The induction by X-rays of chromosome aberrations in germ cells of male guinea-pigs, golden hamsters and rabbits. I. Dose response in post-meiotic stages.

The induction by X-rays of translocations in post-meiotic germ cells of the guinea-pig, golden hamster and rabbit was studied by cytological analysis of male offspring of the irradiated animals. As reported previously for the mouse, the pattern of sensitivity to dominant lethal induction, as indicated by litter-size, was similar to that for translocation induction in both the guinea-pig and golden hamster. In both speciesspermatids were more sensitive than spermatozoa, and in the golden hamster spermatocytes gave a lower yield than spermatids. The translocation frequency among post-meiotic germ cells treated with 600 rad was higher in the rabbit than the guinea-pig, and both were above that for the golden hamster. However, for spermatozoa, species differences with respect to the recovered translocation yield appeared to depend on dose. In the hamster, the translocation frequency after 600 rad, as measured in the female offspring, was similar to that obtained in the male offspring. A small amount of data on the induction of sex-chromosome aneuploidy by 200 rad in golden hamsters suggested that the hamster might be as sensitive as the mouse.     

The induction by X-rays of chromosome aberrations in male guinea-pigs, golden hamsters and rabbits. II. Properties of translocations induced in post-meiotic stages.

Translocations induced by X-rays in post-meiotic germ cells of male guinea-pigs, golden hamsters and rabbits were studied cytologically in the F1 sons of the irradiated males. The percentage of spermatocytes displaying multivalent configurations varied with the translocation, but the average percentage appeared to depend on the species: fewer quadrivalents were observed in hamster than in guinea-pig heterozygotes and most were recorded for rabbit heterozygotes. Chain quadrivalents were more abundant than ring quadrivalents at meiosis for the guinea-pig and hamster, in contrast to the mouse. Too few translocation heterozygotes were examined to determine which meiotic configuration was the more prevalent in the rabbit. In all three species, as in the mouse, translocations were found which caused male sterility, due to partial or complete failure of spermatogenesis, although most translocations caused semi-sterility. For these semi-sterile males both the frequency and time of embryonic death in the progeny appeared to be the same as in the mouse. It is concluded that similar types of chromosome aberrations are induced by X-rays in post-meiotic germ cells of male guinea-pigs, rabbits, golden hamsters and mice.     

The induction by X-rays of chromosome aberrations in male Guinea-pigs, rabbits and golden hamsters. III. Dose-response relationship after single doses of X-rays to spermatogonia.

The induction by X-rays of translocations in spermatogonia was studied by cytological means in spermatocytes derived from them. In the rabbit and guinea-pig hump shaped dose-response curves were obtained, with a linear relationship at the low doses. The shapes of the curves were similar to those reported for the mouse, except that the maximum occurred at 600-700 rad in the mouse as opposed to 300 rad in the guinea-pig and rabbit. Unlike the guinea-pig and rabbit, the golden hamster showed a hump dose-response curve without a definite peak value and with little decrease in yield at high radiation doses. Over the low dose range 100-300 rad, the slopes of the curves of translocation yield were in the order:mouse (highest), rabbit, guinea-pig and hamster. Data on sterile periods suggested that the amount of spermatogonial killing in the rabbit and guinea-pig was as great or greater than in the mouse, and that in the golden hamster it was most severe. It is suggested that the differing shapes of the dose-response curves can be explained by a lower sensitivity to translocation induction in the test species and, also especially in the golden hamster, a greater sensitivity to cell killing. The possibility of extrapolating from these data to other species is discussed.     

The induction by X-rays of chromosome aberrations in male Guinea-pigs and golden hamsters. IV. Dose response for spermatogonia treated with fractionated doses.

The effect of dose fractionation on the induction of translocations by 400 and 600 rad X-rays in spermatogonia of guinea-pigs and hamsters was investigated cytologically. Three types of fractionation were used, dividing the dose into (a) two equal fractions 24 h apart, (b) two equal fractions 8 weeks apart, and (c) eight or twelve equal fractions of 50 rad, at intervals of one week. The two species responded similarly throughout, but gave lower translocation yields than the mouse. The effects of the first and third types of fractionation were similar to those described previously in the mouse, and suggested that a first radiation dose modifies the spermatogonial population so that its sensitivity to a dose 24 h later is altered, and that repeated radiation doses result in development of resistance to translocation induction. After 8-week fractionation the results suggested that in guinea-pigs and hamsters the spermatogonial population had not returned to normal by 8 weeks after the first dose, whereas in the mouse normal sensitivity had returned by this time. The results, reported previously, of single doses of X-rays suggest that the spermatogonial population consists of fractionated doses in the mouse suggest that the sensitive and resistant types represent different phases of the same cell type rather than two distinct types of cell. In the guinea-pig and hamster this question remains open.     

X-ray- and chemically induced germ-line mutation causing phenotypical anomalies in mice

A large and significant increase of phenotypical anomalies was observed in the progeny of ICR parent mice treated before mating with X-rays, urethane, 7,12-dimethylbenz[a]anthracene, ethylnitrosourea (ENU), and 4-nitroquinoline 1-oxide, but the increase was not significant with furylfuramide. Major types of induced anomalies were cleft palate, dwarf, open eyelid, tail anomalies, and exencephalus. Dwarf, open eyelid and tail anomalies were predominant types of viable anomalies and were inherited as if they were dominant mutations with varying expressivity or penetrance. Incidence of prenatal anomalies increased with treated doses of X-rays, urethan, or ENU for both spermatozoa and spermatogonia. Spermatogonia were less sensitive to X-rays and urethane than spermatozoa, while ENU induced a very high incidence of prenatal anomalies by the spermatogonial treatment. In contrast to the previous works with X-rays, there was a clear, almost linear increase of anomalies in the dose range from 0 to 216 rad after spermatogonial exposure. For treatment of oocytes, there was also a clear increase with doses of X-rays and urethane. Doubling doses of X-rays for prenatal anomalies were 12 rad for spermatozoa, 27 rad for spermatogonia, and 19 rad for mature oocytes. These values are similar to those for ordinary mouse mutations. However, the mean rate of prenatal anomalies per rad (1.2 X 10(-4), 6.6 X 10(-5) and 9.1 X 10(-5) for spermatozoa, spermatogonia and mature oocytes, respectively) and that for 1 micrograms/g of ENU (3.4 X 10(-4) for spermatogonia) were 4-40 times higher than that of ordinary mutation in mice, because overall phenotypical abnormalities were scored in this study. Information obtained from the work on phenotypical anomalies is valuable to assess genetic risk of radiation and chemicals, because a majority of human genetic diseases show this kind of irregular and uncertain inheritance and most of the induced anomalies are similar to those found in humans.     

Thermostability of sperm nuclei assessed by microinjection into hamster oocytes

Nuclei isolated from spermatozoa of various species (golden hamster, mouse, human, rooster, and the fish tilapia) were heated at 60 degrees-125 degrees C for 20-120 min and then microinjected into hamster oocytes to determine whether they could decondense and develop into pronuclei. Mature, mammalian sperm nuclei, which are stabilized by protamine disulfide bonds, were moderately heat resistant. For example, they remained capable of pronucleus formation even after pretreatment for 30 min at 90 degrees C. Indeed, a temperature of 125 degrees C (steam) was required to inactivate hamster sperm nuclei completely. On the other hand, nuclei of rooster and tilapia spermatozoa and those of immature hamster and mouse spermatozoa, which are not stabilized by protamine disulfide bonds, were sensitive to heating; although some of them decondensed after exposure to 90 degrees C, none formed male pronuclei. Furthermore, nuclei of mature hamster sperm became heat labile when they were pretreated with dithiothreitol to reduce their protamine disulfide bonds. These observations suggest that the thermostability shown by the nuclei of mature spermatozoa of eutherian mammals is related to disulfide cross-linking of sperm protamines.     

Induction of congenital malformations in the offspring of male mice treated with X-rays at pre-meiotic and post-meiotic stages

The induction of congenital malformations among the offspring of male mice treated with X-rays at pre-meiotic and post-meiotic stages has been studied in two experiments. Firstly, animals were exposed to varying doses (108–504 cGy) of X-rays and mated at various time intervals (1–7, 8–14, 15–21 and 64–80 days post-irradiation), so as to sample spermatozoa, spermatids and spermatogonial stem cells. In the second experiment, only treated spermatogonial stem cells were sampled. One group of males was given a single 500-cGy dose, a second group a fractionated dose (500 + 500 cGy, 24 h apart) and a third group was left unexposed.In the first experiment, induced post-implantation dominant lethality increased with dose, and was highest in week 3, in line with the known greater radiosensitivity of the early spermatid stage. Preimplantation loss also increased with dose and was highest in week 3. There was no clear induction of either pre-implantation or post-implantation loss at spermatogonial stem cell stages.There was a clear induction of congenital malformations at post-meiotic stages, the overall incidence being 2.0 ± 0.32% in the irradiated series and 0.24 ± 0.17% among the controls. The induction was statistically significant at each dose. At the two highest doses the early spermatids (15–21 days) appeared more sensitive than spermatozoa, and at this stage the incidence of malformations increased with dose. The data from Expt. 1 on the induction of malformations by irradiation of spermatogonial stages were equivocal. In contrast, Expt. 2 showed a statistically significant induction of malformations at both dose levels (2.2 ± 0.46% after 500 cGy and 3.1 ± 0.57% after 500 + 500 cGy). The relative sensitivities of male stem cells, post-neiotic stages and mature oocytes to the induction of congenital malformations were reasonably similar to their sensitivities for specific-locus mutations, except that the expected enhancing effect of the fractionation regime used was not seen.Dwarfism and exencephaly were the two most commonly observed malformations in all series.     

Difference in types of radiation-induced structural chromosome aberrations and their incidences between Chinese and Syrian hamster spermatozoa

The effects of ionizing radiations on sperm chromosomes were studied in the Chinese hamster (Crisetulus griseus) and the Syrian (golden) hamster (Mesocrisetus auratus). Testes of mature male Chinese hamsters (CH) were irradiated with X-rays (0.91, 1.82 and 3.63 Gy) and γ-rays (1.10, 2.15, 2.95 and 4.01 Gy) at a single acute dosage, whereas the irradiation was done with lower doses of X-rays (0.45, 0.91 and 1.82 Gy) and γ-rays (0.49, 0.99 and 1.98 Gy) in mature male Syrian hamsters (SH), taking the higher radiosensitivity of this species into consideration. They were mated with normal females within 6 days of exposure. Sperm-derived chromosomes were analyzed in 1125 and 1966 fertilized ova of the CH and the SH, respectively. In both species, there was no great difference in the induction of structural chromosome aberrations between X-irradiated and γ-irradiated spermatozoa. Chromosome-type aberrations were predominantly induced. The incidence of breakage-type aberrations increased linearly, and that of exchange-type aberrations linear-quadratically with increase of dosage. A species-specific difference in chromosomal radiosensitivity of spermatozoa was clear. In spite of the same radiation dosage, the incidence of chromosomally abnormal spermatozoa in the SH was about twice as high as that in the CH (e.g., 27.0% vs. 14.7% at 0.91 Gy of X-rays). The incidences of breakage-type aberrations (69–89%) were far higher than those of exchange-type aberrations (11–31%) in the SH, while the disparity of the two incidences was much smaller in the CH (46–65% vs. 35–54%). Exchange-type aberrations consisted of both chromosome-type and chromatid-type in the SH, while almost all of them were of the chromosome-type in the CH. These results suggest that the DNA-repairing capacity of oocytes is much higher in the CH than in the SH. Moreover, it seems likely that radiation-induced sperm DNA damage is repaired with both pre-replication repair (excision repair) and post-replication repair systems in SH oocytes, whereas the excision repair system operate most exclusively in CH oocytes.     

Cytogenetic effects of X-rays and fission neutrons in female mice

The induction by X-rays of chromosomal damage in oocytes was studied, while the genetic consequences of X- and neutron-induced damage in female mice were looked for by testing offspring for dominant lethality and semi-sterility. None out of 386 sons of hybrid females given 300 rad X-rays showed evidence of semi-sterility or translocation heterozygosity, but 9 out of 294 daughters were diagnosed as semi-sterile. At least 3 and probably 4 of these (1.4%) carried reciprocal translocations, 2 of which caused male sterility. Complete or partial loss of the X-chromosome may have been responsible for some of the other sermi-steriles. Examination of oocytes at metaphase-I during the first and third weeks after X-irradiation with 100 or 400 rad revealed both multivalents (some of the ring quadrivalent type) and fragments (mainly double). These were thought to arise mainly from chromatid intercchanges (both symmetrical and asymmetrical) and isochromatid intrachanges respectively. Since neither the proportion of asymmetrical interchanges nor the amount of hidden damage was known it was not thought possible to predict the magnitude of F₁ effects from metaphase-I findings. The aberration frequency in oocytes rose with dose and (at the 400 rad level only) with time after irradiation, reaching a maximum of 10% multivalents and 22% fragments in the third week after 400 rad. The frequency of univalents showed no consistent trend, but chiasma counts decreased in the first week after 400 rad. The increase in levels of chromosomal damage with dose and time after irradiation was reflected in dominant lethal frequencies after the same radiation-conception intervals and doses of 0–400 rad. Induced post-implantation lethality was over twice as high in the third week after 200–400 rad than in the first. Pre-implantation loss also greatly increased in the third week after 300 or 400 rad; this was associated with increased non-fertilization of ova. No evidence for the induction of translocations in oogonia or resting oocytes by fast neutron irradiation was obtained, although there was evidence for X-chromosomal loss after 200 rad to oocytes. The relative biological effectiveness (RBE) for fission neutrons vs. X-rays with respect to dominant lethal induction in oocytes was found to vary with dose, but seamed to be around 1 at lower levels.     

Intratubular localization of 4-ene-5 beta-reductase and 17 beta-hydroxy-dehydrogenase in immature golden hamster testis

We have reported [1,2] in immature golden hamster testis that 5 beta-reductase is localized in the seminiferous tubules, while 5a-reductase is present in the interstitial tissue and that the 17 beta-ol-dehydrogenase activity is found predominantly in the seminiferous tubules. In the present study, we show the intratubular localization of these enzymes. The left testis of golden hamster was irradiated with 2000R or 8000R of X-rays at 22 days of age. The hamsters were killed at 28 days of age. Homogenates of the left irradiated and right intact testes were incubated with [14C]-4-androstone-3,17-dione and NADPH, and enzyme activity was estimated. Both testes were also examined histologically. The X-irradiation of the testis resulted in an almost complete disappearance of germ cells with a significant decrease in testis weight, but the interstitial tissue and tubular nongerm cells including Sertoli cells remained almost unchanged. However, the activities of 5 beta-reductase and 17 beta-ol-dehydrogenase expressed as nmol formed/testis/h did not decrease at all. These results show that 5 beta-reductase is localized in the tubular nongerm cells including the Sertoli cells and 17 beta-ol-dehydrogenase is present in the tubular nongerm cells and interstitial tissue in immature golden hamster testis.     

Changes in the reciprocal position of the first polar body and oocyte chromosome set in golden hamsters

The golden hamster is an attractive model organism for studying reproductive physiology, oncology, genetics and virology. In an effort to establish experimental protocols necessary for cloning golden hamsters, we examined changes in the reciprocal position of the FPB (first polar body) and chromosome set of MII (the second meiotic metaphase) oocytes of golden hamsters. Oocytes were collected under three different conditions: (i) oocyte direct recovery from the oviduct of hormonally treated donor; (ii) oocyte recovery from the oviduct of hormonally treated donor followed by 5 h/10 h in vitro culture; and (iii) oocyte recovery from ovaries of hormonally treated donors and in vitro maturation. Then oocyte recovery was performed from the oviduct of hormonally treated donors, followed by 5 h in vitro culture with colchicine and/or CB (cytochalasin B). Denuded oocytes were stained with Hoechst 33342 and propidium iodide and evaluated under a microscope. Our results demonstrate that the change in FPB position in relation to the MII oocyte chromosome set increases with age of in vivo-matured oocytes. Cumulus cells can protect the FPB of in vitro-cultured oocytes from degeneration but do not significantly affect its repositioning, and in vitro-matured oocytes age slower. The colchicine has a stronger effect on cytoplasmic protrusions of golden hamster oocytes when compared with CB. These results define conditions for changes in FPB position relative to the MII oocyte chromosome set. Early ovulated oocytes, in vitro-matured oocytes and oocytes treated with colchicine should improve the effectiveness of the cloning procedure in golden hamsters as an animal model for human diseases.     

Measurement of neutron-induced genetic damage in mouse immature oocytes

Recent experimental evidence concerning the nature of radiosensitive targets in mouse immature (resting) oocytes has led to new experimental designs that permit measurement of radiation-induced genetic damage in these important cells. We have previously reported initial results of the detection of genetic damage in mouse immature oocytes using monoenergetic 0.43-MeV neutrons. Here we provide a full report of our data and compare the genetic sensitivity of immature oocytes with those measured by others for maturing oocytes. Until recently, all attempts to detect radiation-induced genetic damage in mouse immature oocytes had failed. This appears to have been because the radiation types and modes of dose delivery used in those studies did not sufficiently spare the hypersensitive lethality target (the plasma membrane) while at the same time deposit enough dose in DNA to produce detectable mutation. Recoil protons from 0.43-MeV neutrons produce short ionization tracks (2.6 micron mean) and can therefore deposit energy in the DNA without simultaneously traversing the plasma membrane. Using these particles, we have obtained dose-response relationships for both chromosome aberrations and dominant lethal mutations in oocytes from females irradiated 8-12 weeks earlier, when oocytes were immature. Results suggest that the intrinsic mutational sensitivity of mouse immature oocytes is not very different from that of maturing oocytes.     

Chromosome aberrations in metaphase II oocytes of Chinese hamster (Cricetulus griseus). I. The sensitivity of the pre-ovulatory phase to triaziquone

In previous investigations with triaziquone, cyclophosphamide, amethopterin and X-rays we showed that the pre-ovulatory stages of mice are sensitive to the induction of numerical and structural chromosome aberrations. In the present investigation, we studied the problem whether or not this sensitivity is restricted to mice. Two doses of triaziquone were injected intraperitoneally to Chinese hamster females at different intervals before ovulation. The ovulated oocytes were collected from the ampulla and analyzed at the metaphase II stage. After treatment with triaziquone, the frequency of both numerical and structural aberrations was significantly increased over the control values. The proportion of induced structural anomalies was higher than that of the numerical ones. Chinese hamsters were less sensitive to the induction of structural and especially numerical anomalies compared with the findings with one strain of mouse.     

Species comparisons concerning radiation-induced dominant lethals and chromosome aberrations

After X-irradiation of post-meiotic stages, male mice, guinea-pigs, rabbits and golden hamsters differed both in general sensitivity to the induction of dominant lethals, and in the relative sensitivity of the various spermatogenic stages. Guinea-pigs were the least sensitive, and hamsters had a different stage sensitivity pattern, with mature sperm the most sensitive stage.     

Down-regulation of membrana granulosa cell gap junctions is correlated with irreversible commitment to resume meiosis in golden Syrian hamster oocytes

One of the currently popular hypotheses for the regulation of meiotic resumption in mammalian oocytes proposes that the preovulatory surge of luteinizing hormone causes down-regulation of follicular gap junctions, which in turn disrupts transfer of a meiotic arrester from the somatic cells into the oocyte. The present study has investigated this hypothesis by examining the integrity of membrana granulosa cell gap junctions during the period of irreversible commitment to maturation of golden Syrian hamster oocytes in vivo. Our results have revealed a significant progressive decrease in the fractional area of cell surface occupied by gap junction membrane with increasing percentage of oocytes irreversibly committed to mature (1.946% and 0.921% fractional gap junction area at 0% and 100% oocytes irreversibly committed to mature, respectively, P less than 0.05). This net loss of membrana granulosa cell gap junctions from the cell surface was accompanied by a significant decrease in density of gap junction particles, whether they were arranged in rectilinear or non-rectilinear packing patterns. Furthermore, the number of gap junction particles per unit area of surface membrane scanned also underwent a significant progressive decrease with increasing percentage of oocytes irreversibly committed to mature. These data with the hamster are consistent with the hypothesis that down-regulation of membrana granulosa cell gap junctions may be of central importance in the regulation of gonadotropic stimulation of meiotic resumption in mammalian oocytes.     

X-ray induced mutation in Syrian hamster fetal cells

Transabdominal X-rays are a risk factor for childhood leukemia, and X-ray exposure of mouse fetuses has led to increases in both mutations and initiated tumors in offspring. However, fetal sensitivity and dose-response characteristics with regard to transplacental mutagenesis by X-rays have never been quantified. In the current experiment, pregnant Syrian hamsters at day 12 of gestation were irradiated with 300-kV X-rays. Twenty-four hours later, the fetuses were removed and their cells were allowed a 5 day expression time in culture. They were then seeded for colony formation and also for mutation selection by 6-thioguanine (6-TG). Mutation frequency was linear over the entire dose range, 10-600 R. The average induced 6-TG mutant frequency was 4.7 x 10(-7) per R. These results suggest that fetal cells are highly sensitive to induction of mutations by X-rays, and that a no-effect threshold is not likely. The 10 R dose caused a 25-fold increase in mutation frequency over the historical control, 45 x 10(-7) versus 1.8 x 10(-7), an increase per R of 2.5-fold. Increased risk of childhood cancer related to obstetrical transabdominal X-ray has also been estimated at 2.5-fold per R. Thus, our results are consistent with mutation contributing to this effect.     

Cytological analysis of partial and total X-chromosome loss induced by X-rays in oocytes of Drosophila melanogaster

With the aid of a cytological technique (analysis of metaphase chromosomes of larval cerebral ganglia) it was shown that, in experiments on X-chromosome loss induced by X-rays in oocytes of Drosophila melanogaster, one has to distinguish between partial and total chromosome loss. For this purpose a scheme has been devised allowing the detection of aberrant F₁ individuals already at the larval stage. After treatment of mature oocytes, X-chromosomal fragments of various sizes were found. On the other hand, most of the X-chromosomal fragments observed after irradiation of immature oocytes had the same size as chromosome IV (“points”). Possibly this finding is, partly at least, simulated by the combined induction of complete X loss and nondisjunction of chromosomes IV. Otherwise preferential breakage close to the X-chromosomal centromere after irradiation of immature oocytes would have to be assumed to account for the observation of “points”.

About 39% (13/33) of the losses induced in mature oocytes by 400 R were shown to be partial ones. Depending on the classification of the “points” observed after treatment of immature oocytes with 3500 R, between 7% (3/43) and 23% (10/43) of the losses were partial ones. No indication was obtained either after irradiation of mature or of immature oocytes that the loss frequencies observed for imagoes and larvae differed from each other, e.g. because of selection.

The two-track component of the dose-effect curve of X-ray-induced (total plus partial) X-chromosome loss seems to be based—completely in the mature, partly in the immature oocyte experiments—on the induction of partial losses requiring two independently produced breaks.     

Chromosome analysis of Murrah buffalo (Bubalus bubalis ) spermatozoa using zona-free hamster oocytes

An interspectific in vitro fertilization system was adopted to analyse sperm chromosomes of Murrah buffalo (Bubalus bubalis ). Superovulation was induced in mature female golden hamsters (Mesocricetus auratus ) to obtain a large number of oocytes. The zona pellucidae were digested by trypsin treatment. Zona free hamster oocytes were penetrated by buffalo spermatozoa capacitated with calcium ionophore A23187. Fertilized ova were cultured in TC 199 medium supplemented with 10% fetal calf serum (FCS). Podophyllotoxin and vinblastine were used to interrupt karyogamy and tubulin polymerization, respectively. Oocytes were fixed by modified gradual fixation air drying method. Slides were stained with 2% Giemsa for 45 min. Analyzable metaphase chromosome spreads were obtained from 22.4+/-3.8% of the penetrated oocytes. Of the 70 sexed spermatozoa, 38 were X-bearing and 32 were Y-bearing spematozoa.     

Studies on chromosome aberrations in the eggs of mice fertilized in vitro after irradiation. II. Chromosome aberrations induced in mature oocytes and fertilized eggs at the pronuclear stage following X-irradiation

Cytological analysis of the first-cleavage metaphase of eggs exposed to X-rays at the mature oocyte stage or the pronuclear stage 4 h after fertilization was performed using the in vitro fertilization technique. The frequency of chromosome aberrations in irradiated mature oocytes increased exponentially with dose, the dose-response relationship being best fitted to the linear-quadratic model. On the other hand, in eggs irradiated at the early pronuclear stage, the frequency increased linearly with dose and the dose-response relationship was best fitted to the linear model. The aberrations were mainly chromosome-type (mature oocytes: 86.0% and pronuclear stage: 88.5%) and the majority were fragments in both cases. Eggs in the early pronuclear stage were markedly more radiation-sensitive than mature oocytes. A comparison of the present results with the previous ones (Matsuda et al., 1985b) showed that the sensitivities to induction of chromosome aberrations were in the order: egg at early pronuclear stage (highest) greater than mature oocyte greater than mature sperm.     

Developing testicular microvasculature in the golden hamster, Mesocricetus auratus: a model for angiogenesis under physiological conditions.

The ultrastructure of the developing testicular microvasculature in the testes of immature (3, 5, 8, 10, 12, 16, 20, 25, 30 and 35 days old) golden hamsters was examined and compared to the testicular microvasculature of adult (3 months old) hamsters. In addition, in 16- to 35-day-old hamsters vascular permeability was studied after localization of injected horseradish peroxidase (HRP). Angiogenic processes were present in the testes of all examined immature hamsters and were most conspicuous between 8 and 25 days of age. These processes were absent in the testes of 3-month-old hamsters. On days 3 and 5, few undifferentiated blood vessels with activated endothelium were present in the interstitial spaces. Endothelial cell migration started from these 'mother vessels' and led to invasion of intertubular spaces by vascular sprouts, before vascularization of peritubular spaces occurred (after day 12). Sprouting endothelial cells were identified by the presence of a basal lamina and characterized by abundant cytoplasm and cell organelles. HRP-positive slits were seen in developing vessels, which opened to form the vascular lumen. HRP exited the vascular lumen through unspecialized endothelial contacts and micropinocytotic vesicles. By day 16, the blood-testis barrier prevented HRP from entering the seminiferous tubules beyond the basal compartment. By days 30 and 35 most testicular microvessels and at the age of 3 months all testicular microvessels were of the mature type, with narrow inactive endothelium and specialized cell contacts (including tight junctions). These results demonstrate that the postnatal vascularization of the testis in the golden hamster is a timed complex process. Due to high permeability, vascular sprouts are likely to influence the metabolic situation and thus the maturation processes of the testis. Angiogenesis in the golden hamster testis shares typical morphological features with angiogenic processes in other organs and species under various pathological and physiological conditions. We therefore conclude that the postnatal testis can be viewed as a physiological model of angiogenesis.