Date of Award

8-2010

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Biochemistry

Advisor

Rebecca Van Beneden

Second Committee Member

Gregory Mayer

Third Committee Member

John P. Wise, Sr.

Abstract

environment, typically anthropogenic in origin, but also from some natural sources. One group of EDCs includes estrogenic compounds, which can exert their effects through modulation of estrogen receptors (ER). Traditionally, examinations of potential estrogenic compounds have focused on markers of reproductive viability. ERs, however, are capable of altering the expression of numerous genes, only some of which are specifically related to reproduction. In addition to reproductive dysfunction, estrogen exposure has been linked to numerous types of cancers. Despite this fact, limited research has been conducted regarding the potential role of estrogenic compounds on disrupting DNA repair. Recently, Notch et al., (2007) described a marked reduction in expression of genes in the important DNA repair pathway, nucleotide excision repair (NER) in the livers of zebrafish exposed to the xenoestrogen 17-α-ethinylestradiol (EE2). This research suggests that addition work should be done to evaluate if other ER ligands also result in potentially deleterious effects on hepatic NER. In nature, fish are exposed to an array of estrogenic compounds, so it is important to ascertain whether decreased expression of NER genes is an effect common to all estrogenic compounds. This thesis tests the hypothesis that environmentally relevant levels of three commonly encountered estrogenic compounds, bisphenol A (BPA), nonylphenol (NP) and sodium arsenite, (NaAs02,(III)) also decrease hepatic expression of NER genes. This was done by examining alterations in two NER genes, XPC and XPA, in the livers of zebrafish exposed to these compounds. Here we show that, at the levels examined, none of these chemicals significantly altered the expression of either NER gene tested. EE2 exposure was used as a positive control, but in this study only led to a significant reduction in XPC levels in exposed males. In addition to XPC and XPA expression, the induction of the egg yolk protein vitellogenin-1 was also measured in exposed fish. Male fish showed increased vitellogenin-1 transcript levels following exposure to BPA and NP, confirming their estrogenicity. Additionally, arsenic exposure decreased hepatic expression of vitellogenin-1 in male zebrafish. This research suggests that at environmental levels, BPA, NP and arsenic may not be a concern for fish in terms of inhibition of NER activity. Induction of vitellogenin confirmed the estrogenicity of NP and BPA, suggesting that they may still be of concern for fish in terms of reproduction. The reduction of vitellogenin in livers of arsenic-exposed fish suggests that arsenic may act as an endocrine disrupter, though further study is required for confirmation and to investigate the mechanism of action. The possibility of strain differences in zebrafish in response to the effects of EE2 on hepatic NER gene expression also warrants further exploration.

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