significant.3. Comparison of these results with the significant rates of induction of dominant lethals and translocations in a previous experiment, in which a dose of 1200 r. acute x-irradiation was given to males of the same hybrid stock, show the existence of a dose-rate effect. Its magnitude cannot at present be accurately estimated.4. The reasons for this effect are discussed. It is concluded that the main cause of the lowered translocation yield is that restitution of breaks will be favoured at low dose-rates, with less opportunity for the formation of interchanges. This could partly account for the lowered rate of induction of dominant lethals as well, but a full explanation is not yet possible.

The overall rates of dominant and recessive lethal and visible mutation induced by spermatogonial X-irradiation of mice

1. Hybrid (C3H♀ × 101♂) male mice were given two doses of 600 r. acute x-irradiation eight weeks apart and outcrossed at the end of their sterile period. Their fully fertile sons were outcrossed and daughters of these sons were backcrossed to them, in order to study the rates of induction in spermatogonia of dominant and recessive lethal and visible mutations, as well as dominant semi-sterility.2. F1litter-size decreased by 15·2% at birth and 15·8% at weaning age, as compared with controls. This decrease was very largely due to dominant lethality acting at about the time of embryonic implantation. There was also a highly significant increase in the incidence of heritable semi-sterility, the estimated rate of induction of reciprocal translocations being 3·3% per gamete.3. The dominant lethality was shown to be partly a secondary consequence of induced translocation heterozygosis. The estimated overall rate of dominant lethal induction was 10·6% per gamete, with ‘primary’ dominant lethals induced at a rate of 4·0% per gamete.4. The estimated mutation rate to dominant visible mutations was 4·6 × 10-7/gamete/r., but this was based on only two mutations in the irradiated series.5. In the backcross generation there was again significantly more embryonic death in the irradiated series, mainly at the small mole stage and this was attributed to induced lethal mutation. The survival in the irradiated series was 96·80% of that in the controls and from this the rate of induction of recessive lethals was calculated to be 2·5 × 10-4/gamete/r. There was no evidence of the induction of lethals acting later than 14 days' gestation.6. The estimated rate of induction of recessive visible mutations was 1·8 × 10-5/gamete/r., but the results showed heterogeneity, probably due to personal factors.7. No significant sex-ratio differences were found.8. The results were compared with those of specific locus and other relevant experiments. The rates of induction of recessive lethal mutations and of recessive visibles were both lower than might have been expected. On these results the mouse was only 4–5 times more sensitive thanDrosophilato the mutagenic effects of radiation.

CYTOGENETIC EFFECTS OF CHEMOSTERILANTS IN MOSQUITOES. II. MECHANISM OF APHOLATE-INDUCED CHANGES IN FECUNDITY AND FERTILITY OF AEDES AEGYPTI (L.)

1. Two-day-old larvae of Aedes aegypti were reared until pupation in 15 ppm apholate, a commonly used insect chemosterilant. This concentration induced almost complete female infecundity. Ovarian dissections of developing females at regular time intervals were made in order to study the underlying basis of reduced fecundity. Apholate greatly inhibited ovarian development. The follicles in treated females remained small and sooner or later underwent complete degeneration. In some of these follicles a distinction into nurse cells and oocytes never took place. In others, a complete breakdown of the follicular epithelium, nurse cells and oocyte was observed. Rarely, one or more follicles completed development in treated females. Many of these failed to hatch after insemination with normal males. This indicates the induction of dominant lethals in these eggs.2. Motile sperms were produced by males emerging from larvae treated at second instar stage. The size of the testes in 9-day-old treated males was not gre...

THE RADIOSENSITIVITY OF GERM CELLS

THE RADIOSENSITIVITY OF GERM CELLS

Genetic radiosensitivity of specific post-dictyate stages in mouse oöcytes

The induction of dominant lethals after X-irradiation of dictyate, later meiotic stages, and the pronuclear stage after fertilization have been compared using the technique of induced ovulation in mice. The injection of gonadotrophins ensures that the time at which the synchronously dividing oöcytes reach any particular meiotic stage is accurately known. Embryonic lethality up to 13½ days was studied after 0 r., 100 r. and 200 r. acute X-irradiation. Metaphase I, anaphase I and metaphase II were the most sensitive stages, with LD50's of about 120 r., 130 r. and 170 r. respectively. The dictyate and pronuclear stages were much less sensitive, with LD50's in the region of 500 r., and sensitivity rose steeply during prophase I. Numbers of corpora lutea decreased with irradiation, the decrease being greatest with irradiation at metaphase I and anaphase I. The ovulation of large numbers of eggs, which increased the preimplantation loss of embryos above normal, and the low luteal counts probably masked lethality to some extent. Results generally agree well with those reported in a number of plant and animal species.

EFFECTS OF X-RAYS ON FEMALE GERM-CELLS OF DROSOPHILA MELANOGASTER. I. DOMINANT LETHAL MUTATION AND OVIPOSITION IN RELATION TO TREATED STAGE.

SummaryThe sensitivity in terms of dominant-lethal induction (strictly speaking: reduced hatchability) has been measured for successive eggs laid by Drosophila melanogaster after irradiation of the female with 1000, 4000 and 6000 rad.Hypersensitivity is found in eggs laid by females aged seven days, during the first 12 hours after irradiation. This is attributed to irradiation of Metaphase I. A lower level of sensitivity is found in eggs laid over the next six days. This is attributed to the irradiation of oocytes in all stages prior to Metaphase I.Finally, a residual incidence of dominant lethals is observed in eggs laid more than six days after irradiation, which are presumed to have been irradiated as oogonia.Oviposition (i.e. rate of maturation of eggs) shows an entirely different radiation response. 4000 rad produces a slight depression of egg-laying during the period of low dominant-lethal production, a more marked depression coinciding with the main production of dominant lethals, and a particularl...

A test for mutagenicity of caffeine in mice.

1. The results are given of an experiment comparing the specific locus mutation-rates in male and in female mice having 0.1% caffeine dissolved in their drinking-water up to the age of ten weeks. Their parents had the same treatment from the time of mating, so that the tested germ-cells might be exposed to caffeine during embryonic development. 2. The mutation-rates in males and females did not differ significantly from each other, nor from the known spontaneous rate; thus there was no evidence for induction of mutations by the caffeine treatment. Neither was there evidence for the induction of dominant lethals following caffeine treatment of males. 3. The treatment did not noticeably affect reproduction, but some mice developed aggressive tendencies towards their cage-mates. Some mice were kept on 0.1% caffeine throughout life: they continued to breed satisfactorily on the whole.

X-IRRADIATION OF THE DEVELOPING MALE GERM CELLS OF TRIBOLIUM CONFUSUM

Young adult males of the flour beetle, T. confusum, have been shown to require about four days, following eclosion, to reach sexual maturity. Subjecting two or three day old males to 1450 or 2900 r of x rays depresses their fertility, as evidenced by the increase in the percentage of inviable eggs produced by their mates. This inviability, probably due in part to the induction of dominant lethals, reaches a maximum value 11 to 12 days following irradiation and then declines. In general, the pattern of response suggests that the various stages of spermatogenesis of T. confusum are differentially sensitive to x-rays. No evidence was found for recovery of irradiated sperm stored by females, or of extended effects on the fertility of the treated males. (auth)

The Protective Effect of Cysteamine against Genetic Damages by X-Rays in Spermatozoa from Mice

of these agents on sex cells of various stages. Kaplan and Lyon (1) made a small test of the possible protective action of cysteamine but found no positive response on dominant lethals in mice. Rugh and Wolff (2) found, however, that cysteamine decreased the sterilizing effect of Xrays in female mice. Wang et al. (3) concluded that injection of cysteamine decreased the transient sterility in irradiated male mice. Mandl (4), studying the number of spermatogonia and pre-spermatocytes in irradiated rats, showed that the reduction was less marked in animals that, prior to irradiation, were given injections of cysteamine. Studies with the same technique as that used by Kaplan and Lyon (1) have been undertaken in order to reinvestigate the effects of cysteamine on the induction of dominant lethals induced in spermatozoa and appearing as post implantation deaths. There were reasons to suspect that agents protecting against somatic damages ought to be effective with regard to genetic damages. In some recent studies, not yet published, Frolen (personal communication) has shown that there is a difference in the rate of dominant lethal mutations induced in spermatozoa from different strains of mice. Furthermore, these strains had previously been studied with regard to their tolerance to acute irradiation. Frolen et al. (5) showed that one of the two strains was extremely sensitive to irradiation (Albino, LD50(30) = 446 r), whereas the other one was very resistant (CBA, LD5o(30) = 748 r). In studies of induction of dominant lethals it was evident that the rate of mutations was higher in the albino than in the CBA strain. Hence, there is an agreement between the sensitivity to somatic damage, as measured by LD5o(30), and the induction of genetic damages in spermatozoa.

A COMPARISON OF THE RELATIVE EFFECTIVENESS OF RADIATIONS OF DIFFERENT AVERAGE LINEAR ENERGY TRANSFER ON THE INDUCTION OF DOMINANT AND RECESSIVE LETHALS IN DROSOPHILA

An investigation was made of the effects of monochromatic 14-Mev fast neutrons and Co/sup 60/ gamma rays on the induction of dominant lethals and of 14- Mev neutrons on the production of sex-linked recessive lethals in Drosophila. These results were compared with those of other reports from this laboratory, In which radiations of different average LET were used. It was shown that the RBE of different radiations for the induction of both genetic effects studied is dependent on the LET of the radiation used. 34 references. (auth)

The rate of induction of dominant lethals inDrosophila melanogaster sperm by X-rays

The rate of X-ray induction of dominant lethals in the sperm of the Oregon-R stock ofDrosophila melanogaster is, at low doses, 12% per 1000 r. for death in the embryo stage, and 20% per 1000 r. for death at any stage between the zygote and the adult. At higher doses of X-rays both rates increase. Over the whole dose range, therefore, the doseaction curve does not fit a single-hit type of action, though this is approximated at low doses.