Fluorescence in-situ hybridisation on biopsies from clam ileocystoplasties and on a clam cancer

The incidence of carcinoma following an enterocystoplasty increases with time and is a major concern after such procedures. The aim of this study was to investigate genetic instability (in the form of numerical chromosomal aberrations) at the enterovesical anastomosis in patients who had undergone a clam ileocystoplasty using fluorescent in-situ hybridisation (FISH). Fluorescent in-situ hybridisation was performed on touch preparation samples prepared from fresh endoscopic biopsies obtained from the enterovesical anastomosis and native bladder remnant (control specimens) of 15 patients who had undergone a clam ileocystoplasty. Fluorescent in-situ hybridisation was also performed on one squamous cell cancer specimen. Significant aneusomic changes were found at the enterovesical anastomosis in all 15 patients. Alterations in chromosome 18 copy number were the most frequent abnormal finding (trisomy 18, n=8; monosomy 18, n=7). Nine patients were monosomic for chromosome 9. Isolated monosomy 8 and trisomy 8 were each found in one patient. The control specimens were all normal. An unusually high incidence of polysomic cells was found in the clam tumour specimen, reflecting the aggressive nature of this cancer. Chromosomal numerical abnormalities occur at the enterovesical anastomosis following a clam ileocystoplasty and chromosome 18 appears to be a particularly good marker of genetic instability. The results of this study indicate that morphologically normal tissue obtained from the enterovesical anastomosis displays evidence of chromosomal instability that may predispose to tumour formation. However, further prospective, blinded, longitudinal studies are required to establish whether predetermined FISH signal patterns in enterocystoplasty cells in urine or obtained by biopsy predict the presence or absence of tumour.

Molecular cytogenetic insights into the ageing syndrome Hutchinson-Gilford Progeria (HGPS)

Hutchinson-Gilford Progeria Syndrome (HGPS) is an extremely rare genetic disorder characterized by premature ageing in childhood and serves as a valuable model for the human ageing process in general. Most recently, point mutations in the lamin A (LMNA) gene on chromosome 1q have been associated with the disease, however how these mutations relate to the complex phenotype of HGPS remains to be established. It has been shown that fibroblasts from HGPS patients are frequently resistant to immortalization with telomerase (hTERT), consistent with the idea that the loss of a dominant acting HGPS gene is a pre-requisite for immortalization. In this study we report the first detailed cytogenetic analysis of hTERT-immortalised HGPS cell lines from three patients and one corresponding primary fibroblast culture. Our results provide evidence for a cytogenetic mosaicism in HGPS with a distinctive pattern of chromosome aberrations in all the HGP clones. Chromosome 11 alterations were observed at a high frequency in each immortalised HGPS cell line but were also present at a lower frequency in the corresponding primary cells. Moreover, we were able to identify the 11q13-->q23 region as a potential site of breakage. Our results are therefore consistent with a role of chromosome 11 alterations in the escape from senescence observed in HGPS cells. In addition to this defined rearrangement, we consistently observed complex chromosomal rearrangements, suggesting that HGPS displays features of chromosomal instability.

Fluorescence in situ hybridisation analysis of chromosomal aberrations in gastric tissue: the potential involvement of Helicobacter pylori

In this series of experiments, a novel protocol was developed whereby gastric cells were collected using endoscopic cytology brush techniques, and prepared, such that interphase fluorescence in situ hybridization (FISH) could be performed. In total, 80 distinct histological samples from 37 patients were studied using four chromosome probes (over 32,000 cells analysed). Studies have previously identified abnormalities of these four chromosomes in upper GI tumours. Using premalignant tissues, we aimed to determine how early in Correa's pathway to gastric cancer these chromosome abnormalities occurred. Aneuploidy of chromosomes 4, 8, 20 and 17(p53) was detected in histologically normal gastric mucosa, as well as in gastritis, intestinal metaplasia, dysplasia and cancer samples. The levels of aneuploidy increased as disease severity increased. Amplification of chromosome 4 and chromosome 20, and deletion of chromosome 17(p53) were the more common findings. Hence, a role for these abnormalities may exist in the initiation of, and the progression to, gastric cancer. Helicobacter pylori infection was determined in premalignant tissue using histological analysis and PCR technology. Detection rates were comparable. PCR was used to subtype H. pylori for CagA status. The amplification of chromosome 4 in gastric tissue was significantly more prevalent in H. pylori-positive patients (n=7) compared to H. pylori-negative patients (n=11), possibly reflecting a role for chromosome 4 amplification in H. pylori-induced gastric cancer. The more virulent CagA strain of H. pylori was associated with increased disease pathology and chromosomal abnormalities, although numbers were small (CagA+ n=3, CagA- n=4). Finally, in vitro work demonstrated that the aneuploidy induced in a human cell line after exposure to the reactive oxygen species (ROS) hydrogen peroxide was similar to that already shown in the gastric cancer pathway, and may further strengthen the hypothesis that H. pylori causes gastric cancer progression via an ROS-mediated mechanism.

Generation of locus-specific probes for interphase fluorescence in situ hybridisation--application in Barrett's esophagus

Despite the wide range of probes commercially available for interphase fluorescence in situ hybridisation (FISH), the supply of locus-specific probes is limited to genes or chromosomal regions commonly altered in genetic diseases or during carcinogenesis. Generation of these probes is therefore desirable to accommodate individual research requirements. Hence, we detail the methodology required to design and produce custom locus-specific interphase FISH probes for any human genomic region of interest and their application was illustrated in cytogenetic investigations of Barrett's tumourigenesis. Previously utilising FISH, we observed that Barrett's tissues demonstrated chromosome 4 hyperploidy [Gut 52 (2003) 623], but as centromeric probes were used in this analysis, it was not known if the whole chromosome was amplified. We consequently generated single-copy sequence probes for the 4p16.3 and 4q35.1 subtelomeric loci. Multicolour FISH was subsequently performed on interphase preparations originating from patients with Barrett's esophagus at varying histological grades, thus demonstrating the whole region of chromosome 4 was amplified within the tissues. Additionally, probes for the DNA methyltransferase genes were produced to determine if gene dosage alterations were responsible for increasing methylation activity during Barrett's neoplastic progression. No significant alterations at the DNMT1 and DNMT3a loci were detected. An increased copy number of these genes is therefore not the basis for the hypermethylation commonly observed in this premalignant lesion.

Investigations into the biological relevance of in vitro clastogenic and aneugenic activity

In the current study we present a view of events leading to chemically induced DNA damage in vitro from both a cytogenetic and molecular aspect, focusing on threshold mediated responses and the biological relevance of DNA damaging events that occur at low and high cellular toxicity levels. Current regulatory mechanisms do not take into account chemicals that cause significant DNA damage only at high toxicity. Our results demonstrate a defined threshold for micronucleus induction after insult with the alkylating agent MMS. Other results define a significant change in gene expression following treatment with chemicals that give rise to structural DNA damage only at high toxicity. Pairs of chemicals with a similar mode of action but differing toxicity levels were chosen, the chemicals that demonstrated structural DNA damage only at high levels of toxicity showed an increase in heat shock protein gene expression whereas the chemicals causing DNA damage events at all levels of toxicity did not induce changes in heat shock gene expression at identical toxicity levels. The data presented indicates that there are a number of situations where the linear dose response model is not appropriate for risk estimation. However, deviation from linear risk models should be dependent upon the availability of appropriate experimental data such as that shown here.

Characterisation of p53 status at the gene, chromosomal and protein levels in oesophageal adenocarcinoma

p53 mutations and loss of heterozygosity have been commonly associated with oesophageal adenocarcinoma. In this investigation, the p53 status of a Welsh population of Barrett's-associated oesophageal adenocarcinomas were fully characterised at the gene sequence, chromosomal, mRNA and protein levels. In total, 31 tumours were examined for p53 gene sequence mutations using RFLP with sequencing, allelic loss of the gene was characterised by FISH, mRNA expression by p53 pathway signalling arrays and protein levels by p53 immunohistochemistry. In all, 9.6% of adenocarcinomas harboured p53 mutations, 24% displayed p53 allelic loss and 83% exhibited p53 protein accumulation. Point mutations and deletions of the gene did not coexist within the same samples. All samples containing p53 mutations also displayed positive immunostaining; however; in the majority of cases, p53 protein accumulation developed in the absence of mutations. The gene expression analysis demonstrated no differences in p53 and mdm-2 transcription levels between the p53 immunonegative and immunopositive samples, indicating other mechanisms underlie the proteins' overexpression. In conclusion, p53 mutations and deletions do not appear to be frequent events in oesophageal adenocarcinomas; however, abnormal accumulation of the protein is present in a vast majority of cases. P53 gene mutations are not the primary cause of protein overexpression--an alternative mechanism is responsible for the positive p53 immunohistochemistry detected.

Detection of p53 mutations in precancerous gastric tissue

Intestinal-type gastric cancer is preceded by gastritis and intestinal metaplasia. There is uncertainty regarding the stage at which genetic alterations in the p53 gene occur. Reactive oxygen species (ROS) may participate in the production of mutations and the inactivation of p53 is due to infection by the bacterium Helicobacter pylori. We have investigated whether alterations of the p53 gene can be detected in gastritis and intestinal metaplasia using the restriction site mutation assay. We also assessed the potential contribution of ROS to p53 inactivation using electron spin resonance spectroscopy (ESR) and correlated with the presence of H. pylori. In all, 35% of the gastritis samples and 45% of the intestinal metaplasia samples were found to contain mutations in exons 5–8 of the p53 gene. Electron spin resonance spectroscopy analysis showed a significant increase in free radical levels in gastritis samples compared with normal, intestinal metaplasia and cancer samples, suggesting that free radicals present in gastritis may contribute to p53 mutations. There was no significant difference in free radical levels between the H. pylori-positive and -negative groups. However, a small subpopulation of the H. pylori-negative patients had much higher levels of free radicals. This suggests a more prominent role for other factors in ROS production.

Chromosome 4 hyperploidy represents an early genetic aberration in premalignant Barrett's oesophagus

BACKGROUND AND AIMS

Characterisation of the underlying molecular mechanisms that promote Barrett's progression may ultimately lead to identification of potential predictive genetic markers that classify patients' malignant risk. In an attempt to understand these causative pathways, fluorescence in situ hybridisation (FISH) was used in this study to determine when specific genetic alterations arise during Barrett's associated neoplastic progression.

METHODS

Endoscopic cytology brushings were obtained from 28 patients with Barrett's metaplasia, 28 with dysplasia (20 low grade dysplasia (LGD) and eight with high grade dysplasia (HGD)), and seven with adenocarcinoma, together with paired control brushings from regions of normal proximal squamous cell epithelium. The exfoliated epithelial cells were washed and deposited onto slides. Probes specific for the centromeres of chromosomes 4, 8, 20, and Y, and locus specific probes for the tumour suppressor genes p16, p53, and Rb were subsequently hybridised.

RESULTS

Aneuploidy was found early in progression, with metaplastic tissues displaying increased copy numbers of chromosomes 4 and 8. Chromosome 4 hyperploidy was found in 89%, 90%, 88%, and 100% of metaplasias, LGD, HGD, adenocarcinomas, respectively, while chromosome 8 hyperploidy occurred in 71%, 75%, 100%, and 100% of patients with the respective staging. Loss of the p16 tumour suppressor gene also presented in metaplastic epithelium (7%) but most other genetic aberrations were only seen in HGD.

CONCLUSIONS

Genetic instability arises well before dysplasia in Barrett's oesophagus, with chromosome 4 and 8 hyperploidy representing the earliest and most common alterations identified. As these aberrations are widespread at all the premalignant stages, there may be genes on chromosomes 4 and 8 that are involved in both the initiation and progression of Barrett's oesophagus.

Detection and characterization of mechanisms of action of aneugenic chemicals

A comprehensive evaluation of the genotoxic potential of chemicals requires the assessment of the ability to induce gene mutations and structural chromosome (clastogenic activity) and numerical chromosome (aneugenic activity) aberrations. Aneuploidy is a major cause of human reproductive failure and an important contributor to cancer and it is therefore important that any increase in its frequency due to chemical exposures should be recognized and controlled. The in vitro binucleate cell micronucleus assay provides a powerful tool to determine the ability of a chemical to induce chromosome damage. The application of an anti-kinetochore antibody to micronuclei allows their classification into kinetochore-positive and kinetochore-negative, indicating their origin by aneugenic or clastogenic mechanisms, respectively. The availability of chromosome-specific centromere probes allows the analysis of the segregation of chromosomes into the daughter nuclei of binucleate cells to evaluate chromosome non-disjunction. Quantitative relationships between the two major causes of aneuploidy, chromosome loss and non-disjunction, can be determined. The mechanisms leading to chromosome loss and non-disjunction can be investigated by the analysis of morphological and structural changes in the cell division apparatus by the application of specific stains and antibodies for various cell division components. We illustrate such analyses by the demonstration of the interaction of the monomer bisphenol-A with the centrosome of the mitotic spindle and the folic acid antagonist pyrimethamine with the centromeres of chromosomes. Both types of modifications lead to the induction of aneuploidy in exposed cells. Our studies also implicate the products of the p53 and XPD genes in the regulation of the fidelity of chromosome segregation at mitosis.

Spontaneous and induced aneuploidy, considerations which may influence chromosome malsegregation

Aneuploidy plays a major role in the production of human birth defects and is becoming increasingly recognised as a critical event in the etiology of a wide range of human cancers. Thus, the detection of aneuploidy and the characterisation of the mechanisms which lead to chromosome malsegregation is an important area of genotoxicological research. As an aid to aneuploidy research, methods have been developed to analyse the mechanisms of chromosome malsegregation and to investigate the role of aneuploidy in tumour progression. The presence of aneuploid cells is a common characteristic of many of tumour cell types as illustrated by the wide range of chromosome number changes detected in post-menopausal breast tumours. To investigate the time of occurrence of aneuploidy during tumour progression, we have studied the chromosome number status of Syrian hamster dermal (SHD) cells cultures progressing to morphological transformation. The production of both polyploid and aneuploid cells is a common feature of progressing cells in this model. The elevation of both progression to morphological transformation and aneuploid frequencies can be produced by exposure to a diverse range of carcinogens and tumour promoters. Analysis of the genotoxic activity of the hormone 17-beta oestradiol demonstrated its ability to induce both chromosome loss and non-disjunction in human lymphoblastoid cells implicating aneugenic activity in hormone related cancers. Mutations in the p53 tumour suppressor gene introduced into human fibroblasts produced modifications in chromosome separation at mitosis which may lead to the production of both aneuploidy and polyploid cells. Our studies indicate that the production of aneuploid cells can be influenced by both endogenous and exogenous factors and occur throughout the progression of normal cells to a malignant phenotype.

The detection of mutations induced in vitro in the human p53 gene by hydrogen peroxide with the restriction site mutation (RSM) assay

We have analysed five mutation hotspots within the p53 gene (codons 175, 213, 248, 249, and 282) for mutations induced by hydrogen peroxide (H(2)O(2)), employing the restriction site mutation (RSM) assay. In addition, four other restriction sites covering non-hotspot codons of exons 5-9 of the p53 gene (codons 126, 153/54, 189 and the 3' splice site of exon 9) were analysed by the RSM assay for H(2)O(2)-induced mutations. Two cell types were concurrently analysed in this study, i.e. primary fibroblast cells and a gastric cancer cell line. Using the RSM assay, H(2)O(2)-induced mutations were only detected in exon 7 of the p53 gene. This was true for both cell types. These mutations were mainly induced in the Msp I restriction site (codon 247/248) and were predominantly GC to AT transitions (71%). Hence these GC to AT mutations were presumably due to H(2)O(2) exposure, possibly implicating the 5OHdC adduct, which is known to induce C to T mutations upon misreplication. Importantly, this study demonstrates that the RSM methodology is capable of detecting rare oxidative mutations within the hotspot codons of the p53 tumour suppressor gene. Hence, this methodology may allow the detection of early p53 mutations in pre-malignant tissues.

Multicolour FISH detection of radioactive iodine-induced 17cen-p53 chromosomal breakage in buccal cells from therapeutically exposed patients

Simultaneous labelling of 17cen and the p53 locus by multicolour FISH was used to monitor radioactive iodine-induced structural and numerical chromosome abnormalities in buccal cells from 29 hyperthyroidism and thyroid cancer patients sampled before and after therapeutic treatment. This novel methodology allowed the efficient detection of 17p deletions leading to p53 allelic deletions, 17p gains and whole chromosome 17 numerical abnormalities in epithelial cells. Highly significant increases in the frequency of cells with (i) 17p abnormalities (1.8-fold; P < 0.001), including p53 monoallelic deletions (2.1-fold; P < 0.001) and 17p gains (3.5-fold; P < 0.001); (ii) chromosome 17 numerical abnormalities (2-fold; P < 0.001); and (iii) simultaneous 17p breakage and chromosome 17 numerical abnormalities (2.3-fold; P < 0.001), were observed after radioactive iodine treatment. As expected, the major contribution to these increases was detected in hyperthyroidism patients compared with thyroid cancer patients who suffered thyroidectomy before radioactive iodine exposure and, therefore, experienced a rapid elimination of the radioisotope. Considering that both the genetic endpoints and the target tissue are extremely relevant in carcinogenesis, it is suggested that the observed genetic damage could contribute to the reported increase in cancer risk of people therapeutically or accidentally exposed to radioactive iodine.

In vitro and in vivo extrapolations of genotoxin exposures: consideration of factors which influence dose-response thresholds

The concept of a threshold of activity of a genotoxic agent is primarily based upon considerations of protective mechanisms and multiple cellular targets, which require inactivation before a toxic response is produced. In this paper, we have considered and evaluated the influences of compound metabolism, DNA lesion formation, mutation induction and sequence content, aneuploidy induction and the influence of repair enzymes upon genetic endpoints produced by both DNA reactive chemicals and by those chemicals which modify non-DNA cellular targets. Thresholds of activity have been evaluated by critical analysis of the published literature and original data analysing both the role of sequence context upon point mutation induction and DNA repair mechanisms upon the sensitivity of cultured cells to the induction of aneuploidy. In the case of DNA reactive chemicals, the presence of a threshold of chemical activity will be dependent upon cellular activities such as those of the Phase II enzymes reducing the activity of chemicals before lesion formation takes place and/or those of the DNA repair enzymes which reduce the proportion of DNA lesions which are processed into DNA sequence changes. Under such conditions, a given exposure of a DNA reactive chemical does not produce a linear or semi-linear increase in DNA lesions or in mutation frequency. However, even when these protective mechanisms are overwhelmed by the high exposures of genotoxic chemicals the biological effects of a genotoxin may be influenced by the sequence context of the gene under consideration. Here, we demonstrate that point mutations are detected at relatively higher frequencies in the non-coding introns compared with the coding exons. Many of the base changes detected in the exons do not produce amino acid changes in the proteins coded for by the genes being monitored for mutation induction. Both sequence context and the types of base changes induced may provide a "buffering" effect reducing the biological consequences of mutation induction. Spindle damaging chemicals, such as colcemid and vinblastine, induce aneuploidy by modifying the numbers of spindle fibres which regulate the segregation of chromosomes during mitosis and meiosis. The redundancy of spindle fibres in the dividing mammalian cell leads to the prediction that only chemical exposures which damage most, if not all, of the fibres will lead to the induction of polyploidy and/or aneuploidy. Such predicted thresholds of chemical activity can be observed when both chromosome loss and non-disjunction are measured in wild type cultures. However, we observed a substantial increase in sensitivity to aneugenic chemicals when measurements were made in primary cell cultures derived from xerodoma pigmentosum and trichothiodystrophy patients. Further studies are necessary to evaluate the consequences of the genetic background of tester strains upon the nature of the dose-response curve of aneugenic chemicals.

The application of comparative genomic hybridization and fluorescence in situ hybridization to the characterization of genotoxicity screening tester strains AHH-1 and MCL-5

AHH-1 TK+/- is a human B cell-derived lymphoblastoid cell line that constitutively expresses a high level of the cytochrome CYP1A1. The MCL-5 cell line was developed by transfection of AHH-1 with cDNAs encoding the human cytochrome P450s, CYP1A2, CYP2A6, CYP2E1, CYP3A4 and microsomal epoxide hydrolase carried in plasmids. The metabolic components of these cell lines make them a useful screening tool for use in mutagenicity studies. Although AHH-1 and MCL-5 are closely related, the two cell lines show differences which cannot be attributed to transfection. In the present study both cell lines were investigated for chromosome stability by comparative genomic hybridization (CGH) and fluorescence in situ hybridization (FISH) using whole chromosome probes and telomeric probes. Amplification in chromosomes 4q, 3q and 9p was observed in both cell lines. To compare the cell lines directly, AHH-1 and MCL-5 DNAs were co-hybridized on the same metaphases using a modified CGH technique. The only difference observed between AHH-1 and MCL-5 was the degree of amplification involving the subtelomeric region of chromosome 4; the additional telomeric region (4q) was translocated onto chromosome 11 and/or chromosome X. FISH was use to show the presence of isochromosomes 3q and 9p in both cell lines with a chromosome number of 48 or higher. These data demonstrate that CGH and FISH with chromosome-specific probes are able to resolve complex karyotypes and to highlight subchromosomal regions involved in rearrangements and potential chromosome fragile sites. Analyses such as those described here may be of considerable value in the determination of the stability of a variety of the cell lines used in the mutagenicity testing of chemicals.

Segregational fidelity of chromosomes in human thyroid tumour cells

Using fluorescence in situ hybridisation (FISH) we have analysed the segregational fidelity of all the human chromosomes during mitotic cell division. The losses and gains of chromosomes were analysed in human polyploid cell lines derived from a well-differentiated papillary thyroid cancer. These thyroid cells can be cultured for more than 300 population doublings. For the purpose of our study the polyploid nature of the cells may act as a protective buffer against the cell-lethal effects of the loss of individual chromosomes. To evaluate the role of the p53 gene product in maintaining the fidelity of chromosome segregation we compared the frequencies of chromosome loss and gain in cultures with wild-type p53 activity (K1E7neo3) and cultures transfected with plasmids expressing a mutant p53 product (K1E7scx6). Cultures were analysed for the presence of both structurally normal and rearranged chromosomes at both early and late passages. Cell cultures with defective p53 activity showed progressive chromosome loss from a median chromosome number of 87-97 to 75-86. Cell growth in cultures with wild-type p53 activity showed the loss of chromosomes 6, 7, and 8 and the gain of 17 and 20. Cultures expressing mutant p53 activity showed the loss of chromosomes 2, 5, 14 and 17 and the gain of 4 and 22. The combination of defective p53 and growth resulted in further destabilisation with the additional losses of chromosomes 3, 11, 15, 16 and 21. Chromosomes 1, 9, 10, 12, 13, 18, 19, X and Y segregated stably under all the culture conditions as did the structurally rearranged marker chromosomes. The study has demonstrated variation in the fidelity of mitotic chromosome segregation and the influence of p53 gene activity upon the segregation of individual human chromosomes.

Chemically induced aneuploidy: investigations into chromosome specific effects in mitosis

Genotoxicity studies of aneuploidy may potentially produce different results depending upon the chromosome selected for analysis if chromosome-specific sensitivities to chemical exposure exist. Any chromosome specificity characteristics that predispose to aneuploidy might interact with environmental exposures in additional different ways related to the mechanism of aneuploidy induction. Thus, we have undertaken an investigation of chromosome-specific effects using morphologically distinct chromosomes in a hybrid cell line. We were able to identify eight different chromosomes simultaneously by dual colour FISH analysis in controls and in cells exposed to a range of griseofulvin concentrations. Certain chromosomes were more frequently involved in aneuploidy, but no simple relationship between chromosome organisation and sensitivity emerged apart from the over-representation of the alien human chromosome. Aneuploidy was detected at higher frequencies in interphase cells compared with metaphase cells. Overall the data indicate that chemically induced aneuploidy may be detected for a variety of chromosomes and cell types using both interphase and metaphase protocols. However, the data obtained should be used with care in the hazard evaluation of chemical aneugens.

Characterization of highly radiosensitive cell lines from a human ovarian small-cell cancer

Cells were obtained at paracentesis from a patient with a rapidly growing ovarian tumor. A monolayer cell line (V7S), a xenograft tumor line (V7), and subsequently a xenograft-derived monolayer cell line (V7M) were established. Histological and immunohistochemical studies of the original tumor, xenograft, and cell lines provided a diagnosis of small-cell carcinoma of the ovary-which is consistent with the clinical course of the patient. V7S and V7M had a predominantly hypodiploid karyotype with a small tetraploid population. The V7M, which has been in long-term culture, also showed a nonrandom translocation involving chromosomes 1 and 14 and monosomy of X. Radiobiologically, V7S, V7, and V7M showed marked radiosensitivity with surviving fractions at 2 Gy, measured by clonogenic assay, of between 0.022 and 0.147. Split-dose experiments provided evidence that this radiosensitivity was not due to an inability in cellular repair. In vivo data from the xenograft (V7) revealed a highly radiosensitive tumor, corroborating the in vitro studies.

Biomonitoring study of a group of workers potentially exposed to traffic fumes

Risk assessment of environmental pollutants is concerned with the identification of compounds in the environment that might be hazardous to human health: measuring exposure levels, measuring cellular damage and then estimating the probability of harm occurring. The feasibility of such a comprehensive approach has been explored in this study of two groups of workers, one of which may be occupationally exposed to exhaust fumes. No statistically significant difference in cellular damage, as measured by the lymphocyte micronucleus assay, was found between these two groups of workers, although clear differences in exposure levels to volatile organic compounds were detected. A number of other factors identified in the study did show clear effects on micronucleus frequency.

A study of the aneugenic activity of trichlorfon detected by centromere-specific probes in human lymphoblastoid cell lines

The potential of the pesticide trichlorfon to induce mitotic aneuploidy has been investigated in genetically engineered human lymphoblastoid cell lines. Trichlorfon failed to induce micronuclei in the AHH-1 and MCL-5 cell lines when treated in media at normal cell culture pH (pH 7.3). Under a treatment pH of 5.5, trichlorfon exposures resulted in the induction of both chromosome loss and chromosome non-disjunction as measured by fluorescence in situ hybridisation (FISH) using a pan-centromeric probe for all human centromeres and centromere probes specific for chromosomes 2, 7 and 18. At treatment concentrations greater than 20 micrograms/ml trichlorfon also induced structural chromosome damage resulting in the production of centromere negative micronuclei.

A comparison of conventional metaphase analysis of Giemsa-stained chromosomes with multi-colour fluorescence in situ hybridization analysis to detect chromosome aberrations induced by daunomycin

Chromosome aberrations induced by daunomycin, a widely used positive control compound for in vitro cytogenetics assays, were identified by multi-colour fluorescence in situ hybridization with probes for chromosomes 1, 2 and 3. The frequency and distribution of aberration types were compared to conventional metaphase analysis of Giemsastained chromosomes from parallel human lymphocyte cultures. Multi-colour chromosome painting was a more sensitive method for detecting daunomycin-induced chromosome aberrations compared with conventional metaphase analysis because: (i) a higher level of statistical significance was achieved at low doses; and (ii) the increases in aberration frequencies compared with controls were greater. The majority of exchanges identified by Giemsastaining were unstable and were likely to lead to cell death. In contrast, those detected by FISH were mostly stable exchanges which may be transmitted to cell progeny. Multicolour FISH using whole chromosome probes may provide an elegant solution to the problem of identifying non-lethal, heritable exchange events. The benefit of this technique is the quantification of a cytogenetic endpoint directly associated with carcinogenesis.

Mitotic non-disjunction as a mechanism for in vitro aneuploidy induction by X-rays in primary human cells

A collaborative study of three laboratories compared the induction of aneuploidy by X-rays in human lymphocytes and fibroblasts. The induction of non-disjunction versus chromosome loss by X-rays was investigated using a variety of aneuploidy detection methods. Chromosome loss was determined by fluorescence in situ hybridization (FISH) with pan-centromeric probes in cytochalasin-B-blocked binucleated cells. Chromosome non-disjunction was estimated by FISH with chromosome-specific centromeric probes in binucleated interphase cells. Chromosomes were counted in parallel in lymphocyte metaphase cells; chromosome counts of the whole karyotype and counts of chromosomes 2 and 8 using chromosome paints. A major observation in spontaneous non-disjunction frequencies concerned the clear difference in frequencies observed between the two painted chromosomes in the same primary cells. When cells were irradiated elevated frequencies were observed for all the different cytogenetic endpoints. Although only a small number of the micronuclei were positive for the centromeric signal and presumably contained whole chromosomes, the absolute number %oC+ increased with dose. Higher rates of non-disjunction were found for irradiated cells; in fibroblasts a statistically significant increase was observed at a dose of 0.5 Gy. The detection of hyperdiploidy by means of chromosome counts and chromosome painting revealed an increase from doses of 1 Gy and higher. Comparison of the different methods detecting different endpoints indicates that non-disjunction may be an important mechanism leading to spontaneous and X-ray-induced aneuploidy. The relative radiosensitivity of aneuploidy induction was compared in two types of primary human cells - lymphocytes and fibroblasts. For chromosome loss both cell types showed similar results, whereas for non-disjunction fibroblasts seemed to be more sensitive. However, these differences may reflect a different sensitivity in the scoring methods used.

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.

An investigation into the activation and deactivation of chlorinated hydrocarbons to genotoxins in metabolically competent human cells

We have investigated the induction of micronuclei by 15 chlorinated hydrocarbons in the cytochalasin B-blocked micronucleus assay utilizing genetically engineered cell lines. The human lymphoblastoid cell line AHH-1, with native cytochrome CYP1A1 activity, the MCL-5 cell line, which stably expresses cDNAs encoding human CYP1A2, 2A6, 3A4, 2E1 and microsomal epoxide hydrolase, and the h2E1 cell line, containing a cDNA for CYP2E1, were used in this study. We have demonstrated the induction of kinetochore-positive micronuclei by two chlorinated solvents, 2,3-dichlorobutane and 1,1, 2-trichloroethane, in the metabolically competent cell lines MCL-5 and h2E1. The MCL-5 and h2E1 cell lines have in addition shown the capacity to produce metabolites in the presence of methylene chloride, carbon tetrachloride, 1,2,3-trichloropropane, tetrachloroethylene, toluene and n-hexane, wich yield elevated micronucleus frequencies compared with the parental cell line AHH-1. Hexachloroethane failed to induce micronuclei in any of the cell lines and 1,2-dichloroethane and 1-chlorohexane induced micronuclei without the requirement for metabolic activation in all three cell lines. The MCL-5 cell line exhibited reduced micronucleus frequencies compared with the AHH-1 and h2E1 cell lines following exposure to 1,2-dichloroethylene, 1,3-dichloropropane, 1,1, 1-trichloroethane and 1,2,3-trichloropropane. The methodology used has shown the ability of metabolically competent cell lines expressing cDNAs encoding the cytochrome P450 isoenzymes to metabolize halogenated hydrocarbons to genotoxic species, including both clastogens and aneugens. The biotransformation of chemicals to aneugenic species has not previously been demonstrated.

A genetically engineered V79 cell line SD1 expressing rat CYP2B1 exhibits chromosomal instability at the integration site of the transfected DNA

The genetically engineered cell line SD1 was constructed by co-transfection of V79 Chinese hamster cells with two plasmids: one containing a full-length cDNA encoding rat CYP2B1 and the second incorporating a selective marker gene. This cell line has been used in gene mutation tests and in cytokinesis-block micronucleus assays to identify procarcinogens which are metabolized by CYP2B1 to reactive metabolites. An elevated frequency of spontaneous micronuclei was recorded in SD1 cells compared to parental V79 cultures. Karyotypic analysis revealed a chromosomal instability which was manifested by amplification of the p-arms of a chromosome designated 'n' (derived from chromosome 8). This chromosome was variable in length and sometimes exhibited a telomeric fusion which led to the formation of a dicentric chromosome. Fluorescence in situ hybridization with digoxigenin-labelled plasmid DNA showed the presence of pSV450 plasmid DNA coamplified with genomic DNA sequences located in the terminal region of chromosome 'n'.

Use of multicolour chromosome painting to identify chromosomal rearrangements in human lymphocytes exposed to bleomycin: a comparison with conventional cytogenetic analysis of Giemsa-stained chromosomes

Exchange aberrations induced by bleomycin were identified by multicolour fluorescence in situ hybridisation (FISH) with probes for chromosomes 1, 2, and 3. The frequency and distribution of aberration types were compared to conventional metaphase analysis of Giemsa-stained chromosomes from the same human lymphocyte cultures. The total percentage of exchanges detectable by painting three pairs of chromosomes with separate colours was calculated as 40%. Giemsa staining revealed predominantly asymmetric chromosome exchanges, which are expected to comprise 50% of the total induced exchanges. Genomic exchange frequencies were, therefore, determined by multiplying the observed frequencies from FISH analysis by 2.5 and the number of asymmetric exchanges identified in Giemsa-stained slides by 2.0. By these calculations, the genomic exchange frequency calculated from chromosome painting exceeded that estimated by Giemsa-staining. This difference was due to the identification by chromosome painting of a unique class of cells in which chromosomes had undergone complex exchanges (nonreciprocal exchanges involving multiple mutual sites). The percentage of cells exhibiting exchanges was similar for both methods.

Procedures for the detection of chemically induced aneuploidy: recommendations of a UK Environmental Mutagen Society working group

The development of assays to detect numerical chromosome aberrations has not kept pace with that for assays used to detect other genotoxicity endpoints such as gene mutations and structural chromosome aberrations, even though the importance of aneuploidy in relation to heritable defects in germ cells and to carcinogenesis in somatic cells is acknowledged. Regulatory bodies at present have no formal requirements concerning aneuploidy detection and decisions are made on a case-by-case basis. The aim of this review is to indicate which assays are available for the detection of chemically induced aneuploidy and what aspects should be taken into account when testing for chemically induced aneuploidy using in vitro, in vivo somatic and in vivo germ cell assays without dictating exact protocols. Our recommendations concentrate on systems that, to date, have been most extensively used and we indicate where future developments may lie. It is important that the currently available and future tests for chemically induced aneuploidy should be adequately validated before being implemented into screening strategies or regulatory guidelines. This requirement has not yet been met and is confounded by the lack of a well defined reference database of animal and human chemical aneugens.

Cellular and chromosomal hypersensitivity to DNA crosslinking agents and topoisomerase inhibitors in the radiosensitive Chinese hamster irs mutants: phenotypic similarities to ataxia telangiectasia and Fanconi's anaemia cells

The mutants irs1, irs2 and irs3 were previously isolated from the Chinese hamster line V79-4 on the basis of their hypersensitivity (2-3-fold) to cell inactivation by X-rays. Here the cross-sensitivities of the irs mutants to an array of chemical mutagens and topoisomerase inhibitors was determined in a differential cytotoxicity assay. Irs2 showed moderate hypersensitivity (2-3-fold) to simple alkylating agents and oxidative mutagens but was most sensitive (8-fold) to the topisomerase I inhibitor camptothecin. In contrast irs2 showed little or no increased sensitivity to four topoisomerase II inhibitors. Irs3 proved to be particularly hypersensitive to DNA crosslinking agents (5-15-fold) such as 1,3-butadiene diepoxide and mitomycin C. Irs1 was hypersensitive (3-fold or greater) to simple alkylating agents, oxidative mutagens and topoisomerase I and II inhibitors and exhibited extreme sensitivity (20-100-fold) to DNA crosslinking agents. The cellular hypersensitivities of irs2 and irs3 were reflected at the level of the chromosome. Camptothecin induced chromosomal aberrations in irs2 consisted almost exclusively of chromatid deletions and exchanges, whilst in irs3 1,3 butadiene diepoxide induced a 50-fold increase in chromatid exchanges compared with V79-4. The nature of irs2's camptothecin hypersensitivity was investigated. Analysis of the protein associated DNA single strand breaks produced by camptothecin indicated that there was no difference between V79-4 and irs2 in either the number of breaks induced or in the rate of their reversal following drug removal. In addition, levels of topoisomerase I activity in V79-4 and irs2 were indistinguishable. The data presented suggest that irs3 is likely to be defective in some aspect of DNA cross-link removal and irs2, whilst showing no gross defect in DNA strand break repair may fail to correctly respond to or repair certain types of strand breaks, possibly those associated with replicating DNA. The phenotypes of irs2 and irs3 respectively show similarities to those of cultured cells from the syndromes ataxia telangiectasia and Fanconi's anaemia.

Micronucleus assays using cytochalasin-blocked MCL-5 cells, a proprietary human cell line expressing five human cytochromes P-450 and microsomal epoxide hydrolase

The MCL-5 cell line is a human lymphoblastoid TK+/- cell line that constitutively expresses a relatively high level of native CYP1A1, four other human cytochromes (CYP1A2, CYP2A6, CYP3A4 and CYP2E1) and microsomal epoxide hydrolase, carried as cDNAs in plasmids. The aim of this study was to evaluate this cell line for its suitability for detecting chromosomal anomalies, employing micronucleus formation in cells blocked at cytokinesis as the indicator of clastogenicity. Results from two laboratories ('ICR' and 'Swansea') using different protocols are reported. In the ICR protocol, aflatoxin B1, sterigmatocystin, benzo[a]pyrene, dibenz[a,h]anthracene, 3-methylcholanthrene, cyclophosphamide, N-nitrosodimethylamine, 2-amino-3,8-dimethylimidazo[4,5-f]-quinoxaline, benzidine, 2-aminofluorene, benzene, tamoxifen and omeprazole were tested and gave positive results. Anthracene, phenanthrene and pyrene were negative. In the Swansea protocol, AHH-1 cells, the parent line which constitutively expresses CYP1A1, but does not contain the genetically engineered human cytochromes or epoxide hydrolase, were tested in parallel with MCL-5 cells. Aflatoxin B1, sterigmatocystin, benzo[a]pyrene, N-nitrosodiethylamine, 2-acetylaminofluorene, benzene, omeprazole and tamoxifen were tested and gave positive results. Of these, only benzo[a]pyrene was equally potent in both cell lines. Assays of tamoxifen and omeprazole included kinetochore staining. Omeprazole, but not tamoxifen, induced a significant level of kinetochore-positive micronuclei. The detection of micronucleus formation in these genetically engineered cells appears to be a rapid, eclectic and sensitive method for screening for genotoxic activity in vitro.

A modified protocol for the cytochalasin B in vitro micronucleus assay using whole human blood or separated lymphocyte cultures

A modified protocol is described for the in vitro analysis of micronuclei in whole blood or separated lymphocyte cultures. The induction of binucleate cells by various concentrations of cytochalasin B (3, 4.5 or 6 micrograms/ml) was examined at two harvest times (68 or 72 h). An optimal yield was obtained by adding cytochalasin B at a dose of 6 micrograms/ml to cultures 44 h after initiation with harvest 24 h (whole blood) or 28 h (separated lymphocytes) later. Cytocentrifuge preparations of lymphocytes (separated from whole blood using commercial preparations of Ficoll either at the commencement of the assay or upon harvest) were stained with Acridine Orange. Using this method, cytokinesis-blocked lymphocytes remain intact and micronuclei are readily identified. The method is suitable for both whole blood and separated lymphocyte cultures, thus allowing direct comparisons of sensitivity to genotoxic agents.

A comparison of two in vitro mammalian cell cytogenetic assays for the detection of mitotic aneuploidy using 10 known or suspected aneugens

Two in vitro cytogenetic assays were evaluated for their ability to detect aneugenic and polyploidy-inducing agents using a battery of 10 known or suspected aneugens supplied as part of the EEC 4th Environmental Research and Development Programme. The compounds tested were colchicine, vinblastine, chloral hydrate, thiabendazole, hydroquinone, thimerosal, cadmium chloride, econazole nitrate, pyrimethamine and diazepam. The cell division aberration assay employed a differential chromosome/spindle staining procedure to detect perturbations of the mitotic division apparatus. This assay was carried out in two pulmonary-derived Chinese hamster cell lines; the immortal DON:Wg3h culture and a low passage LUC2 culture. The second assay involved quantification of metaphase chromosomes, for which only the LUC2 cell line was used, due to the stability of its diploid karyotype. All the chemicals induced spindle disturbances in the immortal line. In addition, all the compounds except cadmium chloride yielded positive results in the LUC2 culture, although many were not as potent. In the low passage line, 8 of the compounds (colchicine, vinblastine, chloral hydrate, thiabendazole, thimerosal, econazole nitrate, pyrimethamine and diazepam) induced aneuploidy and/or tetraploidy. Cadmium chloride was negative in the chromosome enumeration assay and hydroquinone yielded inconclusive results. The study of cell division aberrations was much less time-consuming and technically complex than the counting of metaphase chromosomes. In addition, it provided a degree of mechanistic understanding of the mode of action of some aneugenic and polyploidy-producing agents. However, the enumeration of chromosomes provides a more definitive data set for the evaluation of a chemical's aneugenic potential.

Induction of micronuclei in V79 Chinese hamster cells by hydroquinone and econazole nitrate

Two suspect aneugens (hydroquinone and econazole nitrate) were examined for their ability to induce micronuclei in a number of V79 Chinese hamster cell lines which express rat cytochrome P-450 cDNAs. Hydroquinone elevated micronucleated cell frequencies in a dose-dependent manner in cell lines V79, XEM2 (expresses CYP1A1) and SD1 (expresses CYP2B1). Econazole nitrate was an effective inducer of micronuclei over a narrow dose range in cell lines V79, XEM2 and XEMd-MZ (expresses CYP1A2). The different cell lines showed similar responses to the test agents, indicating that hydroquinone is not a substrate for biotransformation by rat CYP1A1 or CYP2B1, nor is econazole nitrate biotransformed by rat CYP1A1 or CYP1A2.

Morphological transformation of an established Syrian hamster dermal cell with the anti-tussive agent noscapine

Following exposure to the alkaloid noscapine hydrochloride over a concentration range of 10-120 micrograms/ml immortal cultures of Syrian hamster dermal fibroblasts were shown to undergo morphological transformation. The resultant transformed foci produced cultures which were anchorage independent as confirmed by soft agar tests. Karyotype analysis of a noscapine transformed colony demonstrated an increase in chromosome number compared to the immortal culture and the non-random duplication of a translocated chromosome 9 previously identified in the immortal culture. These data indicate that noscapine, which has previously been shown to be a spindle inhibitor and inducer of polyploidy in cultured cells, is capable of inducing in vitro cell transformation. Such data indicate a carcinogenic potential for this widely used cough suppressant.

Assignment of the NRAS protooncogene to chromosome 12 of Syrian hamster by in situ hybridization

The NRAS protooncogene codes for a GTP binding/GTPase p21 protein which resides on the inner surface of the plasma membrane. Using a human cDNA probe for NRAS, we have assigned the gene to Syrian hamster chromosome 12 with the most likely localization being 12qa5.

A study of mitotic division fidelity and numerical chromosome changes in ageing Syrian hamster dermal cells

Events associated with culture ageing in Syrian hamster dermal cells have been studied from the time of culture isolation during continuous passage until they senesced and died. Microscopic examination of mitotic cells using differential staining of chromosome and spindle apparatus assessed the faithfulness of cell division. Other indicators of the quality of cell division were obtained from chromosome counts, micronucleus frequencies and incidences of binucleate cells. A loss of spindle fidelity and an increase in aneuploidy corresponded to the period of culture senescence. The data presented indicate that the loss of division fidelity and chromosome number instability is an important indicator of the progression of a mammalian culture to senescence under in vitro conditions. Such information may provide the basis of a model for the study of factors which modify mitotic fidelity and senescence and provide a methodology for monitoring the suitability of mammalian cultures for commercial usage.

Comparisons of tests for aneuploidy

The fundamental problems that face us in the development of suitable assay systems for the detection of potentially aneugenic (aneuploidy-inducing) chemicals include: (a) the diversity of cellular targets and mechanisms where perturbations of structure and function may give rise to changes in chromosome number, and (b) the phylogenetic differences that exist between species in their mechanism and kinetics of cell division and their metabolic profiles. A diverse range of assay systems have been developed, which have been shown to have potential for use in the detection of either changes in chromosome number or of perturbations of the events which may be causal in the induction of aneuploidy. Chromosome number changes may be detected cytologically by karyotypic analysis, or by the use of specialised strains in which aneuploid progeny may be observed due to phenotypic differences with aneuploid parental cells or whole organisms. Techniques for the detection of cellular target modifications range from in vitro studies of tubulin polymerisation to observations of the behaviour of various cellular organelles and their fidelity of action during the division cycle. The diversity of mechanisms which may give rise to aneuploidy and the qualitative relevance of events observed in experimental organisms compared to man make it unlikely that the detection and risk assessment of the aneugenic activity of chemicals will be possible using a single assay system. Optimal screening and assessment procedures will thus be dependent upon the selection of an appropriate battery of predictive tests for the measurement of the potentially damaging effects of aneuploidy induction.

The effects of benzodiazepines upon the fidelity of mitotic cell division in cultured Chinese hamster cells

4 benzodiazepine sedatives, namely diazepam, medazepam, midazolam and bromazepam were investigated for their effects upon the fidelity of cell division in both low passage number and immortalised Chinese hamster cell lines. The study revealed substantial differences in the effect of these structurally related drugs upon mitosis, which may reflect different mechanisms of action of the drugs in cultured cells. Diazepam and medazepam exposure of immortal and low passage number cells resulted in the formation of monopolar mitotic spindles and subsequent metaphase arrest. The production of these spindles may be explained by the inhibition or centriole separation . In contrast, midazolam and bromazepam failed to produce observable changes in spindle structure. All 4 benzodiazepines produced significant toxicity in low passage number cells whereas, immortalised cells were more resistant to their toxic effects. They all induced metaphase chromosome dislocations in immortalised cells, whereas only diazepam and medazepam produced such effects in the low passage number cell line. In general, immortal cells appeared to be less sensitive to the toxic effects of benzodiazepines than the low passage number cells.

The effect of Michler's ketone on cell division, chromosome number and structure in cultured Chinese hamster cells

The industrial chemical Michler's ketone (MK) has been examined for its ability to induce abnormalities of mitotic cell division and the production of chromosomal aberrations and aneuploidy. MK was shown to produce aberrant cell division stages in cultured mammalian cells probably by interference with centrosome replication leading to the production of monopolar spindles during metaphase, and multipolar telophase spindles, in the first division after exposure. Cells in the second division after exposure to MK showed increased levels of chromosome aneuploidy which is presumed to result from aberrant cell division. There was also some evidence of increased levels of chromosome structural aberrations at concentrations of 1.5 microgram/ml.

The observation of mitotic division aberrations in mammalian cells exposed to chemical and radiation treatments

The fidelity of chromosome segregation and the maintenance of the integrity of the chromosome karyotype of eukaryotic cells is dependent upon the synthesis and functioning of division-related structures such as the nuclear spindle and events such as the attachment of chromosomes to the spindle and their subsequent movement to the poles of the dividing cell. Chemical and physical treatment which modify the synthesis and functioning of division-related events may potentially lead to the production of cells with abnormal chromosome numbers (of both whole chromosome sets and of individual chromosomes). The ability of environmental agents to modify division-related structures in mammalian cells has been assessed by morphological examination of exposed mitotically dividing cells using staining techniques which identify spindle and chromosome structure and by the analysis of the characteristics of microtubule polymerisation in vitro. Such techniques have been used to identify the spindle-modifying effects of chemicals such as the synthetic hormone diethylstilboestrol and modifications of chromosome to spindle attachment in cells exposed to both UV- and X-irradiation. Such modifications of cell-division-related activities may lead to alterations in the fidelity of division events leading to the production of chromosomally abnormal daughter cells with aneuploid or polyploid karyotypes.

Differential staining of chromosomes and spindle and its use as an assay for determining the effect of diethylstilboestrol on cultured mammalian cells

A differential staining technique that allows for the simultaneous visualization of chromosome and spindle fibres has been used to investigate the action of diethylstilboestrol (DES) on cultured human fibroblasts. It was found that the mitotic index increased while spindle-fibre formation was inhibited with increasing DES concentration. Normal cellular division was severely affected by DES exposure in a dose-related manner. It has been demonstrated that this new staining technique may help to show up some mitotic poisons which are an important group currently missed by bacterial and clastogenic tests.

Detection of mitotic and meiotic aneuploidy in the yeast Saccharomyces cerevisiae

A number of genetic systems are described which involve the use of the yeast Saccharomyces cerevisiae. The systems may be used to detect the production of aneuploid cells produced during both mitotic and meiotic cell division in the presence of genetically active chemicals. During mitotic cell division, monosomic colonies (2n - 1) may be detected by plating upon selective medium. Increases in such monosomic colonies are produced by exposure of cells to a number of chemical mutagens such as ethyl methane-sulfonate and mitomycin C. More importantly, monosomic colonies are also induced by nonmutagens such as sulfacetamide and saccharin, which suggests that such chemicals are capable of inducing aneuploidy (aneugenic) in the absence of mutagenic activity. Genetic analysis of aneuploid colonies produced on nonselective medium indicate that at least a proportion of the monosomic colonies were the result of mitotic nondisjunction. During meiotic cell division, disomic cells (n + 1) produced by chromosome nondisjunction may be detected by plating on selective media. The frequency of disomic cells has been shown to increase after exposure to p-fluorophenylalanine.

Radiation-induced mitotic and meiotic aneuploidy in the yeast Saccharomyces cerevisiae

A number of genetic systems are described which in yeast may be used to monitor the induction of chromosome aneuploidy during both mitotic and meiotic cell division. Using these systems we have been able to demonstrate the induction of both monosomic and trisomic cells in mitotically dividing cells and disomic spores in meiotically dividing cells after both UV light and X-ray exposure. The frequency of UV-light-induced monosomic colonies were reduced by post-treatment with photoreactivity light and both UV-light- and X-ray-induced monosomic colonies were reduced by liquid holding post-treatment under non-nutrient conditions. Both responses indicate an involvement of DNA-repair mechanisms in the removal of lesions which may lead to monosomy in yeast. This was further confirmed by the response of an excision-defective yeast strain which showed considerably increased sensitivity to the induction of monosomic colonies by UV-light treatment at low doses. Yeast cultures irradiated at different stages of growth showed variation in their responses to both UV-light and X-rays, cells at the exponential phase of growth show maximum sensitivity to the induction of monosomic colonies at low doses whereas stationary phase cultures showed maximum induction of monosomic colonies at high does. The frequencies of X-ray-induced chromosome aneuploidy during meiosis leading to the production of disomic spores was shown to be dependent upon the stage of meiosis at which the yeast cells were exposed to radiation. Cells which had proceeded beyond the DNA synthetic stage of meiosis were shown to produce disomic spores at considerably lower radiation doses than those cells which had only recently been inoculated into sporulation medium. The results obtained suggest that the yeast sustem may be suitable for the study of sensitivities of the various stages of meiotic cell division to the induction of chromosome aneuploidy after radiation exposure.

The genetic control of liquid-holding recovery and U.V.-induced repair resistance in the yeast, Saccharomyces cerevisiae

Liquid-holding treatment in non-nutrient solutions after U.V.-exposure results in an increased resistance of wild-type (RAD) yeast cells to a second U.V.-treatment (repair resistance). U.V.-sensitive (rad) mutants of yeast which show variation in their response to liquid-holding treatment and a second U.V.-dose-range have been classified into two groups. Mutants of Group 1 show increased viability after post-U.V.-liquid-holding treatment and show repair resistance. In contrast, mutants of Group 2 which show reduced viability during post-U.V.-liquid-holding treatment have the same U.V.-sensitivity, both before and after liquid-holding treatment. Genetic analysis of crosses of the rad mutants to wild-type cultures indicate that the phenotype of repair resistance to U.V.-treatment is under genetic control and depends on the presence of alleles of radiation sensitivity genes, which also confer the property of liquid-holding recovery.

Serum urate and cholesterol levels in Air Force Academy cadets

Serum cholesterol and urate levels were measured in 150 young men at 2- to 4-month intervals during their first 18 months at the U.S. Air Force Academy. During the first week of cadet training, mean serum urate levels rose as high as 9.5 mg/100 m/, but decreased after a Sunday break. During this week, urate levels in excess of 8.49 mg/100 m/ were found in 44% of the subjects. Such levels, while definitely exceeding normal limits, were attributed to acute psychosocial stress rather than to an abnormal or pathological process. One month after the completion of basic military training, mean serum urate levels were within normal limits, as were all subsequent mean urate levels. Mean serum cholesterol levels were elevated at three times - during the first week of training, after the first month of the first academic year, and during a week of intense military training in the following spring. Apparently, urate and cholesterol levels were elevated by different aspects of stress. Elevations of uric acid level appeared to reflect stress that excited fear or insecurity. Elevations of cholesterol levels apeared to reflect a stress which the individual perceived as requiring a sustained increase in physical and/or mental performance.