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Gene expression patterns and life cycle responses of toxicant exposed chironomids

ABSTRACT: Cellular stress responses are frequently presumed to be more sensitive than traditional ecotoxicological life cycle endpoints such as survival and growth. Yet, the focus to reduce test duration and to generate more sensitive endpoints has caused transcriptomics studies to be performed at low doses during short exposures, separately and independently from traditional ecotoxicity tests, making comparisons with life cycle endpoints indirect. Therefore we aimed to directly compare the effects on growth, survival and gene expression of the non-biting midge Chironomus riparius. To this purpose, we analyzed simultaneously life cycle and transcriptomics responses of chironomid larvae exposed to four model toxicants. We observed that already at the lowest test concentrations many transcripts were significantly differentially expressed, while the life cycle endpoints of C. riparius were hardly affected. Analysis of the differentially expressed transcripts showed that at the lowest test concentrations substantial and biologically relevant cellular stress was induced and that many transcripts responded already maximally at these lowest test concentrations. The direct comparison between molecular en life cycle responses after fourteen days of exposure revealed that gene expression is more sensitive to toxicant exposure than life cycle endpoints, underlining the potential of transcriptomics for ecotoxicity testing and environmental risk assessment. Cellular stress responses are frequently presumed to be more sensitive than traditional ecotoxicological life cycle endpoints such as survival and growth. Yet, the focus to reduce test duration and to generate more sensitive endpoints has caused transcriptomics studies to be performed at low doses during short exposures, separately and independently from traditional ecotoxicity tests, making comparisons with life cycle endpoints indirect. Therefore we aimed to directly compare the effects on growth, survival and gene expression of the non-biting midge Chironomus riparius. To this purpose, we analyzed simultaneously life cycle and transcriptomics responses of chironomid larvae exposed to four model toxicants. We observed that already at the lowest test concentrations many transcripts were significantly differentially expressed, while the life cycle endpoints of C. riparius were hardly affected. Analysis of the differentially expressed transcripts showed that at the lowest test concentrations substantial and biologically relevant cellular stress was induced and that many transcripts responded already maximally at these lowest test concentrations. The direct comparison between molecular en life cycle responses after fourteen days of exposure revealed that gene expression is more sensitive to toxicant exposure than life cycle endpoints, underlining the potential of transcriptomics for ecotoxicity testing and environmental risk assessment.

ORGANISM(S): Chironomus riparius

PROVIDER: GSE40010 | GEO | 2013/08/08

SECONDARY ACCESSION(S): PRJNA172384

REPOSITORIES: GEO

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Project description:Cellular stress responses are frequently presumed to be more sensitive than traditional ecotoxicological life cycle endpoints such as survival and growth. Yet, the focus to reduce test duration and to generate more sensitive endpoints has caused transcriptomics studies to be performed at low doses during short exposures, separately and independently from traditional ecotoxicity tests, making comparisons with life cycle endpoints indirect. Therefore we aimed to directly compare the effects on growth, survival and gene expression of the non-biting midge Chironomus riparius. To this purpose, we analyzed simultaneously life cycle and transcriptomics responses of chironomid larvae exposed to four model toxicants. We observed that already at the lowest test concentrations many transcripts were significantly differentially expressed, while the life cycle endpoints of C. riparius were hardly affected. Analysis of the differentially expressed transcripts showed that at the lowest test concentrations substantial and biologically relevant cellular stress was induced and that many transcripts responded already maximally at these lowest test concentrations. The direct comparison between molecular en life cycle responses after fourteen days of exposure revealed that gene expression is more sensitive to toxicant exposure than life cycle endpoints, underlining the potential of transcriptomics for ecotoxicity testing and environmental risk assessment. Cellular stress responses are frequently presumed to be more sensitive than traditional ecotoxicological life cycle endpoints such as survival and growth. Yet, the focus to reduce test duration and to generate more sensitive endpoints has caused transcriptomics studies to be performed at low doses during short exposures, separately and independently from traditional ecotoxicity tests, making comparisons with life cycle endpoints indirect. Therefore we aimed to directly compare the effects on growth, survival and gene expression of the non-biting midge Chironomus riparius. To this purpose, we analyzed simultaneously life cycle and transcriptomics responses of chironomid larvae exposed to four model toxicants. We observed that already at the lowest test concentrations many transcripts were significantly differentially expressed, while the life cycle endpoints of C. riparius were hardly affected. Analysis of the differentially expressed transcripts showed that at the lowest test concentrations substantial and biologically relevant cellular stress was induced and that many transcripts responded already maximally at these lowest test concentrations. The direct comparison between molecular en life cycle responses after fourteen days of exposure revealed that gene expression is more sensitive to toxicant exposure than life cycle endpoints, underlining the potential of transcriptomics for ecotoxicity testing and environmental risk assessment. Four 14-day Chironomus riparius sediment toxicity tests were conducted, one with each toxicant. The surviving larvae were individually flash frozen in liquid nitrogen. For each toxicant we analyzed the gene expression of larvae exposed to low, intermediate and high concentrations. We also included a control and a solvent control. For each treatment we analyzed 10 replicates (individual larvae).

Project description:Whole-transcriptome gene-expression analyses are commonly performed in species that have a sequenced genome and for which microarrays are commercially available. To do such analyses in species with no or limited genome data, i.e. non-model organisms, necessary transcriptomics resources, i.e. an annotated transcriptome and a validated gene-expression microarray, must first be developed. The aim of the present study was to establish an advanced approach for developing transcriptomics resources for non-model organisms by combining next-generation sequencing (NGS) and microarray technology. We applied our approach to the non-biting midge Chironomus riparius, an ecologically relevant species that is widely used in sediment ecotoxicity testing. We sampled extensively covering all C. riparius developmental stages as well as toxicant exposed larvae and obtained from a normalized cDNA library 1.5 M NGS reads totalling 501 Mbp. Using the NGS data we developed transcriptomics resources in several steps. First, we designed 844 k probes directly on the NGS reads, as well as 76 k probes targeting expressed sequence tags of related species. These probes were tested for their affinity to C. riparius DNA and mRNA, by performing two biological experiments with a 1 M probe-selection microarray that contained the entire probe-library. Subsequently, the 1.5 M NGS reads were assembled into 23,709 isotigs and 135,082 singletons, which were associated to ~55 k, respectively, ~61 k gene ontology terms and which corresponded together to 22,593 unique protein accessions. An algorithm was developed that took the assembly and the probe affinities to DNA and mRNA into account, what resulted in 59 k highly-reliable probes that targeted uniquely 95% of the isotigs and 18% of the singletons. Concluding, our approach allowed the development of high-quality transcriptomics resources for C. riparius, and is applicable to any non-model organism. It is expected, that these resources will advance ecotoxicity testing with C. riparius as whole-transcriptome gene-expression analysis are now possible with this species. 1x 1M CGH array with Cy3 labeled C. riparius gDNA and Cy5 labeled A. gambiae gDNA. The microarray was designed against C. riparius mRNA sequencing reads, and has been used to identify trustworthy sequencing reads to design an expression array. This 1M array is therefore not functionally annotated.

Project description:Smoking cessation is the most effective measure for reducing the risk of smoking-related diseases but switching to less harmful products (modified-risk tobacco products) can be an alternative for smokers who would otherwise not quit. In an 18-month chronic carcinogenicity/toxicity study in A/J mice (OECD Test Guideline 453), we assessed aerosol from the Tobacco Heating System 2.2 (THS 2.2), a candidate modified-risk tobacco product based on the heat-not-burn principle, compared with 3R4F cigarette smoke (CS). To capture toxicity- and disease-relevant mechanisms, we complemented standard toxicology endpoints with in-depth systems toxicology analyses. Briefly, female A/J mice were exposed to fresh air (Sham), three concentrations of THS 2.2 aerosol corresponding to nicotine concentrations of 6.7 (Low; L), 13.4 (Medium; M), and 26.8 (High; H) µg nicotine\L test atmosphere, or to one concentration of 3R4F CS (13.4 µg nicotine\L test atmosphere) in whole-body exposure chambers for 6 h per day, 5 days per week, and up to 18 months. Interim dissections were scheduled for months 1, 5, and 10. Male mice were exposed to either fresh air (Sham) or to the high THS 2.2 aerosol concentration for 15 months. Chronic toxicity and carcinogenicity endpoints outlined in the OECD protocol were assessed; detailed findings will be reported separately (Wong et al.). For evaluation of non-OECD endpoints following a systems toxicology approach (proteomics, transcriptomics, and genomics), several tissues were collected for further analysis. Housing and all procedures involving animals were performed in accordance with the approved Institutional Animal Care and Use Committee protocol in an Agri-Food & Veterinary Authority of Singapore-licensed and Association for Assessment and Accreditation of Laboratory Animal Care International-accredited facility, where the care and use of the animals for scientific purposes were in accordance with the National Advisory Committee for Laboratory Animal Research (NACLAR) Guideline (NACLAR, 2004). Animals allocated to the omics endpoints (N=8-20) were dissected within 16-24 h of the last exposure and following randomization of all planned necropsies for the dissection time point in question. All efforts to minimize potential nucleic acid and protein degradation were made, and samples were frozen as rapidly as possible once ex vivo. Lungs collected after month 1 were snap-frozen and the right caudal lobe was used for proteomics analysis. These are the protein expression data for lung tissue assessed by iTRAQ®-based quantitative proteomics.

Project description:Smoking cessation is the most effective measure for reducing the risk of smoking-related diseases but switching to less harmful products (modified-risk tobacco products) can be an alternative for smokers who would otherwise not quit. In an 18-month chronic carcinogenicity/toxicity study in A/J mice (OECD Test Guideline 453), we assessed aerosol from the Tobacco Heating System 2.2 (THS 2.2), a candidate modified-risk tobacco product based on the heat-not-burn principle, compared with 3R4F cigarette smoke (CS). To capture toxicity- and disease-relevant mechanisms, we complemented standard toxicology endpoints with in-depth systems toxicology analyses. Briefly, female A/J mice were exposed to fresh air (Sham), three concentrations of THS 2.2 aerosol corresponding to nicotine concentrations of 6.7 (Low; L), 13.4 (Medium; M), and 26.8 (High; H) µg nicotine\L test atmosphere, or to one concentration of 3R4F CS (13.4 µg nicotine\L test atmosphere) in whole-body exposure chambers for 6 h per day, 5 days per week, and up to 18 months. Interim dissections were scheduled for months 1, 5, and 10. Male mice were exposed to either fresh air (Sham) or to the high THS 2.2 aerosol concentration for 15 months. Chronic toxicity and carcinogenicity endpoints outlined in the OECD protocol were assessed; detailed findings will be reported separately (Wong et al.). For evaluation of non-OECD endpoints following a systems toxicology approach (proteomics, transcriptomics, and genomics), several tissues were collected for further analysis. Housing and all procedures involving animals were performed in accordance with the approved Institutional Animal Care and Use Committee protocol in an Agri-Food & Veterinary Authority of Singapore-licensed and Association for Assessment and Accreditation of Laboratory Animal Care International-accredited facility, where the care and use of the animals for scientific purposes were in accordance with the National Advisory Committee for Laboratory Animal Research (NACLAR) Guideline (NACLAR, 2004). Animals allocated to the omics endpoints (N=8-20) were dissected within 16-24 h of the last exposure and following randomization of all planned necropsies for the dissection time point in question. All efforts to minimize potential nucleic acid and protein degradation were made, and samples were frozen as rapidly as possible once ex vivo. Lungs collected after month 1 were snap-frozen and the right caudal lobe was used for proteomics analysis. These are the protein expression data for the respiratory nasal epithelium assessed by iTRAQÂ®-based quantitative proteomics.

Project description:The main constituents of electronic cigarette liquids are nicotine, propylene glycol (PG), and vegetable glycerin (VG), together with distilled water and flavors. To assess the toxicity of PG/VG mixtures with and without nicotine as basic components of liquids used in e-cigarettes, a 90-day rat inhalation study according to the Organization for Economic Co-operation and Development test guideline 413 was conducted. Sprague-Dawley (SD) rats were nose-only exposed, 6â€‰h/day, 5 days/week to filtered air, or nebulized vehicle (saline), or three concentrations of PG/VG (0.174 mg PG/l + 0.210 mg VG/l; 0.520 mg PG/l + 0.630 mg VG/l; 1.520 mg PG/l + 1.890 mg VG/l) with (test item) and without (reference item) 23 µg nicotine/L. Standard toxicological endpoints were complemented by molecular analyses using transcriptomics, proteomics, and lipidomics. Compared to vehicle exposure, the tested PG/VG aerosols showed only very limited biological effects with no signs of toxicity, both for the standard toxicological endpoints (e.g., histopathology, clinical chemistry) and the systems toxicological analyses (transcriptomics, proteomics, and lipidomics). The addition of nicotine to the PG/VG aerosols (23 Âµg/l) resulted in effects in line with nicotine effects in previous studies. These included up-regulation of xenobiotic enzymes (Cyp1a1 and Fmo3) in the lung and metabolic effects, e.g., reduction in serum lipid concentrations and changes in the expression of metabolic enzymes in the liver. Signs of a generalized stress response to nicotine exposure such as decreased thymus weights were observed; and likely, a subset of the observed metabolic alterations was interlinked with this generalized stress response. Under the conditions of this 90-day SD rat inhalation study, no toxicologically relevant effects of PG/VG aerosols (up to 1.520 mg PG/l + 1.890 mg VG/l) were observed, and the no observed adverse effect level (NOAEL) for PG/VG/nicotine was determined to be 438/544/6.7 mg/kg/day. Further the study demonstrated how complementary systems toxicology analyses can reveal, also in the absence of observable adverse effects, subtoxic and adaptive responses to pharmacologically active compounds such as nicotine.

Project description:The main constituents of electronic cigarette liquids are nicotine, propylene glycol (PG), and vegetable glycerin (VG), together with distilled water and flavors. To assess the toxicity of PG/VG mixtures with and without nicotine as basic components of liquids used in e-cigarettes, a 90-day rat inhalation study according to the Organization for Economic Co-operation and Development test guideline 413 was conducted. Sprague-Dawley (SD) rats were nose-only exposed, 6 h/day, 5 days/week to filtered air, or nebulized vehicle (saline), or three concentrations of PG/VG (0.174 mg PG/l + 0.210 mg VG/l; 0.520 mg PG/l + 0.630 mg VG/l; 1.520 mg PG/l + 1.890 mg VG/l) – with (test item) and without (reference item) 23 µg nicotine/L. Standard toxicological endpoints were complemented by molecular analyses using transcriptomics, proteomics, and lipidomics. Compared to vehicle exposure, the tested PG/VG aerosols showed only very limited biological effects with no signs of toxicity, both for the standard toxicological endpoints (e.g., histopathology, clinical chemistry) and the systems toxicological analyses (transcriptomics, proteomics, and lipidomics). The addition of nicotine to the PG/VG aerosols (23 µg/l) resulted in effects in line with nicotine effects in previous studies. These included up-regulation of xenobiotic enzymes (Cyp1a1 and Fmo3) in the lung and metabolic effects, e.g., reduction in serum lipid concentrations and changes in the expression of metabolic enzymes in the liver. Signs of a generalized stress response to nicotine exposure such as decreased thymus weights were observed; and likely, a subset of the observed metabolic alterations was interlinked with this generalized stress response. Under the conditions of this 90-day SD rat inhalation study, no toxicologically relevant effects of PG/VG aerosols (up to 1.520 mg PG/l + 1.890 mg VG/l) were observed, and the no observed adverse effect level (NOAEL) for PG/VG/nicotine was determined to be 438/544/6.7 mg/kg/day. Further the study demonstrated how complementary systems toxicology analyses can reveal, also in the absence of observable adverse effects, subtoxic and adaptive responses to pharmacologically active compounds such as nicotine.

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Gene expression patterns and life cycle responses of toxicant exposed chironomids

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