An analytical approach to the induction of translocations in the spermatogonia of the mouse

Estimate of the Biological Dose in Hadrontherapy Using GATE

For the evaluation of the biological effects, Monte Carlo toolkits were used to provide an RBE-weighted dose using databases of survival fraction coefficients predicted through biophysical models. Biophysics models, such as the mMKM and NanOx models, have previously been developed to estimate a biological dose. Using the mMKM model, we calculated the saturation corrected dose mean specific energy z1D* (Gy) and the dose at 10% D10 for human salivary gland (HSG) cells using Monte Carlo Track Structure codes LPCHEM and Geant4-DNA, and compared these with data from the literature for monoenergetic ions. These two models were used to create databases of survival fraction coefficients for several ion types (hydrogen, carbon, helium and oxygen) and for energies ranging from 0.1 to 400 MeV/n. We calculated α values as a function of LET with the mMKM and the NanOx models, and compared these with the literature. In order to estimate the biological dose for SOBPs, these databases were used with a Monte Carlo toolkit. We considered GATE, an open-source software based on the GEANT4 Monte Carlo toolkit. We implemented a tool, the BioDoseActor, in GATE, using the mMKM and NanOx databases of cell survival predictions as input, to estimate, at a voxel scale, biological outcomes when treating a patient. We modeled the HIBMC 320 MeV/u carbon-ion beam line. We then tested the BioDoseActor for the estimation of biological dose, the relative biological effectiveness (RBE) and the cell survival fraction for the irradiation of the HSG cell line. We then tested the implementation for the prediction of cell survival fraction, RBE and biological dose for the HIBMC 320 MeV/u carbon-ion beamline. For the cell survival fraction, we obtained satisfying results. Concerning the prediction of the biological dose, a 10% relative difference between mMKM and NanOx was reported.

Delayed manifestation and transmission bias of de novo chromosome mutations: their relevance for radiation health effect

The origin and transmission of de novo chromosome mutations were reviewed on the basis of our chromosome studies in retinoblastoma patients and male infertility. In a series of 264 sporadic retinoblastoma families, gross chromosome rearrangements involving the RB1 locus were identified in 23 cases (8.7%), of which 16 were non-mosaic and 7 were mosaic mutations. The newly formed chromosome mutations, whether they were non-mosaic or mosaic, had a strong bias towards paternally derived chromosome, indicating that they shared a common mechanism where a pre-mutational event or instability is carried over to zygote by sperm and manifested as gross chromosome mutation at the early stages of development. The de novo chromosome mutations are preferentially transmitted through female carriers. This transmission bias is consistent with the finding of higher frequencies of translocation carriers in infertile men (7.69% versus 0.27% in general populations) in whom meiotic progression is severely suppressed, possibly through activation of meiotic checkpoints. Such a meiotic surveillance mechanism may minimize the spreading of newly-arisen chromosome mutations in populations. A quantitative model of meiotic surveillance mechanism is proposed and successfully applied to the published data on ;humped' dose-response curves for radiation-induced spermatogonial reciprocal translocations in several mammalian species.

Human Fetuses do not Register Chromosome Damage Inflicted by Radiation Exposure in Lymphoid Precursor Cells except for a Small but Significant Effect at Low Doses

Human fetuses are thought to be highly sensitive to radiation exposure because diagnostic low-dose X rays have been suggested to increase the risk of childhood leukemia. However, animal studies generally have not demonstrated a high radiosensitivity of fetuses, and the underlying causes for the discrepancy remain unidentified. We examined atomic bomb survivors exposed in utero for translocation frequencies in blood lymphocytes at 40 years of age. Contrary to our expectation of a greater radiosensitivity in fetuses than in adults, the frequency did not increase with dose except for a small increase (less than 1%) at doses below 0.1 Sv, which was statistically significant. We interpret the results as indicating that fetal lymphoid precursor cells comprise two subpopulations. One is small in number, sensitive to the induction of both translocations and cell killing, but rapidly diminishing above 50 mSv. The other is the major fraction but is insensitive to registering damage expressed as chromosome aberrations. Our results provide a biological basis for resolving the long-standing controversy that a substantial risk of childhood leukemia is implicated in human fetuses exposed to low-dose X rays whereas animal studies involving mainly high-dose exposures generally do not confirm it.

A multivariate approach to the association pattern of reciprocal translocations induced by chemicals and ionizing radiation in mouse germ cells

The degree of similarity between chemical and physical agents in their capacity to induce reciprocal translocations was analyzed by means of multivariate analysis techniques. The effect of three different doses of gamma rays, four doses of X-rays and different doses of adriamycin, mitomycin C, thio-tepa and bleomycin was analyzed. Data were arranged in a basic matrix by two methods: cluster analysis and ordination. Two main groups were found, one including doses of 9 and 10 Gy and the other including the remaining lower doses of ionizing radiation and the other chemicals. Various subgroups were found within the second group. Accordingly, using presence/absence data there was not a specific pattern of chromosomal damage induction for physical and chemical agents. The increase in the frequencies of reciprocal translocation observed with 9 and 10 Gy was due to an increase in the kind of multivalent configurations. This variability could be dose dependent. Likewise, the similarity observed in the second group between the chemicals and the lower doses of ionizing radiation could also be dose dependent.

The induction of chromosomal damage and cell killing in mouse spermatogonial stem cells following combined treatments with hydroxyurea, 3-aminobenzamide and X-rays

To analyze in more detail the relation between the sensitivity of spermatogonial stem cells to killing and the induction of genetic damage, mature male mice received combined treatments with hydroxyurea (HU), 3-amino-benzamide (3-AB) and X-rays. Stem cell killing was determined using the repopulation index method and translocations were studied via spermatocyte analysis. HU was administered at 16 or at 48 h before further treatment in order to create stem cell populations with different sensitivities in which the translocation induction and stem cell killing could be studied and compared. The sensitivities for cell death and genetic damage appeared to be strongly correlated: at 16 h after HU significantly higher values were found than at 48 h or in controls without HU pretreatment. By using 3-AB in the treatment schedules we were able to investigate whether the sensitization of stem cells towards cell death and genetic damage is the outcome of a radiation- or drug-induced G1 delay. The effect of 3-AB was most pronounced at 16 h after HU. This confirms that at this interval a large fraction of stem cells is in G1. Our data therefore indicate that all treatments that induce an enrichment of G1 cells also result in a sensitization of stem cells to cell killing or the induction of mutagenic damage.

Enhanced specific-locus mutation response of 101/H male mice to single, acute X-irradiation

The specific-locus mutation yield from 101/H mice following single, acute 6 Gy spermatogonial X-irradiation was significantly higher than both a concurrent C3H/HeH x 101/H F1 hybrid control and historical data obtained with mice of equivalent genotype. There is therefore discord with the reduced translocation response to single X-ray doses previously identified in this strain. By contrast, the mutation yield following a 24-h interval 3 + 3 Gy fractionated X-ray dose was not significantly different from that of its concurrent hybrid control, nor from results obtained by others with mice of the equivalent or different genotypes. Here there is no discord with the translocation response obtained with a 1 + 5 Gy 24-h interval fractionated regime. Appraisal of comparable specific-locus and translocation data indicates that the differing results obtained with the two genetic end-points are not without precedence. This, together with the observation that the responses for cytologically visible deletions and specific-locus mutations are similar, suggests that the latter two events predominantly derive from one-hit events, with translocations deriving from two-hit events and that the probabilities of induction of each type of lesion vary according to the organisation of the nucleus in different phases of the cell cycle.

The radiosensitivity of spermatogonial stem cells in C3H/101 F1 hybrid mice

The radiosensitivity of spermatogonial stem cells of C3H/HeH x 101/H F1 hybrid mice was determined by counting undifferentiated spermatogonia at 10 days after X-irradiation. During the spermatogenic cycle, differences in radiosensitivity were found, which were correlated with the proliferative activity of the spermatogonial stem cells. In stage VIIirr, during quiescence, the spermatogonial stem cells were most radiosensitive with a D0 of 1.4 Gy. In stages XIirr-Virr, when the cells were proliferatively active, the D0 was about 2.6 Gy. Based on the D0 values for sensitive and resistant spermatogonia and on the D0 for the total population, a ratio of 45:55% of sensitive to resistant spermatogonial stem cells was estimated for cell killing. When the present data were compared with data on translocation induction obtained in mice of the same genotype, a close fit was obtained when the translocation yield (Y; in % abnormal cells) after a radiation dose D was described by Y = e tau D, with tau = 1 for the sensitive and tau = 0.1 for the resistant spermatogonial stem cells, with a maximal e tau D of 100.

A quantitative study of spermatogonial multiplication and stem cell renewal in the C3H/101 F1 hybrid mouse

In whole mounts of seminiferous tubules of C3H/101 F1 hybrid mice, spermatogonia were counted in various stages of the epithelial cycle. Furthermore, the total number of Sertoli cells per testis was estimated using the disector method. Subsequently, estimates were made of the total numbers of the different spermatogonial cell populations per testis. The results of the cell counts indicate that the undifferentiated spermatogonia are actively proliferating from stage XI until stage IV. Three divisions of the undifferentiated spermatogonia are needed to obtain the number of A1 plus undifferentiated spermatogonia produced each epithelial cycle. Around stage VIII almost two-thirds of the Apr and all of the Aal spermatogonia differentiate into A1 spermatogonia. It was estimated that there are 2.5 x 10(6) differentiating spermatogonia and 3.3 x 10(5) undifferentiated spermatogonia per testis. There are about 35,000 stem cells per testis, constituting about 0.03% of all germ cells in the testis. It is concluded that the undifferentiated spermatogonia, including the stem cells, actively proliferate during about 50% of the epithelial cycle.

X-ray induced translocations in premeiotic germ cells of monkeys

The induction of reciprocal translocations by various X-ray exposures was studied in spermatogonial stem cells of rhesus monkeys (Macaca mulatta) and stump-tailed macaques (Macaca arctoides) by means of spermatocyte analysis many cell generations after irradiation. The yields of translocations recovered from irradiated stump-tailed macaques were lower than those observed in rhesus monkeys and represent in fact the lowest induction rates per Gy ever recorded for experimental mammals. In the rhesus monkey a humped dose-effect relationship was found with (a) a homogeneous response with (pseudo-)linear kinetics below 1 Gy, (b) much more variability at higher doses, and (c) no induction at all at doses of 4 Gy and above. It is suggested that the post-irradiation proliferation differentiation pattern of surviving rhesus monkey spermatogonial stem cells i mainly responsible for these characteristics of the dose-response curve.

The relationship between induced reciprocal translocations and cell killing of rhesus monkey spermatogonial stem cells after combined treatments with follicle-stimulating hormone and X-rays

The induction of reciprocal translocations in spermatogonial stem cells of monkeys (rhesus and crab-eating), visualized in dividing primary spermatocytes, was studied after combined treatments with follicle-stimulating hormone (FSH, 54 IU/kg/week) and X-rays (1 Gy). No clear differences in the frequencies of induced translocations between FSH-pretreated and non-pretreated animals were recorded. Comparison of these translocation data with studies on cell killing in the same monkeys shows that the ratio between the probabilities that radiation-induced basic lesions kill a cell or produce translocations (the p/c ratio) is of the same order of magnitude as that observed for the mouse. Consequently the well documented differences in radiation response between the rhesus monkey and the mouse cannot be explained by differences in the p/c ratio. It is concluded that differences in multiplication-differentiation patterns of surviving stem-cell spermatogonia after irradiation are probably responsible for the observed differences between mice and rhesus monkeys.

The effect of sampling time on radiation-induced translocation yield in spermatogonial stem cells of male mice, differing in chromosomal constitution and sexual activity

We have investigated the frequency of reciprocal translocations in the first differentiating spermatogonia entering the first meiotic division after 2 x 2.5 Gy X-rays, given 24 h apart, as well as the development of this parameter in later stem-cell generations by studying multivalent configurations at the first meiotic division. Diakinesis-metaphase I cells were found for the first time between 30 and 40 days after irradiation. Subsequently, meiotic stages were sampled at 120, 180 and 280 days post irradiation. From day 40 post irradiation on, half of the males were allowed to impregnate females which enabled us to estimate the length of the post-irradiation sterile period, the development of litter size and the possible effect of sexual activity on the development of reciprocal translocation-containing stem cells. Half of the males were karyologically normal, the other half were homozygous for a reciprocal translocation (T/T) that affects testis weight and about halves sperm production. Irrespective of male karyotype, the first meiocytes had an induced translocation frequency of 9.00 +/- 2.56% (n = 8 males), followed by frequencies of 20.70 +/- 4.87% (n = 15) at 180 days and 20.20 +/- 4.30% (n = 20) at 280 days (males with and without mating behavior showing no difference). At 120 days post irradiation, +/+ males had a frequency of 14.59 +/- 2.97% irrespective of sexual activity. T/T males (120 days post irradiation) that had mated showed a frequency of 18.63 +/- 0.85% (n = 4) compared with 13.64 +/- 2.36% (n = 7) for those that had not. The observed rise of multivalent-carrying spermatocytes in time was highly significant. Notwithstanding the differences in testis weight and epididymal sperm count between the karyotypes, fertile matings occurred on average 72 days after irradiation, though with relatively wide margins. For the T/T karyotype, the first litter was statistically smaller than the subsequent litters. At 78 days post irradiation, testis weights were back in the subnormal range for both karyotypes and hardly improved in time. Restoration of fertility thus coincided with the period just prior to the return to subnormal testis weights. The first diakinesis-metaphase I cells precede those that are numerous enough to accomplish 'return to fertility' by about 2 weeks. Thus differentiation of stem-cell spermatogonia already follows a few days after irradiation. A pattern of spermatogonial cell divisions compatible with 'return to fertility' is only established some 2 weeks later.

Dose-effect relationship for X-ray-induced reciprocal translocations in mouse spermatogonia following pretreatment with 3-aminobenzamide

The influence of 3-aminobenzamide (3-AB) pretreatment on the dose-response relationship for radiation-induced reciprocal translocations in mouse spermatogonial stem cells was studied. The results show that at doses of 3-10 Gy of X-rays the frequencies of translocations were higher in 3-AB-pretreated animals as compared to animals that received X-rays only. The 3-AB pretreatment was not effective at dose levels of 1 and 2 Gy. The shape of the dose-effect curve was similar to that obtained without 3-AB pretreatment, i.e., a humped curve, but the initial slope was clearly steeper and the position of the peak was shifted from 7 to 9 Gy. The effects observed can be explained by a 3-AB-mediated sensitization of normally radioresistant stem cells that are at the stage of stimulation to enter the mitotic cycle, thus increasing the population of radiosensitive spermatogonial stem cells.

The relation between induced reciprocal translocations and cell killing of mouse spermatogonial stem cells after combined treatments with hydroxyurea and X-rays

The induction of reciprocal translocations in mouse spermatogonial stem cells, visualised in dividing primary spermatocytes, was studied after combined treatments with hydroxyurea (250 and 500 mg/kg) and X-rays (6, 8 and 9 Gy). The time intervals between the 2 treatments were 16 h (leading to extremely high cell killing) and 48 h (giving rise to less killing than irradiation alone). Comparison of the observed frequencies of translocations with reported data on stem cell killing (de Ruiter-Bootsma and Davids, 1981) show that the ratio between the probabilities that a radiation-induced basic lesion kills a cell or produces a translocation, theoretically calculated by Leenhouts and Chadwick (1981) to be about 10, can indeed be confirmed experimentally.

Induction of specific locus mutations in mouse spermatogonial stem cells by combined chemical X-ray treatments

Data that demonstrate how the biology of spermatogenesis plays an important role in determining the yield of genetic damage from ionizing radiation are briefly reviewed. It is suggested that for valid extrapolations of data from mouse mutation experiments to man detailed knowledge of the spermatogonial stem cell systems in the two species is required. Two new sets of mouse specific mutation data are presented. (1) When a 2 mg/kg dose of triethylenemelamine (TEM) was used as a conditioning dose and followed 24 h later by 6 Gy X-rays, the mutation yield from spermatogonial stem cells was over twice as high (30.20 X 10(-5)/locus/gamete) as that when the X-ray dose was given alone (13.75 X 10(-5)/locus/gamete). No such effect was found when the TEM was given only 3 h prior to the X-irradiation. Since TEM at the dose used is inefficient at inducing specific-locus mutations, an augmentation of the X-ray response is indicated. It has therefore been concluded that the augmented mutation responses obtained with equal 24 h X-ray fractionations at high doses are attributable to mutation induction by the second dose. The responsive cells would be the formerly resistant component of the stem cell population that had survived the TEM treatment and that had been 'triggered' into a radiosensitive phase by the population depletion. (2) When 2 doses of 500 mg/kg hydroxyurea (HU) were given 3 h apart 3 h prior to 6 Gy X-rays to reduce the numbers of stem cells in the S and G2 phases of the cell cycle exposed to the radiation, the mutation responses was greatly enhanced to a level that is the highest yet recorded per unit X-ray dose (7.10 X 10(-5)/locus/gamete/Gy). No such effect was obtained when the intervals between the HU and X-ray treatments were either shorter (less than 0.5 h) or longer (24 h). It was concluded that X-ray-induced specific-locus mutations derive principally from stem cells in the G1 phase of the cell cycle. The reasons why the X-ray-induced mutation-yields from repopulating stem cells (with a short cell cycle and, hence, short G1 phase) are similar to those from undamaged stem cell populations, in contrast to translocation yields, therefore remains unresolved.

Dose-response relationship for translocation induction in spermatogonia of the crab-eating monkey (Macaca fascicularis) by chronic gamma-ray-irradiation

The induction of reciprocal translocations in spermatogonia of the crab-eating monkey (Macaca fascicularis) by chronic gamma-irradiation (1.8 x 10(-5) Gy/min, about 0.024 Gy/22 h/day) was examined. The frequencies of translocation per cell were 0.15% at 0.3 Gy, 0.27% at 1.0 Gy and 0.33% at 1.5 Gy. The dose-response relationship for translocation yield was a linear one with a regression coefficient (b) of 0.16 x 10(-2). When the slope (b) of the regression line was compared with that at a high dose rate (0.25 Gy/min, b = 1.79 x 10(-2), it was clear that the induction rate of translocations after chronic gamma-irradiation was only about one-tenth of that after high-dose-rate irradiation. Thus, there was evidence for a pronounced dose-rate effect in the crab-eating monkey.

Genetic effects of combined chemical-X-ray treatments in male mouse germ cells

Several studies have shown that the yield of genetic damage induced by radiation in male mouse germ cells can be modified by chemical treatments. Pre-treatments with radio-protecting agents have given contradictory results but this appears to be largely attributable to the different germ cell stages tested and dependent upon the level of radiation damage induced. Pre-treatments which enhance the yield of genetic damage have been reported although, as yet, no tests have been conducted with radio-sensitizers. Another form of interaction between chemicals and radiation is specifically found with spermatogonial stem cells. Chemicals that kill cells can, by population depletion, substantially and predictably modify the genetic response to subsequent radiation exposure over a period of several days, or even weeks. Enhancement and reduction in the genetic yield can be attained, dependent upon the interval between treatments, with the modification also varying with the type of genetic damage scored. Post-treatment with one chemical has been shown to reduce the genetic response to radiation exposure.

Reciprocal translocations in germ cells of male mice receiving external gamma-irradiation

Data reported in the literature up to 1985 on reciprocal translocation induction in male mouse germ cells by external gamma-ray doses ranging from 0.5 to 6.0 Gy delivered at fixed dose rates were analyzed. On the assumption of a non-threshold linear dose response, zero effect at zero dose, and a center of distribution lying on an approximately straight line, calculations were made of linear regression coefficients. These coefficients (b), as a function of the dose rate (P), were well fitted by two straight lines: b = (3.15 +/- 0.59 log P) X 10(-6) for dose rates from 0.01 to 0.1 mGy/min; and b = (7.52 +/- 3.86 log P) X 10(-6) for dose rates ranging from 0.06 to 1.2 X 10(3) mGy/min. The intersection point of these two lines determined the so-called threshold level of the dose rate, namely, 4.6 X 10(-2) mGy/min, at which the effectiveness of external gamma-irradiation is not expected to exceed 2.36 X 10(-6)/mGy. In addition, experiments were undertaken in which yields were recorded of reciprocal translocations in germ cells of male mice exposed to 0.9 Gy of gamma-radiation at dose rates ranging from 6.14 X 10(-3) to 6.14 X 10(2) mGy/min (6 levels); comparisons were made with data published up to 1985 from similar studies using other fixed doses. To do this, translocation yields were expressed as relative yields (F) and their relationship to the dose rate (P) for the individual fixed doses was represented by an equation of the type: F = alpha + beta log P. For most of the equations, the regression coefficients were in good agreement and a single relationship was obtained to represent them. From the analysis performed it follows that, within the 0.6-6.0 Gy dose range, the pattern of the F vs. P relationship is unaffected by the dose. This supports the initial assumption that for the dose range up to 6.0 Gy the dose response for the reciprocal translocation yield is a non-threshold straight-line relationship.

Enhanced spermatogonial stem cell killing and reduced translocation yield from X-irradiated 101/H mice

The spermatogonial stem cells of 101/H mice have been found to be more sensitive to killing by acute X-ray doses than those of the "standard" C3H/HeH X 101/H F1 hybrid. Duration of the sterile period was longer throughout the 0.5-8.0-Gy dose range tested and "recovered" testis weights, taken after recovery of fertility, were more severely reduced. The shapes of the sterile period dose-response curves were similar, but with the 101/H mice the plateau occurred at 3-5 Gy, rather than at 6 Gy. An equivalent observation was made with the testis weight data. The translocation dose-response curve was bell-shaped, as previously found with the hybrid, but yields were lower at all but the lowest doses. Notably, peak yields occurred at 3-5 Gy, rather than at 6 Gy. The altered stem cell killing and genetic responses may be explained either by a higher proportion of radiosensitive cells in the heterogeneous stem cell population or by a higher ratio of cell killing to recoverable chromosome damage which might imply a reduced repair capacity. The latter finds some support in other data. The pattern of genetic response obtained when an X-ray dose was given in two fractions at various intervals was similar in 101/H and the hybrid mice, suggesting that their kinetics of stem cell repopulation following depletion differ little.

Dose-effect relationship for X-ray-induced translocations in spermatogonia of normal and T70H translocation heterozygous mice

The induction of reciprocal translocations in stem cell spermatogonia was studied in normal mice and T70H translocation heterozygotes using spermatocyte analysis many cell generations after irradiation. Dose-response relationships were constructed employing acute X-ray exposures of 1-10 Gy. The obtained results confirmed our earlier observations that T70H heterozygous mice were overall less sensitive to the induction of translocations compared to normals. The shape of the dose-response curve for T70H heterozygotes was also clearly different from normal mice. No simple correlations between cell killing, measured as testis weight loss, and observed frequencies of chromosomal anomalies could be established. In general, selective elimination of translocation carrying stem cells of T70H heterozygotes seem to be mainly responsible for the differences in induction pattern between the two types of mice.

X-ray-induced translocations in marmoset (Callithrix jacchus) stem-cell spermatogonia

The induction of reciprocal translocations in spermatogonial stem cells of marmosets (Callithrix jacchus) was studied after irradiation with different doses of X-rays (50, 100 and 200 rad) via spermatocyte analysis many cell generations later. The obtained results show a dose-effect relationship with clear saturation effects at 200 rad. The recorded frequencies of translocations were much lower than those reported for closely related marmosets (Saguinus fuscicollis and Saguinus oepidus). Possible reasons for this difference are discussed.

Reproductive and genetic effects of continuous prenatal irradiation in the pig

The stem germ cells of the prenatal pig are highly vulnerable to the cytotoxic effects of ionizing irradiation. This study was conducted to determine whether sensitivity to killing was also marked by a sensitivity to mutation and how prenatal depletion of the germ-cell population affects reproductive performance. Germ-cell populations were reduced by continuously irradiating sows at dose rates of either 0.25 or 1.0 rad/day for the first 108 days of gestation. The prenatally irradiated boars were tested for sperm-producing ability, sperm abnormalities, dominant lethality, reciprocal translocations, and fertility. Prenatally irradiated females were allowed to bear and nurture one litter, then tested for dominant lethality in a second litter; germ cell survival and follicular development were assessed in their serially sectioned ovaries. Sperm production was not significantly affected in the 0.25-rad boars, but boars irradiated with 1.0 rad per day produced sperm at only 17% of the control level. Incidence of defective sperm was 4.9% and 11.1% in the 0.25 and 1.0 groups, respectively. Four of the 1.0-rad boars were infertile, but prenatal irradiation apparently caused neither dominant lethality nor reciprocal translocations in fertile males. Number of oocytes was reduced to 66 +/- 7% of control in the 0.25-rad gilts, but reproductive performance was unaffected and no dominant lethality was observed. Only 7 +/- 1% of the oocytes survived in the 1.0-rad group. Reproductive performance was normal for the first litter, but four of the 23 sows tested were infertile at the second litter and a significant incidence of dominant lethality was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for the re-establishment of a heterogeneity in radiosensitivity among spermatogonial stem cells repopulating the mouse testis following depletion by X-rays

Earlier studies have shown that the spermatogonial stem cells of the mouse testis recovering from previous radiation or chemical mutagen exposure give subnormal yields of genetic damage with subsequent X-irradiation. This response has been investigated further: (a) with a high, 9-Gy X-ray dose given 4, 12 or 21 days after a 1-Gy conditioning dose (Expt. 1), and (b) with a 1 + 7-Gy, 24-h fractionation regime given 4 or 14 days after a 1-Gy conditioning dose (Expt. 2). In Expt. 1 the 1 + 9-Gy, 4-day interval regime gave a very low response, lower than obtained previously with an equivalent 1 + 5-Gy treatment. This suggests that a heterogeneity in radiosensitivity, such as exists in unirradiated stem cell populations and absent 24-48 h after radiation depletion, is quickly re-established among the stem cells repopulating the testis. By contrast, the 1 + 7-Gy, 24-h fractionation when given 4 days after the 1-Gy conditioning dose (Expt. 2) gave a very high yield of genetic damage, almost as high as that given by the fractionated (1 + 7 Gy) dose applied to previously unirradiated stem cells. This suggests that the newly established heterogeneity is removed by the second 1-Gy conditioning dose. With longer intervals between treatments, genetic yields consistent with additivity were obtained in Expt. 1; less clear results were obtained Expt. 2. Comparison with earlier data generally suggested that the duration of the repopulating period is dose-dependent. In a third experiment evidence was obtained that genetic damage induced by X-irradiation can be reduced by a subsequent treatment with triethylenemelamine (TEM) during the repopulating phase. This confirmed an earlier finding. Such an interaction could not be demonstrated with two X-ray treatments. An explanation for the X-ray/TEM interaction is offered.

Effects of unequally fractionated X-ray exposures on the induction of chromosomal rearrangements in mouse spermatogonia

The induction of reciprocal translocations in mouse stem-cell spermatogonia was determined following different unequally fractionated X-ray exposures with 24 h between the fractions. The results indicate that quite variable levels of chromosomal damage can be induced using the same exposure schemes. This variation does not seem to be correlated with radiation set-up or mouse strain. In general, with higher conditioning exposures from 12.5 to 300 rad (or R), higher frequencies of translocations were produced using a larger second challenging exposure of 700-900 rad (or R). The increase in yields of aberrations was more or less paralleled by a shift from a strong deviation from a Poisson fit of the number of translocations per spermatocyte, to a good fit, suggesting a transition from the original heterogeneity of the stem cell population to a radiation induced, more homogeneous stage. Earlier observations concerning a threshold dose for sensitization (van Buul and L eonard , Mutation Res., 70 (1980) 95-101) could not be confirmed.

Stem-spermatogonial survival and incidence of reciprocal translocations in the gamma-irradiated boar

To assess the effects of gamma-radiation on stem-cell survival and incidence of reciprocal translocations, boar testes were irradiated with 100, 200, or 400 rad. Stem-cell survival was markedly affected by 100 rad (51% of control) and reduced to 34% of control by 400 rad. Production of differentiating spermatogonia was all but completely interrupted by 200 rad and spermatogonial renewal was incomplete at 12 weeks. From the state of the seminiferous epithelium at 12 weeks, estimates of the percentage of permanent impairment of sperm-producing capacity ranged from 20 +/- 6 (100 rad) to 67 +/- 10 (400 rad). Incidence of translocations peaked at 200 rad and the number occurring at 100 and 400 rad was similar. Kinetics of porcine spermatogonial renewal differs considerably from those of the rodent and, relative to the rodent, this may account for the boar's higher sensitivity to stem-cell killing and lower sensitivity to translocations.

X-ray-induced reciprocal translocations in stem-cell spermatogonia of the rhesus monkey: dose and fractionation responses

Rhesus monkeys received total body or local testes X-irradiation with unfractionated (50, 300, 400, 800 and 850 rad) or fractionated (200 + 200 rad with 24-h interval) exposures. At different times after irradiation, chromosomal analysis was made of C-banded dividing spermatocytes. The observed frequencies of translocation configurations confirmed earlier results about the low induction rate of reciprocal translocations in stem-cell spermatogonia of the rhesus monkey. The absence of any translocation induction at doses of 400 rad and higher indicates an extreme insensitivity of surviving radiation-resistant stem cells for the induction of this type of genetic damage. The frequency of translocations following a fractionated exposure to 400 rad, which is above the peak yield for single exposures, was clearly higher than that obtained when the same dose was applied as a single exposure (0.71 versus 0%), but significantly lower than expected on the basis of additivity of the two fractions (0.71% versus 1.98%).