Enhancing the in vitro and in vivo detection of aneuploidy by fluorescence in situ hybridization with the use of bromodeoxyuridine as a proliferation marker

Aneuploidy is associated with spontaneous abortions, birth defects, and many types of human cancers. Currently there are few assays developed for the efficient detection of aneuploidy in vivo. However, with the recent availability of chromosome-specific DNA probes for the rat, fluorescence in situ hybridization (FISH) techniques could be used for the rapid and sensitive detection of aneuploidy in different tissue and cell types. In order to develop a system that can detect alterations in chromosome number in rat cells in vitro, we treated cultured rat lymphocytes with three aneugens-noscapine hydrochloride (0–150 μM) and vincristine and vinblastine sulfate (0–0.06 μM). 5-Bromo-2-deoxyuridine (BrdU; 1 μM) was added to the culture medium to allow proliferating and non-proliferating cells to be distinguished. To test this assay under in vivo conditions, 21-day-old male Sprague–Dawley rats were subcutaneously implanted with osmotic pumps that delivered BrdU (12 mg/kg per day) continuously. These rats were administered vinblastine sulfate (0, 0.5 and 1 mg/kg) by intraperitoneal injection. The rat lymphocytes and hepatocytes incorporating BrdU were detected by immuno-fluorescent labeling, and FISH with a rat chromosome 4 probe was performed on the labeled and unlabeled cells. Highly significant increases in hyperdiploidy were seen in the replicating rat lymphocytes treated with noscapine, vincristine or vinblastine in vitro and in the rat hepatocytes treated with vinblastine in vivo. In contrast, no significant increase in hyperdiploidy was observed in the non-replicating cells. These results demonstrate that this BrdU-enhanced FISH assay with chromosome-specific rat probes can be used to efficiently detect numerical chromosomal aberrations in vitro and in vivo in slowly or moderately replicating rat tissues. The combination of BrdU-labeling and FISH allows the scoring of hyperdiploidy to be focused on the actively replicating cells, thereby increasing the sensitivity of the FISH technique.     

Ames test-negative carcinogen, ortho-phenyl phenol, binds tubulin and causes aneuploidy in budding yeast

Ortho-phenyl phenol (OPP) is broad-spectrum of fungicides and antibacterial agents. OPP tested negative in an Ames system and positive with respect to the formation of tumors in the urinary bladder in rats when administered in diet, showing attributes of an Ames test-negative carcinogen. It has also been demonstrated that OPP does not bind or cleave DNA in vivo or in vitro, rather dose-dependent protein binding in OPP-treated rats was observed. OPP, however, generates chromosomal aberrations including aneuploidy. Thus, the steps by which Ames test-negative carcinogens exert their effects need to be elucidated. Here, we used an assay of loss of heterozygosity (LOH) in Saccharomyces cerevisiae to determine the biological effects of OPP and its hepatic metabolite phenyl hydroquinone (PHQ). LOH was found to be induced by OPP and PHQ because of a functional chromosome loss: aneuploidy. PHQ bound to and interfered with the depolymerization of tubulin in vitro and arrested the cell-cycle at M and G1. These results indicate that OPP and PHQ damaged tubulin to cause mis-segregation of chromosome by delaying cell-cycle progression through mitosis, and as a consequence caused aneuploidy.     

Hyperdiploidy and apparent aneusomy in mesothelial cells from non-malignant effusions as detected by fluorescence in situ hybridization (FISH)

Interphase cytogenetics by fluorescence in situ hybridization (FISH) can be used to detect malignant cells characterized by chromosomal aneuploidy. However, apparent aneusomy in normal "control" tissues has to be considered when using FISH as diagnostic tool. In effusions as model tissue exposed to metastasis, the definition of cut-off levels for background aneusomy by FISH was aimed in this study. Using centromeric probes representing chromosomes 7, 8, 11, 12, 17 and 18, extensive chromosome copy number enumeration by single-color FISH analysis was performed in pleural and ascitic effusions derived from 15 patients with various, non-malignant diseases. In all effusions, cells with gain of hybridization signals for several or all chromosomes tested were found (in up to 1.94% of cells). A consistent finding was high grade hyperdiploidy (>4 centromeric signals). Mesothelial elements mainly contributed to hyperdiploidy in effusions, as demonstrated by a combined analysis of FISH and immunocytochemistry with staining for cytokeratin. Dual-color FISH analysis showed that hyperdiploidy was predominantly corresponding to polyploidization; however, there were always minor cell populations classified as aneuploid by dual-color FISH. In conclusion, stringent criteria have to be applied to distinguish malignancy-related aneuploidy from background aneusomy by FISH.     

Bimolane induces multiple types of chromosomal aberrations in human lymphocytes in vitro

Bimolane has been commonly used in China for the treatment of psoriasis and various types of cancer. Patients treated with bimolane have been reported to have an increased risk of developing therapy-related leukemias. Although bimolane has been identified as a human leukemia-inducing agent, little is known about its genotoxic effects, and a systematic study of the types of chromosomal alterations induced by this compound has not been performed. In this study, a combination of immunochemical, molecular and conventional cytogenetic techniques has been used to study the chromosomal alterations induced by bimolane in cultured human lymphocytes. Immunochemical staining with the CREST antibody indicated that bimolane induces micronuclei (MN) originating primarily from chromosome breakage. Interestingly fluorescence in situ hybridization (FISH) with differentially labeled chromosomes 1 and 9 centromeric probes indicated that bimolane also caused non-disjunction and polyploidy. Consistent with this, an expedited analysis of Giemsa-stained metaphase chromosomes in bimolane-treated lymphocytes revealed a high frequency of polyploidy/hyperdiploidy as well as dicentric chromosomes, and premature centromeric division (PCD). In addition, bimolane was also found to produce binucleated cells, possibly through an interference with normal functioning of intermediate filaments. As a follow-up to these studies, three different types of commercially available bimolane formulations obtained from different Chinese manufacturers were also evaluated. The effects seen with the formulated bimolane were similar to those seen with the synthesized compound. Our studies indicate that bimolane effectively induces a variety of cellular and chromosomal changes in cultured lymphocytes and that similar alterations occurring in bone marrow stem cells could contribute to the development of the secondary cancers seen in bimolane-treated patients.     

Importance of detecting numerical versus structural chromosome aberrations

The aim is to review briefly the key questions related to aneuploidy/polyploidy and to compare the advantages and disadvantages of the in vitro micronucleus test to assess aneuploidy/polyploidy in vitro. The key questions that will be addressed, concern the importance of polyploidy for health, and cancer in particular, the mechanisms leading to aneuploidy and polyploidy, and the survival of aneuploid/polyploid cells.The recently recognised contribution of numerical chromosome changes to carcinogenesis triggered the development and the implementation of tests specifically aiming at the detection of aneugens in the test battery for mutagenicity and carcinogenicity. The validation of the in vitro micronucleus test in combination with the identification of in vitro divided cells with the cytokinesis-block methodology and of centromeres with pancentromeric or chromosome specific centromeric probes fluorescence in situ hybridisation (FISH) provides a sensitive, easy to score and powerful test which allows assessment of cell proliferation, the discrimination between chromosome breaks, chromosome loss and chromosome non-disjunction and polyploidy. Moreover, classic histology permits the estimation of necrosis and apoptosis on the same slide. The cytokinesis-blocked micronucleus assay could be considered as a multi-endpoint test for genotoxic responses to clastogens/aneugens. This methodology has also shown to be capable of identifying threshold values for the induction of chromosome loss and/or non-disjunction by microtubule inhibitors, data which are particularly important for risk calculations. Similar approaches were conducted in vivo on bone marrow in mice and rats (except for identification of chromosome non-disjunction), and are in development for gut in mice.     

Molecular cytogenetic characteristics of chromosome imbalance in cells of spontaneous human abortion fetuses with low proliferative activity in vitro

Karyotyping of noncultivated cells of 60 first-trimester spontaneous abortions (blighted ova and missed abortions) was carried out using fluorescence in situ hybridization (FISH) with centromere-specific DNA probes for all chromosomes of the karyotype. Conventional cytogenetic study of these abortions was impossible because of cell culture failures. The algorithm is proposed for molecular cytogenetic FISH analysis of interphase karyotypes. Chromosome abnormalities were found in 32 fetuses (53.3%). In groups of missed abortions and blighted ova, the frequency of numerical chromosome abnormalities was 50 and 60%, respectively. Both the numerical chromosome abnormalities typical of spontaneous human abortions (autosomal trisomies, sex chromosome aneuploidy, and polyploidy) and a relatively rare type of genomic imbalance unidentifiable by standard cytogenetic analysis (autosomal monosomies 7, 15, 21, and 22 in mosaic state) were observed. The frequency of these type of chromosome abnormalities comprised 19% of all known karyotype abnormalities determined in spontaneously perished embryos. Note that the level of confined placental mosaicism in embryos with low cell proliferative activity was 25%, which is substantially higher than the corresponding parameter (1-2%) determined by prenatal diagnosis of chromosome abnormalities in developing embryos. The results of interphase FISH analysis of cells with low proliferative activity in vitro suggest that the pathology of early fetal development and missed abortion in humans are associated with a wider spectrum of chromosome abnormalities.     

Molecular Cytogenetic Characteristics of Chromosome Imbalance in Spontaneous Human Abortion Cells with Low Proliferative Activity in Vitro

Karyotyping of noncultivated cells of 60 first-trimester spontaneous abortions (blighted ovum and missed abortions) was carried out using fluorescence in situ hybridization (FISH) with centromere-specific DNA probes for all chromosomes of the karyotype. Conventional cytogenetic study of these abortions was impossible because of cell culture failures. The algorithm is proposed for molecular cytogenetic FISH analysis of interphase karyotypes. Chromosome abnormalities were found in 32 fetuses (53.3%). In groups of missed abortions and blighted ovum, the frequency of numerical chromosome abnormalities was 50 and 60%, respectively. Both the numerical chromosome abnormalities typical of spontaneous human abortions (autosomal trisomies, sex chromosome aneuploidy, and polyploidy) and a relatively rare type of genomic imbalance unidentifiable by standard cytogenetic analysis (autosomal monosomies 7, 15, 21, and 22 in mosaic state) were observed. The frequency of these type of chromosome abnormalities comprised 19% of all known karyotype abnormalities determined in spontaneously aborted embryos. Note that the level of confined placental mosaicism in embryos with low cell proliferative activity was 25%, which is substantially higher than the corresponding parameter (1–2%) determined by prenatal diagnosis of chromosome abnormalities in developing embryos. The results of interphase FISH analysis of cells with low proliferative activity in vitro suggest that the pathology of early fetal development and missed abortion in humans are associated with a wider spectrum of chromosome abnormalities.     

Induction of aneuploidy by mitotic arrestants in mouse bone marrow

Most human and animal carcinogens induce gene mutation, chromosome breakage or other types of DNA lesions. However, recent studies indicate that some carcinogens do not directly damage DNA, but may cause missegregation of chromosomes resulting in aneuploidy production. Aneuploidy-producing agents pose serious genetic hazards to the human population. Such agents may cause genomic imbalance not only in somatic cells which may result in cancer development, but also in germinal cells which may result in the production of abnormal offspring (e.g. Down's syndrome). To limit human exposure to potential aneuploidy-producing agents, such agents must first be identified in experimental animals. The present study demonstrates that vinblastine and colcemid are capable of inducing aneuploidy in bone marrow cells of treated mice. Both of these compounds are chemotherapeutic agents that arrest mitosis by interfering with the formation of spindle microtubules. Single intraperitoneal injections of vinblastine, at a dose of 9 mg/kg, were found to produce 1.5-5.2% of hyperdiploidy in all of the 10 treated mice sampled at 17-96 h after injection. Only the frequency of hyperdiploidy was determined because hypodiploid cells could result from artifactual chromosome loss during slide preparation. At 0.9 mg/kg, vinblastine was found to produce 0.5-3.5% of hyperdiploidy in 8 of the 10 treated animals. The frequency of hyperdiploid cells in animals treated with colcemid was low. A dose as high as 37 mg/kg was found to produce only 0.5-1% of hyperdiploidy in 3 of the 10 treated animals, and hyperdiploidy was observed only in animals sampled at 17-24 h. In 10 mice treated with saline alone, no hyperdiploid cells were observed. Unlike cell cultures where vinblastine and colcemid had been shown to be equally effective in producing aneuploidy, vinblastine was found in this study to be a much more potent aneuploidy inducer than colcemid in mice.     

Rotenone induces aneuploidy, polyploidy and endoreduplication in cultured Chinese hamster cells

The clastogenic potential of rotenone, an insecticide, was investigated in cultured Chinese hamster cells. Rotenone induced aneuploidy (hypodiploidy and hyperdiploidy), polyploidy, and endoreduplication, but not structural chromosome aberrations. The highest frequency of polyploidy and endoreduplication was 58.8% and 3.0%, respectively, when cells were treated with rotenone at 1.0 microgram/ml for 30 h.     

Preferential S-phase pairing of the imprinted region on distal mouse chromosome 7.

Fluorescence in situ hybridization (FISH) has been used to visualize the spatial orientation of homologous chromosome regions in interphase nuclei of exponentially growing mouse fibroblasts. Simultaneous labeling of replicating DNA with the halogenated base analog 5-bromodeoxyuridine (BrdU) shows preferential somatic pairing of the imprinted region on distal mouse chromosome 7 during the S phase of the cell cycle. Trans-interactions between oppositely imprinted chromosome regions may be important for the maintenance of imprinting.     

Molecular mechanisms involved in the toxicity of orthophenylphenol and its sodium salt

Hiraga and Fujii have recently reported that F344 rats consuming diets with high levels of sodium orthophenylphenate (SOPP) developed bladder tumors after 13–91 weeks (Fd. Cosmet. Toxicol., 19 (1981) 303). Several dose levels were tested and doses above 1.0% SOPP by weight appeared to cause an increase in both toxicity and bladder carcinogenicity. In order to put these studies into better perspective, the effects of feeding diets containing SOPP or orthophenylphenol (OPP) to F344 male rats for varying lengths of time were characterized.Hyperplasia of the bladder epithelium was noted in rats consuming diets containing 2% SOPP (equivalent to 1000–1500 mg/kg/day) after 1–2 weeks, with epithelial thickening increasing through 90 days. No bladder lesions were seen in the group consuming 2% OPP but focal kidney lesions were noted. In contrast to the results reported by Hiraga and Fujii, no tumors of the urinary tract were observed following 90 days of consumption of the 2% SOPP diet.The potential of these chemicals to induce genotoxic lesions was studied. No detectable increases in the reversion rates of Salmonella typhimurium (strains TA 98, TA 100, TA 1535, TA 1537 and TA 1538) were seen at concentrations of SOPP up to 5.8 · 10^?4 M. SOPP also failed to produce a detectable increase in unscheduled DNA synthesis in primary rat hepatocytes at concentrations up to 1 · 10^?4 M. No covalently-bound radioactivity was observed in DNA purified from the bladders of rats gavaged with 500 mg/kg [¹⁴C]SOPP or [¹⁴C]OPP (detection limit < 1 alkylation/10⁶ nucleotides). These results suggest little or no genotoxicity for OPP or SOPP.The metabolism of OPP and SOPP in male F344 rats was shown to be dose-dependent. After gavage with 50 mg/kg or less, most of the administered material was recovered in the urine as glucuronide or sulfate conjugates of the parent material. After gavage with 500 mg/kg a new metabolite, apparently produced by mixed function oxidases, was observed. This metabolite was characterized by gas chromatography/mass spectroscopy as a conjugate of dihydroxybiphenyl. It is postulated that the potentially reactive metabolites produced by this oxidative pathway may be associated with the toxicity induced by high concentrations of OPP or SOPP.Thus the bladder toxicity and carcinogenicity of SOPP and the renal toxicity of OPP appear to occur only following the administration of high doses which saturate the normal conjugation pathways. However, since no genotoxicity was detected even at saturating doses, it appears unlikely that exposure to subtoxic doses would cause any significant increase in carcinogenic risk.     

Chromosome-level homeology in paleopolyploid soybean (Glycine max) revealed through integration of genetic and chromosome maps

Soybean has 20 chromosome pairs that are derived from at least two rounds of genomewide duplication or polyploidy events although, cytogenetically, soybean behaves like a diploid and has disomic inheritance for most loci. Genetically anchored genomic clones were used as probes for fluorescence in situ hybridization (FISH) to determine the level of postpolyploid chromosomal rearrangements and to integrate the genetic and physical maps to (1) assign linkage groups to specific chromosomes, (2) assess chromosomal structure, and (3) determine the distribution of recombination along the length of a chromosome. FISH mapping of seven putatively gene-rich BACs from linkage group L (chromosome 19) revealed that most of the genetic map correlates to the highly euchromatic long arm and that there is extensive homeology with another chromosome pair, although colinearity of some loci does appear to be disrupted. Moreover, mapping of BACs containing high-copy sequences revealed sequestration of high-copy repeats to the pericentromeric regions of this chromosome. Taken together, these data present a model of chromosome structure in a highly duplicated but diploidized eukaryote, soybean.     

Quantitative Analysis of Centromeric FISH Spots during the Cell Cycle by Image Cytometry

Two-color fluorescence in situ hybridization (FISH) with chromosome enumeration DNA probes specific to chromosomes 7, 11, 17, and 18 was applied to CAL-51 breast cancer cells to examine whether the fluorescence intensity of FISH spots was associated with cell cycle progression. The fluorescence intensity of each FISH spot was quantitatively analyzed based on the cell cycle stage determined by image cytometry at the single-cell level. The spot intensity of cells in the G₂ phase was larger than that in the G_0/1 phase. This increased intensity was not seen during the early and mid S phases, whereas the cells in the late S phase showed significant increases in spot intensity, reaching the same level as that observed in the G₂ phase, indicating that alpha satellite DNA in the centromeric region was replicated in the late S phase. Thus, image cytometry can successfully detect small differences in the fluorescence intensities of centromeric spots of homologous chromosomes. This combinational image analysis of FISH spots and the cell cycle with cell image cytometry provides insights into new aspects of the cell cycle. This is the first report demonstrating that image cytometry can be used to analyze the fluorescence intensity of FISH signals during the cell cycle.     

染色体畸形变与膀胱癌发生发展的相关性研究

目的：通过荧光原位杂交技术（FISH）结合病理分级,探讨染色体畸形变与膀胱癌发生和发展的关系。方法：采用3、7、9、17号染色体着丝粒探针和9P16区带探针对105例膀胱癌复发患者尿液脱落细胞进行荧光原位杂交．观察膀胱癌复发患者中3、7、9、17号染色体的畸形变情况并分析其与患者临床和病理特征之间的关系。结果：105例膀胱癌复发患者中,3、7、9和17号染色体的非整数倍突变率分别是21．9％、29．5％、12．4％、和36．2％,与患者的性别、年龄无显著相关性（P〉0．05）。仅7号染色体畸变与膀胱癌的病理分级具有显著相关性[（P〈0．05）。结论：7号染色体畸形变与复发膀胱癌的病理分级显著相关。     

GLPp16/CSP17 探针在膀胱尿路上皮癌诊断中的应用

目的:探讨荧光原位杂交技术辅助诊断膀胱尿路上皮癌的可行性。方法:标记为17号染色体着丝粒及9号染色体p16位点9p21区带探针,采用荧光原位杂交技术(Fluorescence in Situ Hybridization FISH)对80例膀胱肿瘤患者尿液间期细胞核进行荧光原位杂交,以20例健康志愿者作为正常对照组,建立阈值。以术后病理结果作为诊断"金标准",对80例膀胱肿瘤患者同时行尿脱落细胞学检查,与FISH进行比较。结果:17号染色体和9p21的畸变率分别为57.5%和63.8%。17号染色体畸变率主要表现为多倍体,与膀胱癌的分级有显著相关性(P<0.01);9号染色体畸变率主要变现为染色体缺失,与膀胱癌分期分级均无相关性(P>0.05)。尿脱落细胞学灵敏度为12.2%,FTSH技术灵敏度为86.5%;两者差异有统计学意义(P<0.01)。结论:荧光原位杂交技术可以作为膀胱尿路上皮癌诊断的一项重要方法,并可能在预后判断中具有重要临床意义。     

染色体畸形变与膀胱癌发生发展的相关性研究

目的:通过荧光原位杂交技术(FISH)结合病理分级,探讨染色体畸形变与膀胱癌发生和发展的关系。方法:采用3、7、9、17号染色体着丝粒探针和9P16区带探针对105例膀胱癌复发患者尿液脱落细胞进行荧光原位杂交,观察膀胱癌复发患者中3、7、9、17号染色体的畸形变情况并分析其与患者临床和病理特征之间的关系。结果:105例膀胱癌复发患者中,3、7、9和17号染色体的非整数倍突变率分别是21.9%、29.5%、12.4%、和36.2%,与患者的性别、年龄无显著相关性(P0.05)。仅7号染色体畸变与膀胱癌的病理分级具有显著相关性(P0.05)。结论:7号染色体畸形变与复发膀胱癌的病理分级显著相关。     

Analysis of chromosome segregation during preimplantation genetic diagnosis in both male and female translocation heterozygotes

Individuals carrying translocations suffer from reduced fertility or spontaneous abortions and seek help in form of assisted reproductive technology (ART) and preimplantation genetic diagnosis (PGD). While most translocations are relatively easy to detect in metaphase cells, the majority of embryonic cells biopsied in the course of in vitro fertilization (IVF) procedures are in interphase. These nuclei are thus unsuitable for analysis by chromosome banding or painting using fluorescence in situ hybridization (FISH). Thus several methods have been devised to detect translocation imbalance through FISH in single cells for purpose of PGD, among them polar body chromosome painting, interphase FISH with combination of subtelomeric and centromeric probes, breakpoint spanning probes, and cell conversion. Results with PGD indicate a significant decrease in spontaneous abortions, from 81% before PGD to 13% after PGD. They also indicate very high rates of chromosome abnormalities in embryos from translocation carriers, 72% for Robertsonian translocations and 82% for reciprocal translocations. Sperm analysis was found to be a good predictor of IVF and PGD outcome, with samples with more than 60% abnormal forms indicating poor prognosis. Similarly, the predictability from first PGD cycle results for future cycles was 90%. In summary, PGD can help translocation carriers to achieve viable pregnancies, but the success of the process is conversely related to the baseline of unbalanced gametes.     

Interphase cytogenetics in pathology: principles, methods, and applications of fluorescence in situ hybridization (FISH)

 Characteristic chromosome aberrations have been identified in various tumors. Fluorescence in situ hybridization (FISH) using specific probes that are generated by vector cloning or in vitro amplification and labeled with fluorescent dyes allow for the detection of these genetic changes in interphase cells. This technique, that is also referred to as ”interphase cytogenetics”, can be performed in cytological preparations as well as in sections of routinely formaldehyde-fixed and paraffin-embedded tissue. In cancer research and diagnostics, interphase cytogenetics by FISH is used to detect numerical chromosome changes and structural aberrations, e.g., translocations, deletions, or amplifications. In this technical overview, we explain the principles of the FISH method and provide protocols for FISH in cytological preparations and paraffin sections. Moreover, possible applications of FISH are discussed. Accepted: 22 July 1997     

Simultaneous detection of X- and Y-bearing human sperm by double fluorescence in situ hybridization

Double fluorescence in situ hybridization (FISH) was used to detect sex chromosomes in decondensed human sperm nuclei. Biotinylated X chromosome specific (TRX) and digoxigenin-labeled Y chromosome specific (HRY) probes were simultaneously hybridized to sperm preparations from 12 normal healthy donors. After the hybridization, the probes were detected immuno-cytochemically, using two different and independent affinity systems. Ninety-six percent of the 12,636 sperm showed fluorescent labeling, of which 47.4% were haploid X and 46.8% were haploid Y. A frequency of 0.46% of XX-bearing sperm (0.28% disomic, 0.18% diploid) and 0.38% YY-bearing sperm (0.21% disomic, 0.17% diploid) was found. The overall proportions of X- and Y-bearing sperm in the ejaculates were 47.9% and 47.2%, respectively, which was not significantly different from the expected 50:50 ratio. In addition 0.21% of cells appeared to be haploid XY-bearing sperm, 0.62% were diploid XY-bearing cells, and 0.05% of cells were considered to be tetraploid cells. The application of double FISH to human sperm using X-chro-mosome and Y-chromosome probes has allowed a more accurate assessment of the sex chromosal complements in sperm than single FISH method and quinacrine staining for Y-bodies. © 1993 Wiley-Liss, Inc.     

Arylarnine N-acetyltransferase as a potential biornarker in bladder cancer: fluorescent in situ hybridization and irnmunohistochernistry studies

Arylamine N-acetyltransferase isoenzymes NAT1 and NAT2 are encoded at two polymorphic loci on human chromosome 8p22. The two loci have previously been identified using chimeric Yeast Artificial Chromosome (YAC) clones encoding either NAT1 or NAT2 as probes for metaphase chromosomes using fluorescent in situ hybridization. The 8p22 region has been demonstrated to be deleted in highly invasive bladder tumours and since NAT isoenzymes participate in the metabolism of arylamine bladder carcinogens, it is important to determine whether NAT1 and NAT2 gene loci are included in the region of deletion. We describe here the application of a cosmid clone for NAT2 as a biomarker for Fluorescent In Situ Hybridization (FISH) on interphase nuclei of exfoliated bladder cells. We also describe a 70kb probe for NAT1 which is a candidate for a suitable biomarker for use in similar FISH studies. lmmunohistochemical staining of bladder tumour sections with a polyclonal anti-peptide antibody specific for the NATl isoenzyme as a biomarker for NAT1 protein expression is also shown.