| Environmental contamination with man-made and petroleum derived chemicals is a pervasive and insidious issue for both wildlife and human health. My dissertation research focused on the effect of two classes of environmental contaminants, polycyclic aromatic hydrocarbons (PAHs) and phthalates, on early teleost development. PAHs are a class of widespread environmental contaminants that are a major component of fossil fuels and coal-tar creosote, a widely used wood preservative in the United States. PAHs are also formed during the incomplete combustion of organic matter, and are therefore present in atmospheric pollution as well as urban run-off. Phthalate esters are a class of anthropogenic chemicals that are used as plasticizers to impart flexibility to PVC resins, and are also added to many consumer products including cosmetics and packaging ink. The production and use of these chemicals has led to widespread environmental contamination.;Using a model vertebrate species, the zebrafish (Danio rerio ), I have characterized both the morphological and cellular effects of phenanthrene and dibutyl phthalate on axis determination. I have established that these environmental contaminants are capable of disrupting development in both invertebrate and vertebrate species by disrupting the Wnt/beta-catenin signaling pathway. Using Western blot analysis and antibodies specific to the phosphorylation state of GSK-3beta, I examined whether these chemicals affect inhibitory phosphorylation at serine 9 on GSK-3beta. No change in the phosphorylation state of GSK-3beta was detected in exposed embryos. I also tested whether phenanthrene and dibutyl phthalate could directly inhibit GSK-3beta kinase activity in an in vitro kinase assay. These environmental contaminants had no direct effect on the kinase activity of GSK-3beta. I present evidence from the literature that indicates that phenanthrene and dibutyl phthalate likely act independently of the aryl-hydrocarbon (Ah) receptor in my studies.;The ability of phenanthrene and dibutyl phthalate to modulate the beta-catenin signaling pathway represents a novel mechanism of toxicity for these chemicals and warrants concern, both ecologically and potentially for human health. Disregulation of beta-catenin signaling has been linked to carcinogenesis, and activating mutations within the Wnt signaling pathway cause 90% of colorectal cancers. The ability of PAHs and dibutyl phthalate to modulate this pathway represents a unique mechanism for carcinogenesis.;In addition to exploring the mechanism for contaminant effects on this signaling pathway, I have also translated my results with zebrafish to the estuarine Pacific herring, Clupea pallasi. Pacific herring are important both ecologically and commercially. Because the Wnt/beta-catenin signaling pathway is so remarkably well conserved among animal species, and because PAHs and phthalates are such widespread environmental chemicals, these results could have wide-reaching implications for ecosystem health. This research will allow predictions to be made about early life stage failure in the environment, and could contribute to our understanding of unexplained recruitment losses.;Lastly, I examined the ability of two known oxidative stressors, lead acetate and hydrogen peroxide, to induce morphological abnormalities that were homologous to those observed with PAHs. PAHs, both singly and in mixtures, have been shown to increase oxidative damage in aquatic vertebrates and invertebrates. I also test whether processed water can protect against the toxic action of these pro-oxidants, alone, or in combination with a known antioxidant (lipoic acid). Embryos exposed to lead acetate or hydrogen peroxide did not exhibit abnormalities characteristic of dorsal-ventral axis disruption, but did show a suite of abnormalities at the larval stage, including spinal curvatures, cardiac edema and yolk sac edema. My results suggest that under certain conditions processed water media is an active agent, with the ability to attenuate toxicological responses that differ from Control media. (Abstract shortened by UMI.)... |
