Project description:The aquatic midge, Chironomus tentans, is a keystone species in aquatic ecosystem and used as a model organism to assess chemicals toxicity in aquatic environment. To characterize midge’s cellular and molecular responses to pesticides, we established cDNA library with 10,000 cDNA elements representing 2,456 C. tentans unique genes. Blast2go identified 49 genes potentially involved in xenobiotics metabolism, including 24 cytochrome p450s (CYPs), 14 esterases (ESTs) and 11 glutathione-s-transferases (GSTs). Based on 2,456 unique genes, a cDNA microarray was developed to monitor gene expression profiles in 4th instar larvae under chlopyrifos (0.1 µg/L and 0.5 µg/L) and 1000 µg/L atrazine 48-hr exposure. We identified 149, 435 and 244 genes were significantly differentially expressed (p-value ≤0.05 with expression ratios ≥2.0) after 0.1 µg/L, 0.5 µg/L chlopyrifos, and 1000 µg/L atrazine application, respectively. Sixteen insect detoxification genes (11 CYPs, 3 GSTs and 2 esterases) were validated by qPCR and their expressions were significantly either up- or down-regulated under chlorpyrifos and atrazine exposure, especially the expression of 10 CYPs were significantly induced after chlopyrifos and atrazine exposure. The up-regulated CYPs might be involved in xenobiotic activation and/or degradation. Furthermore, we also found 5 differentially expressed hemoglobin genes. The expression changes of hemoglobins might be an adaption mechanism of C. tentans to hypoxic condition caused by xenobiotic exposure. This study provides a platform for further functional studies of pesticide-insect interactions in C. tentans.
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).