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Gene Expression changes induced by exposure to field water samples collected at Walker Mine, CA

ABSTRACT: Our research goal is to illustrate the potential of gene expression profiling to discriminate between polluted and non-polluted field sites and predict the presence of a specific contaminant. Using a gene expression analysis, we challenged our custom Daphnia magna cDNA microarray to determine the presence of a specific metal toxicant in blinded field samples collected from two copper mines in California. We compared the gene expression profiles from our field samples to previously established expression profiles for Cu, Cd, and Zn. The expression profiles from the Cu containing field samples clustered with the Cu specific gene expression profiles. Many of the previously discovered copper biomarkers were also differentially expressed in the field samples, suggesting that gene expression analysis is capable of producing robust biomarkers of exposure, which can be validated in field studies. In addition, our study revealed that upstream field samples containing undetectable levels of Cu caused the differential expression of only a few genes, lending support for the concept of a No Observed Transcriptional Effect Level (NOTEL). If confirmed by further studies, the NOTEL may play an important role in discriminating polluted and non-polluted sites in future monitoring efforts. Keywords: ecotoxicogenomic exposure study

ORGANISM(S): Daphnia magna

PROVIDER: GSE7666 | GEO | 2008/06/09

SECONDARY ACCESSION(S): PRJNA99733

REPOSITORIES: GEO

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Project description:Copper-limiting growth conditions were thought to cause an induction of genes possibly involved in copper uptake and sorting. This rationale in mind, we performed microarray analyses on B. japonicum cells grown in three variations of the BVM minimal medium. Variant 1 contained 2 M-NM-<M CuSO4 (copper excess). Variant 2 was prepared in HCl-treated glassware without any copper added (copper starvation). The residual copper concentration in this copper-starvation medium was analyzed by GF-AAS and determined to be 5 nM. Variant 3 (extreme copper limitation) was prepared like variant 2 but with the addition of 10 M-NM-<M BCS and 1 mM ascorbic acid where BCS chelates Cu(I) selectively, and ascorbic acid reduces any Cu(II) to Cu(I). Changes in the transcription profiles were recorded by the pairwise comparison of cells grown in variant 2 vs. 1, and variant 3 vs. 2. Only a small set of genes were differentially up- or down-regulated when copper-starved cells were compared with cells grown in copper excess. Most notably, five genes located adjacent to each other on the B. japonicum genome displayed an increased expression: bll4882 to bll4878. The five genes were named pcuA, pcuB, pcuC, pcuD, and pcuE (mnemonic of proteins for Cu trafficking). The genes with decreased expression are either of unknown function or M-bM-^@M-^S not surprisingly M-bM-^@M-^S play a role in copper resistance. Extreme copper limitation (variant 3 vs. 2) did not further enhance the expression of the five pcu genes. Instead, another cluster of adjacent genes was strongly up-regulated: bll0889 to bll0883, which code for unidentified transport functions. Incidentally, the list also includes the copper chaperone ScoI. Taken together, copper-limiting growth conditions have led to the de-repression of genes potentially involved in copper acquisition. Microarray-based transcriptome analysis of B. japonicum 110spc4 wild-type cells grown under normal, copper-limiting and copper excess conditions

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Gene Expression changes induced by exposure to field water samples collected at Walker Mine, CA

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