Showing papers on "Sister chromatid exchange published in 1977"

Automatic measurement of sister chromatid exchange frequency.

Abstract: An automatic system for detecting and counting sister chromatid exchanges in human chromosomes has been developed. Metaphase chromosomes from lymphocytes which had incorporated 5-bromodeoxyuridine for two replication cycles were treated with the dye 33258 Hoechst and photodegraded so that the sister chromatids exhibited differential Giemsa staining. A computer-controlled television-microscope system was used to acquire digitized metaphase spread images by direct scanning of microscope slides. Individual objects in the images were identified by a thresholding procedure. The probability that each object was a single, separate chromosome was estimated from size and shape measurements. An analysis of the spatial relationships of the dark-chromatid regions of each object yielded a set of possible exchange locations and estimated probabilities that such locations corresponded to sister chromatid exchanges. A normalized estimate of the sister chromatid exchange frequency was obtained by summing the joint probabilities that a location contained an exchange within a single, separate chromosome over the set of chromosomes from one or more cells and dividing by the expected value of the total chromosome area analyzed. Comparison with manual scoring of exchanges showed satisfactory agreement up to levels of approximately 30 sister chromatid exchanges/cell, or slightly more than twice control levels. The processing time for this automated sister chromatid exchange detection system was comparable to that of manual scoring.

Sister Chromatid Exchange

Abstract: EARLY RESULTS 1 83 Sister Chromatid Exchange in Meiosis 1 83 Sister Chromatid Exchange in Somatic Cells 1 84 Isolabeling 1 86 Sister Chromatid Exchanges-Spontaneous or Induced? 1 86 RESULTS FROM NEW METHODS FOR DETECTING SISTER CHROMA TID EXCHANGES 1 86 Reasons for Differential Staining 1 87 Harlequin Chromosomes and Chromosome Structure 1 89 Multiple sister chromatid exchanges 1 90 Autoradiographic image spread 1 90 Labeling for more than one replication cycle 1 90 The Question 0/ Spontaneous Levels 0/ Sister Chromatid Exchanges 1 9 1 Location 0/ Sister Chromosome Exchanges in the Chromosome 1 93 Sister Chromatid Exchanges and Human Genetic Diseases 1 93 Sister Chromatid Exchanges as Indicators 0/ Mutagenic Carcinogens 1 94 Lesions Responsible for Sister Chromatid Exchange Formation 1 96 CONCLUSION 1 97

Chromosome Aberrations and Sister Chromatid Exchanges in Chinese Hamster Cells Exposed to Various Chemicals

Abstract: To evaluate its usefulness for detection of mutagenicity and oncogenicity of chemicals, the frequency of chromosome aberrations and sister chromatid exchanges (SCE) was examined in cultured Chinese hamster cells exposed to 33 kinds of chemical agents, including 2 aromatic hydrocarbons, 7 amine derivatives, 3 phenols, 6 carboxylic acid derivatives, 4 azo compounds, 7 heterocyclic compounds, and 4 other types of agents. Among them, 7 chemicals, including 5 known oncogens (N-n-butyl-N-nitrosourethan, N-methyl-N-nitrosourea, beta-propiolacton, methylazoxymethanol acetate, and propane sultone) and 2 non-oncogens (potassium sorbate and sodium benzoate) were inducers of aberrations and/or SCE, although the effective doses for the last two agents were considerably higher. The mutagenic activities estimated by chromosome aberrations were not necessarily the same for a given chemical when estimated by SCE. Slightly to moderately increased rates of SCE or aberrations were noticed among the other 26 chemicals. However, these values were usually without a clear dose relationship.

Sister chromatid exchanges induced by mutagenic carcinogens in normal and xeroderma pigmentosum cells

Abstract: XERODERMA pigmentosum (XP) is a human disease characterised by sensitivity to sunlight1, a high incidence of skin cancer1 and a deficiency in DNA repair2. Investigations of DNA damage and repair in XP cells exposed to chemical carcinogens3–8 had led to the classification of these agents in two groups: those in which damage can be repaired by apparently normal levels of excision repair (for example, monofunctional alkylating agents) and those in which it cannot (for example, 4-nitroquinoline-1-oxide) (Table 1). In XP cells, normal excision of MMS9 or MNNG10 damage is correlated with normal levels of chromosome aberrations, and reduced excision repair of 4NQO damage is correlated with high levels of chromosome aberrations9, indicating that unrepaired damage is correlated with high levels of aberrations. It has recently been found that although sister chromatid exchanges (SCEs) differ from aberrations in many ways, they are far more sensitive indicators of chromosomal damage11. We therefore considered that a comparison of excision repairability with the yields of SCEs induced by chemicals might be informative in elucidating mechanisms of SCE formation. The results indicate that, contrary to the results with aberrations, the frequency of induced SCEs is higher in XP cells than in normal cells whether or not XP cells can perform normal amounts of excision repair of the chemically-induced damage. The data indicate that the lesions and/or subsequent events that give rise to chromosome aberrations are different from those leading to sister chromatid exchange and that SCE formation in XP cells is the most sensitive mammalian system yet described for detecting possible genetic effects of chemicals.

Sister Chromatid Exchange and Chromosome Aberration Analysis With the Use of Several Carcinogens and Noncarcinogens: Brief Communication

Abstract: Several chemical carcinogens and noncarcinogens were tested for their ability to induce sister chromatid exchanges (SCE) and structural chromosome aberrations in cultured V79-4 Chinese hamster cells. All of the direct-acting carcinogens induced a large increase in SCE frequency. Two chemicals, which are mutagenic in microorganisms but whose carcinogenicity is poorly documented, also increased the frequency of SCE. Carcinogenic polycyclic hydrocarbons caused an increased incidence of SCE only when a metabolizing feeder layer was used, whereas no increase was observed with noncarcinogenic polycyclic hydrocarbons. The other noncarcinogens also did not influence the SCE frequency. Although some chemicals increased the frequency of structural chromosome aberrations, no correlation was found between the frequencies of SCE and aberrations.

Replication bypass model of sister chromatid exchanges and implications for Bloom's syndrome and Fanconi's anemia.

Abstract: A model of the sister chromatid exchange (SCE) process is outlined as a replication mechanism to bypass DNA crosslinks. The model suggests that when normal bidirectional replication advances from both sides towards a crosslink along the two opposite parental strands, the complementary parental strand segments can be temporarily displaced at each contralateral 5′ side from the crosslink. The free ends produced in this first step will be terminally aligned but will have opposite polarity. The second step of the bypass can, however, be completed by either of two rejoining processes—terminal ligation of the free ends via nascent Okazaki pieces or aberrant complementation by overlapping the free ends. This bypass mechanism (1) allows replication to continue past a crosslink leaving it intact but (2) results in the switching of parental strands and their attached incomplete nascent strands above and below the crosslink site producing an exchange between sister chromatids. This model is compatible with the findings of current SCE studies using the new BUDR/stain techniques as well as with previous autoradiographic studies. It also suggests that the chromatid breaks and deletions in Fanconi's Anemia represent a defect in step two of the replication bypass mechanism and that the high frequency of SCE's and quadriradials in Bloom's Syndrome represent the SCE overload effects of a defect in crosslink repair.

Elevated sister chromatid exchange rate in lymphocytes of subjects treated with arsenic

Abstract: An elevated sister chromatid exchange (SCE) rate was found in the lymphocytes of six patients treated with arsenic. All had stigmata of arsenic use as well as biopsy-proven skin cancers. The arsenic exposed patients had a mean of 14.00 SCE/mitosis while 44 normal controls had a mean of 5.8 SCE/mitosis. Chromosome breakage analysis revealed no difference between the two groups. SCE rate has been shown to be elevated in a variety of systems where cell cultures or experimental animals were exposed to known mutagens and carcinogens. We suggest that the relationship carcinogen exposure-elevated SCE rate-cancer may also be valid in humans treated with arsenic.

The interaction of Hoechst 33258 and BrdU substituted DNA in the formation of sister chromatid exchanges

Abstract: Sister chromatid exchanges (SCEs) are induced in cultured Chinese hamster cells by treatment with 5-bromodeoxyuridine (BrdU) or with Hoechst 33258 (H33258) plus BrdU. The SCE frequencies depend upon the number of H33258 molecules available per cell (or per base pair) and the number of brdU molecules available per cell, and not solely upon molarity. In addition, H 33258 and BrdU act synergistically to induce SCEs. At low BrdU concentrations H33258 induces very few SCEs. At high BrdU concentrations and similar concentrations of H33258, however, SCE frequencies are significantly increased. SCE frequencies decrease with time in successively harvested cells because of the depletion of H33258 from the medium due to DNA binding.

Sister chromatid exchange and chromatid interchange as possible manifestation of different DNA repair processes.

Abstract: SISTER chromatid exchange (SCE) is a symmetrical exchange between a newly duplicated chromatid and its sister1. The demonstration that many agents that damage DNA also increase the frequency of SCE2 suggests that SCE is a reflection of a basic DNA repair process, and perhaps a cytological manifestation of post-replication repair of a recombinational character2–6. The question then arises as to the correlation between SCE and chromatid aberration, particularly chromatid interchange (CI), which also occurs as a consequence of exchange between newly duplicated chromatids7,8. To investigate whether these two types of exchange are due to the same molecular event, I have studied the reaction of SCE and CI to caffeine and cyclo-heximide in endoreduplication mitoses of cultured human embryonic skin fibroblasts. I report here evidence suggesting that the events involved are separate.

Inhibitory effects of selenium on 1,2-dimethylhydrazine and methylazoxymethanol colon carcinogenesis: correlative studies on selenium effects on the mutagenicity and sister chromatid exchange rates of selected carcinogens.

Abstract: Selenium (Se) inhibition of either the activation of test compounds and/or mutagenic events elicited by activated compounds is suggested by experimental rat assays, mutagenesis assays, and assays with human lymphocytes in culture. The colon tumor incidence in 1,2-dimethylhydrazine (DMH)-treated rats was reduced from 87% to 40% by 4 ppm Se supplements in the drinking water. Supplemental Se decreased the total number of colon tumors induced by DMH more than three-fold and by methylazoxymethanol (MAM) almost two-fold. Coexposure of Salmonella typhimurium TA 1538 to an effective molar ratio of Se/2-acetylaminofluorene=10, Se/N-OH-acetylaminofluorene=10 and SE/N-OH-aminofluorene=300 reduced the mutagenicity to 65, 68, and 61% of their respective controls with mutagen alone. With a molar ratio of Se/N-OH-AAF=100, Se reduced the activity to 28% of the mutagenicity of N-OH-AAF alone. Preliminary data indicating MAM is mutagenic in S. typhimurium TA 1535 and His G 46(6837) are presented. In toxicity studies exposure of human lymphocyte cultures to 1.3 X 10(-9) to 1.6 X 10(-5) M Se yielded sister chromatid exchange (SCE) rates equivalent to background levels of 6--7 SCE per cell. The SCE frequencies of lymphocytes cultured with Se and selected carcinogens are discussed.

Sister chromatid exchange in dyskeratosis congenita lymphocytes.

Abstract: Sister chromatid exchange (SCE) frequency in chromosomes from lymphocytes of a patient with dyskeratosis congenita was 12-2 per mitosis. Our 33 normal controls had a mean of 5-4 SCE per mitosis and 5 patients with Fanconi's anaemia averaged 7-6 SCE per mitosis. The rate of chromosome breakage was only 0-5% in the dyskeratosis congenita patient and 0 to 2-5% in controls, while the Fanconi's anaemia patients showed higher values.

Psoralen/UVA treatment and chromosomes. I. Aberrations and sister chromatid exchange in human lymphocytes in vitro and synergism with caffeine.

Abstract: Treatment of human lymphocytes in vitro with trimethylpsoralen or 8-methoxypsoralen and UVA irradiation (PUVA) induced chromosome damage, mainly constrictions and gaps, but also breaks and exchanges, and increased the frequency of sister chromatid exchange (SCE). The localization of the chromosome aberrations was nonrandom. The coincidence of many PUVA hits with mercaptoenthanol hits suggests that PUVA may have other targets in the cell than the DNA, perhaps the folding proteins of the chromosomes and the nuclear membrane/chromatin attachment organelles. Caffeine increased in a synergistic way the chromosome aberration yield if added after PUVA treatment, but there was no effect when caffeine was present before and during PUVA treatment. The SCE frequency was increased in the presence of caffeine.

Sister chromatid exchanges in lymphocytes of psoriatics after treatment with 8-methoxypsoralen and long wave ultraviolet radiation.

Abstract: Sister chromatid exchange rates in cultured cells from the blood of patients receiving photochemotherapy have been examined as an indicator of possible genetic hazards of the treatment to patients with psoriasis. Lymphocytes of untreated patients with psoriasis appear to have sister chromatid exchange rates after 72 h of culture indistinguishable from normal subjects and there is no evidence from these studies that sister chromatid exchanges are significantly increased in the lymphocytes of patients receiving photochemotherapy. Cells from blood taken from patients who had been given 8-methoxypsoralen orally 2 h before and then irradiated with UV-A in vitro were found to have an increased exchange rate which could be related to the presence of the drug in the peripheral circulation.

The distribution of mitomycin C-induced sister chromatid exchanges in the euchromatin and heterochromatin of the Indian muntjac.

Abstract: The frequency of sister chromatid exchanges (SCEs) induced by mitomycin C (MMC) in Indian Muntjac chromosomes was determined by the fluorescence plus Giemsa (FPG) technique. Using scanning cytophotometry the relative DNA content of each chromosome was measured with and without acid or alkali pretreatments for C-banding. During acid and alkali treatments, euchromatin lost 20 to 30% of its DNA, while heterochromatin lost less than 5%; an intermediate DNA loss was observed for the short arm of the X chromosome. After growth of cells in the presence of MMC during the first cycle and in the presence of bromodeoxyuridine (BrdU) during the first and second cycles of DNA replication, SCEs in the euchromatin were proportional to DNA content. SCEs at the junctions between the neck of the X chromosome and the long and short arms occurred more frequently than expected. A threshold effect for the induction of SCEs was observed in regions resistant to DNA extraction by acid and alkali treatments (i.e., the neck and short arm of the X chromosome). At high concentrations of MMC, the frequency of SCE at each junction appears to plateau at 0.5.

Benzpyrene-induced sister chromatid exchanges in lymphocytes of patients with lung cancer.

Abstract: The effect of benzpyrene on sister chromatid exchange was determined in PHA-stimulated lymphocytes of 18 patients with lung cancer and 11 controls without cancer or bronchopulmonary diseases. Patients and controls did not differ either with respect to the spontaneous rate of sister chromatid exchanges or in their response to the carcinogen. We conclude that individual susceptibility to lung cancer cannot be detected by an individual response to benzpyrene, at least in lymphocytes and at the chromosomal level.

Rate of sister chromatid exchanges in mammalian cells differing in diploid numbers.

Abstract: The rate of sister chromatid exchanges (SCE) under identical experimental conditions is the same in various mammalian species irrespective of their diploid chromosome numbers.

Analysis of karyotype variation following carcinogen treatment of Chinese hamster primary cell lines.

Abstract: Chinese hamster primary fibroblasts derived from several embryos were treated with the carcinogens benzo(a)pyrene, 7,12-dimethylbenz(a)anthracene or N-methyl-N'-nitro-N-nitrosoguanidine. Karyotype analysis, sister chromatid exchange frequency, evidence of transformation by growth in agar, cell morphology and reaction to cytocholasin B were tested at regular intervals over many culture passages. Carcinogen treatment was found to shorten the time period before onset of permanent karyotypically changed stem and side lines and in vitro transformation. Chromosomes X, 6 and 10 were more frequently involved in all cultures in these karyotype changes which were usually preceded by a period of chromosome variation. Spontaneous chromatid aberrations and aneuploidy increased in frequency with time in culture and generally appeared prior to the expression of transformation. No specific chromosomes were involved with the different carcinogens. There was no correlation between in vitro transformation and karyotype evolution and the criteria for transformation were present independently of one another. It is suggested that the lack of correlation between the parameters tested indicates that the expression of in vitro transformation is a result of selection for growth advantage from a cell population expressing an increasing degree of genetic instability and variation with time in culture.

Sister chromatid exchanges in human lymphocytes exposed to 8-methoxypsoralen and long wave UV radiation prior to incorporation of bromodeoxyuridine

Abstract: Human lymphocytes exposed to the effects of long wave UV radiation in the presence of 8-methoxypsoralen prior to stimulation by PHA show dose related sister chromatid exchanges after 2 replication cycles in vitro. This has implications for interpreting the processes involved and for monitoring DNA damaging agents in vivo.

Human sister chromatid exchange caused by methylazoxymethanol acetate.

Abstract: The incidence of sister chromatid exchange was determined in human leucocyte cultures treated with methylazoxymethanol acetate. In all individuals examined, treated cultures manifested a significantly higher frequency of sister chromatid exchanges than controls. Two concentrations of MAM AC were tested in blood cultures from nine individuals. The concentrations varied from individual to individual since they were determined by means of individual dose-response curves, which involved [ 3 H]-thymidine incorporation in PHA-stimulated short-term lymphocyte cultures versus MAM AC concentration. The lower concentration was less than the TD 50 dose. Compared to control cultures, the lower concentration caused a higher incidence of sister chromatid exchange in eight of nine individuals. The cumulative mean value for all control cultures was 5.32 exchanges per cell while that for cultures treated with the higher concentration was 10.73.

Chromosome Effects Induced by Low Levels of Mutagens

Abstract: In the past, the standard way to quantify the cytogenetic effects of mutagens has been to study the chromosome aberrations induced in somatic cells. The types of aberrations formed and the kinetic patterns of their induction, however, vary depending upon the mutagen and the part of the cell cycle treated,making inter-comparisons between mutagens rather difficult. For instance, with ionizing radiations chromosome aberrations that affect both chromatids of the chromosome identically are induced when G1 cells are treated, whereas when S or G2 cells are irradiated, chromatid aberrations are found (1). With ultraviolet light and with most chemical mutagens, on the other hand, mainly chromatid aberrations are found irrespective of the stage of the cell cycle treated. Ionizing radiations thus appear capable of breaking chromosomes at the time of treatment, whereas the other mutagens seem to induce lesions that lead to aberration formation as the cell proceeds through the S phase during which the chromosomes replicate.