Differential Giemsa staining of sister chromatids and the study of chromatid exchanges without autoradiography

Influence of low doses of BrdU and estimation of spontaneous SCE in CHO chromosomes: three-way differential staining and an immunoperoxidase method

The influence of low doses of 5-bromodeoxyuridine (BrdU) on the occurrence of sister chromatid exchanges (SCEs) during the first cell cycle, when unsubstituted DNA templates replicate in the presence of the halogenated nucleoside (SCE1) has been assessed in third mitosis (M3) Chinese hamster ovary (CHO) cells showing three-way differential (TWD) staining. In addition, lower concentrations of BrdU, not detectable by Giemsa staining, have been tested by a high resolution immunoperoxidase method (anti-BrdU monoclonal antibody) and SCEs were scored in second mitosis (M2) cells. Our findings was a dose-response curve for SCE1 that allows an estimated mean spontaneous yield of 1.32/cell per cell cycle by extrapolation to zero concentration of BrdU. On the other hand, when the total SCE frequency corresponding to the first and second rounds of replication (SCE1 + SCE2) found in M3 chromosomes was compared with the yield of SCEs scored in M2 cells grown in BrdU at doses lower than 1 microM no further reduction was achieved. This seems to indicate that SCEs can occur spontaneously in this cell line, though the estimated frequency is higher than that reported in vivo.

Cytogenetic damage induced in human lymphocytes by sodium bisulfite

The frequencies of chromosomal aberrations (CA), sister-chromatid exchanges (SCE), and micronuclei (MN) in human blood lymphocytes exposed to sodium bisulfite (sulfur dioxide) at various concentrations ranging from 5 x 10(-5) M to 2 x 10(-3) M in vitro were studied. It was shown that sodium bisulfite (NaHSO3 and Na2SO3, 1:3 M/M) caused an increase in SCE and MN in human blood lymphocytes in a dose-dependent manner, and also induced mitotic delays and decreased mitotic index. For CA, our results indicated that sodium bisulfite induced an increase of chromatid-type aberrations in lymphocytes from three of four donors in a dose-dependent manner. The chemical at low concentrations induced chromatid-type aberrations, but not chromosome-type aberrations; high concentrations induced both chromatid- and chromosome-type aberrations. No cytogenetic damage in human lymphocytes was induced by sodium sulfate. The results have confirmed that sulfur dioxide is a clastogenic and genotoxic agent.

Induction of endoreduplication in double minutes of the human neuroblastoma cells and the replication pattern

Induction of endoreduplication (ERD) using Hoechst 33258 as well as colcemid was carried out in cultured neuroblastoma (NB) line cells. In these endoreduplicated cells, the majority of double minutes (DMs) appeared to take a diplochromosome like configuration to form a cluster consisting of four minute elements, assuming a complex DM. Sister chromatid differential staining (SCD) using 5-bromo-2'-deoxyuridine (BrdUrd) revealed the non-random distribution of the stained chromatids among four chromatids composing each diplochromosome, suggesting the occurrence of so-called "outside replication" of DNA strands during the process of ERD. The same pattern of differential staining was also found in the quadruple minutes of each endoreduplicated DM. Since DMs are acentric, the present results suggest that centromeres do not play any essential role in the formation of diplochromosomes observed in the conventional cytologic preparations and that centromeres are probably not responsible for the phenomenon of the "outside replication" of DNA strands.

A survey of lymphocyte chromosomal damage in Slovenian workers exposed to occupational clastogens

Assays for sister-chromatid exchanges (SCE), unstable chromosome and chromatid aberrations and micronuclei were performed on blood lymphocytes from persons exposed protractedly to radiation or chemical hazards in the workplace. There was a general tendency with all endpoints examined for the yields to increase with years of working in the industry. This was especially marked for SCE. By comparison with a control group of administrative workers the levels of damage were higher, usually significantly so, in the occupational groups. These comprised workers at a nuclear research reactor, a hospital diagnostic X-ray department, a coal mine and a mercury ore mine.

Directly acting geno- and cytotoxic agents from a wild mushroom Dermocybe sanguinea

The wild mushroom, Dermocybe sanguinea, contains several anthraquinone pigments, of which emodin (1,3,8-trihydroxy-6-methylanthraquinone) is quantitatively the most important. In our preliminary tests, Dermocybe sanguinea extracts were genotoxic without metabolic activation. The ethanol extract of Dermocybe sanguinea was fractionated by flash chromatography, and the emodin contents of the fractions were determined by HPLC. Their genotoxicities were assayed using a bacterial repair assay and sister-chromatid exchange analysis. The cytotoxicity of the fractions was assayed with mouse hepatoma cells using growth inhibition as the endpoint. The results of the biological tests were compared with those obtained with pure emodin. It was concluded that, in addition to emodin, Dermocybe sanguinea contains several other geno- and cytotoxic compounds.

Enhanced expression of stomach cancer antigen derived from malignantly transformed bloom syndrome cells previously labeled with bromodeoxyuridine

Bromodeoxyuridine (BrdU) greatly enhanced expression of stomach (ST) cancer antigen (CA) that originated from a malignantly transformed Bloom syndrome (BS) cell line (BS-SHI-4M), although the expression was suppressed with a decrease in sister chromatid exchange (SCE) in the presence of deoxythymidine (dT) or deoxycytidine (dC) and enhanced with an increase in SCE with deoxyguanosine (dG) or deoxyadenosine (dA). Although the exact mechanisms for enhancing CA by BrdU treatment are unknown, these findings appeared to be of special interest because of the parallelism of CA expression and SCE alterations. The finding that BrdU enhancement of the ST CA was effective not only in the immunofluorescence (IF) protocol but also in the band appearance of Western blotting would be worthwhile as a sensitive serodiagnosis of cancer. The 118-kd band obtained from proteins of ST CA cells previously labeled with BrdU was clearly more darkly stained than that from nonlabeled cells and enabled eight weak-positive ST CA to show strong-positive levels retaining complete negativity to nonmalignant sera. Some ST cancer sera (advanced cancer), which originally gave a negative reaction in the nonlabeled condition, still inhibited negative reaction even in BrdU-labeled ST CA cells, however. The inability to detect cancer antibody in our assay might be due to immunocomplexes. Acid dissociation and ultrafiltration of sera from six of seven advanced ST cancers (originally IF negative) have allowed detection of antibody responses to ST CA by Western blot assay with enhanced reactivity as compared with the negativity under native serum conditions. This technique provides a reasonable avenue for study of the mechanisms of CA expression and serodiagnosis.

A simple and convenient method for gaining pure populations of lymphocytes at the first mitotic division in vitro

This paper describes a simple method for obtaining pure populations of human lymphocytes at the first in vitro mitotic division (M-1) by continuous treatment with colchicine or colcemid. When colchicine (7.2 x 10(-8) M) or colcemid (4.8 x 10(-8) M) was added to cultures 0-24 h after initiation, cultures harvested at 54 h had more than 99.9% of mitotic cells in the first metaphase (M-1). We showed that not only more analyzable M-1 cells may be obtained, but staining for sister-chromatid differentiation may be avoided.

Sister-chromatid exchange induction produced by in vivo and in vitro exposure to alpha-asarone

The effect of alpha-asarone, a chemical with hypocholesterolemic properties extracted from Guatteria gaumeri, on SCE induction was studied both in human lymphocytes in vitro and in murine bone marrow cells in vivo. A slight but consistent increase in SCE was observed in both biological systems.

Sister-chromatid exchanges in operating room personnel

Sister-chromatid exchange (SCE) analysis was carried out in 67 operating room personnel (anaesthetists M.D.; anaesthesia nurses and anaesthesia unit technicians) exposed to waste anaesthetic gases such as halothane, nitrous oxide and isoflurane and in 50 healthy unexposed controls. The SCE frequencies were increased significantly in operating room personnel as compared to controls. A significant increase in SCEs was found in non-smoking operating room personnel as compared to non-smoking controls. This study supports the existence of an association between occupational exposure to mutagens and an increase in SCEs in lymphocytes.

Effect of chloramphenicol on sister chromatid exchange in bovine fibroblasts

The genotoxic potential of different chloramphenicol concentrations (5, 20, 40 and 60 micrograms ml-1) was investigated in bovine fibroblast primary lines by sister chromatid exchange assay. Chloramphenicol acted for long enough to ensure similar effects to persistent storage in the kidney. In this experiment 10 micrograms ml-1 of 5-bromodeoxyuridine was added for 60 hours for all doses of chloramphenicol and to the control. When the tissue culture cells were exposed to increasing doses, increased numbers of sister chromatid exchanges developed. Differences were significantly different to the control.

Effect of bromodeoxyuridine on the proliferation and growth of ethyl methanesulfonate-exposed P3 cells: relationship to the induction of sister-chromatid exchanges

Although sister-chromatid exchange (SCE) analysis is recognized as an indicator of exposure to DNA-damaging agents, the results of these analyses have been confounded by the use of bromodeoxyuridine (BrdUrd) to differentially label the sister chromatids. Not only does BrdUrd itself induce SCE, it also modulates the frequency of SCE induced by certain DNA-damaging agents. In order to examine this effect of BrdUrd on SCE frequency, an indirect method which lends itself to measurements both with and without BrdUrd was employed. Human teratocarcinoma-derived (P3) cells were exposed to ethyl methanesulfonate (EMS) and cultured with increasing concentrations of BrdUrd for lengths of time corresponding to one, two, and three generations of cell growth. At each time point, the distribution of nuclei among the phases of the cell-cycle and cell growth were evaluated for each concentration and chemical. A statistical model was employed which tested both for the main effects of chemicals and culture times and for interactions between these factors. Both EMS and BrdUrd significantly affected the percentages of nuclei within the cell-cycle. Exposure to EMS resulted in decreases in the percentages of nuclei in G0 + G1 and increases in the G2 + M compartment. Exposure to BrdUrd affected the size of the G0 + G1 compartment as well as the percentage of S-phase nuclei. Cell growth was reduced as a consequence of increasing EMS concentration and as a function of BrdUrd concentration; the effects of these chemicals were more readily apparent at the later time points. Most importantly, for both the cell-cycle kinetics data and the cell growth data, no evidence of an interaction between the effects of EMS and the effects of BrdUrd was detected statistically. These results may be interpreted to mean that while both EMS and BrdUrd affect the induction of SCE, under the conditions of this experiment, the effects are additive rather than interactive.

The human collagen X gene. Complete primary translated sequence and chromosomal localization

We report on the complete primary translated sequence of human alpha 1(X) collagen, deduced from a genomic clone, and the chromosomal localization of the human collagen X gene. The primary translated product of human collagen X is encoded by two exons of 169 bp and approx. 2940 bp. The 169 bp exon encodes 15 bp of 5'-end untranslated sequence, 18 amino acid residues (54 bp) of signal peptide and 33 1/3 amino acid residues (100 bp) of the N-terminal non-collagenous domain. The 2940 bp exon encodes 4 2/3 amino acid residues (14 bp) of the N-terminal non-collagenous domain, the complete triple-helical domain of 463 amino acid residues (1389 bp), the complete C-terminal non-collagenous domain of 161 amino acid residues (483 bp) and 1054 bp of 3'-end untranslated sequence up to and including a potential cleavage/polyadenylation signal. The size of the intron separating the two exons, as estimated by partial sequencing and Southern-blot analyses, is approx. 3200 bp. By a combination of somatic cell hybrid screening and hybridization in situ the human collagen X gene (COL10A1) has been assigned to the distal end of the long arm of chromosome 6 at the locus 6q21-6q22.3.

Molecular cloning of human lysyl oxidase and assignment of the gene to chromosome 5q23.3-31.2

Lysyl oxidase (EC 1.4.3.13) initiates the crosslinking of collagens and elastin by catalyzing oxidative deamination of the epsilon-amino group in certain lysine and hydroxylysine residues. We report here on the isolation and characterization of cDNA clones for the enzyme from human placenta and rat aorta lambda gt11 cDNA libraries. A cDNA clone for human lysyl oxidase covers all the coding sequences, 230 nucleotides of the 5' and 299 nucleotides, of the 3' untranslated sequences, including a poly(A) tail of 23 nucleotides. This cDNA encodes a polypeptide of 417 amino acid residues, including a signal peptide of 21 amino acids. Sequencing of two rat lysyl oxidase cDNA clones indicated six differences between the present and the previously published sequence for the rat enzyme [Trackman et al. (1990) Biochemistry 29: 4863-4870], resulting in frameshifts in the translated sequence. The human lysyl oxidase sequence was found to be 78% identical to the revised rat sequence at the nucleotide level and 84% identical at the amino acid level, with the degree of identity unevenly distributed between various regions of the coded polypeptide. Northern blot analysis of human skin fibroblasts RNA indicated that the human lysyl oxidase cDNA hybridizes to at least four mRNA species; their sizes are about 5.5, 4.3, 2.4, and 2.0 kb. Analysis of a panel of 25 human x hamster cell hybrids by Southern blotting mapped the human lysyl oxidase gene to chromosome 5, and in situ hybridization mapped it to 5q23.3-31.2.(ABSTRACT TRUNCATED AT 250 WORDS)

The genetic toxicology of 5-bromodeoxyuridine in mammalian cells

The thymidine analog, BrdUrd, induces many biological responses which are of importance to the field of genetic toxicology and related disciplines. These include the induction of SCE, specific-locus mutations, and toxicity, inhibition of cell proliferation, and the expression of fragile sites in the human genome. In early models which addressed the mechanisms of the biological effects of BrdUrd exposure, two pathways were proposed to account for the induction of the biological responses. Incorporation of the enol form of BrdUrd into the nascent DNA strand after pairing with deoxyguanosine was proposed as one pathway, whereas the incorporation of BrdUrd opposite adenosine in place of thymidine was proposed as the second pathway. Many novel and sophisticated techniques have been applied to the study of the mechanism of the induction of biological effects by BrdUrd leading to a substantial increase in our understanding of these mechanisms. However, the experimental evidence clearly supports the contention that BrdUrd exerts its effects on eukaryotic cells through mechanisms similar to those originally proposed to explain the genotoxicity of BrdUrd.

Fine mapping of probes in the adenomatous polyposis coli region of chromosome 5 by in situ hybridization

The gene for adenomatous polyposis coli has been localized to 5q21-22. We have mapped six probes from this region using isotopic or nonisotopic in situ hybridization. Using tritium-labeled probes we localized II227 (D5S37) to 5q14-15 and ECB27 (D5S98) to 5q21. Following hybridization with biotin-labeled probes, the positions of signals along the chromosomes were measured as fractional length relative to the length of the chromosome arm from centromere to qter (FLcen-qter). Ninety-five percent confidence limits, compared with standard karyotypes, provided the corresponding band localization. By this method we localized Cllpll (D5S71) to FLcen-qter 0.407-0.452 (5q21.1-21.3), ECB27 to FLcen-qter 0.426-0.473 (5q21.3), YN5.48 (D5S81) to FLcen-qter 0.459-0.496 (5q21.3-22.2), and ECB134 (D5S97) to FLcen-qter 0.509-0.533 (5q22.3-23.1). ECB220 had three sites of hybridization, a major site at FLcen-qter 0.460-0.492 (5q21.3-22.1) and minor sites at FLcen-qter 0.299-0.339 (5q14.3-15) and FLcen-qter 0.629-0.691 (5q23.3-31.2). We have shown that the chromosome 5 breakpoint in a t(5;15) translocation from a patient with Gardner's syndrome (GM03314) is between Cllpll and ECB27. Linkage data are presented suggesting that ECB27 is located on the same side of the APC locus as II227. These and published results including data on several constitutional deletions (M, SD, and brothers PW and ND) give a probable order of [cen] - [II227, proximal SD breakpoint] - [Cllpll] - [proximal PW/ND, M breakpoint(s), GM03314 breakpoint] - [ECB27] - [APC] - [YN5.48] - [distal PW/ND breakpoint] - [ECB134] - [distal M breakpoint] - [qter]. The major site of ECB220 appears to be between ECB27 and the distal PW/ND breakpoint; the distal SD breakpoint is distal to YN5.48.

Variations of chromosome radiation sensitivity in fetal and adult mice during gestation

Mice were exposed to 2 Gy of gamma-rays at various days of pregnancy, and just before and after gestation. Chromosomes were analyzed 4 h after irradiation in spontaneously dividing hematopoietic cells from liver for fetuses and bone marrow for mothers. On average, there was significantly less chromosome damage in fetuses than in mothers. A very strong increase of chromosome breakage was observed in mothers at days 16-19 of gestation. This increase parallels that of gestation hormones, suggesting a direct relationship. The differences between fetuses and mothers in relation to gestation age result from the increase in the rate of chromatid and chromosome breaks but not of chromatid exchanges, which remained stable. This suggests that a DNA repair step involved in joining broken extremities is the cause. More experiments are needed to understand the origin of these variations of radiation sensitivity and the possible extrapolation of these observations to other species.

Revell revisited

The controversy of the Classic versus the Exchange theories for the origin of simple chromatid breaks is outlined. Using BrdU harlequin sister-chromatid differentiation four Revell ratios can be defined and these have been obtained and tested as a block in V79 hamster cells. The values are quite different from the simple predictions. However, values similar to those observed (taken as a block) can be readily simulated from Revell theory by making the assumption that intra-chromatid events are dominant (0.7:0.3). They can also be obtained from contingency modelling of Classic theory using the same assumption plus the additional constraint that there is no contribution from isolated single lesions (Poisson class 1). If this latter assumption is correct, then the frequency of breaks involving a colour-jump (ratio III) should not decline to zero as the dose falls. A dose-response experiment shows that it does not, but remains approximately constant at about 12%, even in the unirradiated control. An added complication arises when we discover for the TB/BB situation, that whilst neither breaks nor gaps show any excess BB involvement (sensitisation), lesions involved in interchanges show at least a 2-fold BB excess. Clearly, the chromatid discontinuities we are scoring are not behaving as would be expected of a residue of unrejoined primary breaks (Classic theory) and we infer also that they are not 'simple'.

Regional chromosomal assignment of carcinoembryonic antigen gene (CEA) to chromosome 19 at band q13.2

Carcinoembryonic antigen (CEA), a glycoprotein, is one of the most widely used human tumor markers. It is a member of a gene family comprising about 10 closely related genes and might be found throughout mammalians. Recently, two parts of a genomic DNA for CEA were isolated and sequenced. Using these genomic DNA fragments as probes we assigned the human CEA gene to chromosome 19 at the band q13.2 by in situ hybridization.

Evidence that methanol inhalation does not induce chromosome damage in mice

Mice were exposed by inhalation to 800 or 4000 ppm methanol for 5 days, and cytogenetic effects were analyzed in blood erythrocytes, lung cells, and testicular germ cells. The results were uniformly negative; no increased frequencies of micronuclei in blood cells, of sister-chromatid exchanges, chromosome aberrations, or micronuclei in lung cells, or of synaptonemal complex damage in spermatocytes were found. From the standpoint of risk assessment, these experimental studies do not reveal any evidence of a cytogenetic hazard associated with inhalation of methanol.

Gene mapping of human bilirubin UDP-glucuronosyl transferase on 1q21-q23 by a cell sorter and in situ hybridization

The human liver bilirubin UDP-glucuronosyl transferase (bilirubin UDPGT) [EC 2.4.1.17] is responsible for the enzyme deficiency in Crigler-Najjar syndrome and/or Gilbert's syndrome. The UDPGT, former shows severe jaundice resulted from a complete absence of bilirubin while the latter has a mild manifestation due to a reduction of the enzyme activity. The gene locus of bilirubin UDPGT was mapped to chromosome 1 by spot-blot hybridization using a cell-sorter, and its regional locus was assigned to 1q21-q23 by high resolution in situ hybridization.

Sister chromatid exchanges, proliferating rate index, and micronuclei in biomonitoring of internal exposure to vinyl chloride monomer in plastic industry workers

The frequency of micronuclei (MN), sister chromatid exchange (SCEs), and the proliferating rate index in peripheral blood lymphocytes from 93 individuals were measured. Fifty-two of the individuals were workers in the plastics industry where they were exposed to vinyl chloride monomer while the remaining 41 individuals served as a control group. In our results, an increase of SCEs and MN, as well as inhibited cell kinetics, was observed in the group of exposed workers. Of the tests used, SCE was found to be the most sensitive endpoint for indicating a biological response. However, since methods for restricting the MN analysis to only cells at risk (i.e., second generation interphase cells) were not used, this statement requires verification.

Sister chromatid exchanges in peripheral lymphocytes of urinary tract infection treated with nitrofurantoin

Nitrofurantoin, a widely used antibacterial agent in the therapy of urinary tract infections of bacterial origin, has been widely discussed in recent years due to its genotoxicity. Sister chromatid exchanges (SCE) were studied in lymphocyte cultures of 15 urinary tract infection patients before and after medication with daily oral doses of 10 mg/kg or 400 mg nitrofurantoin for 10 days. Both stages exhibited similar average numbers of SCE in circulating lymphocytes. The number of SCE was larger in smokers. The results of this study suggest that the short-term exposure to nitrofurantoin does not cause detectable cytogenetic abnormalities.

On the time course of the interactions between DNA breaks in the production of a radiation-induced chromosome exchange aberration

Quiescent human lymphocytes were X-irradiated and allowed to repair for various times at 37 degrees C before the cells were challenged with the DNA-repair inhibitor ara-C. The observed yield of chromosome exchange aberrations (dicentrics) was about twice the yield induced by X-rays alone, if ara-C was added immediately after irradiation. The yield as a function of the repair time between X-irradiation and ara-C treatment decreased with a half-life of 15-30 min and was almost down to the baseline yield for X-rays alone after 1 h. This shows that an exchange aberration can be formed from a short-lived DNA break. In contrast, previously published results from dose-split experiments demonstrate that the half-life of the interacting DNA breaks is of the order of several hours. A model is proposed which can account for the different estimates of the time course of the interactions involved in the process which leads to an exchange aberration.

Chromosome-type exchange aberrations are induced by inhibiting repair of UVC-induced DNA lesions in quiescent human lymphocytes

Human lymphocytes in the quiescent stage were UVC-irradiated and then incubated for 90 min in the presence of the DNA-repair inhibitor ara-C. The cells were then cultured and analyzed for chromosome aberrations. A single treatment with UVC or ara-C gives rise to a very low yield of dicentrics, whereas the combined treatment can induce a high frequency of these chromosome-type aberrations. The yield in the combined treatment is approximately proportional to the square of the UVC fluence in the range 1-3 J/m2. In addition, the experiments demonstrate that synergistic effects arise when cells are treated with UVC + ara-C and then exposed to X-rays. The results can be explained on the assumption that the UVC + ara-C treatment induces DNA double-strand breaks which, to the first approximation, are randomly distributed over the chromosomes. These breaks are able to interact with each other as well as with X-ray-induced DNA double-strand breaks to form a chromosome-type exchange aberration.

Chromosome damage in untreated tuberculosis patients

The frequency of chromosomal aberrations and sister chromatid exchanges (SCEs) were estimated in the lymphocytes of 95 untreated tuberculosis patients to evaluate the chromosomal damage with reference to bacterial invasion. The frequency of chromosomal aberrations was significantly higher in tuberculosis patients compared to controls (p less than 0.001) while the SCE frequency did not show any statistically significant differences. These findings indicate that the basic mechanism of formation of chromosomal aberrations and SCE are different and they suggest that the tubercle bacillus might be capable of inducing chromosome damage.

Sister chromatid exchanges in the lymphocytes of tuberculosis patients receiving short-term chemotherapy

The frequency of sister chromatid exchanges was estimated in tuberculosis patients undergoing three different short term chemotherapy regimens (2SHRZ, 2HRZ and 2H2R2Z2), to evaluate the possible genetic damage caused by anti-tuberculous drugs. Of the three combinations studied, two combinations (2SHRZ and 2HRZ), which were administered daily, enhanced the frequency of sister chromatid exchanges significantly (p less than 0.05), while the third bi-weekly combination (2H2R2Z2) did not show any significant enhancement in the frequency of sister chromatid exchanges. These results are of importance in the treatment of tuberculosis, and indicate the need to select a drug combination that is equally efficient in the control of disease and at the same time less harmful to the genome of the patient.

Immunophenotype and sister chromatid differentiation: a combined methodology for analyzing cell proliferation in unfractionated lymphocyte cultures

Combination of the MAC (morphology, antibody, chromosomes) and harlequin staining procedures offers a method for direct analysis of cell kinetics in cultures of unfractionated hematopoietic cells. In the present study unfractionated human mononuclear leukocyte cultures were stimulated with PHA or PWM mitogens and exposed to bromodeoxyuridine for various periods. For MAC, cytospin preparations were made and cells were classified with monoclonal B and T antibodies by the immunoperoxidase technique. After differentiation of the different lymphocyte subsets, the cells were stained by a fluorescence-plus-Giemsa method to distinguish sister chromatids and to determine the proportions of first, second, third, or subsequent mitoses among the previously identified subsets. The results showed (1) that the relative proportions of mitotic T and B cells are the same regardless of the mitogen used; (2) that T and B lymphocytes proliferate faster in cultures stimulated by PWM than in those stimulated by PHA; and (3) that T cells enter mitosis earlier than B cells when PHA or PWM are used as mitogens.

Localization of the gene encoding a type I protein phosphatase catalytic subunit to human chromosome band 11q13

A cDNA encoding one isoform (PP1 alpha) of the catalytic subunit of human protein phosphatase 1 has been isolated and used to map the human PP1 alpha gene (PPP1A) to chromosome band 11q13 by analysis of somatic cell hybrids and in situ hybridization. Neoplasms that map to 11q13 are discussed in the light of the recent findings that PP1 alpha is a putative tumor suppressor and that it plays a key role in the control of mitosis.

Chromosome reproduction: units of DNA for segregation

Evidence is summarized which indicates that the DNA loop anchoring proteins in chromosomes are effectively heterodimers that stack and are fastened into a bilaterally symmetrical array along the chromonemal axis. The evidence consists primarily of the observations made twenty five to thirty years ago on the pattern of sister chromatid exchanges and the way the DNA chains are sorted in the formation of diplochromosomes in cells that have undergone endoreduplication. The evidence indicates that each chain of DNA in the single duplex, which is assumed to run the length of a chromosome, is anchored to a bilaterally symmetrical axis of heterodimers that sort the two original chains among the four derived chromatids of each diplochromosome in a very precise way. These observations are considered in the context of investigations on the nature of scaffold proteins and the loop anchorage sequences, as well as the advances being made on the nature of DNA binding proteins and the roles of topoisomerase II.

Type 5 acid phosphatase. Sequence, expression and chromosomal localization of a differentiation-associated protein of the human macrophage

The purple acid phosphatases and uteroferrin belong to a diverse multifunctional class of binuclear iron-containing proteins that includes haemerythrin and ribonucleotide reductase. In the pig, uteroferrin has been implicated in the delivery of iron to the foetus, but the role of the related human type 5 acid phosphatase that is principally found in resident tissue macrophages is not yet clear. To define further the function of this metalloenzyme, we have isolated and sequenced a cDNA clone for type 5 acid phosphatase and investigated expression of its gene in human tissues. The phosphatase clone contains an open reading frame of 975 bp and encodes a protein of 325 amino acids, including a signal peptide of 19 residues and two potential sites for N-glycosylation. The type 5 acid phosphatase gene mapped to the short arm of human chromosome 19 and was found to have a restriction fragment length polymorphism on digestion with XbaI. Expression of phosphatase mRNA was restricted to mononuclear phagocytes and the enzyme was induced greater than 20-fold on transformation of normal human monocytes to macrophages by culture in serum-supplemented medium. Type 5 acid phosphatase thus represents a tightly regulated system for the study of molecular events in the differentiation programme of the normal macrophage.

Sister chromatid exchanges in patients with oral submucous fibrosis

The incidence of sister chromatid exchange (SCE) was investigated in the lymphocyte chromosomes of 45 patients with oral submucous fibrosis and 56 age- and sex-matched nonsmoking controls. The frequency of SCE was 9.26 +/- 2.15 in patients with oral submucous fibrosis, which was significantly higher than the mean SCE value of 5.49 +/- 1.24 observed in normal controls. The frequency of SCE in patients with oral submucous fibrosis addicted to the habit of betel with tobacco chewing, "bidi"/cigarette smoking and combined habits of chewing and smoking of tobacco were 8.12 +/- 1.69, 9.43 +/- 1.87, and 10.06 +/- 2.28, respectively. These values were also significantly higher as compared with the SCE values observed in normal controls.

Localisation of the gene encoding the catalytic gamma subunit of phosphorylase kinase to human chromosome bands 7p12-q21

Skeletal muscle phosphorylase kinase has the structure (alpha beta gamma delta)4 where the alpha and beta subunits are regulatory components, the gamma subunit possesses catalytic activity and the delta subunit is identical to the calcium binding protein calmodulin. A rabbit skeletal muscle cDNA for the gamma subunit has been used to map the human gene (PYKG1) to 7p12-q21, by analysis of somatic cell hybrids and in situ hybridisation. The data suggest that the skeletal muscle gamma subunit gene is located just above the centromere of chromosome 7, with further cross-hybridising sequences at 7q21 and 11p11-14. The liver gamma subunit is distinct and its mRNA does not cross-hybridize with the skeletal muscle gamma subunit cDNA. These results indicate that autosomal human phosphorylase kinase deficiencies affecting both liver and muscle are likely to be caused by a defect in the autosomally determined beta subunit, rather than the gamma subunit.

Levels of sister-chromatid exchanges in hybrids between Bloom syndrome B-lymphoblastoid cells and various cell lines with lymphoid malignancy

The present study has been undertaken to examine the effect of cell hybridization of Bloom syndrome (BS) B-lymphoblastoid cell lines (LCLs) and various cell lines from lymphoid malignancies in order to clarify the relationship between sister-chromatoid exchange (SCE) and malignant conditions. Cell hybridization studies have shown that though BS high-SCE frequencies were completed by fusion with normal cells, fusion with various malignant cell lines did not result in complete normalization of BS SCEs, with 15-30 SCEs remaining per hybrid cell, demonstrating possibly common defects in DNA of BS and malignant cells. These findings strongly support the idea that the characteristic high SCE frequency in BS cells has some connection with the malignant condition, and that at least one step in carcinogenesis is either accompanied by the production of SCEs, or that SCEs themselves cause such a step to occur.

Induction of nuclear aberrations by smokeless tobacco in epithelial cells of human oral mucosa

Cytologic and cytogenetic studies were performed to assess the prevalence of somatic cell genetic damage in 48 young adults equally divided to represent users and nonusers of smokeless tobacco. Exposure was ascertained by measuring saliva cotinine using capillary gas chromatography. Squamous epithelial cells sampled from the oral mucosa demonstrated significant cytologic alterations associated with tobacco exposure. The frequency of micronucleated cells was significantly (P less than .01) higher in the labial mucosa of exposed (2.22%) compared to unexposed (0.27%) individuals. The frequency of micronuclei varied widely between exposed subjects but was higher in heavily (2.48%) compared to lightly (1.29%) exposed individuals as measured by saliva cotinine levels. Morphologic classification of epithelial cell nuclei showed that the frequency of cells with normal nuclear structure was significantly (P less than .01) reduce in exposed individuals. Analysis of oral epithelial cells of five additional nonusers of smokeless tobacco but wearers of orthodontic appliances to stimulate abrasion demonstrated no difference from the nonexposed control group. Unlike the case with cigarette smokers, peripheral lymphocyte sister-chromatid exchange frequency was not affected by exposure to smokeless tobacco. The oral cytology data, however, support an interpretation of exposure-dependent nuclear alterations, including micronuclei, in the oral epithelium associated with the use of smokeless tobacco. Altogether, results suggest that use of smokeless tobacco may cause genetic damage to cells in the oral epithelium.

Impact of medical genetics on environmental medicine

Medical genetics as a discipline has contributed basic knowledge of great applicability in environmental medicine, e.g. 1) the demonstration that environmental agents may cause chromosomal damage, 2) that chromosome aberrations are correlated with increased risks for cancer and spontaneous abortion, and 3) that the susceptibility to cyto- and genotoxic damage may be influenced by genetic factors. This paper discusses examples of applications of genetic knowledge in environmental medicine and areas for future research.

The human alpha 2(XI) collagen gene (COL11A2) maps to the centromeric border of the major histocompatibility complex on chromosome 6

Type XI collagen, a minor structural component of cartilage fibrils, is composed of three chains, alpha 1(XI), alpha 2(XI), and alpha 3(XI). Using a cloned fragment of the human alpha 2(XI) collagen gene (COL11A2) as a molecular probe for in situ hybridization and somatic cell hybrid mapping, we have localized the gene to the short arm of chromosome 6, region 21.3. By exploiting the rich source of probes provided by the major histocompatibility complex (MHC) genes, which also map to this chromosomal band, we have constructed macrorestriction maps of the region by pulsed-field gel electrophoresis and have localized the alpha 2(XI) collagen gene to the centromeric extreme of the MHC. Finally, we have demonstrated, by the isolation of overlapping cosmid clones, that the gene is 45 kb centromeric to the HLA-DPB2 locus and oriented with the 3' end toward the MHC. The COL11A2 locus thus demarcates the proximal boundary of the MHC. This finding may have implications for the understanding of certain MHC-linked diseases.

A standardized method for the three-way differential staining of plant chromosomes and the scoring of SCEs per cell cycle

We have made use of 2 alternative methodologies to obtain 3-way differential staining (TWD) in third-mitosis (M3) chromosomes of Allium cepa, which involve different uptakes of bromodeoxyuridine (BrdU) through 3 cell divisions, in order to evaluate the sister-chromatid exchanges (SCE) frequency on a per-cell-cycle basis. The main innovation introduced by us to the original protocols previously reported has been the use of 5-fluorodeoxyuridine (FdU) to inhibit endogenous thymidine (dT) synthesis. By using different [BrdU]:[dT] ratios in the presence of FdU the relative incorporation of BrdU into replicating DNA can be controlled. The use of 2 different approaches to obtain 3-way differentiation of sister chromatids allowed us to evaluate the role of BrdU in the induction of SCEs in our system. Both procedures rendered nearly 100% of M3 chromosomes showing TWD. An additional advantage of our methodologies is their high degree of reproducibility.

Localization of the Surfeit gene cluster containing the ribosomal protein gene L7a to chromosome bands 9q33-34

The Surfeit gene cluster which contains at least four very tightly spaced unrelated genes, one of which encodes the ribosomal protein L7a, has been localized by an analysis of somatic cell hybrids to the long arm of chromosome 9. By the use of in situ hybridization the Surfeit locus has been further mapped to 9q33-34.

Increased sister-chromatid exchanges (SCEs) and chromosomal fragilities by BrdU in a human mutant B-lymphoblastoid cell line

From an X-irradiated human B-lymphoblastoid cell line (CCRF-SB), we have isolated a unique mutant clone (CCRF-SB-T1) which reveals high frequencies of sister-chromatid exchanges (SCEs) and chromosomal fragilities in the C-band regions of chromosomes Nos. 1, 9 and 16, when exposed to high concentrations of bromodeoxyuridine (BrdU). A clear BrdU dose-dependent increase of SCEs (9.6 SCEs/cell at 0.05 mM, 40 SCEs/cell at 0.37 mM on average) in this mutant was observed. Relative contributions of nucleoside and a thymidine (dT) analog of BrdU to high SCEs were studied, since an unusual SCE response to BrdU led us to suspect the significance of BrdU incorporation into DNA and dT pool disturbances. Addition of deoxycytidine (dC), dT or both dC and dT causes an increase of SCEs. On the other hand, deoxyadenosine (dA) and deoxyguanosine (dG) did not have significant effects on SCEs in SB-T1 cells. These results suggest that disturbances of pyrimidine-nucleotide synthesis, including gross imbalance of nucleotide pools, play a pivotal role in the high SCE induction of SB-T1 cells by BrdU.

Sister chromatid exchange in human chromosomes from normal individuals and epileptic patients on combinations of anticonvulsants

Sister chromatid exchange (SCE) frequency, a sensitive indicator in mutagenicity testing, and mitotic index (MI) have been studied to observe genotoxic effects in epileptic patients on routine combinations of anticonvulsant therapy. All patients, both male and female and from various age groups, revealed an increased frequency of SCE per metaphase and a low MI (P less than 0.001) with respect to controls. A nonsignificant decrease in SCE frequency has been observed with an increase in the age of onset of epilepsy. Although the SCE frequency increased and the MI decreased in some groups with respect to the duration of epilepsy, there was no difference observed in SCE frequency with the duration of therapy.

In vitro induction of chromosome damage by sulphasalazine in human lymphocytes

Two different endpoints, sister-chromatid exchange and micronucleus induction, were measured in human peripheral blood lymphocytes stimulated to divide in short-term in vitro cultures. The cultures were exposed to sulphasalazine and 6 of its metabolites for 72 h in the absence of any exogenous metabolic activation system. Analysis of the sister-chromatid exchange and micronuclei frequencies clearly indicates that sulphasalazine itself is capable of inducing both sister-chromatid exchange and micronuclei while sulphapyridine and its acetylated metabolites only induce sister-chromatid exchange. 5-Aminosalicylic acid, the therapeutic moiety of sulphasalazine, and its acetylated metabolite did not induce either sister-chromatid exchange or micronuclei at the concentrations tested. The data from these in vitro experiments are discussed in relation to the previously reported elevations in sister-chromatid exchange and micronucleus frequencies in inflammatory bowel disease patients receiving sulphasalazine therapy.

Chromosome abnormalities and sister chromatid exchanges in children with acute intoxication due to inhalation of volatile substances

Deliberate inhalation of volatile substances is a common and harmful practice among young persons worldwide. Recently, we described chromosome damage in children who chronically inhale volatile agents. Clinical and cytogenetic studies were performed for 15 "sniffing" children (13 boys and 2 girls), the purpose of which was to define the chromosomal effect of the acute intoxication. A significant increase in the rate of chromosome abnormalities and in the frequency of sister chromatid exchanges (SCEs) was found in sniffers vs. controls. The values were also higher in children who were acutely intoxicated than in those who chronically inhaled volatile agents. Clinical, socioeconomic, and cytogenetic findings are also discussed.

Assignment of the gene encoding the beta-subunit of the human fibronectin receptor (beta-FNR) to chromosome 10p11.2

A cDNA corresponding to the beta-subunit of the human fibronectin receptor (beta-FNR) was used as a probe in Southern blot analysis of mouse/human somatic cell hybrid DNAs and in in situ hybridization to metaphase chromosomes. The beta-FNR cDNA detects sequences present on human chromosome 10 as well as recognizing homologous sequences in the genome of the mouse parent of the somatic cell hybrids. In situ hybridization refined the localization of human sequences reacting with the beta-FNR cDNA to 10p11.2. The A-1A5 monoclonal antibody which recognizes the beta-subunit of the fibronectin receptor on the cell surface was used to confirm that the sequences present on chromosome 10 correspond to those required for expression of beta-FNR.

Constitutive heterochromatin polymorphism and chromosome damage in viral hepatitis

The frequencies of chromosomal aberrations and sister-chromatid exchanges (SCEs) were scored in relation to constitutive heterochromatin in 100 patients with viral hepatitis B, 100 patients with viral hepatitis A and 100 age- and sex-matched normal controls. 23.4%, 15% and 4% of the cells showed chromosomal aberrations in patients with hepatitis B, hepatitis A and normal controls respectively. Non-random involvement of chromosomal aberrations were also noted in chromosome 1 of patients with hepatitis B and A as compared to normal controls. The frequencies of SCEs (mean +/- S.D.) were found to be 10.40 +/- 2.83 in hepatitis B and 8.70 +/- 2.34 in hepatitis A. These values were significantly higher than the SCE frequency (mean +/- S.D.) of 5.88 +/- 2.25 observed in normal controls (P less than 0.001). The intra-chromosomal distribution of SCEs revealed a relatively increased incidence of SCEs in chromosome 1 of patients with hepatitis B and A as compared to normal controls. Analysis of constitutive heterochromatin polymorphism showed chromosome 1 qh+ to be the most frequent variant in patients with hepatitis B and A as compared to normal controls. The increased involvement of C-band variant 1 qh+ in patients with hepatitis B and A as compared to normal controls may indicate that extra heterochromatin offers additional sites for viral integration.

Sister chromatid exchanges in the lymphocytes of patients with oral leukoplakia

The incidence of sister chromatid exchange (SCE) was investigated in lymphocyte chromosomes of 59 patients with oral leukoplakia and 65 age- and sex-matched nonsmoking controls. The frequency of SCE was found to be 8.61 +/- 1.89 in patients with oral leukoplakia, which was significantly higher than the mean SCE value of 5.58 +/- 1.26 observed in normal controls. The frequency of SCE in patients with oral leukoplakia addicted to the single habit of betel with tobacco chewing, bidi/cigarette smoking, and combined habits of chewing and smoking of tobacco were found to be 7.95 +/- 1.63, 8.17 +/- 1.66, and 9.23 +/- 2.14, respectively. These values were also significantly higher as compared to the SCE values observed in normal controls.

Sister chromatid exchange and chromosome abnormalities in uremic patients

Chronic renal failure heightens the risk of malignancy. We therefore examined lymphocytes from 44 uremic patients and 24 normal controls for chromosome abnormalities and sister chromatid exchange (SCE) rate. This is the first report of SCE in uremia. Uremia was found to increase structurally abnormal chromosomes and elevate the rate of SCE. These cytogenetic changes in uremia may play a role in the heightened risk of cancer.

Construction of a genetic map of human chromosome 17 by use of chromosome-mediated gene transfer

We used somatic-cell hybrids, containing as their only human genetic contribution part or all of chromosome 17, as donors for chromosome-mediated gene transfer. A total of 54 independent transfectant clones were isolated and analyzed by use of probes or isoenzymes for greater than 20 loci located on chromosome 17. By combining the data from this chromosome-mediated gene transfer transfectant panel, conventional somatic-cell hybrids containing well-defined breaks on chromosome 17, and in situ hybridization, we propose the following order for these loci: pter-(TP53-RNP2-D17S1)-(MYH2-MYH1)-D17Z 1-CRYB1-(ERBA1-GCSF-NGL)-acute promyelocytic leukemia breakpoint-RNU2-HOX2-(NGFR-COLIAI-MPO)-GAA-UM PH-GHC-TK1-GALK-qter. Using chromosome-mediated gene transfer, we have also regionally localized the random probes D17S6 to D17S19 on chromosome 17.