gene expression

Environmental risk assessment through chemical analysis reflects the condition in rivers only at the time of sampling and measuring all the present chemical substances is impossible.

Peroxisome proliferator activated receptor (PPARs) are members of the of the nuclear hormone receptor superfamily and are implicated in a variety of fundamental biological processes such as lipid metablism, inflammation and cell differentiation. PPARs are ligand mediated transcription factors that can be activated by a group of structurally diverse man-made chemicals, the so called peroxisome prolferators (PPs). This class of PPAR ligands consists of - apart from natural and synthetic fatty acids - a vast amount of human pharmaceuticals (e.g. fibrates) and perfluoralkyl compounds (e.g. PFOS and PFOA), a “new” class of environmental pollutents of which only recently the importance and worldwide dispersion has been reported.

Abstract

This study investigates the importance of water and food as exposure sources of three model contaminants with different physico-chemical properties and modes of action to zebrafish. It is explored to what extend uptake via water or food results in different responses and toxic effects. The responses and effects are studied at molecular, cellular and organismal level using genomics, proteomics and physiological approaches. The project aims to provide a in depth understanding of how different substances interact with a model system taking into account key factors such as developmental stage, exposure route and exposure time. The results of the genomics and proteomics analysis should considerable enlarge our understanding of the molecular mechanisms of toxicity and defense.

Daphnia magna, a frequently used standard organism in laboratory toxicity testing was chosen for this study. In laboratory toxicity testing it is often assumed that organisms will respond in a similar manor as in a field situation. However, in realistic environments multiple factors and stressors, such as the differences in temperature, food availability, etc.... may strongly interfere with responses to pollutant stress. Moreover, organisms are almost always exposed to mixtures of chemical stressors in natural situations. From a toxicological point of view, these interactions can highly influence the overall impact of chemical stressors.

Transgenic cells - be it prokaryotic or eukaryotic - were introduced in environmental toxicology thanks to biotechnology and genetic engineering. Such cellular systems typically combine a promoter::operator, which acts as the sensing element, with a reporter gene coding for an easily detectable protein. In the absence of toxicant the repressor is bound to the operator and expression of the reporter is blocked. Under stress conditions, the repressor is released from the operator and reporter expression is switched on either through direct interaction with the repressor or through a cascade of connected responses (signal transduction). Important aspects in the different transgenic models are a sensitive promoter, which is reliable and relevant for a certain stress, and a reporter gene allowing efficient detection of the gene product thanks to a specific substrate or, ideally detectable as such. Most, if not all, reporter proteins can be detected using optical, immunological or electrochemical methods. Many different sensing strains and cell lines of different genera have already been constructed for the detection of specific analytes such as metals, aromatic compounds and genotoxic compounds.