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D. magna exposed to fluoranthene and pyrene - both as single compounds and binary mixtures

ABSTRACT: Daphnia are an important and widely studied model species in ecological and toxicological studies throughout the world and an official (OECD) recommended test organism. Their small size, wide distribution and easy growth conditions make this an organism ideal for functional genomics based studies, including metabolic profiling and transcriptomics. In this study we used an integrated systems approach in which transcriptomic, metabolomic and energetic responses of juvenile (4 days old) daphnids were evaluated in response to exposure to two poly aromatic hydrocarbons (pyrene and fluoranthene) and binary mixtures thereof. In addition, these responses were linked to responses measured during chronic experiments (21 days) assessing survival, growth and reproductive traits. Custom Daphnia magna microarrays were used to assess transcriptomic changes. Hierarchical cluster analysis did not result in a clear distinction between the single compounds suggesting similar molecular modes of action. Cluster analysis with both the single compounds and the binary mixture treatments resulted in a separation of treatments based on differences in toxic ratios rather than component differences. Changes in the metabolic profiles of the organisms were investigated using Nuclear Magnetic Resonance spectroscopy and Gas and Liquid Chromatography Mass Spectrometry. These multivariate metabolomic datasets were analysed with Principal Components Analysis and Partial Least Squares Discriminant Analysis. The major metabolite changes responsible for the differences observed indicated a disturbance in aminosugar metabolism in all cases. The study demonstrates the potential of ’omics’ to provide screening tools for monitoring of the freshwater environment – in invertebrate species - which is reasonably rapid, cost-effective and has the potential to greatly increase the amount of information obtained from aquatic toxicology testing.

ORGANISM(S): Daphnia magna

PROVIDER: GSE16869 | GEO | 2009/12/31

SECONDARY ACCESSION(S): PRJNA117573

REPOSITORIES: GEO

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Project description:Daphnia are an important and widely studied model species in ecological and toxicological studies throughout the world and an official (OECD) recommended test organism. Their small size, wide distribution and easy growth conditions make this an organism ideal for functional genomics based studies, including metabolic profiling and transcriptomics. In this study we used an integrated systems approach in which transcriptomic, metabolomic and energetic responses of juvenile (4 days old) daphnids were evaluated in response to exposure to two poly aromatic hydrocarbons (pyrene and fluoranthene) and binary mixtures thereof. In addition, these responses were linked to responses measured during chronic experiments (21 days) assessing survival, growth and reproductive traits. Custom Daphnia magna microarrays were used to assess transcriptomic changes. Hierarchical cluster analysis did not result in a clear distinction between the single compounds suggesting similar molecular modes of action. Cluster analysis with both the single compounds and the binary mixture treatments resulted in a separation of treatments based on differences in toxic ratios rather than component differences. Changes in the metabolic profiles of the organisms were investigated using Nuclear Magnetic Resonance spectroscopy and Gas and Liquid Chromatography Mass Spectrometry. These multivariate metabolomic datasets were analysed with Principal Components Analysis and Partial Least Squares Discriminant Analysis. The major metabolite changes responsible for the differences observed indicated a disturbance in aminosugar metabolism in all cases. The study demonstrates the potential of âomicsâ to provide screening tools for monitoring of the freshwater environment â in invertebrate species - which is reasonably rapid, cost-effective and has the potential to greatly increase the amount of information obtained from aquatic toxicology testing. Two independent experiments were performed, each with two biological replicates. As a result, every treatment was measured four times with the exception of the two highest mixtures doses where we only had two available replicates. In general, a universal reference design was used in which the reference sample was a pool composed of aliquots from all samples. Dye-bias effects were accounted for by labeling two samples of every treatment with Cy3 and two with Cy5. Exp1Rep1 (reference Cy3, sample Cy5); Exp1Rep2 (reference Cy5, sample Cy3); Exp2Rep1 (reference Cy5, sample Cy3) and Exp2Rep2 (reference Cy3, sample Cy5)

Project description:The recent development of a custom cDNA microarray platform for one of thé standard organisms in aquatic toxicology, Daphnia magna, opened up new ways to mechanistic insights of toxicological responses. In this study, gene expression and (sub)organismal responses (Cellular Energy Allocation, growth) were assayed after short-term waterborne metal exposure. Microarray analysis of Ni-exposed daphnids revealed several affected functional gene classes, of which the largest ones were involved in different metabolic processes (mainly protein and chitin related processes), cuticula turnover, transport and signal transduction. Furthermore, genes involved in oxygen transport and heme metabolism (hemoglobin, δ-aminolevilunate synthase) were down-regulated. Applying a Partial Least Squares regression on nickel fingerprints and biochemical (sub)organismal parameters revealed a set of co-varying genes (hemoglobin, RNA terminal phosphate cyclase, a ribosomal protein and an “unknown” gene fragment). An inverse relationship was seen between the mRNA expression levels of different cuticula proteins and available energy reserves. In addition to the nickel exposure, daphnids were exposed to binary mixtures of nickel and cadmium or nickel and lead. Using multivariate analysis techniques, the mixture gene expression fingerprints (Ni2++Cd2+, Ni2++Pb2+) were compared to those of the single metal treatments (Ni2+, Cd2+, Pb2+). It was hypothesized that the molecular fingerprints of the mixtures would be additive combinations of the gene expression profiles of the individual compounds present in the mixture. However, our results clearly showed additionally affected pathways after mixture treatment (e.g. additional affected genes involved in carbohydrate catabolic processes and proteolysis), indicating interactive molecular responses which are not merely the additive sum of the individual metals. These findings, although indicative of the complex nature of mixture toxicity evaluation, underline the potential of a toxicogenomics approach in gaining more mechanistic information on the effects of single compounds and mixtures.

Project description:The aim of this mRNA expression profiling experiment was to screen for ecotoxicogenomic fingerprints in juvenile daphnids (daphnia magna) as aquatic vertebrate non-target model exposed to sub lethal concentrations of Fipronil. Fipronil is a widely used insecticide applied for crop protection against field pests and Ectoparasites. The Insecticide Resistance Action Committee (IRAC) classified Fipronil after its mode of action (MoA) in the target organism as a GABA-gated chloride channel blocker (Group 2). The goal is to identify toxicogenomic profiles with predictive character and identify potential molecular key events (KE) explaining upstream adverse effects. This will provide useful information to refine and improve existing adverse outcome pathways (AOP). Furthermore, integrating the obtained profiles for this and other tested chemicals in a collective database will enable us in the future to derive predictions about the ecotoxicological hazard for chemcials with unknown apical effects, based on similarly altered transcriptomic and proteomic profiles. In a modified version of the acute immobilisation test (OECD 202), 50 juvenile Daphnids were exposed to two sub lethal concentrations of Fipronil for 48 hours under static conditions. Each test comprised of a low exposure (LE), high exposure (HE) and a negative control (NC) group and was performed in triplicates. At 48 hours after introducing the daphnids into the test solutions, RNA and protein was extracted from living daphnids with NucleoSpin RNA/Protein kit (Macherey-Nagel). RNA quality was assessed with a 2100 Bioanalyzer system (Agilent) before messenger RNA was purified (PolyA selection with TruSeq RNA Library Prep Kit v2) and sequenced on an Illumina HiSeq 4000 System (Illumina) in 50 bp single read mode, producing roughly 30 million reads per sample. Adapter sequences were removed with trimmomatic and sequences were aligned to the D. magna reference genome (daphmag2.4) using STAR. Counting of feature mapped reads was performed through featureCounts. Library gene count tables were then merged to a single count matrix as input for count normalization and differential gene expression analysis with DESeq2.

Project description:The aim of this mRNA expression profiling experiment was to screen for ecotoxicogenomic fingerprints in juvenile daphnids (daphnia magna) as aquatic vertebrate non-target model exposed to sub lethal concentrations of Imidacloprid. Imidacloprid is is a popular insecticide widely applied in agriculture and by veterinarians against ectoparasites.The Insecticide Resistance Action Committee (IRAC) classified Imidacloprid after its mode of Action (MoA) in the target organism as a nicotinic acetylcholine receptor (nAChR) competitive modulator (Group 4). The goal is to identify toxicogenomic profiles with predictive character and identify potential molecular key events (KE) explaining upstream adverse effects. This will provide useful information to refine and improve existing adverse outcome pathways (AOP). Furthermore, integrating the obtained profiles for this and other tested chemicals in a collective database will enable us in the future to derive predictions about the ecotoxicological hazard for chemcials with unknown apical effects, based on similarly altered transcriptomic and proteomic profiles. In a modified version of the acute immobilisation test (OECD 202), 50 juvenile Daphnids were exposed to two sub lethal concentrations of Imidacloprid for 48 hours under static conditions. Each test comprised of a low exposure (LE), high exposure (HE) and a negative control (NC) group and was performed in triplicates. At 48 hours after introducing the daphnids into the test solutions, RNA and protein was extracted from living daphnids with NucleoSpin RNA/Protein kit (Macherey-Nagel). RNA quality was assessed with a 2100 Bioanalyzer system (Agilent) before messenger RNA was purified (PolyA selection with TruSeq RNA Library Prep Kit v2) and sequenced on an Illumina HiSeq 4000 System (Illumina) in 50 bp single read mode, producing roughly 30 million reads per sample. Adapter sequences were removed with trimmomatic and sequences were aligned to the D. magna reference genome (daphmag2.4) using STAR. Counting of feature mapped reads was performed through featureCounts. Library gene count tables were then merged to a single count matrix as input for count normalization and differential gene expression analysis with DESeq2.

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D. magna exposed to fluoranthene and pyrene - both as single compounds and binary mixtures

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