Dietary exposure of largemouth bass to OCPs changes expression of genes important for reproduction

Abstract

Dieldrin and p,p′-DDE are ubiquitous contaminants known to act as endocrine disruptors, causing impaired development and reproduction in fish and wildlife. In order to elucidate the mechanisms by which dieldrin and p,p′-DDE cause endocrine disruption in largemouth bass (Micropterus salmoides), fish were exposed subchronically through the diet to both contaminants. Following 120 days of exposure, p,p′-DDE decreased estradiol in females, but increased 11-ketotestosterone in both sexes. Dieldrin on the other hand, decreased estradiol and 11-ketotestosterone in both sexes. Both pesticides also altered steady state mRNA expression levels of a set of genes chosen to represent three possible mechanisms of endocrine disruption: (1) direct interaction with soluble sex steroid receptors, (2) biosynthesis of endogenous sex hormones, and (3) metabolism of endogenous hormones. p,p′-DDE acted as a weak estrogen, increasing the expression of vitellogenin and estrogen receptor α in the liver. p,p′-DDE also altered the expression of genes involved in the synthesis of endogenous hormones as well as their metabolism. Dieldrin, on the other hand, only altered expression of vitellogenin and not estrogen receptor α . Dieldrin also altered the expression of genes involved in hormone synthesis and metabolism, and it dramatically lowered plasma hormone levels. Both pesticides targeted expression of genes involved in all three modes of action, suggesting that they each have multiple modes of action.

Effects of acute dieldrin exposure on neurotransmitters and global gene transcription in largemouth bass (Micropterus salmoides) hypothalamus

“…LMB genes follow nomenclature rules set out for zebrafish (www.ZFIN.org). LMB ar and esr-beta b were investigated because of previous evidence that dieldrin regulates the abundance of these transcripts in LMB gonad and liver (Garcia-Reyero et al, 2006). LMB gst , gpx , hsp70 were chosen because each is involved in the general and oxidative stress response and dieldrin induces these responses in tissues of both fish (Pedrajas et al, 1995) and mammals (Hatcher et al, 2007).…”

Identification and Transcriptional Modulation of the Largemouth Bass, Micropterus salmoides, Vitellogenin Receptor During Oocyte Development by Insulin and Sex Steroids1

“…The set of primers employed for LMB esr1, esr2a, esr2b, ar, and 18S rRNA (rn18) were used as previously reported [32][33][34].…”

Exposure to p,p′-DDE or dieldrin during the reproductive season alters hepatic CYP expression in largemouth bass (Micropterus salmoides)

“…p,p′-DDE and dieldrin are both reported to have estrogenic and anti-androgenic activity, so it is possible that they acted directly at steroid receptors (Andersen et al, 2002). However, assays in Atlantic salmon, channel catfish and LMB indicate that dieldrin has little or no estrogenic activity (Tollefsen et al, 2003;Gale et al, 2004;Garcia-Reyero et al, 2006). Exposure to p,p′-DDE and dieldrin for 4 months altered endogenous levels of the major sex steroids in both male and female LMB, but there is no clear correlation between the changes of either androgens or estrogens and the changes observed in LMB hepatic CYP3A expression as a result of OCP exposure.…”