Studies on the induction of translocations in mouse spermatogonia. IV. Effects of acute gamma-irradiation

The rate of induction of reciprocal translocations by 56–816 R exposures of mouse spermatogonia to acute γ-irradiation (95 R/min) was determined by cytological examination of descendant spermatocytes. The dose-response relationship did not differ significantly from linearity and had a regression coefficient of 1.8·10⁻⁴ per R with respect to translocations per spermatocyte. Further analysis at exposures below 816 R (considered less likely to produce distortion) showed that the quadratic regression of best fit had too small a square-law component to account for the very low frequency of translocations obtained after chronic γ-exposures in a previous experiment. The possibility is discussed that there is some extra factor, besides the diminution of the square-law component, which operates to reduce the yield after protracted exposures.     

Increased velocity and induction of chemotactic response in mouse spermatozoa by follicular and oviductal fluids.

The dynamic parameters of mouse sperm cells exposed to follicular and oviductal fluids were assessed. Spermatozoa were tracked on a chemotactic Zigmond chamber and recorded using a videomicroscopy system. The results were evaluated with computer-supported image analysis. Follicular fluid at a dilution of 10(-4) markedly increased the proportion of spermatozoa with high velocity, and stimulated chemotactic behaviour. The highest velocities were observed in sperm cells exposed to oviductal fluid, and a greater proportion of these cells had high velocity compared with those exposed to follicular fluid. Chemotaxis was induced in spermatozoa exposed to oviductal fluid at dilutions of 10(-3) and 10(-5). These results suggest the presence of temporal subpopulations of responsive spermatozoa, considering the distance travelled towards both follicular and oviductal fluids and the proportion of sperm cells migrating towards the gradient in the highest distance ranges. This is the first report on the effect of isolated follicular and oviductal fluids on dynamic parameters and chemotaxis of mouse spermatozoa. The findings support previous work showing that the motility and directionality of mouse sperm cells is increased by factors in the microenvironment of the egg. Although the significance of these factors in vivo is unknown, it is possible that there is a relay mechanism involving sequential activity of both oviductal and follicular fluids to direct the male gametes towards the egg.     

X-ray induction of autosomal translocations in spermatozoa of Drosophila melanogaster and maternal effects of X.Y-chromosomes.

Wild-type ORK Drosophila melanogaster males were given an exposure of 3000 R X-radiation. Mature sperm were then sampled by mating to X.Y/X.Y, X.Y/X, or X/X females that carried markers on the second and third chromosomes for the detection of induced autosomal translocations. Two pairs of maternal stocks were used and heterozygous X.Y/X females were obtained by making both reciprocal crosses. The highest frequencies of induced translocations were obtained with X/X females. In one series these frequencies are higher than those obtained with either X.Y/X or X.Y/X.Y females. In the other series a uniform frequency of translocations was obtained with all types of female, except for one of the two types of heterozygous female, which gave lower frequencies. The experiments have provided data which show that the addition of Y-chromosomes to the maternal genome does not have a specific effect on the recovery of induced paternal autosomal translocations. Maternal Y-chromosomes increased the proportions of fertile F1 males, this effect being consistent in direction but varying in degree.     

The induction of reciprocal translocations in mouse germ cells by chemicals and ionizing radiations. I. Dose-response relationships and combined effects of bleomycin with thio-tepa and gamma-rays

The effect of bleomycin (BLM) on mouse stem cells has been analysed using the spermatocyte test. The dose-response relationships after treatment with doses of 20, 40 and 60 mg/kg of the compound as well as the combined effect of BLM and gamma-rays and BLM and thio-tepa (TT) were studied. A positive, significant correlation between the dose of BLM and the frequency of translocations was found. Two different responses were found when the yields of translocations induced after combined treatments, separated by a lapse of 24 h, were compared with the sum of translocation frequencies induced after the corresponding single treatments: (1) Potentiation, in the treatments with 1 Gy plus 9 Gy and 60 mg/kg of BLM plus 9 Gy; (2) additivity, in the treatments with 60 mg/kg of BLM plus 1 Gy, 1 Gy plus 60 mg/kg of BLM, and 0.2 mg of TT plus 60 mg/kg of BLM. In mice irradiated with 1 Gy plus 9 Gy and mice treated with 60 mg/kg of BLM plus 9 Gy, similar translocation yields were found. The potentiating effect of BLM is similar to that obtained with non-radiomimetic compounds such as triethylenemelamine, cyclophosphamide and adriamycin. These results are discussed taking into account the hypothesis of germ cell selection, and the dose of radiation employed.     

Activation of mouse lymphocytes inhibits induction of rapid cell death by x-irradiation

A distinctive property of the resting lymphocyte is its ability to die rapidly in interphase after x-irradiation. Suspensions of thymocytes and peripheral lymphocytes from BALB/c mice were irradiated with doses ranging from 10 to 10,000 rad (0.1 to 100 Grays), and their viability was measured by eosin dye exclusion at intervals through 3 days of culture. After an initial latent period of a few hours, viability declined exponentially in a dose-dependent fashion. Doses as low as 20 rad caused some lymphocytes to die rapidly. After 1000 rad, 90% of the cells became nonviable in 15 to 20 hr and 99% in 25 to 35 hr. Peripheral lymphocytes showed a somewhat earlier loss of viability than did thymocytes, and were killed especially rapidly by 10,000 rad. Enriched T cells and B cells were killed by irradiation at equal rates, and medullary thymocytes were killed at the same rate as the whole thymocyte population. In contrast with resting cells, T and B lymphocytes activated by mitogens were not subject to such rapid induction of cell death. Irradiation with 1000 rad reduced the viability of activated cells by only 50% at a time when less than 1% of nonstimulated lymphocytes remained alive. Similarly, cloned lines of antigen-specific helper and cytotoxic T cells showed only a delayed and slow loss of viability after receiving 1000 rad. The state of activation can therefore be a significant determinant of the immunologic consequences of irradiation.     

Analysis of translocations observed in three different populations. I. Reciprocal translocations

A sample of 437 reciprocal translocations was classified into three groups according to their method of ascertainment (Group I = couples with repeated abortions; Group II = karyotypically unbalanced carriers; Group III = balanced translocation heterozygotes). Statistical analysis showed that the distributions of chromosome breaks observed in the three groups could not be accounted for by chromosome arm length alone. In couples with repeated abortions, an excess of breaks in 7p, 17p, and 22q was found, whereas in the balanced translocation heterozygotes an excess of breaks was found only in 11q. An excess of breaks was found in arms 9p, 14p, 18p, 18q, 21q, and 22q in karyotypically unbalanced probands. A significant decrease of breaks in the medial chromosome regions was accompanied by a concomitant increase in the terminal regions in all groups. The three groups demonstrated different distributions of chromosome arm involvement in the observed translocations. Balanced translocation heterozygotes had the highest frequency of large (greater than the length of 4p) translocated segments and an excess in the frequency of large-large translocations, whereas karyotypically unbalanced probands had the highest frequency of small (shorter than 21q) translocations and an excess in the frequency of small-small translocations. For each type of chromosomal imbalance observed, the balanced translocation heterozygotes demonstrated the greatest potential imbalance and the karyotypically unbalanced probands the least.