Transgenic strains of the nematode C. elegans in biomonitoring and toxicology: effects of captan and related compounds on the stress response

Physiological (haematological, growth and endocrine) and biochemical biomarker responses in air-breathing catfish, Clarias batrachus under long-term Captan® pesticide exposures

The sub-lethal toxicity of Captan® on selected haematological (Hemoglobin, Haematocrit, Mean Corpuscular Hemoglobin) growth (Condition factor, Hepatosomatic Index, Specific Growth Rate), biochemical (serum glucose, protein), and endocrine parameters (growth hormone, T₃ and T₄) in Clarias batrachus was examined under chronic exposures. Captan® was administered at predetermined exposure concentrations (0.53 and 1.06 mg/L) and monitored on days 15, 30, and 45 of the experimental periods. The experimental groups showed significantly lower values (p < 0.05) of haemoglobin content, hematocrit, MCH in Captan® exposed fish compared to control. Serum protein, k-factor and SGR were significantly lower in exposed fish. Endocrine responses (T₃ and T₄) emerged as the most sensitive biomarker category, depicting modulated responses between sub-chronic exposure at day-15 and chronic responses at day-45. In general, biomarker depictions indicate that Captan® exposures are capable of inducing stress-specific effects at the biochemical and physiological levels negatively impacting the overall health and longevity of such animals.

Food bacteria and synthetic microparticles of similar size influence pharyngeal pumping of Caenorhabditis elegans

Toxicity tests using the model organism Caenorhabditis elegans have shown that exposure to small microplastics such as polystyrene (PS) beads lead to high body burdens and dietary restrictions that in turn inhibit reproduction. Pharyngeal pumping is the key mechanism of C. elegans for governing the uptake of food and other particles and can be easily monitored by determining the pumping rates. In this study, pharyngeal pumping of C. elegans was examined in response to increasing quantities of food bacteria (E. coli: 10⁶-10¹⁰ cells ml^-1) and synthetic particles (10⁷-10⁹ beads ml^-1) of similar size (1 µm). While the average pumping rate of C. elegans exposed to E. coli depended on the density of the bacterial cells, this was not the case for the synthetic beads. At 10⁷ items ml^-1, bacterial cells and synthetic beads triggered a basic stimulation of the pumping rate, independent of the nutritional value of the particle. At quantities >10⁷ items ml^-1, however, the nutritional value was essential to maximize the pumping rate, as it was upregulated only by E. coli cells, which can be chemosensorially recognized by C. elegans. Given the unselective uptake of all particles in the size range of bacteria, restricting the pumping rates for particles with low nutritional value to a basic rate, prevents the nematodes from wasting energy by high-frequency pumping, but still allows a food-quality screening at low food levels.

Benzo[a]pyrene and Caenorhabditis elegans: defining the genotoxic potential in an organism lacking the classical CYP1A1 pathway

Benzo[a]pyrene (BaP) is bioactivated in most organisms by the cytochrome P450 (CYP) enzymes, mainly CYP1A1, ultimately resulting in the reactive metabolite BaP-7,8-dihydrodiol-9,10-epoxide (BPDE) capable of covalently binding to DNA and forming adducts. This step has been defined as the key process in cancer initiation in humans. However, limited knowledge is available about the consequences of BaP exposure in organisms lacking this classical CYP1A1 pathway, one example is the model nematode Caenorhabditis elegans. The aim of this study was to define the genotoxic potential of BaP in C. elegans and to advance our understanding of xenobiotic processing in the absence of the CYP1A1 pathway. Exposure to high concentrations of BaP (0-40 µM) significantly affected life cycle endpoints of C. elegans, which were manifested by a reduced reproductive output and shortened life span. An optimised comet assay revealed that DNA damage increased in a dose-dependent manner; however, no bulky DNA adducts (dG-N²-BPDE) were observed by ³²P-postlabelling. Global transcriptomic analysis by RNA-Seq identified responsive transcript families, most prominently members of the cyp-35 and UDP-glucuronosyltransferases (UGTs) enzyme families, both of which are linked to xenobiotic metabolism. Strains harbouring mutations in the cyp-35A2 and cyp-35A3 genes were notably less prone to BaP-mediated toxicity, and BaP led to longevity in cyp-35A5 mutants. In summary, BaP induces transcriptional, genotoxic and phenotypic responses in C. elegans, despite the absence of the classical CYP1A1 bioactivation pathway. This provides first evidence that parallel pathways are implicated in BaP metabolism in C. elegans and this seems to be mediated via the cyp-35 pathway.

Curcumin and β-caryophellene attenuate cadmium quantum dots induced oxidative stress and lethality in Caenorhabditis elegans model system

Curcumin (CUR) and β-caryophellene (BCP) are well known bioactive phytomolecules which are known to reduce oxidative stress in living organisms. Therefore, the present study was envisaged to explore the possible effects of CUR and BCP in suppression of cadmium quantum dots (CdTe QDs) induced toxicity in Caenorhabditis elegans. CdTe QD are luminescent nanoparticles extensively exploited for in vivo imaging, but long term bioaccumulation confer deleterious effects on living organisms. The 24-h LC50 and LC100 of CdTe QD were found to be 18.40 μg/ml and 100 μg/ml respectively. The CdTe QD exposure elevated HSP-16.2 expression mediating induction of the stress response. The CdTe QD lethality was due to increment in ROS and decline in SOD and GST expression. The present study demonstrates improved survival in BCP (50 μM) and CUR (20 μM) treated worms by over 60% (P<0.01) and 50% (P<0.029) in CdTe QD (100 μg/ml) exposed worms. Furthermore, BCP and CUR attenuate oxidative stress triggered by QD. The present study for the first time demonstrates CdTe QD toxicity remediation via BCP and CUR. The future investigations can unravel underlying protective effects of phytomolceules for remediating cyotoxicolgical effects of QDs.

The Energy Metabolism in Caenorhabditis elegans under The Extremely Low-Frequency Electromagnetic Field Exposure

A literal mountain of documentation generated in the past five decades showing unmistakable health hazards associated with extremely low-frequency electromagnetic fields (ELF-EMFs) exposure. However, the relation between energy mechanism and ELF-EMF exposure is poorly understood. In this study, Caenorhabditis elegans was exposed to 50 Hz ELF-EMF at intensities of 0.5, 1, 2, and 3 mT, respectively. Their metabolite variations were analyzed by GC-TOF/MS-based metabolomics. Although minimal metabolic variations and no regular pattern were observed, the contents of energy metabolism-related metabolites such as pyruvic acid, fumaric acid, and L-malic acid were elevated in all the treatments. The expressions of nineteen related genes that encode glycolytic enzymes were analyzed by using quantitative real-time PCR. Only genes encoding GAPDH were significantly upregulated (P < 0.01), and this result was further confirmed by western blot analysis. The enzyme activity of GAPDH was increased (P < 0.01), whereas the total intracellular ATP level was decreased. While no significant difference in lifespan, hatching rate and reproduction, worms exposed to ELF-EMF exhibited less food consumption compared with that of the control (P < 0.01). In conclusion, C. elegans exposed to ELF-EMF have enhanced energy metabolism and restricted dietary, which might contribute to the resistance against exogenous ELF-EMF stress.

Genetic revelation of hexavalent chromium toxicity using Caenorhabditis elegans as a biosensor

The interaction of heavy metals such as hexavalent chromium, Cr (VI) with the environment drastically influences living organisms leading to an ecological imbalance. Caenorhabditis elegans, a saprophytic nematode having 60-80% homology with human genes offers a distinct advantage to be used as a biosensor for the appraisal of heavy metal-induced environmental toxicity and risk monitoring. The present study examines the toxicity effects of K2Cr2O7 as Cr (VI) on stress-related gene expression and morphometric parameters of C. elegans under in vitro conditions to identify genetic markers for environmental pollution. Alterations in growth and modified gene expression were observed in Cr (VI)-exposed N2 worms. The 24-h median lethal concentration for Cr (VI) was observed as 158.5 mgl(-1). Use of the responses of stress-related gene expression suggests that C. elegans can be used as an efficient biosensor for figuring out the precise route of Cr (VI)-induced environmental toxicity in a quick, simple, and inexpensive manner.

High concentration of vitamin E decreases thermosensation and thermotaxis learning and the underlying mechanisms in the nematode Caenorhabditis elegans

α-tocopherol is a powerful liposoluble antioxidant and the most abundant isoform of vitamin E in the body. Under normal physiological conditions, adverse effects of relatively high concentration of vitamin E on organisms and the underlying mechanisms are still largely unclear. In the present study, we used the nematode Caenorhabditis elegans as an in vivo assay system to investigate the possible adverse effects of high concentration of vitamin E on thermosensation and thermotaxis learning and the underlying mechanisms. Our data show that treatment with 100-200 µg/mL of vitamin E did not noticeably influence both thermosensation and thermotaxis learning; however, treatment with 400 µg/mL of vitamin E altered both thermosensation and thermotaxis learning. The observed decrease in thermotaxis learning in 400 µg/mL of vitamin E treated nematodes might be partially due to the moderate but significant deficits in thermosensation, but not due to deficits in locomotion behavior or perception to food and starvation. Treatment with 400 µg/mL of vitamin E did not noticeably influence the morphology of GABAergic neurons, but significantly decreased fluorescent intensities of the cell bodies in AFD sensory neurons and AIY interneurons, required for thermosensation and thermotaxis learning control. Treatment with 400 µg/mL of vitamin E affected presynaptic function of neurons, but had no remarkable effects on postsynaptic function. Moreover, promotion of synaptic transmission by activating PKC-1 effectively retrieved deficits in both thermosensation and thermotaxis learning induced by 400 µg/mL of vitamin E. Therefore, relatively high concentrations of vitamin E administration may cause adverse effects on thermosensation and thermotaxis learning by inducing damage on the development of specific neurons and presynaptic function under normal physiological conditions in C. elegans.

Effect of Thiovit® Jet on the structure of thoracic microtrichia/trichomes in Drosophila melanogaster

Widely used fungicides and pesticides are known to have profound effect on several nontarget organisms, which is a cause of concern. The present study aims to demonstrate the effect of a fungicide, Thiovit® Jet on the structure of epidermal microtrichia (trichome) of the dorsal thorax in Drosophila melanogaster. External morphology and structural variations of thoracic appendages have been extensively studied using scanning electron microscope from flies treated with different concentrations of Thiovit Jet (20, 30, 40 or 200 μg/ml). Similar to the effect of other fungicides like captan and captafol which are reported to produce somatic mutations in the same organism, the present study successfully demonstrates variation in the trichome/microtrichia structure of the dorsal thorax of D. melanogaster. Structural variations were observed to be associated with different concentrations of Thiovit Jet (30, 40 and 200 μg/ml), but the maximum notable change was found with 40 μg/ml treatment. The gross abnormality in the trichome structure may be due to mutation in proteins associated with normal cuticular deposition.

Different effects of polycyclic aromatic hydrocarbons in artificial and in environmental mixtures on the free living nematode C. elegans

Polycyclic aromatic hydrocarbons (PAHs) are known to exert mutagenic and carcinogenic effects. Research on extracted organic matter (EOM) from environmental mixtures has indicated several mechanisms of intracellular damage in living organisms. The toxic effect of environmental pollutants is usually assessed on cell systems or in single species. We used the model organism Caenorhabditis elegans to compare the effect of synthetic PAHs with that of the EOM from environmental mixtures. The biological effect was measured by monitoring the expression level of some crucial genes, sensitive parameters of the organism's response. The results indicate the ability of C. elegans to counteract damage by mounting a stress-response only in the presence of EOM. On the other hand the exposure of C. elegans to a mixture of synthetic PAHs determines the silencing of the transcriptional machinery, thus preventing the synthesis of proteins that are important for both the damage repair mechanism and survival itself. The results strongly indicate that the study of environmental toxicant effects at the molecular level may provide information on their mechanism of action.

Investigating bacterial sources of toxicity as an environmental contributor to dopaminergic neurodegeneration

Parkinson disease (PD) involves progressive neurodegeneration, including loss of dopamine (DA) neurons from the substantia nigra. Select genes associated with rare familial forms of PD function in cellular pathways, such as the ubiquitin-proteasome system (UPS), involved in protein degradation. The misfolding and accumulation of proteins, such as α-synuclein, into inclusions termed Lewy Bodies represents a clinical hallmark of PD. Given the predominance of sporadic PD among patient populations, environmental toxins may induce the disease, although their nature is largely unknown. Thus, an unmet challenge surrounds the discovery of causal or contributory neurotoxic factors that could account for the prevalence of sporadic PD. Bacteria within the order Actinomycetales are renowned for their robust production of secondary metabolites and might represent unidentified sources of environmental exposures. Among these, the aerobic genera, Streptomyces, produce natural proteasome inhibitors that block protein degradation and may potentially damage DA neurons. Here we demonstrate that a metabolite produced by a common soil bacterium, S. venezuelae, caused DA neurodegeneration in the nematode, Caenorhabditis elegans, which increased as animals aged. This metabolite, which disrupts UPS function, caused gradual degeneration of all neuronal classes examined, however DA neurons were particularly vulnerable to exposure. The presence of DA exacerbated toxicity because neurodegeneration was attenuated in mutant nematodes depleted for tyrosine hydroxylase (TH), the rate-limiting enzyme in DA production. Strikingly, this factor caused dose-dependent death of human SH-SY5Y neuroblastoma cells, a dopaminergic line. Efforts to purify the toxic activity revealed that it is a highly stable, lipophilic, and chemically unique small molecule. Evidence of a robust neurotoxic factor that selectively impacts neuronal survival in a progressive yet moderate manner is consistent with the etiology of age-associated neurodegenerative diseases. Collectively, these data suggest the potential for exposures to the metabolites of specific common soil bacteria to possibly represent a contributory environmental component to PD.

Toxicity of polycyclic aromatic hydrocarbons to the nematode Caenorhabditis elegans

The presence of polycyclic aromatic hydrocarbons (PAHs) in the environment has attracted much concern owing to their mutagenic and carcinogenic properties. Regulatory authorities have favored the use of biological indicators as an essential means of assessing potential toxicity of environmental pollutants. This study aimed to assess the toxicity of acenaphthene, phenanthrene, anthracene, fluoranthene, pyrene, and benzo[a]pyrene to Caenorhabditis elegans by measuring LC50 and EC50 values for growth and reproduction. The exposure to all chemicals was carried out in aqueous medium. All PAHs showed a low acute toxicity to C. elegans. There was no significant mortality in C. elegans after 24 h of exposure at PAH concentrations within (and indeed above) their respective solubility limits. Prolonged exposure (72 h) at high concentrations for acenaphthene (70,573 microg/L), phenanthrene (3758 microg/L), anthracene (1600 microg/L), fluoranthene (1955 microg/L), pyrene (1653 microg/L), and benzo[a]pyrene (80 microg/L) produced mortality. Results also showed that reproduction and growth were much more sensitive parameters of adverse response than lethality, and consequently may be more useful in assessing PAH toxicity using C. elegans. In comparison with previous studies, C. elegans was found to be approximately 2-fold less sensitive to acenaphthene, 5-fold less sensitive to phenanthrene, and 20-fold less sensitive to fluoranthene than Daphnia magna. However, the 48-h LC50 for benzo[a]pyrene (174 microg/L) reported in the present study with C. elegans was similar to that reported elsewhere for Daphnia magna (200 microg/L). Although C. elegans indicated greater sensitivity to benzo[a]pyrene than Artemia salina (174 microg/L vs. 10000 microg/L), the organism showed less sensitivity to pyrene (8 microg/L vs. 2418 microg/L), fluoranthene (40 microg/L vs. 2719 microg/L), and phenanthrene (677 microg/L vs. 4772 microg/L) than Artemia salina. Caenorhabditis elegans, while not the most sensitive of species for PAH toxicity assessment, may still hold applicability in screening of contaminated soils and sediments.

Caenorhabditis elegans as a Biological Model for Multilevel Biomarker Analysis in Environmental Toxicology and Risk Assessment

While in some instances, loss of diversity results from acute toxicity (e.g. major pollution incidents), in most cases it results from long-term sub-lethal effects that alter the relative competitive ability and fitness of certain organisms. In such cases the sub-lethal effects will cause a physiological response in the organism that ultimately leads to community level changes. Very sensitive tools are now available to study sub-lethal responses at the molecular level. However, relating such laboratory measurements to ecological effects represents a substantial challenge that can only be met by investigation at all scales (molecular, individual organism and community level) with an appropriate group of organisms. Among the various in vertebrates which can be used as model organisms in such a way, the soil nematode, Caenorhabditis elegans appear to be a promising biological model to diagnose environmental quality. This paper reviews the current status of multilevel biomarkers in environmental toxicology, and C. elegans as promising organisms for this approach.

Caenorhabditis elegans: an emerging model in biomedical and environmental toxicology

The nematode Caenorhabditis elegans has emerged as an important animal model in various fields including neurobiology, developmental biology, and genetics. Characteristics of this animal model that have contributed to its success include its genetic manipulability, invariant and fully described developmental program, well-characterized genome, ease of maintenance, short and prolific life cycle, and small body size. These same features have led to an increasing use of C. elegans in toxicology, both for mechanistic studies and high-throughput screening approaches. We describe some of the research that has been carried out in the areas of neurotoxicology, genetic toxicology, and environmental toxicology, as well as high-throughput experiments with C. elegans including genome-wide screening for molecular targets of toxicity and rapid toxicity assessment for new chemicals. We argue for an increased role for C. elegans in complementing other model systems in toxicological research.

Altered bacterial metabolism, not coenzyme Q content, is responsible for the lifespan extension in Caenorhabditis elegans fed an Escherichia coli diet lacking coenzyme Q

Coenzyme Q(n) is a fully substituted benzoquinone containing a polyisoprene tail of distinct numbers (n) of isoprene groups. Caenorhabditis elegans fed Escherichia coli devoid of Q(8) have a significant lifespan extension when compared to C. elegans fed a standard 'Q-replete'E. coli diet. Here we examine possible mechanisms for the lifespan extension caused by the Q-less E. coli diet. A bioassay for Q uptake shows that a water-soluble formulation of Q(10) is effectively taken up by both clk-1 mutant and wild-type nematodes, but does not reverse lifespan extension mediated by the Q-less E. coli diet, indicating that lifespan extension is not due to the absence of dietary Q per se. The enhanced longevity mediated by the Q-less E. coli diet cannot be attributed to dietary restriction, different Qn isoforms, reduced pathogenesis or slowed growth of the Q-less E. coli, and in fact requires E. coli viability. Q-less E. coli have defects in respiratory metabolism. C. elegans fed Q-replete E. coli mutants with similarly impaired respiratory metabolism due to defects in complex V also show a pronounced lifespan extension, although not as dramatic as those fed the respiratory deficient Q-less E. coli diet. The data suggest that feeding respiratory incompetent E. coli, whether Q-less or Q-replete, produces a robust life extension in wild-type C. elegans. We believe that the fermentation-based metabolism of the E. coli diet is an important parameter of C. elegans longevity.

Toxic effects of di(2-ethylhexyl)phthalate on mortality, growth, reproduction and stress-related gene expression in the soil nematode Caenorhabditis elegans

In this study, di(2-ethylhexyl)phthalate (DEHP) toxicities to Caenorhabditis elegans were investigated using multiple toxic endpoints, such as mortality, growth, reproduction and stress-related gene expression, focusing on the identification of chemical-induced gene expression as a sensitive biomarker for DEHP monitoring. The possible use of C. elegans as a sentinel organism in the monitoring of soil ecosystem health was also tested by conducting the experiment on the exposure of nematode to field soil. Twenty-four-hour median lethal concentration (LC50) data suggest that DEHP has a relatively high potential of acute toxicity to C. elegans. Decreases in body length and egg number per worm observed after 24h of DEHP exposure may induce long-term alteration in the growth and reproduction of the nematode population. Based on the result from the C. elegans genome array and indicated in the literatures, stress proteins, metallothionein, vitellogenin, xenobiotic metabolism enzymes, apoptosis-related proteins, and antioxidant enzyme genes were selected as stress-related genes and their expression in C. elegans by DEHP exposure was analyzed semi-quantitatively. Expression of heat shock protein (hsp)-16.1 and hsp-16.2 genes was decreased by DEHP exposure. Expression of cytochrome P450 (cyp) 35a2 and glutathione-S-transferease (gst)-4, phase I and phase II of xenobiotic metabolism enzymes, was increased by DEHP exposure in a concentration-dependent manner. An increase in stress-related gene expressions occurred concomitantly with the deterioration on the physiological level, which suggests an increase in expression of those genes may not be considered as a homeostatic response but as a toxicity that might have physiological consequences. The experiment with the soil from the landfill site suggests that the potential of the C. elegans biomarker identified in laboratory conditions should be calibrated and validated for its use in situ.

Xenobiotic detoxification in the nematode Caenorhabditis elegans

The nematode Caenorhabditis elegans is an important model organism for the study of such diverse aspects of animal physiology and behavior as embryonic development, chemoreception, and the genetic control of lifespan. Yet, even though the entire genome sequence of this organism was deposited into public databases several years ago, little is known about xenobiotic metabolism in C. elegans. In part, the paucity of detoxification information may be due to the plush life enjoyed by nematodes raised in the laboratory. In the wild, however, these animals experience a much greater array of chemical assaults. Living in the interstitial water of the soil, populations of C. elegans exhibit a boom and bust lifestyle characterized by prodigious predation of soil microbes punctuated by periods of dispersal as a non-developing alternative larval stage. During the booming periods of population expansion, these animals almost indiscriminately consume everything in their environment including any number of compounds from other animals, microorganisms, plants, and xenobiotics. Several recent studies have identified many genes encoding sensors and enzymes these nematodes may use in their xeno-coping strategies. Here, we will discuss these recent advances, as well as the efforts by our lab and others to utilize the genomic resources of the C. elegans system to elucidate this nematode's molecular defenses against toxins.

Comparative evaluation of genotoxicity of captan in amphibian larvae (Xenopus laevis and Pleurodeles waltl) using the comet assay and the micronucleus test

Captan (N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide) is a fungicide used to inhibit the growth of many types of fungi on plants used as foodstuffs. The toxic and genotoxic potentials of captan were evaluated with the micronucleus test (MNT; AFNOR,2000) and the comet assay (CA) using amphibian larvae (Xenopus laevis and Pleurodeles waltl). Acute toxicity results showed that captan was toxic (1) to Xenopus larvae exposed to from 2 mg/L to 125 or 62.5 microg/L, depending on the nature of the water [reconstituted water containing mineral salts or mineral water (MW; Volvic, Danone, France)] and (2) to Pleurodeles exposed to from 2 mg/L to 125 microg/L in both types of water. The MNT results obtained in MW showed that captan (62.5 microg/L) was genotoxic to Xenopus but not genotoxic to Pleurodeles at all concentrations tested. CA established that the genotoxicity of captan to Xenopus and Pleurodeles larvae depended on the concentration, the exposure times, and the comet parameters (tail DNA, TEM, OTM, and TL). The CA and MNT results were compared for their ability to detect DNA damage at the concentrations of captan and the exposure times applied. CA showed captan to be genotoxic from the first day of exposure. In amphibians, CA appears to be a sensitive and suitable method for detecting genotoxicity such as that caused by captan.

Using nematodes in soil ecotoxicology

Nematodes represent a very abundant group of soil organisms and non-parasitic species are important for soil quality and in the soil food web. In recent years, it has been shown that nematodes are appropriate bioindicators of soil condition and they are also suitable organisms for laboratory toxicity testing. The aims of this paper are to overview and critically assess methods and approaches for researching soil nematode ecotoxicology. In natural ecosystems, nematode abundance and community structure analyses were proved to be sensitive indicators of stress caused by soil pollutants and ecological disturbance. Community structure analyses may be approached from a functional or ecological point of view; species are divided into groups according to their feeding habits or alternatively the maturity index is calculated according to their ecological strategy. Many environmental factors have the potential to affect nematode community, which consequently results in high space and time variability. This variance is major handicap in field ecotoxicological studies because pollutant-nematode relationships are obscured. For prospective risk assessment of chemicals, several toxicity tests with nematodes were developed and are increasingly used. Sensitivity of these tests is comparable to tests with other soil species (e.g. enchytraeids, earthworms and springtails) while tests are less demanding to space and time. Most studies have focused on metal toxicity but organic compounds are almost overlooked. Endpoints used in tests were often mortality, reproduction or movement, but more sublethal endpoints such as feeding or biomarkers have been used recently too. Although there is an increasing amount of knowledge in soil nematode ecotoxicology, there is still a lot of various issues in this topic to research.

Expression profiling of five different xenobiotics using a Caenorhabditis elegans whole genome microarray

The soil nematode Caenorhabditis elegans is frequently used in ecotoxicological studies due to its wide distribution in terrestrial habitats, its easy handling in the laboratory, and its sensitivity against different kinds of stress. Since its genome has been completely sequenced, more and more studies are investigating the functional relation of gene expression and phenotypic response. For these reasons C. elegans seems to be an attractive animal for the development of a new, genome based, ecotoxicological test system. In recent years, the DNA array technique has been established as a powerful tool to obtain distinct gene expression patterns in response to different experimental conditions. Using a C. elegans whole genome DNA microarray in this study, the effects of five different xenobiotics on the gene expression of the nematode were investigated. The exposure time for the following five applied compounds beta-NF (5 mg/l), Fla (0.5 mg/l), atrazine (25 mg/l), clofibrate (10 mg/l) and DES (0.5 mg/l) was 48+/-5 h. The analysis of the data showed a clear induction of 203 genes belonging to different families like the cytochromes P450, UDP-glucoronosyltransferases (UDPGT), glutathione S-transferases (GST), carboxylesterases, collagenes, C-type lectins and others. Under the applied conditions, fluoranthene was able to induce most of the induceable genes, followed by clofibrate, atrazine, beta-naphthoflavone and diethylstilbestrol. A decreased expression could be shown for 153 genes with atrazine having the strongest effect followed by fluoranthene, diethylstilbestrol, beta-naphthoflavone and clofibrate. For upregulated genes a change ranging from approximately 2.1- till 42.3-fold and for downregulated genes from approximately 2.1 till 6.6-fold of gene expression could be affected through the applied xenobiotics. The results confirm the applicability of the gene expression for the development of an ecotoxicological test system. Compared to classical tests the main advantages of this new approach will be the increased sensitivity and it's potential for a substance class specific effect determination as well as the large numbers of genes that can be screened rapidly at the same time and the selection of well regulated marker genes to study more in detail.

Differential Hypoxia Response of hsp-16 Genes in the Nematode

Small heat shock proteins are induced by various stresses. We here report the differential hypoxia responses of the hsp-16 genes in the nematode. The hsp-16.1 and hsp-16.2 genes in Caenorhabditis elegans responded to hypoxia, while hsp-16.41 and hsp-16.48, which share the promoter regions with hsp-16.1 and hsp-16.2, respectively, did not. For comparative genomic analysis, we identified ten hsp-16 genes in the nematode C.briggsae from the genome database. The comparison of the promoter sequences revealed a new conserved sequence block, CAC(A/T)CT, that was required for the orientation-dependent hypoxia response, but not for other stress responses such as heat or ethanol. We propose a working model for the orientation-dependent promoter usage between two genes sharing the promoter region. We also discuss a possible application of the hypoxia-inducible promoter for conditional gene expression.

Caenorhabditis elegans as model system for rapid toxicity assessment of pharmaceutical compounds

INTRODUCTION

The model organism Caenorhabditis elegans is widely used for genetic studies as well as a living biomonitor in ecotoxicology. In this study, we investigated whether C. elegans may represent a suitable model for rapid preliminary toxicity studies of pharmaceutical compounds.

METHODS

For this purpose, we used the EGFR kinase inhibitors BIBU1361, BIBX1382, and an inactive chemical analogue BIBU1476. As a first parameter to score for toxicity, we determined lethality of the wild-type C. elegans strain N2 (Bristol) in the presence of the compounds. The transgenic C. elegans strain PC72 (lacZ, heat shock protein-16 [hsp-16] construct) was used as a report organism for toxic effects. PC72 expresses beta-Galactosidase which is induced by hsp-16 in direct response when exposed to toxic compounds. The expression of beta-Galactosidase in cells was subsequently visualized by histochemical staining with X-Gal.

RESULTS

A rank order of potency with respect to lethality was established: BIBU1361>BIBX1382>>BIB1476. The induction of beta-Galactosidase was concentration-dependent for each compound and demonstrated the same order of potency as observed for lethality. Furthermore, these compounds showed the same order for lethality in rodents, the first requirement of validation.

DISCUSSION

These results indicate that wild-type C. elegans and the transgenic strain PC72 are both suitable models to determine the toxicity of pharmaceutical compounds. This approach allows for an easy and fast ranking of compound toxicity, which may lead to a more rational choice for further in vivo tests.

Evaluation of toxic potential of captan: Induction of hsp70 and tissue damage in transgenic Drosophila melanogaster (hsp70-lacZ) Bg9

The study investigated the working hypothesis that a widely used fungicide captan exerts toxic effects on nontarget organisms. Transgenic Drosophila melanogaster (hsp70-lacZ) was used as a model by assaying stress gene expression as an endpoint for cytotoxicity and also to evaluate whether stress gene expression is sufficient enough to protect and to prevent tissue damage against toxic insult of the chemical. The study was further extended to understand the effect of the pesticide on development, life cycle, and reproduction of the organism and finally to evaluate a concentration of the chemical to be nontoxic to the organism. The study showed that (i) captan causes cytotoxicity at and above 0.015 ppm; (ii) at 0.0015 ppm captan, absence of hsp70 expression in the exposed organism was evaluated as the concentration referred to as no observed adverse effect level (NOAEL) for Drosophila; (iii) emergence pattern of flies was affected only at the highest concentration of captan by 4 days, while hatching and survivorship were unaffected even at this concentration; (iv) reproductive performance was significantly affected only at 125.0 and 1250.0 ppm captan, while in the lower dietary concentrations no such deleterious effects were observed; (v) at 1250.0 ppm, hsp70 failed to protect the cells from toxicant assault after 48 h exposure, thus leading to tissue damage as revealed by Trypan Blue staining. The present study shows the cytotoxic potential of captan and further reveals the application of stress genes in determining NOAEL and its expression as bioindicator of exposure to environmental contaminants.

Interaction of a free-living soil nematode, Caenorhabditis elegans, with surrogates of foodborne pathogenic bacteria

Free-living nematodes may harbor, protect, and disperse bacteria, including those ingested and passed in viable form in feces. These nematodes are potential vectors for human pathogens and may play a role in foodborne diseases associated with fruits and vegetables eaten raw. In this study, we evaluated the associations between a free-living soil nematode, Caenorhabditis elegans, and Escherichia coli, an avirulent strain of Salmonella Typhimurium, Listeria welshimeri, and Bacillus cereus. On an agar medium, young adult worms quickly moved toward colonies of all four bacteria; over 90% of 3-day-old adult worms entered colonies within 16 min after inoculation. After 48 h, worms moved in and out of colonies of L. welshimeri and B. cereus but remained associated with E. coli and Salmonella Typhimurium colonies for at least 96 h. Young adult worms fed on cells of the four bacteria suspended in K medium. Worms survived and reproduced with the use of nutrients derived from all test bacteria, as determined for eggs laid by second-generation worms after culturing for 96 h. Development was slightly slower for worms fed gram-positive bacteria than for worms fed gram-negative bacteria. Worms that fed for 24 h on bacterial lawns formed on tryptic soy agar dispersed bacteria over a 3-h period when they were transferred to a bacteria-free agar surface. The results of this study suggest that C. elegans and perhaps other free-living nematodes are potential vectors for both gram-positive and gram-negative bacteria, including foodborne pathogens in soil.

Tissue-specific expression, heat inducibility, and biological roles of two hsp16 genes in Caenorhabditis elegans

In this report we have examined two new heat shock protein (HSP16) proteins in the nematode Caenorhabditis elegans encoded by the open reading frames F08H9.3 and F08H9.4. The F08H9.3 and F08H9.4 genes are oriented in the same direction next to each other on the chromosome, not sharing any promoter region, unlike other hsp16 genes that share common promoters in pairs. The F08H9.3 and F08H9.4 proteins were expressed in a tissue-specific manner, unlike the other four HSP16 proteins. F08H9.3 was expressed in the pharynx, and F08H9.4 in the excretory canal and a few neuronal cells. While F08H9.3 was weakly induced by heat shock only in the same tissue as under the normal condition, F08H9.4 was newly induced in the intestine. RNA interference experiments showed that these two proteins are required for survival under the heat shock condition.

Evaluation of an in vitro hsp70 induction test for toxicity assessment of complex mixtures: comparison with chemical analyses and ecotoxicity tests

The aim of this study was to assess the potential of a human cell line containing the hsp70 promoter linked to the chloramphenicol acetyltransferase reporter gene in evaluating the toxic potential of complex mixtures. Cells were exposed to eluates of industrial wastes and the cellular responses were compared with the metal contents of the samples and with standardized aquatic (microalgal growth inhibition, daphnia Immobilization, bacterial luminescence inhibition, Ceriodaphnia dubia reproduction inhibition) and terrestrial (earthworm lethality, plant growth inhibition) tests. The hsp70 promoter was significantly induced by 11 of 14 samples, with different dose-response patterns. Significant correlations of in vitro induction potency with aquatic ecotoxicity, especially with chronic tests, and with the metal contents of the samples were observed. Our study provides new information on the relevance of hsp70 gene induction as a criterion of toxicity and suggests its usefulness for the detection of toxicity associated with metallic pollution in complex mixtures.

Defining the molecular and cellular basis of toxicity using comparative models

A critical element of any experimental design is the selection of the model that will be used to test the hypothesis. As Claude Bernard proposed over 100 years ago "the solution of a physiological or pathological problem often depends solely on the appropriate choice of the animal for the experiment so as to make the result clear and searching." Likewise, the Danish physiologist August Krogh in 1929 wrote that "For a large number of problems there will be some animal of choice, or a few such animals, on which it can be most conveniently studied." This scientific principle has been validated repeatedly in the intervening years as investigators have described unique models that exploit natural differences in chemical and molecular structure, biochemical function, or physiological response between different cells, tissues, and organisms to address specific hypotheses. Despite the power of this comparative approach, investigators have generally been reluctant to utilize nonmammalian or nonclassical experimental models to address questions of human biology. The perception has been that studies in relatively simple or evolutionarily ancient organisms would provide little insight into "complex" human biology. This perception, although always somewhat misguided, is now even less tenable given the results of the genome sequencing projects, which demonstrate that the human genome is remarkably similar to that of evolutionarily ancient organisms. Thus, the various life forms on Earth share much more in common then anyone had previously envisioned. This realization provides additional rationale for the use of nonclassical experimental models and provides perhaps the strongest validation of Bernard's and Krogh's assertions. This overview emphasizes some of the special attributes of alternative animal models that may be exploited to define the molecular and cellular basis of toxicity. For each attribute, selected examples of animal models and experimental approaches are presented. It focuses on the areas of neurotoxicology, reproductive and developmental toxicology, organ systems toxicology, carcinogenesis, and functional genomics/toxicogenomics and highlights the use of fish, avian, Drosophila, Caenorhabditis elegans, and yeast models in such studies.

kin-18, a C. elegans protein kinase involved in feeding

TAO1 and TAO2 are recently described protein kinases whose initial characterization has placed them at the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase kinase (MEKK) level of stress-responsive MAPK pathways. Because their physiological roles have not been identified, we sought to study their C. elegans homolog to learn more about their functions. kin-18 encodes a previously uncharacterized protein in C. elegans whose catalytic domain shares over 60% identity with TAO1 and TAO2. We demonstrate that KIN-18 is a protein of 120 kDa whose promoter is active in the pharynx and intestine of C. elegans. To learn more about TAO/KIN-18 function, we studied how expression of constitutively active forms of TAO1 or KIN-18 would affect the physiology of intact worms. Strains of C. elegans expressing active forms of TAO1 or KIN-18 exhibit altered pharyngeal electrophysiology as measured by electropharyngeogram. These worms grow more slowly and lay fewer eggs, phenotypes that could result from reduced feeding. We have also identified a C. elegans gene that encodes a protein kinase similar to mammalian MAPK/ERK Kinase (MEK) 4 whose promoter is active in the pharynx. It is phosphorylated by TAO1 in vitro and physically interacts with TAO1.

Isolation and characterization of pmk-(1-3): three p38 homologs in Caenorhabditis elegans

p38, a member of the mitogen-activated protein kinase (MAPK) superfamily, is activated in response to a variety of cellular stresses and ligands. Since the genome of the nematode C. elegans has been sequenced, we sought to identify and characterize the nematode homolog of mammalian p38. By sequence analysis and RT-PCR, we isolated cDNAs encoding three kinases, PMK-1, PMK-2, and PMK-3, which we call p38 map kinases due to their high sequence identity with p38. The three genes are contiguous on chromosome IV and comprise an operon. By use of a GFP reporter, we found that the promoter of the pmks is active throughout the intestine. An active form of MAPK/ERK kinase 6 (MEK6) phosphorylated and activated recombinant PMK-1 and PMK-2 in vitro. PMK-1 and PMK-2 phosphorylated activating transcription factor-2 (ATF-2), indicating an activity similar to mammalian p38. When transfected into mammalian cells, these kinases, like p38, are stimulated by osmotic stresses.

Applications and pitfalls of stress-proteins in biomonitoring

The vast number of potentially hazardous chemicals and the complex interactions that can occur between them in environmental mixtures, call for inexpensive, early and sensitive endpoints that reflect their biological effect. The existing validated bioassays, mostly based on lethality or reproduction, have been shown to be inadequate in respect of their sensitivity, the duration and expense of the test. In contrast, changes at biochemical level are usually the first detectable responses to environmental perturbation. Because these alterations underlie all effects at higher organisational level, they have often been shown to be very sensitive indicators of pollution. Stress-proteins (also referred to as heat-shock proteins or hsp) have recently been recognised as being one of the primary defence mechanisms that are activated by the occurrence of denatured proteins in the cell. Four major stress-protein families of 90,70,60 and 16-24 kDa are the most prominent and are frequently referred to as hsp90, hsp70, hsp60 and low molecular weight (LMW) stress-proteins. Three aspects of stress-proteins have been characterised that are essential if they want to be used as biomarkers of pollution: (1) they are part of the cellular protective response; (2) their synthesis is likely to be induced by a large number of chemicals; and (3) they are highly conserved in all organisms from bacteria to plants and man. Also, field studies have shown (be it for a limited number of stressors) that the stress response can occur even at the minute concentrations of pollutants that are usually found in the environment. However, increasing knowledge on the kinetics and persistence of the stress response to complex environmental mixtures, on the influence of both physiological and environmental parameters (pH, eutrophication, ellipsis), on the constitutive levels of stress-proteins and on the acquisition of tolerance, is required before one could safely apply stress-proteins to assess on-site pollution. Still, included in a test battery of complementary bioassays, stress protein may be very valuable as tier I biomarkers, i.e. broad response biomarkers that are used for preliminary screening of the environment.

A Caenorhabditis elegans MAP kinase kinase, MEK-1, is involved in stress responses

The c-Jun N-terminal kinase (JNK), a member of the mitogen-activated protein kinase (MAPK) family, was shown to be involved in the response to various stresses in cultured cells. However, there is little in vivo evidence indicating a role for a JNK pathway in the stress response of an organism. We identified the Caenorhabditis elegans mek-1 gene, which encodes a 347 amino acid protein highly homologous to mammalian MKK7, an activator of JNK. Mek-1 reporter fusion proteins are expressed in pharyngeal muscle, uterus, a portion of intestine, and neurons. A mek-1 deletion mutant is hypersensitive to copper and cadmium ions and to starvation. A wild-type mek-1 transgene rescued the hypersensitivity to the metal ions. Double mutants of mek-1 with an eat-5, eat-11 or eat-18 mutation, which are characterized by a limited feeding defect, showed distinct growth defects under normal conditions. Expression of an activated form of MEK-1 in the whole animal or specifically in the pharynx inhibited pharyngeal pumping. These results suggest a role for mek-1 in stress responses, with a focus in the pharynx and/or intestine.

Association of several small heat-shock proteins with reproductive tissues in the nematode Caenorhabditis elegans

Immunohistochemical data on 10 of the 14 small heat-shock (smHSPs) proteins in fourth larval stage and adult Caenorhabditis elegans show that the tissues expressing the greatest number of smHSPs are vulva (HSP12s, HSP43 and, under stress, HSP16s) and spermatheca (HSP12s, HSP25, HSP43 and, under stress, HSP16s). HSP43 is also expressed in male tail structures, and following heat-shock HSP16s are expressed in spermatids and spermatozoa.

The toxicity of dithiocarbamate fungicides to soil nematodes, assessed using a stress-inducible transgenic strain of Caenorhabditis elegans

The dithiocarbamate fungicides maneb and mancozeb induce a short-term stress response in a transgenic Caenorhabditis elegans strain (PC72) carrying a reporter lacZ gene under the control of a homologous heat shock (hsp16) promoter. This response can be readily monitored as induced beta-galactosidase activity, either by in situ staining or by a quantitative fluorometric enzyme assay. Particularly strong responses are induced by mancozeb (three- to fivefold above controls at 500 microg mL(-1)), causing acute toxicity at concentrations comparable to those recommended for field application (2 mg mL(-1)). Although much of this fungicide is adsorbed by soil, sufficient (ca. 6%) enters the soil water compartment to cause mild stress in the transgenic worm assay. Among possible metabolites from mancozeb breakdown, neither Mn2+ nor ethylenethiourea (ETU) is particularly toxic even at 10% of the optimum mancozeb dosage. Stress responses to a range of other pesticides are also reported, and in several cases it is clear that a nontarget soil species (here, transgenic C. elegans) may be sensitive to low-level contamination.

Electromagnetic fields enhance the stress response at elevated temperatures in the nematode Caenorhabditis elegans

We have studied the effect of extremely low frequency electromagnetic fields (ELF-EMF) in the presence of a second stressor (mild heat shock) on the expression of a lacZ reporter gene under the control of hsp16 or hsp70 promoters in two transgenic strains of C. elegans. The expression of the reporter gene was studied by scoring animals with induced beta-galactosidase activity after staining in toto or by biochemical quantitation of the enzyme activity, respectively. In our experimental setup we were able to expose the animals to 50 Hz magnetic flux density of 0-150 microT and at the same time control temperature with high precision (+/-0.1 degrees C). Experimental conditions were defined for which EMF strongly enhances the expression of the reporter gene.

Cloning of the oxidative stress-responsive genes in Caenorhabditis elegans

Defense systems against free radicals and reactive oxygen species minimize the lethal and mutagenic consequences of these destructive agents. To investigate the genetic response to oxidative stress in a eukaryote, we cloned and characterized oxidative stress-responsive genes by comparing gene expression in the free-living nematode Caenorhabditis elegans under atmospheric conditions and high oxygen concentrations using a method of RNA arbitrarily primed polymerase chain reaction method (RAP-PCR). We identified four genes whose expression levels increase under high oxygen. These encoded 18 s, 5.8 s and 26 s rRNAs, 16 kDa heat shock proteins (hsp16-1 and 16-48) and a vacuolar ATPase G subunit. In addition, we also established that oxi-1, an oxidative stress-responsive gene we previously cloned, encodes a family of proteins related to human E6-AP ubiquitin-protein ligase. The similarity between human and nematode was 54% in one conserved amino acid region.

Structure-function studies on small heat shock protein oligomeric assembly and interaction with unfolded polypeptides

The small heat shock protein (smHSP) and alpha-crystallin genes encode a family of 12-43-kDa proteins which assemble into large multimeric structures, function as chaperones by preventing protein aggregation, and contain a conserved region termed the alpha-crystallin domain. Here we report on the structural and functional characterization of Caenorhabditis elegans HSP16-2, a 16-kDa smHSP produced only under stress conditions. A combination of sedimentation velocity, size exclusion chromatography, and cross-linking analyses on wild-type HSP16-2 and five derivatives demonstrate that the N-terminal domain but not most of the the C-terminal extension which follows the alpha-crystallin domain is essential for the oligomerization of the smHSP into high molecular weight complexes. The N terminus of HSP16-2 is found to be buried within complexes which can accommodate at least an additional 4-kDa of heterologous sequence per subunit. Studies on the interaction of HSP16-2 with fluorescently-labeled and radiolabeled actin and tubulin reveal that this smHSP possesses a high affinity for unfolded intermediates which form early on the aggregation pathway, but has no apparent substrate specificity. Furthermore, both wild-type and C-terminally-truncated HSP16-2 can function as molecular chaperones by suppressing the thermally-induced aggregation of citrate synthase. Taken together, our data on HSP16-2 and a unique 12.6-kDa smHSP we have recently characterized demonstrate that multimerization is a prerequisite for the interaction of smHSPs with unfolded protein as well as for chaperone activity.

Unique structural features of a novel class of small heat shock proteins

Small heat shock proteins (smHSPs) and alpha-crystallins constitute a family of related molecular chaperones that exhibit striking variability in size, ranging from 16 to 43 kDa. Structural studies on these proteins have been hampered by their tendency to form large, often dynamic and heterogeneous oligomeric complexes. Here we describe the structure and expression of HSP12.6, a member of a novel class of smHSPs from the nematode Caenorhabditis elegans. Like other members of its class, HSP12.6 possesses a conserved alpha-crystallin domain but has the shortest N- and C-terminal regions of any known smHSP. Expression of HSP12.6 is limited to the first larval stage of C. elegans and is not significantly up-regulated by a wide range of stressors. Unlike other smHSPs, HSP12.6 does not form large oligomeric complexes in vivo. HSP12.6 was produced in Escherichia coli as a soluble protein and purified. Cross-linking and sedimentation velocity analyses indicate that the recombinant HSP12.6 is monomeric, making it an ideal candidate for structure determination. Interestingly, HSP12.6 does not function as a molecular chaperone in vitro, since it is unable to prevent the thermally induced aggregation of a test substrate. The structural and functional implications of these findings are discussed.