THE EFFECTS OF ENDOCRINE DISRUPTING COMPOUNDS ON NUCLEOTIDE EXCISION REPAIR IN ZEBRAFISH (DANIO RERIO) LIVER

THE EFFECTS OF ENDOCRINE DISRUPTING COMPOUNDS ON NUCLEOTIDE EXCISION REPAIR IN ZEBRAFISH

 (DANIO RERIO) LIVER

By Gregory Daniel Ballard

Thesis Co-advisors: Dr. Rebecca Van Beneden and Dr. Greg Mayer

A Lay Abstract of the Thesis Presented

in Partial Fulfillment of the Requirements for the

Degree of Master of Science

(in Biochemistry)

August, 2010

Endocrine disrupting compounds (EDCs) alter the function or regulation of some part of the endocrine system.  One group of EDCs is estrogenic compounds, which can mimic the effects of estrogens.  Traditionally, examination of estrogenic compounds has focused on alterations in reproductive health.  Estrogens, however, can affect numerous processes throughout the body, many of which are unrelated to reproduction.  Additionally, estrogens have been linked to increased cancer risk, possibly through inhibition of DNA repair.  Recently, Notch et al. (2007) described reduced expression of genes involved in the important DNA repair pathway, nucleotide excision repair (NER) in the livers of zebrafish exposed to 17-α-ethinylestradiol (EE2), the estrogen found in oral contraceptive. 

As estrogenic compounds are pervasive in the environment, it is important to ascertain whether they all decreased expression of NER genes.  This thesis tests the hypothesis that environmentally relevant levels of three estrogenic compounds, bisphenol A (BPA), nonylphenol (NP) and sodium arsenite, (NaAsO₂) also decrease hepatic expression of NER genes. This was examined by measuring the expression of two NER genes, XPC and XPA, in the livers of zebrafish exposed to these compounds.  This thesis shows that 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.  The expression of vitellogenin1, a gene which is highly expressed following exposure of male fish to estrogens, was also measured.  Male fish showed increased vitellogenin1 expression following exposure to BPA and NP.  Interestingly, arsenic exposure decreased expression of vitellogenin1 in male zebrafish.

This research suggests environmental levels of BPA, NP and arsenic may not be a concern for fish in terms of reduced DNA repair.  Vitellogenin1 results confirm that NP and BPA act as estrogen mimics, suggesting that they may be a concern for reproduction in fish.  The reduction of vitellogenin1 in arsenic-exposed fish suggests that arsenic may inhibit the effects of estrogens.  The possibility of altered sensitivities to EE2 between different strains of zebrafish also warrants further exploration.