Detection of chromosome malsegregation to the daughter nuclei in cytokinesis-blocked transgenic mouse splenocytes

Detection of premature segregation of centromeres in persons exposed to ionizing radiation

We have analyzed the frequency of premature centromeric division (PCD) in medical personnel professionally exposed to low doses of radiation. They had chromosome aberrations (CAs) involving dicentric chromosomes, ring chromosomes, acentric fragments, chromosome breaks, and chromatid breaks. The study included 30 exposed subjects and 23 controls who were each analyzed by a conventional cytogenetics procedure and subsequently by fluorescent in situ hybridization (FISH). The latter was applied particularly in order to verify PCD in a specific chromosome (chromosome 18) in both metaphases and interphase nuclei. The results revealed a significant difference (p < 0.001) in frequencies between the two groups (exposed and controls) for all the observed variables (CAs), metaphases with PCD (MPCD), total number of chromosomes with PCD (TPCD), number of PCD metaphases in acrocentric chromosomes (MAPCD), and the total number of acrocentric chromosomes with PCD (TAPCD). The doses of ionizing radiation absorbed by the subjects' bodies were measured with thermoluminescent dosimeters once a month during the duration of occupational exposure. They were expressed in mSv, as mean annual effective doses for the period of exposure. The Spearman rank test showed a high positive correlation between total life effective dose and frequency of CAs and PCD. Based on the results obtained in this study, we suggest that PCD, as a phenomenon manifesting chromosomal instability (CIN), should be considered as a suitable cytogenetic biomarker for individuals occupationally exposed to ionizing radiation.

Chromosome aberrations: past, present and future

Spontaneous and induced chromosome aberrations have been studied over more than a century. The resolution of detection of aberrations has depended on the improvement of available techniques. An overview on the major high lights in this area of research, from the time of solid staining to fluorescence in situ hybridization technique is presented in this review.

Differences in malsegregation rates obtained by scoring ana-telophases or binucleate cells

In this work we have applied in situ hybridization with alphoid centromeric probes specific to chromosomes 7 and 11 to ana-telophase cells from human primary fibroblasts. The aim was to visualize the events leading to aneuploidy directly during anaphase, analyse the induction of aneuploidy during this mitotic stage and compare the frequencies of chromosome malsegregation observed in ana-telophases with the estimated malsegregation obtained in binucleate cells after a short cytochalasin B treatment. Significantly higher frequencies of chromosome loss and chromosome non-disjunction were observed in fibroblasts undergoing ana-telophase during recovery from a nocodazole-induced mitotic arrest compared with binucleate cells obtained by a further 30 min incubation with cytochalasin B. Using the same experimental schedule, analysis of hybridization signals in mononucleate cells showed higher frequencies of polyploid nuclei in cytochalasin B-treated cultures, indicating that part of the ana-telophases observed after release from the nocodazole-induced mitotic arrest may give rise to polyploid mononucleate cells instead of binucleate ones. A reduced distance between spindle poles was also measured in cells undergoing ana-telophase in the presence of cytochalasin B. Our study suggests that in nocodazole and cytochalasin B-treated cultures the shorter pole-to-pole distance may favour the reformation of a single membrane around telophase chromosomes, especially when several lagging chromosomes lie between the two future daughter nuclei. This would give rise to polyploid mononucleate cells at the ensuing interphase.

A high yield of translocations parallels the high yield of sister chromatid exchanges in the CHO mutant EM9

The fluorescence plus Giemsa (FPG) and fluorescence in situ hybridization (FISH) techniques have been used to determine, respectively, the frequencies of sister chromatid exchanges (SCEs) and stable chromosome aberrations (translocations) induced by different concentrations of BrdU in the Chinese hamster ovary cell mutant EM9 and its parental line AA8. The results indicate that BrdU induced a high frequency of SCEs and translocations in EM9 as compared with AA8, and that the translocation/dicentric ratio was also higher in the mutant cell line than in the parental cell line in both untreated and BrdU-treated cultures. These observations may indicate a possible relationship between the molecular mechanisms involved in the formation of SCEs and translocations.

Micronuclei, centromere-positive micronuclei and chromosome nondisjunction in cytokinesis blocked human lymphocytes following mitomycin C or vincristine treatment

The influence of sampling time on the frequencies of micronuclei, centromere-positive micronuclei and chromosome nondisjunction was investigated in binucleated lymphocytes following treatment with a known clastogen (mitomycin C) or an aneuploidy-inducing agent (vincristine sulfate). Cytochalasin B (6 micrograms/ml) was added 44 h after mitogen stimulation and cultures were harvested 12, 28, 36 and 48 h thereafter. Micronucleated cells and micronuclei were significantly induced by the two treatments at all sampling times. Furthermore, in situ hybridization with an 'all centromeres' probe showed that vincristine-induced micronuclei were prevalently centromere-positive whereas in mitomycin C-treated cultures only a minor fraction of induced micronuclei contained the hybridization signals. Chromosome nondisjunction rates, as measured by in situ hybridization with chromosome 7- and 11-specific alphoid probes, significantly increased following vincristine treatment. Chromosome nondisjunction and total micronucleus frequencies were found to increase with time both in controls and in mutagen-treated cultures, whereas the percentage of centromere-positive micronuclei in the different treatments was not influenced by the sampling time. Our data suggest that even in the presence of 6 micrograms/ml cytochalasin B, the abnormal segregation of binucleated cells may contribute to the baseline level of micronuclei and influence the results obtained. The introduction of a short cytochalasin B treatment (between 12 and 28 h) in the cytokinesis-blocked micronucleus assay may avoid the cytochalasin B effect on micronucleus frequencies.

Analysis of DES-induced micronuclei in binucleated rat fibroblasts: comparison between FISH with a rat satellite I probe and immunocytochemical staining with CREST serum

The usefulness of fluorescence in situ hybridization (FISH) with rat satellite I DNA was compared with immunocytochemical staining with CREST serum for the analysis of the content of micronuclei from primary rat fibroblasts. We analyzed micronuclei induced in vitro by the aneugenic compound diethylstilbestrol (DES) or the clastogenic compound mitomycin C (MMC). Since a centromeric probe was not available for the rat, we isolated rat satellite I DNA by PCR with primers designed on the basis of the known rat satellite I DNA sequence. The PCR products obtained as well as the cloned PCR products showed hybridization to the centromeric regions of a large number of chromosomes, but not of chromosome 1, 19, 20, X and Y. Clone 18-5 was further analyzed and was shown to contain at least 4 repeats of the rat satellite I family. This probe, which hybridizes in the centromeric region of 34 of the 42 chromosomes, was used throughout the study as a probe for the FISH analysis of the micronuclei. For the immunocytochemical staining, the commonly used commercial anti-centromeric antibodies could not be used because of the weakness of the fluorescent signals given. Consequently, CREST serum of a single patient was used, which showed bright and distinct signals on the kinetochores of each chromosome. After treatment of the cells with the aneugen DES an increase in centromere (FISH) and kinetochore (CREST) positive micronuclei was found, whereas after treatment with the clastogen MMC, the percentage of centromere-positive micronuclei was similar to that observed in controls. Analysis of a large number of DES-induced micronuclei showed that the immunocytochemical method is equally as or slightly less sensitive for the detection of chromosomes in micronuclei and we therefore recommend FISH with probe 18-5 for the detection of chromosome loss in rat cells.

An in vivo micronucleus assay for detecting the clastogenic effect in rat kidney cells

A micronucleus assay in vivo has been developed that is based on the use of freshly isolated kidney cells from mononephrectomized rats. In this validation study, a statistically significant increase in the frequency of micronucleated cells was detected in rats given i.p. a single dose of four kidney carcinogens, N-nitrosodimethylamine, N-nitrosodiethylamine, N-ethyl-N-hydroxyethylnitrosamine and N-nitroso-N-methylurea. The clastogenic effect was more marked when the same dose was injected for 3 successive days. As compared to controls, treated rats displayed a reduction in the frequency of binucleated cells, presumably due to a toxicity-induced inhibition of cellular proliferation. The proposed method should be suitable for the detection of the clastogenic effect of procarcinogens biotransformed into reactive species in the kidney.

The detection and evaluation of aneugenic chemicals

Although aneuploidy makes a significant contribution to both somatic and inherited disease the mechanisms by which environmental chemicals may induce numerical chromosome aberrations are only poorly defined. The European Union Project was aimed to further our understanding of those chemical interactions with the components of the mitotic and meiotic cell division cycle which may lead to aneuploidy and to characterise the parameters such as cellular metabolism which may influence the activity of aneugenic chemicals. C-mitosis can be induced by the highly lipophilic polychlorinated biphenyl and the completion of mitosis and cleavage can be modified by agents which deplete cellular levels of reduced glutathione. Modifications of the fidelity of chromosome segregation were produced by inhibiting the functioning of topoisomerase II during chromatid separation. In contrast, the modification of centromere integrity resulted in chromosome breakage as opposed to disturbance of segregation. Modifiers of tubulin assembly and centriolar functioning in somatic cells such as acrylamide, vinblastine and diazepam reproduced their activity in rodent bone marrow and male germ cells. The analysis of chromosome malsegregation in Aspergillus nidulans by a structurally related series of halogenated hydrocarbons was used to develop a QSAR model which had high predictive value for the results of fungal tests for previously untested related chemicals. Metabolic studies of potential aneugens in genetically engineered human lymphoblastoid cells demonstrated the detoxification of the aneugenic activity of chloral hydrate and the activation of 2,3-dichlorobutane, 1,1,2-trichloroethane and trichloroethylene by Phase I biotransforming enzymes. Cell transformation studies in Syrian hamster dermal cultures using a panel of 22 reference and or potential aneugens indicated that 15 of the 22 produced positive results following single exposures. Five of the aneugens which were negative following single exposures produced positive results where cultures were continuously exposed for up to 6 weeks to low concentrations following a single non-transforming exposure to the mutagen dimethyl sulphate. The transformation studies indicate that a significant proportion of chemical aneugens are potential complete carcinogens and/or co-carcinogens. To optimise the enumeration of chromosomes following exposure to potential chemical aneugens whole chromosome paints and centromere specific probes suitable for use in fluorescence in situ hybridisation (FISH) were developed for the rat, mouse and Chinese hamster and selected human probes evaluated for their suitability for routine use. Molecular chromosome probes were used to develop protocols for enumerating chromosomes in metaphase cells and centromeres and micronuclei in interphase cells. The analysis of segregation of specific centromeres in binucleate cells following cytochalasin B treatment was shown to be a potentially valuable system for characterising non-disjunction following chemical exposure. Whole chromosome paints and centromere specific probes were used to demonstrate the presence of dose-response thresholds following treatment with a reference panel of spindle inhibiting chemicals. These data indicate that the FISH technology is suitable for evaluating the relative hazards of low-dose exposures to aneugenic chemicals.

X-ray induced translocations in bone marrow cells of scid and wild type mice detected by fluorescence in situ hybridization using mouse chromosome specific DNA libraries

Radiation induced chromosomal aberrations in bone marrow cells of scid and normal mice were studied at different sampling times. Fluorescence in situ hybridization (FISH) with DNA libraries specific for chromosomes 1, 11 and 13 was applied to identify the stable types of chromosomal aberrations in addition to the unstable ones. The results obtained confirm earlier observations on stem cell spermatogonia in that, contrary to the situation in normal mice, only very low levels of translocations could be recovered from scid mice at relatively long sampling times (3 weeks). However, studies at a 24 h sampling period demonstrated substantial induction of translocations in scid mice. This suggests enhanced elimination of translocation carrying cells in scid mice during successive cell proliferation, possibly via falling apart of the translocation at the original points of exchange or due to lethal damage at the translocation break points.