Gene Expression Profiling in Daphnia magna Part I: Concentration-Dependent Profiles Provide Support for the No Observed Transcriptional Effect Level

Abstract

Ecotoxicogenomic approaches to environmental monitoring provide holistic information, offer insight into modes of action, and help to assess the causal agents and potential toxicity of effluents beyond the traditional end points of death and reproduction. Recent investigations of toxicant exposure indicate dose-dependent changes are a key issue in interpreting genomic studies. Additionally, there is interest in developing methods to integrate gene expression studies in environmental monitoring and regulation, and the No Observed Transcriptional Effect Level (NOTEL) has been proposed as a means for screening effluents and unknown chemicals for toxicity. However, computational methods to determine the NOTEL have yet to be established. Therefore, we examined effects on gene expression in Daphnia magna following exposure to Cu, Cd, and Zn over a range of concentrations including a tolerated, a sublethal, and a nearly acutely toxic concentration. Each concentration produced a distinct gene expression profile. We observed differential expression of a very few genes at tolerated concentrations that were distinct from the expression profiles observed at concentrations associated with toxicity. These results suggest that gene expression analysis may offer a strategy for distinguishing toxic and nontoxic concentrations of metals in the environment and provide support for a NOTEL for metal exposure in D. magna. Mechanistic insights could be inferred from the concentration-dependent gene expression profiles including metal specific effects on disparate metabolic processes such as digestion, immune response, development and reproduction, and less specific stress responses at higher concentrations.

Gene Expression Profiling in Daphnia magna, Part II: Validation of a Copper Specific Gene Expression Signature with Effluent from Two Copper Mines in California

“…We selected candidate biomarkers that were both associated with Cu or general metal exposure from our previous microarray studies (6,10) and differentially expressed in the five mine samples containing high levels of Cu. These include biomarkers predicative of general metal exposure, metallothionein (MT) (a) DV437799, monoxygenase DV437798, slit homologue DV437805, cellulase DV437797, and preamylase ES408209, and those specific for Cu exposure, inositol monophosphatase (IMPase) DV437806, lectin DV437813, and ES408276.…”

“…This study is the continuation of our work to establish and validate gene expression profiles for Cu, Cd, and Zn in Daphnia magna. In a companion paper, we reported gene expression profiles for these metals over a range of nontoxic and toxic concentrations and showed that a concentration exists corresponding to a no observed transcriptional effect level (NOTEL) (10). We next challenged our D. magna microarray to discriminate between polluted and nonpolluted field samples using the theory of the NOTEL and predict the contaminant present in the polluted samples.…”

Thermal evolution offsets the elevated toxicity of a contaminant under warming: A resurrection study in Daphnia magna

“…This may be partly explained by the upregulation of the detoxification gene metallothionein MT‐b under nZnO exposure at 20°C. The related MT‐a gene was not induced by nZnO in this study, which is similar to previous findings showing that in D. magna, MT‐b is more sensitive to metal exposure compared to MT‐a (Poynton et al., 2008). …”

“…Primer sequences and the qRT–PCR protocol were from Poynton et al. (2008). Briefly, total RNA was isolated using the Trizol extraction method (Invitrogen, Belgium) following DNase treatment (Fermentas, Germany).…”

It’s All in the Genes: How Genotype Can Impact Upon Response to Contaminant Exposure and the Implications for Biomonitoring in Aquatic Systems

“…Maes et al, 2005;Matson et al, 2006); and 4. genome-wide changes in genetic diversity (e.g. Armendariz et al, 2004;Connon et al, 2008;Poynton et al, 2008; for reviews on evolutionary toxicology, see : Bickham, 2011;Theodorakis & Wirgin, 2002;van Straalen & Timmermans, 2002).…”