The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
Qinghua Shi - One of the best experts on this subject based on the ideXlab platform.
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chromosome nondisjunction yields tetraploid rather than aneuploid Cells in human cell lines
Nature, 2005Co-Authors: Qinghua Shi, Randall W KingAbstract:A hypothesis about cancer initiation, first proposed nearly a century ago, has stood the test of time. German biologist Theodor Boveri suggested that a failure of cell division might produce tetraploid Cells (containing a double chromosome quota) that then undergo multipolar mitosis, leading to genome instability that can trigger cancer. Fujiwara et al. tested the hypothesis using an actin inhibitor to block cell division and generate tetraploid Cells. The resulting Cells can be transformed in vitro and also generate tumours in mice. The transformed Cells exhibit massive genomic instability, including an amplification of a region containing genes associated with breast cancers. A second study shows that accurate chromosome segregation is coupled to the completion of cytokinesis in human Cells. It had been assumed that if a pair of chromosomes failed to separate during cell division, two aneuploid daughter Cells (not containing a multiple of the haploid chromosome number) would form. Instead, mitosis is halted and tetraploid Cells are produced at least initially. This mechanism may explain why the loss or gain of a single chromosome is relatively rare in cancers and it may help prevent some cancers though tetraploid Cells are, as Boveri suggested, also prone to forming cancers. Although mutations in cell cycle regulators or spindle proteins can perturb chromosome segregation1,2,3,4,5,6,7, the causes and consequences of spontaneous mitotic chromosome nondisjunction in human Cells are not well understood. It has been assumed that nondisjunction of a chromosome during mitosis will yield two aneuploid daughter Cells. Here we show that chromosome nondisjunction is tightly coupled to regulation of cytokinesis in human cell lines, such that nondisjunction results in the formation of tetraploid rather than aneuploid Cells. We observed that spontaneously arising Binucleated Cells exhibited chromosome mis-segregation rates up to 166-fold higher than the overall mitotic population. Long-term imaging experiments indicated that most Binucleated Cells arose through a bipolar mitosis followed by regression of the cleavage furrow hours later. Nondisjunction occurred with high frequency in Cells that became Binucleated by furrow regression, but not in Cells that completed cytokinesis to form two mononucleated Cells. Our findings indicate that nondisjunction does not directly yield aneuploid Cells, but rather tetraploid Cells that may subsequently become aneuploid through further division. The coupling of spontaneous segregation errors to furrow regression provides a potential explanation for the prevalence of hyperdiploid chromosome number and centrosome amplification observed in many cancers8,9.
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chromosome nondisjunction yields tetraploid rather than aneuploid Cells in human cell lines
Nature, 2005Co-Authors: Qinghua Shi, Randall W KingAbstract:Although mutations in cell cycle regulators or spindle proteins can perturb chromosome segregation, the causes and consequences of spontaneous mitotic chromosome nondisjunction in human Cells are not well understood. It has been assumed that nondisjunction of a chromosome during mitosis will yield two aneuploid daughter Cells. Here we show that chromosome nondisjunction is tightly coupled to regulation of cytokinesis in human cell lines, such that nondisjunction results in the formation of tetraploid rather than aneuploid Cells. We observed that spontaneously arising Binucleated Cells exhibited chromosome mis-segregation rates up to 166-fold higher than the overall mitotic population. Long-term imaging experiments indicated that most Binucleated Cells arose through a bipolar mitosis followed by regression of the cleavage furrow hours later. Nondisjunction occurred with high frequency in Cells that became Binucleated by furrow regression, but not in Cells that completed cytokinesis to form two mononucleated Cells. Our findings indicate that nondisjunction does not directly yield aneuploid Cells, but rather tetraploid Cells that may subsequently become aneuploid through further division. The coupling of spontaneous segregation errors to furrow regression provides a potential explanation for the prevalence of hyperdiploid chromosome number and centrosome amplification observed in many cancers.
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increased nondisjunction of chromosome 21 with age in human peripheral lymphocytes
Mutation Research, 2000Co-Authors: Qinghua Shi, Jianfang Che, I D Adle, J Zhang, Renee H Marti, Xira Zhang, Xiangnia ShaAbstract:Abstract Fluorescence in situ hybridization (FISH) on Binucleated Cells with chromosome-specific DNA probes provides a convenient way to visualize reciprocal segregation patterns in daughter nuclei, and overcomes most problems related to the artefactual loss or gain of chromosomes that flaw chromosome preparations. In this study, FISH was employed to evaluate age- and sex-effects on spontaneous malsegregation, nondisjunction and loss of chromosome 21 in human lymphocytes after the first division in culture. A total of 68 healthy nonsmokers and nondrinkers of alcohol (37 males and 31 females) were grouped by age as Group I (0–10 years), Group II (20–30 years), Group III (40–50 years) and Group IV (60–70 years), with at least seven subjects per group and sex. FISH with a pericentric chromosome 21 specific DNA probe was carried out on Binucleated lymphocytes, cytokinesis-blocked by cytochalasin B (6 μg/ml for 26 h) at 44 h after initiation of cultures. Linear regression analyses demonstrated a significant age-related increase in the frequency of micronuclei without chromosome 21 (MN-21)( r =0.73, p r =0.69, p χ 2 ) test on the frequencies of MN-21 showed significant age-related differences in both males and females, except males in Group III and Group IV ( p >0.05). A significant sex-related difference was found only in subjects over 60 years ( p Loss of chromosome 21, occurring at mean levels of 0.38‰ in all Binucleated Cells and 0.24‰ in Binucleated Cells containing four FISH signals, was shown not to be age- or sex-related. A positive age-related increase in nondisjunction of chromosome 21 was shown in males ( r =0.50, p r =0.61, p r =0.55, p p p
Michael Fenech - One of the best experts on this subject based on the ideXlab platform.
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automated detection of nucleoplasmic bridges for dna damage scoring in Binucleated Cells
International Conference on Pattern Recognition, 2010Co-Authors: Changming Sun, Michael Fenech, Pascal Vallotton, Philip J ThomasAbstract:Quantification of DNA damage, which may be caused by radiation or exposure to chemicals, is very important and can be very time consuming and subject to variability if carried out visually. The quantification of scoring DNA damage includes biomarkers such as micronuclei, nucleoplasmic bridges, and nuclear buds as scored in cytokinesis-blocked Binucleated Cells. In this paper, we present a new algorithm based on a shortest path technique that enables us to detect the nucleoplasmic bridges joining two nuclei in cell images of Binucleated Cells. The effectiveness of our algorithm is illustrated using a set of cell images. We believe that this is the first time that a feasible automated nucleoplasmic bridge detection system has been reported.
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humn project detailed description of the scoring criteria for the cytokinesis block micronucleus assay using isolated human lymphocyte cultures
Mutation Research-genetic Toxicology and Environmental Mutagenesis, 2003Co-Authors: Michael Fenech, Micheline Kirschvolders, Wushou P Chang, Nina Holland, Stefano Onassi, Errol ZeigeAbstract:Criteria for scoring micronuclei and nucleoplasmic bridges in Binucleated Cells in the cytokinesis-block micronucleus assay for isolated human lymphocyte cultures are described in detail. Morphological characteristics of mononucleated Cells, Binucleated Cells, and multinucleated Cells as well as necrotic and apoptotic Cells and nuclear buds are also described. These criteria are illustrated by a series of schematic diagrams as well as a comprehensive set of colour photographs that are of practical assistance during the scoring of slides. These scoring criteria, diagrams and photographs have been used in a HUman MicronNucleus (HUMN) project inter-laboratory slide-scoring exercise to evaluate the extent of variability that can be attributable to individual scorers and individual laboratories when measuring the frequency of micronuclei and nucleoplasmic bridges in Binucleated Cells as well as the nuclear division index. The results of the latter study are described in an accompanying paper. It is expected that these scoring criteria will assist in the development of a procedure for calibrating scorers and laboratories so that results from different laboratories for the cytokinesis-block micronucleus assay may be more comparable in the future.
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A mathematical model of the in vitro micronucleus assay predicts false negative results if micronuclei are not specifically scored in Binucleated Cells or in Cells that have completed one nuclear division.
Mutagenesis, 2000Co-Authors: Michael FenechAbstract:A mathematical model is described that predicts the effect of altered nuclear/cell division kinetics and cytotoxicity on micronucleus expression in vitro when the micronucleus assay is performed without discriminating between Cells that have divided once and Cells that have not divided after genotoxic insult. The model is based on the probabilities of: (i) a viable cell completing nuclear division; (ii) micronucleus expression in a cell that completes nuclear division after genotoxic insult; (iii) a cell not dividing and surviving as a mononuclear cell; (iv) a cell dying by necrosis or apoptosis. The model predicts: (i) false negative results for relatively weak chromosome damaging agents that also inhibit nuclear division, if micronuclei are scored in mononucleated Cells without discriminating between divided and non-divided Cells; (ii) this tendency for a false negative result when scoring micronuclei without discriminating between non-divided and once-divided mononuclear Cells increases with cell lines and culture conditions that do not result in optimal rates of nuclear division (i.e. >90% of dividing Cells); (iii) the absolute increment in micronucleus frequency in Binucleated Cells is at least 2-fold greater than that observed in mononucleated Cells when nuclear division is not inhibited and this difference increases with increasing nuclear inhibition. The number of dead Cells does not influence the micronucleus frequency if only viable Cells are considered when determining the micronucleus frequency ratio. The results from this model suggest that the micronucleus assay when performed by scoring mononucleated Cells, without restricting the score to those Cells that have divided once after genotoxic insult, is prone to produce false negative results and, therefore, cannot be considered reliable or conclusive. Scoring of micronuclei in cytokinesis-blocked Binucleated Cells is predicted by the model to provide consistent results under all culture conditions and based on these theoretical results should be considered the preferred choice.
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necrosis apoptosis cytostasis and dna damage in human lymphocytes measured simultaneously within the cytokinesis block micronucleus assay description of the method and results for hydrogen peroxide
Mutagenesis, 1999Co-Authors: Michael Fenech, Jimmy Crott, Julie Turner, Shauna BrownAbstract:A method is described for the inclusion of apoptotic and necrotic Cells in the cell counts obtained in the cytokinesis-block micronucleus (CBMN) assay, which is conventionally used solely for the assessment of chromosome breakage, chromosome loss and frequency of dividing Cells. The morphological criteria for the recognition and discrimination between necrotic, apoptotic and viable Cells are described. Using this comprehensive method we have evaluated the cytotoxic and genotoxic effects of hydrogen peroxide (0-100 microM) in lymphocytes exposed in RPMI 1640 medium. The results obtained indicated significant (P < 0.05) correlations between hydrogen peroxide concentration and the frequency of micronucleated Cells (r = 0.39), necrotic Cells (r = 0.73), apoptotic Cells (r = -0.26) and Binucleated Cells (r = -0.55). Almost similar results were obtained using the cytosine arabinoside modification of the CBMN assay, which enables excision-repaired sites to be converted to micronuclei. Some of the above end-points were significantly (P < 0.05) correlated with each other (necrosis and apoptosis, R = -0.39; necrosis and micronucleated cell frequency, R = 0.46; necrosis and Binucleated Cells, R = -0.78; apoptosis and Binucleated Cells, R = 0.32). It was therefore necessary to use multiple regression analysis to identify the main event induced by hydrogen peroxide, which was necrosis (beta = 0.57, P = 0.0001) and not micronucleus formation (beta = 0. 15, P = 0.1332). Using an ELISA assay we showed that hydrogen peroxide did not induce 8-hydroxydeoxyguanosine. Our data show that the proposed comprehensive test system may provide a better procedure for classifying potential toxic chemicals and enable discrimination between agents that primarily induce cytotoxic effects as opposed to genotoxic effects. The integration of apoptosis and necrosis into the micronucleus assay may also be of practical use in radiosensitivity studies.
Randall W King - One of the best experts on this subject based on the ideXlab platform.
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chromosome nondisjunction yields tetraploid rather than aneuploid Cells in human cell lines
Nature, 2005Co-Authors: Qinghua Shi, Randall W KingAbstract:A hypothesis about cancer initiation, first proposed nearly a century ago, has stood the test of time. German biologist Theodor Boveri suggested that a failure of cell division might produce tetraploid Cells (containing a double chromosome quota) that then undergo multipolar mitosis, leading to genome instability that can trigger cancer. Fujiwara et al. tested the hypothesis using an actin inhibitor to block cell division and generate tetraploid Cells. The resulting Cells can be transformed in vitro and also generate tumours in mice. The transformed Cells exhibit massive genomic instability, including an amplification of a region containing genes associated with breast cancers. A second study shows that accurate chromosome segregation is coupled to the completion of cytokinesis in human Cells. It had been assumed that if a pair of chromosomes failed to separate during cell division, two aneuploid daughter Cells (not containing a multiple of the haploid chromosome number) would form. Instead, mitosis is halted and tetraploid Cells are produced at least initially. This mechanism may explain why the loss or gain of a single chromosome is relatively rare in cancers and it may help prevent some cancers though tetraploid Cells are, as Boveri suggested, also prone to forming cancers. Although mutations in cell cycle regulators or spindle proteins can perturb chromosome segregation1,2,3,4,5,6,7, the causes and consequences of spontaneous mitotic chromosome nondisjunction in human Cells are not well understood. It has been assumed that nondisjunction of a chromosome during mitosis will yield two aneuploid daughter Cells. Here we show that chromosome nondisjunction is tightly coupled to regulation of cytokinesis in human cell lines, such that nondisjunction results in the formation of tetraploid rather than aneuploid Cells. We observed that spontaneously arising Binucleated Cells exhibited chromosome mis-segregation rates up to 166-fold higher than the overall mitotic population. Long-term imaging experiments indicated that most Binucleated Cells arose through a bipolar mitosis followed by regression of the cleavage furrow hours later. Nondisjunction occurred with high frequency in Cells that became Binucleated by furrow regression, but not in Cells that completed cytokinesis to form two mononucleated Cells. Our findings indicate that nondisjunction does not directly yield aneuploid Cells, but rather tetraploid Cells that may subsequently become aneuploid through further division. The coupling of spontaneous segregation errors to furrow regression provides a potential explanation for the prevalence of hyperdiploid chromosome number and centrosome amplification observed in many cancers8,9.
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chromosome nondisjunction yields tetraploid rather than aneuploid Cells in human cell lines
Nature, 2005Co-Authors: Qinghua Shi, Randall W KingAbstract:Although mutations in cell cycle regulators or spindle proteins can perturb chromosome segregation, the causes and consequences of spontaneous mitotic chromosome nondisjunction in human Cells are not well understood. It has been assumed that nondisjunction of a chromosome during mitosis will yield two aneuploid daughter Cells. Here we show that chromosome nondisjunction is tightly coupled to regulation of cytokinesis in human cell lines, such that nondisjunction results in the formation of tetraploid rather than aneuploid Cells. We observed that spontaneously arising Binucleated Cells exhibited chromosome mis-segregation rates up to 166-fold higher than the overall mitotic population. Long-term imaging experiments indicated that most Binucleated Cells arose through a bipolar mitosis followed by regression of the cleavage furrow hours later. Nondisjunction occurred with high frequency in Cells that became Binucleated by furrow regression, but not in Cells that completed cytokinesis to form two mononucleated Cells. Our findings indicate that nondisjunction does not directly yield aneuploid Cells, but rather tetraploid Cells that may subsequently become aneuploid through further division. The coupling of spontaneous segregation errors to furrow regression provides a potential explanation for the prevalence of hyperdiploid chromosome number and centrosome amplification observed in many cancers.
Ricard Marcos - One of the best experts on this subject based on the ideXlab platform.
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genotoxicity of the organochlorine pesticides 1 1 dichloro 2 2 bis p chlorophenyl ethylene dde and hexachlorobenzene hcb in cultured human lymphocytes
Chemosphere, 2008Co-Authors: Soukaina Ennaceur, Ricard Marcos, Driss RidhaAbstract:Abstract The possible genotoxic potential of 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE), which is a metabolite of dichlorobiphenyltrichloroetane (DDT), and hexachlorobenzene (HCB), which are organochlorine pesticides have been evaluated in vitro by using human lymphocytes as test system. Genetic damage was determined by scoring the frequency of micronuclei (MN) in primary lymphocyte cultures obtained from different donors. The results indicated that, under the experimental conditions used, the DDT metabolite DDE was able to induce significant increases in the frequency of micronucleated Cells, which indicate a certain clastogenic and/or aneugenic potential. DDE was tested in the range of 10–80 mM, but the only concentration producing a significant genotoxic effect was 80 mM. On the other hand, HCB was unable to induce a significant increase in the MN frequency in the range of concentrations assayed, from 0.005 to 0.1 mM. The selected concentrations of DDE and HCB were chosen according to their toxicity in cell blood cultures; higher concentrations reduced significantly cell proliferation and produced a low frequency of Binucleated Cells. In conclusion, the results indicate that a genotoxic risk is associated with the exposure to DDE at concentrations 80 mM and above.
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radioactive iodine induces clastogenic and age dependent aneugenic effects in lymphocytes of thyroid cancer patients as revealed by interphase fish
Mutagenesis, 1997Co-Authors: Maria Jose Ramirez, Jordi Surralles, A Creus, Pere Galofre, Ricard MarcosAbstract:131Irelated Increase in the incidence of thyroid cancer has been reported in exposed children. However, little is known about the eventual genotoxic effects of 131I in exposed humans. Thyroid cancer patients are usually treated with 131I and, therefore, they provide us with an opportunity to study cytogenetic damage induced by known doses of this radionuclide. FISH techniques have been employed to study the origin of micronuclei as well as X chromosome nondisjunction and X chromosome numerical abnormalities in lymphocytes from 131I-treated women suffering from thyroid cancer. Blood was sampled before and 1 week after 131I treatment Cells were analysed with either pancentromeric FISH to classify micronuclei or X chromosome centromere-specific FISH in mononucleated and Binucleated Cells to evaluate X chromosome numerical abnormalities and non-disjunction respectively. Our data indicate that 131I-induced clastogenic and age-dependent aneugenic effects in the lymphocytes of exposed patients. The X chromosome was not preferentially involved in the aneugenic effect induced by 131I. It is concluded that besides its major clastogenic effect, 131I can also induce an X chromosome-independent aneugenic activity mainly in patients with spontaneous proneness to chromosome loss.
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the effect of cytochalasin b concentration on the frequency of micronuclei induced by four standard mutagens results from two laboratories
Mutagenesis, 1994Co-Authors: Jordi Surralles, Francesca Degrassi, Antonio Antoccia, Caterina Tanzarella, A Creus, F Peris, N Xamena, Ricard MarcosAbstract:: In a previous collaborative work, we have recently shown that the cytochalasin-B (Cyt-B) concentration used in the human lymphocytes cytokinesis-block micronucleus (CBMN) assay is an important variable in the baseline micronuclei (MN) frequency as well as in the percentage of Binucleated Cells obtained. Now we have investigated how Cyt-B concentration modulates the MN frequency induced in whole blood human lymphocyte cultures by two clastogens (ethyl methanesulphonate and mitomycin-C) and two aneugens (colchicine and vincristine sulphate). The experimental design includes six donors, two concentrations of Cyt-B (3 and 6 micrograms/ml), two concentrations of the four chemicals tested and the exchange of slides between laboratories. The statistical analysis of the results shows: (i) non-significant differences in the MN frequencies and in the toxicity results between scorers from each laboratory, except for 0.06 microM colchicine at 3 micrograms/ml Cyt-B; (ii) an induction of MN by all genotoxic agents tested, the frequencies being lower with 6 than with 3 micrograms/ml Cyt-B, in control and aneugen-treated cultures; and (iii) significant differences between Cyt-B concentrations in several treatments, obtaining lower MN frequencies and higher values for nuclear division index and % Binucleated Cells when 6 micrograms/ml Cyt-B was used. Bearing in mind these results as well as the toxicity data showing that 6 micrograms/ml Cyt-B is much more effective in blocking cytokinesis, we can conclude that the use of 3 micrograms/ml Cyt-B may overestimate the induced frequency of MN.
Paul Van Hummelen - One of the best experts on this subject based on the ideXlab platform.
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the in vitro micronucleus test a multi endpoint assay to detect simultaneously mitotic delay apoptosis chromosome breakage chromosome loss and non disjunction
Mutation Research-genetic Toxicology and Environmental Mutagenesis, 1997Co-Authors: Micheline Kirschvolders, Azeddine Elhajouji, Enrico Cundari, Paul Van HummelenAbstract:Abstract Genotoxicity testing aims to detect a large range of genetic damage endpoints and evaluate such results in context of cell survival. The cytokinesis block micronucleus test offers the advantage to provide simultaneously information on both cell cycle progression and chromosome/genome mutations. Indeed, 1. frequencies of cytokinesis-blocked Binucleated Cells (and polynucleated) are good estimators of the mitotic rate; 2. frequencies of apoptotic figures in mononucleated and Binucleated Cells provide a measure for cell death before or after cell division; 3. combination of fluorescence in situ hybridization (FISH) for centromere/telomeres and micronucleus scoring allows discrimination between clastogenic and aneugenic events; 4. detection of FISH signals for chromosome specific sequences in both macronuclei and micronuclei, discriminates between aneuploidy due to chromosome non-disjunction or to chromosome loss. The cytokinesis block in vitro micronucleus test is thus a cytogenetic multi-test providing mechanistic information with a simple, rapid, objective, microscopical analysis.