Steroidogenesis and phase II conjugation during the gametogenesis of thicklip grey mullet (Chelon labrosus) from a population showing intersex condition

Reproductive health and endocrine disruption in smallmouth bass (Micropterus dolomieu) from the Lake Erie drainage, Pennsylvania, USA

Smallmouth bass Micropterus dolomieu were sampled from three sites within the Lake Erie drainage (Elk Creek, Twentymile Creek, and Misery Bay, an embayment in Presque Isle Bay). Plasma, tissues for histopathological analyses, and liver and testes preserved in RNALater® were sampled from 30 smallmouth bass (of both sexes) at each site. Liver and testes samples were analyzed for transcript abundance with Nanostring nCounter® technology. Evidence of estrogenic endocrine disruption was assessed by the presence and severity of intersex (testicular oocytes; TO) and concentrations of plasma vitellogenin in male fish. Abundance of 17 liver transcripts associated with reproductive function, endocrine activity, and contaminant detoxification pathways and 40 testes transcripts associated with male and female reproductive function, germ cell development, and steroid biosynthesis were also measured. Males with a high rate of TO (87-100%) and plasma vitellogenin were noted at all sites; however, TO severity was greatest at the site with the highest agricultural land cover. Numerous transcripts were differentially regulated among the sites and patterns of transcript abundance were used to better understand potential risk factors for estrogenic endocrine disruption. The results of this study suggest endocrine disruption is prevalent in this region and further research would benefit to identify the types of contaminants that may be associated with the observed biological effects.

Transcription pattern of reproduction relevant genes along the brain-pituitary-gonad axis of female, male and intersex thicklip grey mullets, Chelon labrosus, from a polluted harbor

The reproductive cycle of teleost fishes is regulated by the brain-pituitary-gonad (BPG) axis. The transcription profile of genes involved in the reproduction signalling in the BPG-axis differs in females and males during the gametogenic cycle. Impacts of endocrine disrupting chemicals on these signalling pathways in fish are known, but the participation of the BPG-axis in the development of the intersex condition is not well understood. Intersex thicklip grey mullets (Chelon labrosus) have been identified in several estuaries from the SE Bay of Biscay, revealing the presence of feminizing contaminants in the area. In previous studies, transcription patterns of genes related with steroidogenesis and gamete growth have been shown to differ among female, male and intersex mullets. However, many components of the reproduction control have not been studied yet. The aim of this study was to assess the transcription levels of target BPG-axis genes in female, male and intersex mullets captured in the polluted harbour of Pasaia, during their gametogenic cycle. After histologically examining the gonads, the transcription levels of previously sequenced target genes were measured by qPCR: kiss2, gpr54 and gnrh1 in brain, fshβ and lhβ in pituitary and fshr and lhr in gonads. In both females and males, brain genes were most transcribed in early gametogenesis, proving their relevance in the onset of both oogenesis and spermatogenesis. Pituitary gonadotropins in females showed upregulation as oogenesis progressed, reaching the highest transcription levels at vitellogenic stage, while in males transcript levels were constant during spermatogenesis. Transcription levels of gonadotropin receptors showed different patterns in ovaries and testes, suggesting differing function in relation to gametogenesis and maturation. Intersex mullets showed transcription levels of brain target genes similar to those observed in females at cortical alveoli stage and to those in mid spermatogenic males. In intersex testes the transcription pattern of gonadotropin receptor fshr was downregulated in comparison to non-intersex testes.

Toxicology tailored low density oligonucleotide microarray for the thicklip grey mullets (Chelon labrosus): Biomarker gene transcription profile after caging in a polluted harbour

In aquatic organisms inhabiting polluted waters genes are activated to build an adaptive/compensatory defence against the possible effects of pollutants. Such responses can be used as biomarkers of exposure to chemical compounds, outlining the molecular mechanisms activated under specific pollution scenarios. With the aim of exploiting such approach in environmental health assessment, toxicologically relevant gene fragments were sequenced in the thicklip grey mullet (Chelon labrosus) and a toxicologically tailored low-density (160 genes) oligonucleotide microarray was customised. The tool was validated comparing organ/sex specific gene expression profiles and characterising responses under laboratory exposure to model chemicals. Finally, juvenile mullets were caged in a polluted harbour and hepatic gene expression profiles analysed after 5 and 21 days of deployment. Cages were deployed in the inner (IH) and outer (OH) Pasaia harbour, Bay of Biscay. Mussels (Mytilus galloprovincialis) were also caged as biological matrix for chemical bioaccumulation analysis and stress biomarkers measurements. Slightly higher concentrations of chemicals (metals, tributyltin, PAHs, phthalates) were quantified in IH than in OH, fish bile metabolites also revealing higher availability of PAHs in IH. Lysosome membrane stability in mussels was reduced, indicating stress condition in both sites. The developed microarray discriminated mullets showing distinctive expression profiles depending on site and deployment time. Genes related to immune and hypoxia responses were regulated comparing IH and OH at day 5. Phase I and II biotransformation genes, such as cyp2, cyp3 and ugt, were up-regulated in IH, together with the aryl hydrocarbon receptor 2 (ahr2) and the ahr repressor. Similarly, TBT-binding proteins and genes involved in lipid metabolism (pparγ, cyp7) were up-regulated with deployment time. Even if nowadays higher throughput approaches for gene expression analyses are available, the developed mullet tool constitutes a comprehensive tool to assess molecular responses of mullets exposed to pollutants, although it remains to be explored whether it can be applied to assess pollutant exposure in active pollution monitorings and in environmental health assessment.

Effects of dietary crude oil exposure on molecular and physiological parameters related to lipid homeostasis in polar cod (Boreogadus saida)

Polar cod is an abundant Arctic key species, inhabiting an ecosystem that is subjected to rapid climate change and increased petroleum related activities. Few studies have investigated biological effects of crude oil on lipid metabolism in this species, despite lipids being a crucial compound for Arctic species to adapt to the high seasonality in food abundance in their habitat. This study examines the effects of dietary crude oil exposure on transcription levels of genes related to lipid metabolism (peroxisome proliferator-activated receptors [ppar-α, ppar-γ], retinoic X receptor [rxr-β], palmitoyl-CoA oxidase [aox1], cytochrome P4507A1 [cyp7α1]), reproduction (vitellogenin [vtg-β], gonad aromatase [cyp19a1]) and biotransformation (cytochrome P4501A1 [cyp1a1], aryl hydrocarbon receptor [ahr2]). Exposure effects were also examined through plasma chemistry parameters. Additional fish were exposed to a PPAR-α agonist (WY-14,643) to investigate the role of PPAR-α in their lipid metabolism. The dose-dependent up-regulation of cyp1a1 reflected the activation of genes related to PAH biotransformation upon crude oil exposure. The crude oil exposure did not significantly alter the mRNA expression of genes involved in lipid homeostasis except for cyp7α1 transcription levels. Plasma levels of cholesterol and alanine transaminase showed significant alterations in fish exposed to crude oil at the end of the experiment. WY exposure induced a down-regulation of ppar-α, an effect contrary to studies performed on other fish species. In conclusion, this study showed clear effects of dietary crude oil exposure at environmentally relevant concentrations on xenobiotic biotransformation but revealed only weak alterations in the lipid metabolism of polar cod.

Development of a lipovitellin-based sandwich ELISA for determination of vitellogenin in the marine medaka Oryzias melastigma

A lipovitellin (Lv) based sandwich enzyme-linked immunosorbent assay (ELISA) was developed to quantify vitellogenin (Vtg) in marine medaka (Oryzias melastigma). Lv and Vtg were purified from the unfertilized eggs and the whole body homogenates (WBH) of estradiol (E₂)-exposed fish. The purified Lv sample appeared as three clear bands (118, 112 and 100 kDa) in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and was identified as an Lvs mixture from VtgAa and VtgAb by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) analysis. Polyclonal antibody against marine medaka VtgAa was also raised. Compared with Vtg, Lv was more stable to heat stress (37 °C for 8 h or 4 °C for a week) and repeated freeze/thaw stress. In addition, western blot analysis revealed that marine medaka Vtg and Lv had similar immunogenicity. Therefore, in this study, Lv was applied instead of Vtg as the standard to establish an ELISA. The Lv standard curve was parallel to serial WBH dilutions of E₂-exposed fish, and the absorbance values were very low in control male samples, suggesting the specificity and feasibility of the method for Vtg quantification. The developed assay was sensitive with the detection limit of 3.1 ng/mL and had a working range between 15.6 and 500 ng/mL. The intra- and inter-assay coefficients of variation were both below 5%. Moreover, the standard curves of Lv antigen treated under different stresses were almost identical, indicating high robustness of the assay. Overall, our study provides an important methodology reference for quantification of marine medaka Vtg.

Alteration in molecular markers of oocyte development and intersex condition in mullets impacted by wastewater treatment plant effluents

Wastewater Treatment Plant (WWTP) discharges are an important source of endocrine disrupting chemicals (EDCs) into the aquatic environment. Fish populations inhabiting downstream of WWTP effluents show alterations in gonad and gamete development such as intersex condition, together with xenoestrogenic effects such as vitellogenin up-regulation. However, the molecular mechanisms participating in the development of intersex condition in fish are not elucidated. The aim of this study was to assess the impact of two WWTPs effluents (Gernika and Bilbao-Galindo situated in the South East Bay of Biscay) with different contaminant loads, in thicklip grey mullet (Chelon labrosus) populations inhabiting downstream, examining the presence and severity of intersex condition, during two seasons. Molecular markers of xenoestrogenicity and oocyte differentiation and development (vtgAa, cyp19a1a, cyp19a1b, cyp11b, foxl2, dmrt1 and gtf3a) were also studied. Intersex mullets were identified downstream of both WWTPs and vtgAa was upregulated in intersex and non intersex males. Sex dependent differential transcription levels of target genes were detected in mullets from Galindo. However, no such pattern was observed in mullets from Gernika, suggesting an attenuating effect over studied genes caused by a higher presence of EDCs in this site, as indicated by the elevated prevalence of intersex mullets in this population. In conclusion, no direct association between xenoestrogenic responses and intersex condition was established. Mullets from Gernika showed signs of severe EDC exposure compared to those from Galindo, as demonstrated by the higher prevalence of intersex males and the reduction in transcription profile differences between sexes of gametogenic gene markers.