Molecular responses of the Murray river rainbowfish, Melanotaenia fluviatilis exposed to endocrine disrupting chemicals
Creators: name: Shanthanagouda, Admane
Publisher: name: RMIT University
Year: 2024

description: Endocrine Disrupting Chemicals (EDCs) are those that interfere with the endocrine system of animals, primarily impacting the steroidogenic hormone pathways. Sources of these chemicals include sewage, industrial waste, urban and agricultural runoff. In Australia, there is little information available on the effects of environmental pollutants including EDCs on Australian native fish species, and even less information on the effects of EDCs at the proteomic or genomic level in Australian fish. Therefore, this PhD project investigated the effects of selected EDCs on aromatase and vitellogenin at the molecular level in the Australian native Murray River rainbowfish, <em>M. fluviatilis</em>.<br><br>The ovarian (cyp19a1a) and brain (cyp19a1b) aromatase gene isoforms were isolated and characterised from <em>M. fluviatilis</em> for the first time in this study. The sequence information enabled the construction of a phylogenetic tree and it was observed that the aromatase gene isoforms of <em>M.fluviatilis</em> showed a high identity with pejerrey, a closely related athernid species. The observation confirmed the close taxonomic relationship of these two species, despite their current geographical separation. The expression of aromatase isoforms was studied using qPCR. The <em>cyp19a1a </em>was exclusively expressed in the ovarian tissue and <em>cyp19a1b</em> was predominantly expressed in the brain of both sexes. In addition, the aromatase gene expression was also studied during ontogeny. <em>cyp19a1a</em> was not detected in any of the developmental stages studied and reflected gonad differentiation has not yet begun. On the contrary <em>cyp19a1b</em> was expressed in all selected developmental stages. <br><br>Next, a series of aqueous exposure experiments were conducted for 96 h on both sexes of adult <em>M. fluviatilis</em> to evaluate the effects of selected EDCs including 17β-estradiol (E2), nonylphenol (NP), bisphenol A and fadrozole on aromatase gene expression. In addition, the effect of E2 and NP on vitellogenin gene and protein expression in male <em>M. fluviatilis </em>was also studied. With exposure to E2 and NP, a significant reduction in the expression of <em>cyp19a1a</em> in ovarian tissues at the two lowest exposure concentrations was observed. At higher concentrations of E2 and NP, <em>cyp19a1a</em> was completely inhibited in ovarian tissues. Similarly, <em>cyp19a1b</em> was significantly downregulated in the brain of male fish exposed to E2 and NP. However, <em>cyp19a1b</em> in gonads of both sexes and brain of female fish exposed to E2 was initially upregulated and then downregulated. Expression of <em>cyp19a1b</em> in female fish brain was upregulated at both exposure concentrations of NP. With exposure to BPA, <em>cyp19a1a</em> in the gonads of the rainbowfish was not significantly affected. The expression of <em>cyp19a1b</em> in the brain and gonads of both sexes contrasted with each other with exposure to both BPA and fadrozole.<br><br>Collectively, the results of this study suggested that the tested EDCs can have a disruptive effect on the steroidogenic pathways of <em>M. fluviatilis</em> and hence sex differentiation, sexual behaviour and reproductive cycles in this fish. Based on the results obtained, <em>M. fluviatilis</em> can be used as a model species to assess the impact of the EDCs in the Australian freshwater ecosystem and both aromatase and vitellogenin could be used as potential biomarkers of exposure.<br><br>