Genotoxic effects in wild rodents (Rattus rattus and Mus musculus) in an open coal mining area

Coal is a mixture of a variety of compounds containing mutagenic and carcinogenic polycyclic aromatic hydrocarbons. Exposure to coal is considered as an important non-cellular and cellular source of reactive oxygen species that can induce DNA damage. In addition, spontaneous combustion can occur in coal mining areas, further releasing compounds with detrimental effects on the environment. In this study the comet assay was used to investigate potential genotoxic effects of coal mining activities in peripheral blood cells of the wild rodents Rattus rattus and Mus musculus. The study was conducted in a coal mining area of the Municipio de Puerto Libertador, South West of the Departamento de Cordoba, Colombia. Animals from two areas in the coal mining zone and a control area located in the Municipio de Lorica were investigated. The results showed evidence that exposure to coal results in elevated primary DNA lesions in blood cells of rodents. Three different parameters for DNA damage were assessed, namely, DNA damage index, migration length and percentage damaged cells. All parameters showed statistically significantly higher values in mice and rats from the coal mining area in comparison to the animals from the control area. The parameter "DNA Damage Index" was found to be most sensitive and to best indicate a genotoxic hazard. Both species investigated were shown to be sensitive indicators of environmental genotoxicity caused by coal mining activities. In summary, our study constitutes the first investigation of potential genotoxic effects of open coal mining carried out in Puerto Libertador. The investigations provide a guide for measures to evaluate genotoxic hazards, thereby contributing to the development of appropriate measures and regulations for more careful operations during coal mining.     

Effects of chronic exposure to coal in wild rodents (Ctenomys torquatus) evaluated by multiple methods and tissues

Rio Grande do Sul (RS) coal is low quality and typically obtained by strip mining. In a recent study concerning 2 years of biomonitoring in coal regions, we demonstrated the genotoxicity of coal and related products on blood cells of native rodents, from RS, Brazil. With the goal of studying the variations in the effects of RS coal on different tissues of the same rodent, we utilized, besides the single cell gel (SCG) and micronucleus (MN) assay on blood, histological analyses and SCG assay of bone marrow, spleen, kidney, liver and lung cells, and MN assay of bone marrow and spleen cells. In addition, to identify agents that can potentially influence the results, concentrations of several heavy metals were analyzed in livers and in soil, and the total concentration of hydrocarbons in the soil was determined. Rodents exposed to coal were captured at two different sites, Butiá and Candiota, in RS. Reference animals were obtained from Pelotas, where there is no coal mining. This report provides chemical and biological data from coal regions, indicating the possible association between Zn, Ni, Pb and hydrocarbons in the induction of DNA damage (e.g. single strand-breaks and alkali-labile sites) determined by the alkaline SCG assay in cells from Ctenomys torquatus. The results of the present SCG study indicate that coal and by-products not only induce DNA damage in blood cells, but also in other tissue cells, mainly liver, kidney and lung. Neither the MN assay nor histopathological observations showed significant differences; these analyses may be useful under circumstances where genotoxicity is higher. In conclusion we believe that the in vivo genotoxicity of coal can be biomonitored by the SCG assay, and our studies suggest that wild rodents, such as C. torquatus are useful for monitoring genotoxic damage by both methods, the SCG assay and the MN test.     

Nutritional supplement chromium picolinate generates chromosomal aberrations and impedes progeny development in Drosophila melanogaster

Chromium picolinate, [Cr(pic)₃], is a popular nutritional supplement found in a variety of consumer products. Despite its popularity, safety concerns over its use have arisen. The supplement has been shown to generate clastogenic damage, mitochondrial damage, oxidative damage, and mutagenic effects in cultured cells and oxidative DNA damage and lipid peroxidation in rats. Recently [Cr(pic)₃] has been demonstrated to generate heritable genetic change and delays in progeny development in Drosophila melanogaster. Based on the damage to chromosomes of cultured cells and of animal models, similar chromosome damage appeared to be a likely source of the mutagenic effects of the supplement in Drosophila. The current three-part study examines the effects of several chromium-containing supplements and their components on hatching and eclosion rates and success of development of first generation progeny of adult Drosophila fed food containing these compounds. It further examines the effects of the compounds on longevity of virgin male and female adults. Finally, the chromosomes in the salivary glands of Drosophila late in the third instar larval stage, which were the progeny of Drosophila whose diets were supplemented with nutritional levels of [Cr(pic)₃], are shown to contain on average over one chromosomal aberration per two identifiable chromosomal arms. No aberrations were observed in chromosomes of progeny of untreated flies. The results suggest that human consumption of the supplement should be a matter of concern and continued investigation to provide insight into the requirements of chromium-containing supplements to give rise to genotoxic effects.     

采煤塌陷影响下土壤含水量变化对柠条气孔导度、蒸腾与光合作用速率的影响

采煤塌陷引起的土壤环境因子的变化对矿区植物生长的影响越来越受到人们的关注,气孔导度、蒸腾与光合作用作为环境变化响应的敏感因子,研究植物气孔导度、蒸腾与光合作用的变化是揭示荒漠矿区自然环境变化及其规律的重要手段之一。研究采煤塌陷条件下植物光合生理的变化是探究煤炭开采对植物叶片水分蒸腾散失和CO_2同化速率影响的关键环节,是探讨采煤塌陷影响下植物能量与水分交换动态的基础,而采煤矿区植物叶片气孔导度、蒸腾与光合作用速率对采煤塌陷影响下土壤含水量变化的响应如何尚不清楚。选取神东煤田大柳塔矿区52302工作面为实验场地,以生态修复物种柠条为研究对象,对采煤塌陷区和对照区柠条叶片气孔导度、蒸腾和光合作用速率以及土壤体积含水量进行监测,分析了采煤塌陷条件下土壤含水量的变化以及其对柠条叶片气孔导度、蒸腾与光合作用速率的影响。结果显示:(1)煤炭井工开采在地表形成大量裂缝,破坏了土体结构,潜水位埋深降低,土壤含水量均低于沉陷初期,相对于对照区,硬梁和风沙塌陷区土壤含水量分别降低了18.61%、21.12%;(2)柠条叶片气孔导度、蒸腾和光合作用速率均与土壤含水量呈正相关关系;煤炭开采沉陷增加了地表水分散失,加剧了土壤水分胁迫程度,为了减少蒸腾导致的水分散失,柠条叶片气孔阻力增加,从而气孔导度降低,阻碍了光合作用CO_2的供应,从而导致柠条叶片光合作用速率的降低,蒸腾速率也显著降低。     

Evaluation of an automated in vitro micronucleus assay in CHO-K1 cells

When chlorine is used as a disinfectant for drinking water it may react with organic materials present in or released by the water pipes and thus form by-products that may represent a genotoxic hazard. The aim of this study was to assess the potential genotoxicity and cytotoxicity of extracts of chlorinated drinking water supplied by local aquifers of two Italian towns, Plants 1 and 2, located in the sub-Alpine area and on the Po plain, respectively. The raw water fell within the legal limits with regards to its chemical and physical properties. Water from Plant 2 contained higher levels of total organics (TOC) and nitrate than water from Plant 1. Water was sampled at different points along the distribution networks to evaluate the influence of the system on the amount and quality of the by-products. Cytotoxic and genotoxic damage was assessed in freshly isolated human white blood cells (WBC) and Hep-G2 cells by use of the micronucleus (MN) test and the Comet assay to measure primary DNA damage. While they did not show significant cytotoxicity, all Plant 1 water concentrates induced short-time genotoxic effects on leukocytes at concentrations ≥1 Lequiv./mL. Plant 2 samples were able to induce cytotoxic effects in both Hep-G2 cells and leukocytes. Furthermore, although there was no significant increase in MN frequency, DNA migration was strongly increased both in human leukocytes (≥0.5 Lequiv./mL, 1 h treatment, water samples collected from all points) and in Hep-G2 cells (≥0.75 Lequiv./mL, 24 h treatment, tap water sampled at the nearest distribution point). The current use of these in vitro cytotoxicity/genotoxicity tests together with the normal chemical analyses could provide information to help water-works managers and health authorities evaluate drinking water quality and adopt strategies to reduce genotoxic compounds in tap water and prevent human exposure to these compounds.     

Assessment of the genotoxicity in toad Bufo raddei exposed to petrochemical contaminants in Lanzhou Region, China

Single cell gel electrophoresis or comet assay, micronucleus (MN) test and global DNA methylation detection were used to assess the genotoxicity in toad Bufo raddei exposed to the petrochemical (mainly oil and phenol) polluted area in Lanzhou Region (LZR) comparing with a relatively unpolluted area in Liujiaxia Region (LJXR). The results from the present study indicated that DNA damage and MN frequency in toad from LZR were significantly higher than those from LJXR at the same sampling month, whereas the degree of global DNA methylation was lower, which implies that the petrochemical contaminants at environmental level in LZR were genotoxic to B. raddei. The degree of genotoxic damage was obviously related with the extent of pollution among the three sampling months in LZR. The significantly positive correlations between DNA damage and concentrations of oil and/or phenol existed in liver cells but erythrocytes, implying that liver is more suitable as a sentinel tissue for the assessment of genotoxic impact of low-level contamination. The results from both comet assay and global DNA methylation detection on liver cells showed that the genotoxicity varied significantly with oil and/or phenol concentrations, suggesting that these two methods are relatively sensitive and suitable for monitoring the genotoxicity of petrochemical pollutants on amphibians.     

Genotoxicity of gliotoxin, a secondary metabolite of Aspergillus fumigatus, in a battery of short-term test systems

The genotoxic effects of gliotoxin, a known fungal secondary metabolite, were studied. Gliotoxin was purified from cultivation medium of Aspergillus fumigatus isolated from the indoor air of a moisture problem house. The genotoxicity of gliotoxin was assessed both in bacterial test systems including bacterial repair assay, Ames Salmonella assay and SOS-chromotest, and in mammalian cells using single cell gel (SCG) electrophoresis assay and sister-chromatid exchange (SCE) test. Gliotoxin was found to be genotoxic in the bacterial repair assay but, not in the Salmonella test or SOS-chromotest. A dose-related increase in DNA damage was observed in mouse RAW264.7 macrophages exposed to gliotoxin for 2 h in plain medium in the SCG assay. In contrast to the positive response in the SCG assay, gliotoxin did not induce any clear, dose-related increase in SCEs in Chinese hamster ovary (CHO) cells.     

An initial assessment of the genotoxic impact of the Sea Empress oil spill by the measurement of DNA adduct levels in the intertidal teleost Lipophrys pholis

The Sea Empress oil spill resulted in the release of vast quantities of potentially genotoxic contaminants into the coastal environment of the county of Pembrokeshire (UK). We are at present attempting to determine the potential genotoxic impact of the incident upon the native marine species of the area. Here we describe the levels of DNA adducts in specimens of the intertidal teleost, Lipophrys pholis, exposed to extensive oil contamination as an indication of exposure to potential genotoxins. We detected elevated levels of adducts in L. pholis specimens from an area that underwent heavy oil contamination as compared to specimens from a clean reference area devoid of oil contamination. These preliminary studies indicated that the oil contamination induced DNA adducts in the L. pholis specimens, which could potentially cause genetic damage in this native marine species. Further studies are now required to assess the full extent of the genotoxic impact of the oil spill upon the Pembrokeshire area's native marine life.     

Modulation of cellular defense processes in human lymphocytes in vitro by a 1,4-dihydropyridine derivative

The aim of this pilot study was to assess whether a compound of the β-carbonyl-1,4-dihydropyridine series (AV-153 or sodium 3,5-bis-ethoxycarbonyl-2,6-dimethyl-1,4-dihydropyridine-4-carboxylate), which has high efficiency in stimulating DNA repair, can simultaneously modulate apoptosis in human cells. Peripheral blood lymphocytes of healthy donors were used in this study. DNA strand-break rejoining was assessed with the alkaline comet assay after a 3-h incubation of lymphocytes in the presence of a wide range of concentrations of AV-153 (10⁻¹⁰–10⁻⁵ M). Apoptotic and micronucleated (MN) cells were scored in phytohaemagglutinin-stimulated lymphocytes after a 72-h incubation with AV-153, using the standard cytokinesis-blocked micronucleus test. The study revealed dual effects of AV-153 on cellular defense systems against endogenously generated DNA damage: the compound per se simultaneously reduces DNA strand breaks and stimulates apoptosis, with a maximal efficiency of 76% and 42%, respectively; in contrast, after genotoxic stress (2 Gy of gamma-radiation) AV-153 reduces DNA strand breaks, the number of MN cells and apoptotic cells in a similar dose-dependent manner. A maximal efficiency of 67% was found for reduction of DNA strand breaks, while for MN cells and apoptotic cells the efficiencies were, respectively, 47% and 44%. While limited in number, these preliminary studies show the direct correlation between the efficiency of AV-153 in reduction of radiation-induced DNA breaks and MN cells on one side, and in reduction of apoptosis on the other. It suggests that the major target of the compound's action on genotoxic stress is DNA repair, followed by reduction of the number of damaged cells entering apoptosis.     

Genotoxic damage in polychaetes: A study of species and cell-type sensitivities

The marine environment is becoming increasingly contaminated by environmental pollutants with the potential to damage DNA, with marine sediments acting as a sink for many of these contaminants. Understanding genotoxic responses in sediment-dwelling marine organisms, such as polychaetes, is therefore of increasing importance. This study is an exploration of species-specific and cell-specific differences in cell sensitivities to DNA-damaging agents in polychaete worms, aimed at increasing fundamental knowledge of their responses to genotoxic damage. The sensitivities of coelomocytes from three polychaetes species of high ecological relevance, i.e. the lugworm Arenicola marina, the harbour ragworm Nereis diversicolor and the king ragworm Nereis virens to genotoxic damage are compared, and differences in sensitivities of their different coelomic cell types determined by use of the comet assay. A. marina was found to be the most sensitive to genotoxic damage induced by the direct-acting mutagen methyl methanesulfonate (MMS), and showed dose-dependent responses to MMS and the polycyclic aromatic hydrocarbon benzo(a)pyrene. Significant differences in sensitivity were also measured for the different types of coelomocyte. Eleocytes were more sensitive to induction of DNA damage than amoebocytes in both N. virens and N. diversicolor. Spermatozoa from A. marina showed significant DNA damage following in vitro exposure to MMS, but were less sensitive to DNA damage than coelomocytes. This investigation has clearly demonstrated that different cell types within the same species and different species within the polychaetes show significantly different responses to genotoxic insult. These findings are discussed in terms of the relationship between cell function and sensitivity and their implications for the use of polychaetes in environmental genotoxicity studies.     

Establishment of the comet assay in the freshwater snail Biomphalaria glabrata (Say, 1818)

The single cell gel eletrophoresis or the comet assay was established in the freshwater snail Biomphalaria glabrata. For detecting DNA damage in circulating hemocytes, adult snails were irradiated with single doses of 2.5, 5, 10 and 20 Gy of ⁶⁰Co gamma radiation. Genotoxic effect of ionizing radiation was detected at all doses as a dose-related increase in DNA migration. Comet assay in B. glabrata demonstrated to be a simple, fast and reliable tool in the evaluation of genotoxic effects of environmental mutagens.     

DNA damage and repair in somatic and germ cells in vivo

Alkylation-induced germ cell mutagenesis in the mouse versus Drosophila is compared based on data from forward mutation assays (specific-locus tests in the mouse and in Drosophila and multiple-locus assays in the latter species) but not including assays for structural chromosome aberrations. To facilitate comparisons between mouse and Drosophila, forward mutation test results have been grouped into three categories. Representatives of the first category are MMS (methyl methanesulfonate) and EO (ethylene oxide), alkylating agents with a high s value which predominantly react with ring nitrogens in DNA. ENU (N-ethyl-N-nitrosourea), MNU (N-methyl-N-nitrosourea), PRC (procarbazine), DEN (N-nitrosodiethylamine), and DMN (N-nitrosodimethylamine) belong to the second category. These agents have in common a considerable ability for modification at oxygens in DNA. Cross-linking agents (melphalan, chlorambucil, hexamethylphosphoramide) from the third category.The most unexpected, but encouraging outcome of this study is the identification of common features for three vastly different experimental indicators of genotoxicity: hereditary damage in Drosophila males, genetic damage in male mice, and tumors (TD₅₀ estimates) in rodents. Based on the above three category classification scheme the following tentative conclusions are drawn. Monofunctional agents belonging to category 1, typified by MMS and EO, display genotoxic effects in male germ cell stages that have passed meiotic division. This phenomenon seems to be the consequence of a repair deficiency during spermiogenesis for a period of 3–4 days in Drosophila and 14 days in the mouse. We suggest that the reason for the high resistance of premeiotic stages, and the generally high TD₅₀ estimates observed for this class in rodents, is the efficient error-free repair of N-alkylation damage. If we accept this hypothesis, then the increased carcinogenic potential in rodents, seen when comparing category 2 (ENU-type mutagens) to category 1 (MMS-type mutagens), along with the ability of category 2 genotoxins to induce genetic damage in premeiotic stages, must presumably be due to their enhanced ability for alkylations at oxygens in DNA; it is this property that actually distinguishes the two groups from each other. In contrast to category 1, examination of class 2 genotoxins (ENU and DEN) in premeiotic cells of Drosophila gave no indication for a significant role of germinal selection, and also removal by DNA repair was less dramatic compared to MMS. Thus category 2 mutagens are expected to display activity in a wide range of both post- and premeiotic germ cell stages. A number of these agents have been demonstrated to be among the most potent carcinogens in rodents. In terms of both hereditary damage and the initiation of cancers (low TD₅₀), cross-linking agents (category 3) comprise a considerable genotoxic hazard. Doubling doses for the mouse SLT have been determined for four cross-linking agents not requiring metabolic conversion and in all four cases the doubling doses for these agents were lower than those for MMS, DES and EMS. In support of this conclusion, two of 10 genotoxic agents, for which data on chromosomal aberrations were available for both somatic cells and germ cells in mice, were cross-linking agents and again the doubling dose estimates are lower than for monofunctional agents. Four cross-linking agents induced mutations in stem cell spermatogonia indicating that this type of agent can be active in a wide range of germ cell stages.Quite in contrast to what is generally observed in unicellular systems and in mammalian cells in culture, both cross-linking agents and MMS-type mutagens (high s value) predominantly produce deletion mutations in postmeiotic male germ cell stages. This is the uniform picture found for both Drosophila and the mouse. It is concluded that in vitro systems, in contrast to Drosophila germ cells, fail to predict this very intriguing feature of mouse germ line mutagenesis. In addition to their potential for induction of deletions and other rearrangements, cross-linking agents are among the most efficient inducers of mitotic recombination in Drosophila. Thus there are several mechanisms by which cross-linking agents may cause loss of heterozygosity for long stretches of DNA sequences, leading to expression of recessive genes. Since a substantial portion of agents used in the chemotherapy of cancers have cross-linking potential, the potential hazards of hereditary damage and cancers associated with this class of genotoxins should, in our opinion, receive more attention than they have in the past.     

Genotoxic risk and oxidative DNA damage in HepG2 cells exposed to perfluorooctanoic acid

Perfluorooctanoic acid (C8HF15O2, PFOA) is widely used in various industrial fields for decades and it is environmentally bioaccumulative. PFOA is known as a potent hepatocarcinogen in rodents. But it is not yet clear whether it is also carcinogenic in humans, and the genotoxic effects of PFOA on human cells have not yet been examined. In this study, the genotoxic potential of PFOA was investigated in human hepatoma HepG2 cells in culture using single cell gel electrophoresis (SCGE) assay and micronucleus (MN) assay. In order to clarify the underlying mechanism(s) we measured the intracellular generation of reactive oxygen species (ROS) using dichlorofluorescein diacetate as a fluorochrome. The level of oxidative DNA damage was evaluated by immunocytochemical analysis of 8-hydroxydeoxyguanosine (8-OHdG) in PFOA-treated HepG2 cells. PFOA at 50-400 microM caused DNA strand breaks and at 100-400 microM MN in HepG2 cells both in a dose-dependent manner. Significantly increased levels of ROS and 8-OHdG were observed in these cells. We conclude that PFOA exerts genotoxic effects on HepG2 cells, probably through oxidative DNA damage induced by intracellular ROS.     

In vivo Comet assay on isolated kidney cells to distinguish genotoxic carcinogens from epigenetic carcinogens or cytotoxic compounds

The objective of this study was to determine the ability of the alkaline in vivo Comet assay (pH > 13) to distinguish genotoxic carcinogens from epigenetic carcinogens when performed on freshly isolated kidney cells and to determine the possible interference of cytotoxicity by assessing DNA damage induced by renal genotoxic, epigenetic or toxic compounds after enzymatic isolation of kidney cells from OFA Sprague–Dawley male rats. The ability of the Comet assay to distinguish (1) genotoxicity versus cytotoxicity and (2) genotoxic versus non-genotoxic (epigenetic) carcinogens, was thus investigated by studying five known genotoxic renal carcinogens acting through diverse mechanisms of action, i.e. streptozotocin, aristolochic acids, 2-nitroanisole, potassium bromate and cisplatin, two rodent renal epigenetic carcinogens: d-limonene and ciclosporine and two nephrotoxic compounds: streptomycin and indomethacin. Animals were treated once with the test compound by the appropriate route of administration and genotoxic effects were measured at the two sampling times of 3–6 and 22–26 h after treatment. Regarding the tissue processing, the limited background level of DNA migration observed in the negative control groups throughout all experiments demonstrated that the enzymatic isolation method implemented in the current study is appropriate. On the other hand, streptozotocin, 20 mg/kg, used as positive reference control concurrently to each assay, caused a clear increase in the mean Olive Tail Moment median value, which allows validating the current methodology.Under these experimental conditions, the in vivo rodent Comet assay demonstrated good sensitivity and good specificity: all the five renal genotoxic carcinogens were clearly detected in at least one expression period either directly or indirectly, as in the case of cisplatin: for this cross-linking agent, the significant decrease in DNA migration observed under standard electrophoresis conditions was clearly amplified when the duration of electrophoresis was increased up to 40 min. In contrast, epigenetic and nephrotoxic compounds failed to induce any signifcant increase in DNA migration. In conclusion, the in vivo rodent Comet assay performed on isolated kidney cells could be used as a tool to investigate the genotoxic potential of a test compound if neoplasic/preneoplasic changes occur after subchronic or chronic treatments, in order to determine the role of genotoxicity in tumor induction. Moreover, the epigenetic carcinogens and cytotoxic compounds displayed clearly negative responses in this study. These results allow excluding a DNA direct-acting mechanism of action and can thus suggest that a threshold exists. Therefore, the current in vivo rodent Comet assay could contribute to elucidate an epigenetic mechanism and thus, to undertake a risk assessment associated with human use, depending on the exposure level.     

C. elegans RAD-5/CLK-2 defines a new DNA damage checkpoint protein

Background: In response to genotoxic stress, cells activate checkpoint pathways that lead to a transient cell cycle arrest that allows for DNA repair or to apoptosis, which triggers the demise of genetically damaged cells.Results: During positional cloning of the C. elegans rad-5 DNA damage checkpoint gene, we found, surprisingly, that rad-5(mn159) is allelic with clk-2(qm37), a mutant previously implicated in regulation of biological rhythms and life span. However, clk-2(qm37) is the only C. elegans clock mutant that is defective for the DNA damage checkpoint. We show that rad-5/clk-2 acts in a pathway that partially overlaps with the conserved C. elegans mrt-2/S. cerevisiae RAD17/S. pombe rad1(+) checkpoint pathway. In addition, rad-5/clk-2 also regulates the S phase replication checkpoint in C. elegans. Positional cloning reveals that the RAD-5/CLK-2 DNA damage checkpoint protein is homologous to S. cerevisiae Tel2p, an essential DNA binding protein that regulates telomere length in yeast. However, the partial loss-of-function C. elegans rad-5(mn159) and clk-2(qm37) checkpoint mutations have little effect on telomere length, and analysis of the partial loss-of-function of S. cerevisiae tel2-1 mutant failed to reveal typical DNA damage checkpoint defects.Conclusions: Using C. elegans genetics we define the novel DNA damage checkpoint protein RAD-5/CLK-2, which may play a role in oncogenesis. Given that Tel2p has been shown to bind to a variety of nucleic acid structures in vitro, we speculate that the RAD-5/CLK-2 checkpoint protein may act at sites of DNA damage, either as a sensor of DNA damage or to aid in the repair of damaged DNA.     

Construction of a functional network for common DNA damage responses in Escherichia coli

In this study, we aim to identify a common, general mode of toxic action in Escherichia coli when experiencing DNA damage, irrespective of the agents used. We conducted or collected 69 microarray data from seven different DNA damaging agents. In a quantitative manner, we constructed a probable DNA damage stress network, entitled the ‘Functional Linked Network (FLN)’, which consists of 399 significantly perturbed genes and the 1283 interactions among them. The SOS response related genes (LexA modules) were found to be dominantly activated by DNA damage, irrespective of the agents. Several minor, plausible modules were also implicated in this network, and appear to be related with the metabolic inhibition response to DNA damage or mediate the induction of SOS response. This systems and comparison approach across a variety of genotoxic agents may serve as a starting point to specify some of the unknown and common features of DNA damage responses in bacteria.     

v-myb Transformation of Xeroderma pigmentosum human fibroblasts: Overexpression of the c-Ha-ras oncogene in the transformed cells

Human Xeroderma pigmentosum “normal” fibroblasts AS16 (XP4 VI) were transformed after transfection with a recombinant v-myb clone. In this clone (pKXA 3457) derived from avian myeloblastosis virus (AMV), the expression of the oncogene sequences is driven by the AMV U-5 LTR promoter. The transformed cells (ASKXA), which have integrated a rearranged v-myb oncogene, grow in agar, are not tumorigenic in nude mice, and express a 45-kDa v-myb protein. The HMW DNA of these cells transform chicken embryo fibroblasts. The c-Ha-ras oncogene is overexpressed in the ASKXA cells but not in the parental “normal” AS16 cells and a revertant clone (ASKXA Cl 1.1 G). Our results lead to the conclusion that the XP fibroblasts are phenotipically transformed by the presence of the transfected v-myb oncogene, which is able to induce an overexpression of the c-Ha-ras gene.     

<Emphasis Type="Italic">RAD18</Emphasis> gene product of yeast <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> controls mutagenesis induced by hydrogen peroxide

Within eukaryotes, tolerance to DNA damage is determined primarily by the repair pathway controlled by the members of the RAD6 epistasis group. Genetic studies on a yeast Saccharomyces cerevisiae model showed that the initial stage of postreplication repair (PRR), i.e., initiation of replication through DNA damage, is controlled by Rad6–Rad18 ubiquitin-conjugating enzyme complex. Mutants of these genes are highly sensitive to various genotoxic agents and reduce the level of induced mutagenesis. In this case, the efficiency of mutagenesis suppression depends on the type of damage. In this study we showed that DNA damage induced by hydrogen peroxide at the same mutagen doses causes significantly more mutations and lethal events in the rad18 mutant cells compared to control wild-type cells.