Showing papers on "Sister chromatid exchange published in 2004"
TL;DR: Using chromosome orientation fluorescence in situ hybridization, it is found that postreplicative exchange events involving a telomere and another TTAGGG-repeat tract occur at remarkably high frequencies in ALT cells and rarely or never in non-ALT cells, including cell lines with very long telomeres.
Abstract: Telomere maintenance activity is a hallmark of cancer. In some telomerase-negative tumors, telomeres become lengthened by alternative lengthening of telomeres (ALT), a recombination-mediated DNA replication process in which telomeres use other telomeric DNA as a copy template. Using chromosome orientation fluorescence in situ hybridization, we found that postreplicative exchange events involving a telomere and another TTAGGG-repeat tract occur at remarkably high frequencies in ALT cells (range 28-280/100 metaphases) and rarely or never in non-ALT cells, including cell lines with very long telomeres. Like the ALT phenotype itself, the telomeric exchanges were not suppressed when telomerase was activated in ALT cells. These exchanges are telomere specific because there was no correlation with sister chromatid exchange rates at interstitial locations, and they were not observed in non-ALT Bloom syndrome cells with very high sister chromatid exchange rates.
312 citations
TL;DR: Bub1 maintains the steady-state levels and centromeric localization of Sgo1 in mitosis of human cells, which means that Bub1 protectsCentromeric cohesion through Shugoshin inMitosis.
Abstract: Sister chromatids in mammalian cells remain attached mostly at their centromeres at metaphase because of the loss of cohesion along chromosome arms in prophase. Here, we report that Bub1 retains centromeric cohesion in mitosis of human cells. Depletion of Bub1 or Shugoshin (Sgo1) in HeLa cells by RNA interference causes massive missegregation of sister chromatids that originates at centromeres. Surprisingly, loss of chromatid cohesion in Bub1 and Sgo1 RNA-interference cells does not appear to require the full activation of separase but, instead, triggers a mitotic arrest that depends on Mad2 and Aurora B. Bub1 maintains the steady-state levels and centromeric localization of Sgo1. Therefore, Bub1 protects centromeric cohesion through Shugoshin in mitosis.
265 citations
TL;DR: This report is the first to provide evidence of a statistically significant increase of structural CAs and of SCEs/cell associated with a reduction of the MI in all OTA- and ZEA-treated bovine lymphocyte cultures and a clear reproducible reducing effect of OTA on cell viability mediated by enhanced apoptosis.
Abstract: Ochratoxin A (OTA) and zearalenone (ZEA), two naturally occurring contaminants of animal feed, have been implicated in several mycotoxicoses in farm livestock but there is little information on their genotoxicity and toxicity in these species. Therefore, we investigated on the cytogenetic and cytotoxic effects of both OTA and ZEA in in vitro cultures of bovine lymphocytes. We determined chromosome aberrations (CAs) and sister chromatid exchanges (SCEs) as well as the mitotic index (MI) and cell viability following OTA and ZEA treatment. This report is the first to provide evidence of a statistically significant increase of structural CAs and of SCEs/cell associated with a reduction of the MI in all OTA- and ZEA-treated bovine lymphocyte cultures and a clear reproducible reducing effect of OTA on cell viability mediated by enhanced apoptosis. OTA-induced programmed cell death was not limited to bovine lymphocytes, as comparable data were demonstrated in the human leukemic T-cell line Jurkat.
146 citations
TL;DR: Reviewing the investigations published in scientific journals during 1990–2003 attempts to identify probable reason(s) for the conflicting results and makes recommendations for future research to address some of the controversial observations.
Abstract: Vijayalaxmi and Obe, G. Controversial Cytogenetic Observations in Mammalian Somatic Cells Exposed to Radiofrequency Radiation. Radiat. Res. 162, 481–496 (2004). During the years 1990–2003 a large number of investigations were conducted using rodents, cultured rodent and human cells, and freshly collected human blood lymphocytes to determine the genotoxic potential of exposure to radiofrequency (RF) radiation. The results of most of these studies (58%) did not indicate increased damage to the genetic material (assessed from DNA strand breaks, incidence of chromosomal aberrations, micronuclei and sister chromatid exchanges) in cells exposed to RF radiation compared to sham-exposed and/or unexposed cells. Some investigations (23%) reported an increase in such damage in cells exposed to RF radiation. The observations from other studies (19%) were inconclusive. This paper reviews the investigations published in scientific journals during 1990–2003 and attempts to identify probable reason(s) for the co...
131 citations
TL;DR: Comprehensive screening for genetic interactions with a replication gene revealed a connection between initiation of DNA replication and sister chromatid cohesion, and a genetic interaction between orc5-1 and the cohesin mutant scc1-73 suggested that ORC function contributes to sister chrom atid cohesion.
Abstract: Mutations in genes encoding the origin recognition complex (ORC) of Saccharomyces cerevisiae affect initiation of DNA replication and transcriptional repression at the silent mating-type loci. To explore the function of ORC in more detail, a screen for genetic interactions was undertaken using large-scale synthetic lethal analysis. Combination of orc2-1 and orc5-1 alleles with the complete set of haploid deletion mutants revealed synthetic lethal/sick phenotypes with genes involved in DNA replication, chromatin structure, checkpoints, DNA repair and recombination, and other genes that were unexpected on the basis of previous studies of ORC. Many of these genetic interactions are shared with other genes that are involved in initiation of DNA replication. Strong synthetic interactions were demonstrated with null mutations in genes that contribute to sister chromatid cohesion. A genetic interaction between orc5-1 and the cohesin mutant scc1-73 suggested that ORC function contributes to sister chromatid cohesion. Thus, comprehensive screening for genetic interactions with a replication gene revealed a connection between initiation of DNA replication and sister chromatid cohesion. Further experiments linked sister chromatid cohesion genes to silencing at mating-type loci and telomeres.
121 citations
TL;DR: The results suggest that defective chromatin assembly caused by asf1Δ leads to DSBs that can be repaired by SCE, affecting genetic stability.
Abstract: Histone chaperone Asf1 participates in heterochromatin silencing, DNA repair and regulation of gene expression, and promotes the assembly of DNA into chromatin in vitro. To determine the influence of Asf1 on genetic stability, we have analysed the effect of asf1Δ on homologous recombination. In accordance with a defect in nucleosome assembly, asf1Δ leads to a loss of negative supercoiling in plasmids. Importantly, asf1Δ increases spontaneous recombination between inverted DNA sequences. This increase correlates with an accumulation of double-strand breaks (DSBs) as determined by immunodetection of phosphorylated histone H2A and fluorescent detection of Rad52–YFP foci during S and G2/M phases. In addition, asf1Δ shows high levels of sister chromatid exchange (SCE) and is proficient in DSB-induced SCE as determined by physical analysis. Our results suggest that defective chromatin assembly caused by asf1Δ leads to DSBs that can be repaired by SCE, affecting genetic stability.
105 citations
TL;DR: It is concluded that ORD activity suppresses sister chromatid exchange and stimulates inter-homologue crossovers, thereby promoting homologue bias during meiotic recombination in Drosophila.
Abstract: During meiosis, sister chromatid cohesion is required for normal levels of homologous recombination, although how cohesion regulates exchange is not understood. Null mutations in orientation disruptor (ord) ablate arm and centromeric cohesion during Drosophila meiosis and severely reduce homologous crossovers in mutant oocytes. We show that ORD protein localizes along oocyte chromosomes during the stages in which recombination occurs. Although synaptonemal complex (SC) components initially associate with synapsed homologues in ord mutants, their localization is severely disrupted during pachytene progression, and normal tripartite SC is not visible by electron microscopy. In ord germaria, meiotic double strand breaks appear and disappear with frequency and timing indistinguishable from wild type. However, Ring chromosome recovery is dramatically reduced in ord oocytes compared with wild type, which is consistent with the model that defects in meiotic cohesion remove the constraints that normally limit recombination between sisters. We conclude that ORD activity suppresses sister chromatid exchange and stimulates inter-homologue crossovers, thereby promoting homologue bias during meiotic recombination in Drosophila.
85 citations
TL;DR: It is suggested that also XRCC1 polymorphism affects CA frequencies, thus apparently influencing DNA repair phenotype, and whether these or other genetic polymorphisms could explain the observed cancer risk predictivity of high CA frequency is examined.
Abstract: Elevated levels of chromosomal aberrations (CAs) in peripheral blood lymphocytes, widely used as a cytogenetic biomarker of genotoxic effects, have been linked to cancer predisposition. However, tobacco smoking, occupational carcinogen exposure, or time since CA analysis do not appear to explain the cancer predictivity of CAs. Alternatively, the observed CA-cancer association could reflect unidentified exposures or individual susceptibility. We assessed the effects of genetic polymorphisms of DNA repair proteins and xenobiotic-metabolizing enzymes (XMEs) on the levels of CAs and sister chromatid exchanges (SCEs) in peripheral lymphocytes of 145 (CAs) and 60 (SCEs) healthy Caucasians. Genotypes of DNA repair genes X-ray repair cross-complementation group 1 (XRCC1 codons 194, 280, 399) and 3 (XRCC3 codon 241 [corrected]), and XME genes glutathione-S-transferase (GST) M1 and T1 and N-acetyl transferase 2 (NAT2) were determined using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP)-based methods. After Poisson regression adjustment for age, sex, smoking, country, and genotypes, a higher frequency of chromosome-type breaks was observed for NAT2 slow acetylators (in nonsmokers) and GSTT1 null subjects (in smokers). Individuals carrying variant alleles for XRCC1 codons 280 and 194 showed a decreased level of chromosome-type breaks. The effect of GSTM1 null and XRCC1 codon 399 genotypes on the frequency of CAs was modified by smoking. In linear regression models adjusting for age, sex, smoking, and genotypes, none of the polymorphisms significantly affected SCE frequency, although GSTT1 null subjects had a slightly elevated SCE level. Our results are in line with earlier findings on the influence of NAT2, GSTT1, and GSTM1 polymorphisms on the level of lymphocyte chromosome damage and suggest that also XRCC1 polymorphism affects CA frequencies, thus apparently influencing DNA repair phenotype. It remains to be examined whether these or other genetic polymorphisms could explain the observed cancer risk predictivity of high CA frequency.
80 citations
TL;DR: ASP was not mutagenic for Salmonella typhimurium TA98 and TA100 strains in the absence and presence of S9 mix and also Ames/Salmonella/ microsome test.
Abstract: In the present study, the genotoxic effects of the low-calorie sweetener aspartame (ASP), which is a dipeptide derivative, was investigated using chromosome aberration (CA) test, sister chromatid exchange (SCE) test, micronucleus test in human lymphocytes and also Ames/Salmonella/ microsome test. ASP induced CAs at all concentrations (500, 1000 and 2000 microg/ml) and treatment periods (24 and 48 h) dose-dependently, while it did not induce SCEs. On the other hand, ASP decreased the replication index (RI) only at the highest concentration for 48 h treatment period. However, ASP decreased the mitotic index (MI) at all concentrations and treatment periods dose-dependently. In addition, ASP induced micronuclei at the highest concentrations only. This induction was also dose-dependent for 48 hours treatment period. ASP was not mutagenic for Salmonella typhimurium TA98 and TA100 strains in the absence and presence of S9 mix.
67 citations
ENEA1
TL;DR: Evaluating the effects of 50 Hz magnetic fields in human blood cells exposed in vitro, using several methodological approaches for the detection of genotoxicity found no synergistic effect with ionizing radiation and a slight but significant decrease of cell proliferation was evident.
Abstract: In the past, epidemiological studies indicated a possible correlation between the exposure to ELF fields and cancer. Public concern over possible hazards associated with exposure to extremely low frequency magnetic fields (ELFMFs) stimulated an increased scientific research effort. More recent research and laboratory studies, however, have not been able to definitively confirm the correlation suggested by epidemiological studies. The aim of this study was to evaluate the effects of 50 Hz magnetic fields in human blood cells exposed in vitro, using several methodological approaches for the detection of genotoxicity. Whole blood samples obtained from five donors were exposed for 2 h to 50 Hz, 1 mT uniform magnetic field generated by a Helmholtz coil system. Comet assay, sister chromatid exchanges (SCE), chromosome aberrations (CA), and micronucleus (MN) tests were used to assess DNA damage, one hallmark of malignant cell transformation. The effects of a combined exposure with X-rays were also evaluated. Results obtained do not show any significant difference between ELFMFs exposed and unexposed samples. Moreover, no synergistic effect with ionizing radiation has been observed. A slight but significant decrease of cell proliferation was evident in ELFMFs treated samples and samples subjected to the combined exposure. Bioelectromagnetics 25:41–48, 2004. © 2003 Wiley-Liss, Inc.
56 citations
TL;DR: It is hypothesized that intestinal bacteria play an important role in carcinogenicity of dimethylarsinic acid and cytotoxic and genotoxic effects in urinary bladder.
TL;DR: It is suggested that chloral hydrate has moderate genotoxic potential in infants when given for sedation, and sister chromatid exchange and micronuclei frequencies were significantly increased after treatment.
Abstract: Chloral hydrate is a sedative commonly used in pediatric medicine. It was evaluated for genotoxicity in cultured peripheral blood lymphocytes of infants who were given chloral hydrate for sedation. Sister chromatid exchange and micronucleus frequencies were determined before and after chloral hydrate administration. After treatment, the frequencies of sister chromatid exchange and micronuclei were significantly increased, suggesting that chloral hydrate has moderate genotoxic potential in infants.
TL;DR: Results provide important data on the genotoxicity of cis-[Pt(AF)2Cl2] and indicate its beneficial properties as a potential anticancer drug, especially in comparison with cis-DDP.
Abstract: Short-term tests that detect genetic damage have provided information needed for evaluating carcinogenic risks of chemicals to man. The mutagenicity of cis-bis(3-aminoflavone)dichloroplatinum(II) (cis-[Pt(AF)2Cl2]) in comparison with cis-diamminedichloroplatinum(II) (cis-DDP) was evaluated in the standard plate-incorporation assay in four strains of Salmonella typhimurium: TA97a, TA98, TA100 and TA102, in experiments with and without metabolic activation. It was shown that cis-[Pt(AF)2Cl2] acts directly and is mutagenic for three strains of S. typhimurium: TA97a, TA98 and TA100. In comparison with cis-DDP this compound showed a weaker genotoxicity. Contrary to cis-DDP it has not shown toxic properties in the tester bacteria. The genotoxicity of both tested compounds was evaluated using chromosomal aberration, sister chromatid exchange and micronucleus assays, without and with metabolic activation, in human lymphocytes in vitro. The inhibitory effects of both compounds on mitotic activity, cell proliferation kinetics and nuclear division index were also compared. In all test systems applied, cis-[Pt(AF)2Cl2] was a less effective clastogen and a weaker inducer of both sister chromatid exchanges and micronuclei in comparison with cis-DDP, with and without metabolic activation. cis-[Pt(AF)2Cl2] has a direct mechanism of action and is less cytostatic and cytotoxic than the other compound. These results provide important data on the genotoxicity of cis-[Pt(AF)2Cl2] and indicate its beneficial properties as a potential anticancer drug, especially in comparison with cis-DDP.
TL;DR: In this paper, a microhomology-mediated end joining of double strand breaks was used to pinpoint the site of sister chromatid fusion, consistent with all described sclera fusions.
Abstract: Amplification of the copy number of oncogenes is frequently associated with tumor progression. Often, the amplified DNA consists of large (tens to hundreds of kilobases) ‘head-to-head’ inverted repeat palindromes (amplicons). Several mechanisms have been proposed to explain palindrome formation but their relative contributions in nature have been difficult to assess without precise knowledge of the sequences involved at the junction of natural amplicons. Here, we have sequenced one such junction and compared this sequence to the un-rearranged structure, allowing us to pinpoint the site of sister chromatid fusion. Our results support a novel model, consistent with all described sister chromatid fusions, in which sister chromatid fusion is initiated by microhomology-mediated end joining of double strand breaks.
TL;DR: A method to differentially label sister chromatids with biotin-16-2′-deoxyuridine-5′-triphosphate (biotin-dUTP) circumventing the disadvantage of BrdU is developed, applied to study the SCEs induced by ionizing and UV radiation as well as by mitomycin C, DNaseI and AluI.
Abstract: The DNA lesions responsible for the formation of sister chromatid exchanges (SCEs) have been the object of research for a long time. SCEs can be visualized by growing cells for either two rounds of re
TL;DR: The significantly higher frequency of exchange in young smoking women may indicate that initial damage to the DNA in many of these women has probably already occurred, thus causing an increased risk of developing cancer later in life.
Abstract: Rates of sister chromatid exchange in dividing human peripheral blood lymphocytes were determined and compared between smoking and non smoking young women between the ages of 16 and 25. Chromosomes block-stained with Giemsa were also examined for chromosome aberrations. A striking difference in the frequency of sister chromatid exchange was found between young women who smoked and those who did not. Smokers scored a significantly higher, F(1) = 15.99, p = 0.0015, rate of sister chromatid exchange than non smokers. Smokers scored a higher mean of SCEs per cell (12.771, SD 3.53) than non smokers (9.712, SD 2.53). Smokers also scored a higher range of SCEs (4 to 28) as opposed to non smokers (4 to 17). No statistical difference was found between smokers and non smokers for the frequency of chromosome aberrations. The significantly higher frequency of exchange in young smoking women may indicate that initial damage to the DNA in many of these women has probably already occurred, thus causing an increased risk of developing cancer later in life.
TL;DR: Differential staining with Hoechst dye and Giemsa allows the newly synthesized DNA within a chromatid to be recognized, since BrdU incorporation results in much weaker staining.
Abstract: Sister chromatid exchange (SCE) refers to the interchange of DNA between replication products. The technique for detecting such exchanges takes advantage of the semiconservative nature of DNA synthesis. 5'-bromodeoxyuridine (BrdU) is incorporated into the newly synthesized DNA. Using standard culturing techniques, Colcemid is added to the culture and conventional cytogenetic preparations are made. Differential staining with Hoechst dye and Giemsa allows the newly synthesized DNA within a chromatid to be recognized, since BrdU incorporation results in much weaker staining. SCEs represent a point of DNA template exchange during strand synthesis, visualized as asymmetric chromatid staining or "harlequin" chromosomes.
TL;DR: The analysis revealed that SG treatment did not significantly affect the distribution of cells among the different phases of the cell cycle, indicating that the alkaloid was not cytotoxic to the bone marrow cells at the doses tested.
Abstract: Sanguinarine (SG), a benzophenanthridine alkaloid, has been shown to possess anti-microbial, anti-inflammatory and antioxidant properties. In the UK and USA its salts has been in use in mouthwashes and toothpastes to inhibit dental plaque and improve gingival health. In India and Nepal consumption of mustard oil contaminated with argemone seeds containing sanguinarine, was associated with “dropsy” syndrome. In the present study, SG was evaluated in vivo in mouse bone marrow cells for its ability to induce clastogenicity and DNA damage in terms of increased sister chromatid exchange (SCE) frequencies. Doses of 5, 10, and 15 mg/kg body weight of SG given intra peritoneally induced a positive dose-dependent significant clastogenicity and SCE frequency increases (trend test α ≤ 0.05). The minimum effective concentration to induce clastogenic and DNA damage was 10 mg of SG/kg body weight. In addition to examining SCEs, the BrdUrd-differential technique was utilized to assess the effect of SG on cell replication. The analysis revealed that SG treatment did not significantly affect the distribution of cells among the different phases of the cell cycle. The proliferation rate index and average generation time data were statistically non-significant. This indicated that the alkaloid was not cytotoxic to the bone marrow cells at the doses tested. Based on the results of the present findings, the use of this alkaloid should be restricted.
TL;DR: A derivative of Revell’s model has been proposed whereby both spontaneous and radiation-induced chromatid breaks result from DSB signaling and rearrangement processes from within large looped chromatin domains, and it is postulated that the disappearance of chromatids breaks with time results from the completion of such rearrangements, rather than from the rejoining of DSB.
Abstract: The wide range of sensitivities of stimulated T-cells from different individuals to radiation-induced chromatid breakage indicates the involvement of several low penetrance genes that appear to link elevated chromatid breakage to cancer susceptibility. The mechanisms of chromatid breakage are not yet fully understood. However, evidence is accumulating that suggests chromatid breaks are not simply expanded DNA double-strand breaks (DSB). Three models of chromatid breakage are considered. The classical breakage-first and the Revell "exchange" models do not accord with current evidence. Therefore a derivative of Revell's model has been proposed whereby both spontaneous and radiation-induced chromatid breaks result from DSB signaling and rearrangement processes from within large looped chromatin domains. Examples of such rearrangements can be observed by harlequin staining whereby an exchange of strands occurs immediately adjacent to the break site. However, these interchromatid rearrangements comprise less than 20% of the total breaks. The rest are thought to result from intrachromatid rearrangements, including a very small proportion involving complete excision of a looped domain. Work is in progress with the aim of revealing these rearrangements, which may involve the formation of inversions adjacent to the break sites. It is postulated that the disappearance of chromatid breaks with time results from the completion of such rearrangements, rather than from the rejoining of DSB. Elevated frequencies of chromatid breaks occur in irradiated cells with defects in both nonhomologous end-joining (NHEJ) and homologous recombination (HR) pathways, however there is little evidence of a correlation between reduced DSB rejoining and disappearance of chromatid breaks. Moreover, at least one treatment which abrogates the disappearance of chromatid breaks with time leaves DSB rejoining unaffected. The I-SceI DSB system holds considerable promise for the elucidation of these mechanisms, although the break frequency is relatively low in the cell lines so far derived. Techniques to study and improve such systems are under way in different cell lines. Clearly, much remains to be done to clarify the mechanisms involved in chromatid breakage, but the experimental models are becoming available with which we can begin to answer some of the key questions.
TL;DR: The present study showed that the ascorbic acid and curcumin were more effective than carotenoid and flavonoid, though all provide protection against the genotoxicity of hydrocortisone.
TL;DR: Lymphocyte cells from 30 Maltese and Syrian derivative goats reared in southern Italy underwent sister chromatid exchange (SCE) test, and the number of SCEs in chromosome 1 was significantly higher (P > 0.001) than expected from relative chromosome length.
Abstract: Lymphocyte cells from 30 Maltese and Syrian derivative goats (13 males and 17 females) reared in southern Italy underwent sister chromatid exchange (SCE) test. For the 902 cells we studied, the SCE-mean values were 6.6 k 3.0 per cell for both breeds. The SCE-frequency did not follow a Poisson distribution. The simultaneous visualization of SCEs and G-hands in the lightly stained chromatid allowed the study of SCE-distribution in chromosomes 1 and X. The number of SCEs in chromosome 1 was significantly higher (P > 0.001) than expected from relative chromosome length. No statistical differences between the numbers of SCEs in the active (early-replicating) and inactive (late-replicating) X-chromosomes of female cells were found.
Journal Article•
TL;DR: The nature of benzene-induced chromosomal aberrations and supposed consequence on human health is reviewed and the new possibilities in chromosomal alterations identification by molecular cytogenetic methods are presented.
Abstract: Adverse effects associated with occupational exposure to benzene have often been reported in humans. It has been shown, that benzene causes chromosomal aberrations, sister chromatid exchanges and micronuclei in lymphocytes of exposed workers. In addition to evidence by conventional cytogenetic methods, the genotoxic effect of benzene has also been proved by a more specific approach based on fluorescence in situ hybridization with DNA probes. In the present paper, the nature of benzene-induced chromosomal aberrations and supposed consequence on human health is reviewed. The new possibilities in chromosomal alterations identification by molecular cytogenetic methods are also presented.
TL;DR: The present study suggests that replication fork arrest, which is similar to the early phases of HR, leads to a high frequency of recombination, resulting in SCEs, and shows that SCE may be mediated by HR.
Abstract: We conducted the recombination and sister chromatid exchange (SCE) assays with five chemicals (hydroxyurea (HU), resveratrol, 4-hydroxy-trans-stilbene, 3-hydroxy-trans-stilbene, and mitomycin C) in Chinese hamster cell line SPD8/V79 to confirm directly that SCE is a result of homologous recombination (HR) SPD8 has a partial duplication in exon 7 of the endogenous hprt gene and can revert to wild type by homologous recombination All chemicals were positive in both assays except for 3-hydroxy-trans-stilbene, which was negative in both HU, resveratrol, and 4-hydroxy-trans-stilbene were scavengers of the tyrosyl free radical of the R2 subunit of mammalian ribonucleotide reductase Tyrosyl free radical scavengers disturb normal DNA replication, causing replication fork arrest Mitomycin C is a DNA cross-linking agent that also causes replication fork arrest The present study suggests that replication fork arrest, which is similar to the early phases of HR, leads to a high frequency of recombination, resulting in SCEs The findings show that SCE may be mediated by HR
TL;DR: It is suggested that chromatin-remodeling complexes also have a role in the generation of sister-chromatid cohesion, but it remains unclear whether they do so by facilitating the recruitment of cohesin to specific chromosomal sequences or by modifying an event at replication forks giving rise to cohesion between sister DNAs.
TL;DR: The increased rates of spontaneous sister chromatid exchanges in BRCA2 heterozygous mutation carriers indicate a BRCa2 haploinsufficiency, which might be an important factor for the accumulation of structural chromosomal alterations with the consequence of damage in as yet unidentified genes.
TL;DR: It is shown that BRCA2-defective cells are not completely impaired in HR by strand invasion although the spontaneous HR rate is 10-fold lower than that in wild-type cells.
Abstract: The BRCA2 tumour suppressor protein is involved in maintaining genetic stability through its role in homologous recombination (HR), where it mediates RAD51-dependent strand invasion. Here, we show that BRCA2-defective cells are not completely impaired in HR by strand invasion although the spontaneous HR rate is 10-fold lower than that in wild-type cells. Furthermore, a DNA double-strand break (DSB) triggers HR repair by strand invasion also in BRCA2-defective cells, but less efficiently. Thus, either the strand invasion pathway(s) in which BRCA2 operates is still operative in the absence of a functional BRCA2, albeit at a reduced frequency, or there is a separate pathway for strand invasion still functional in BRCA2-deficient cells. Consistent with the latter hypothesis, we show that HR events occurring in BRCA2-defective cells differ from HR events in wild-type cells. These data suggest that BRCA2-defective hamster cells are impaired in short tract gene conversion but maintain proficiency in sister chromatid exchange.
TL;DR: The usefulness of determining the spontaneous level of SCE/cell in domestic animals is discussed in relation to its possible application for a more precise evaluation of the genotoxic effects of environmental pollutants.
Abstract: The spontaneous level of sister chromatid exchange (SCEs) in the goat, estimated by exposing peripheral blood lymphocytes to 0.1 pg/ml of 5-bromodeoxyuridine (BrdU), was 3.28 k 1.71 SCE/cell, 1.64 SCE/cell generation and 0.027 SCE/chromosome. The dose-response curve of SCE/cell, observed by exposing the cells to 0.1, 0.25, 0.5, 1.0, 2.5, and 5.0 pg/ml of BrdU, rose rapidly from 0.1 to 0.5 pg/ml, remained fairly stable from 0.5 to 1.0 pg/ml and rose less rapidly from 1.0 to 5.0 pg/ml of BrdU. The frequency distribution of sister chromatid exchanges/cell and that of chromosomes showing various number of exchanges followed the Poisson probability at all BrdU levels; only at 5.0 pg/ml of BrdU was the fit found on the border of the 5 % probability level. The usefulness of determining the spontaneous level of SCE/cell in domestic animals is discussed in relation to its possible application for a more precise evaluation of the genotoxic effects of environmental pollutants. Din0 Di Berurdino, Departmeni of Animal Science, Via Universira 133, 80055 Portici-Napoli, italv
TL;DR: In this paper, the authors investigated whether garlic extract has any influence on asbestos-mediated genotoxicity and concluded that garlic extract may be an efficient, physiologically tolerable quencher of asbestos-induced mutagenecity, may be mediated by the generation.