Project description:Toxaphene (TOX) is an organochlorine pesticide (OCPs) that remains abundant in the environment due to its heavy use in agriculture, its persistence, and its atmospheric transport. In Florida, the north shore of Lake Apopka was heavily used for agriculture decades ago, and TOX remains present in the soil. Wild largemouth bass inhabit the lake, and are potentially exposed to a variety of OCPs. While other OCPs (dieldrin, methoxychlor, p,p’DDE) have been studied for their endocrine disrupting effects in largemouth bass, there are little data available for TOX. Here we performed a 2-month feeding study of male and female largemouth bass with TOX-laced food to mimic the levels found in fish at Lake Apopka. Subsamples of the gonad and liver were collected and preserved in 10% buffered formalin for histopathology and reproductive staging. Plasma levels of vitellogenin (Vtg) testosterone (T) and 17β-estradiol (E2) were quantified and snippets of testis and ovaries were placed into culture to determine ex vivo production of hormones. Lastly, transcriptomics was conducted in both the male testis and liver, as most studies investigating OCPs have analyzed female ovary/liver and data are scarce for OCPs and male bass. Female GSI did not change with TOX but was trending towards a decrease while male GSI did not change with exposure. Female vitellogenin decreased with toxaphene by ~40% but male vitellogenin was not induced. Female and male E2 and T were not different following dietary exposure compared to control bass and this corresponded to ex vivo culture experiments, which revealed no change in E2 and T production from the gonads. Taken together, TOX did not alter the production of E2 and T directly in the gonad tissue. In the testis, transcriptomics revealed that androgen receptor/beta-2-microglobulin signaling was up-regulated while insulin-related pathways were suppressed with TOX. In the liver, the transcriptome analysis revealed an overwhelming suppression in immune-related signaling cascades (e.g. lectin-like receptor and ITSM-Containing Receptor signaling, CD16/CD14 Proinflammatory Monocyte Activation, and CD38/CD3 -> JUN/FOS/NF-kB Signaling in T-cell Proliferation). Ninety percent of the pathways were reduced between 10 to 40% in median network expression. Reduced immune pathways are consistent with other studies investigating OCPs in fish. In the current study, TOX, at the concentrations tested in the diet, did not act as a weak estrogen as many other OCPs do, but rather appeared to be acting as an antiestrogen (or androgen) based upon reduced female Vtg and activation of androgen-receptor mediated pathways in the testis. These data contribute to a comprehensive transcriptomic-physiological framework for TOX and suggests that endocrine disruption may not be the result of direct effects on steroidogenesis in the gonad, but may rather occur at higher levels of the reproductive axis.

Project description:BackgroundOocyte maturation in fish involves numerous cell signaling cascades that are activated or inhibited during specific stages of oocyte development. The objectives of this study were to characterize molecular pathways and temporal gene expression patterns throughout a complete breeding cycle in wild female largemouth bass to improve understanding of the molecular sequence of events underlying oocyte maturation.MethodsTranscriptomic analysis was performed on eight morphologically diverse stages of the ovary, including primary and secondary stages of oocyte growth, ovulation, and atresia. Ovary histology, plasma vitellogenin, 17β-estradiol, and testosterone were also measured to correlate with gene networks.ResultsGlobal expression patterns revealed dramatic differences across ovarian development, with 552 and 2070 genes being differentially expressed during both ovulation and atresia respectively. Gene set enrichment analysis (GSEA) revealed that early primary stages of oocyte growth involved increases in expression of genes involved in pathways of B-cell and T-cell receptor-mediated signaling cascades and fibronectin regulation. These pathways as well as pathways that included adrenergic receptor signaling, sphingolipid metabolism and natural killer cell activation were down-regulated at ovulation. At atresia, down-regulated pathways included gap junction and actin cytoskeleton regulation, gonadotrope and mast cell activation, and vasopressin receptor signaling and up-regulated pathways included oxidative phosphorylation and reactive oxygen species metabolism. Expression targets for luteinizing hormone signaling were low during vitellogenesis but increased 150% at ovulation. Other networks found to play a significant role in oocyte maturation included those with genes regulated by members of the TGF-beta superfamily (activins, inhibins, bone morphogenic protein 7 and growth differentiation factor 9), neuregulin 1, retinoid X receptor, and nerve growth factor family.ConclusionsThis study offers novel insight into the gene networks underlying vitellogenesis, ovulation and atresia and generates new hypotheses about the cellular pathways regulating oocyte maturation.

Dataset Information

Transcriptome and physiological effects of toxaphene on the liver-gonad reproductive axis in male and female largemouth bass (Micropterus salmoides).

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets