The regulation of aromatase and androgen receptor expression during gonad development in male and female European eel.

This research investigated the regulation of aromatase and androgen receptor gene expression in the brain-pituitary-gonad (BPG) axis of male and female European eels (Anguilla anguilla) during induced sexual maturation. Complete A. anguilla aromatase (aa-cyp19a1) and partial androgen receptor α and ß (aa-ara and aa-arb) sequences were isolated, and qPCR assays were validated and used for quantification of transcript levels for these three genes. Expression levels of the genes varied with sex, tissue and stage of maturation. aa-arb was expressed at higher levels than aa-ara in the pituitary and gonad in both sexes, suggesting aa-arb is the physiologically most important androgen receptor in these tissues. In the female brain, a decrease in aa-ara and an increase in aa-cyp19a1 were observed at the vitellogenic stage. In contrast, a progressive increase in all three genes was observed in the pituitary and ovaries throughout gonadal development, with aa-arb and aa-cyp19a1 reaching significantly higher levels at the vitellogenic stage. In the male pituitary, a decrease in aa-arb and an increase in aa-cyp19a1 were observed at the beginning of spermatogenesis, and thereafter remained low and high, respectively. In the testis, the transcript levels of androgen receptors and aa-cyp19a1 were higher during the early stages of spermatogenesis and decreased thereafter. These sex-dependent differences in the regulation of the expression of aa-ara, aa-arb and cyp19a1 are discussed in relation to the role of androgens and their potential aromatization in the European eel during gonadal maturation.

Variations in the gene expression of zona pellucida proteins, zpb and zpc, in female European eel (Anguilla anguilla) during induced sexual maturation.

Vertebrate eggs are surrounded by an extracellular glycoprotein coat termed zona pellucida (ZP). Integrity of ZP is critical for a correct embryo development. Two zona pellucida protein genes (zpb and zpc) from European eel were characterized, specific qPCR assays developed and their expression in immature males and females carried out. An experimental group of silver-stage eel females was maintained at 18 °C and hormonally induced to sexual maturation by weekly injections of carp pituitary extract during 12 weeks. Changes in zpb and zpc expression during sexual maturation were studied in liver and ovary by qPCR. In liver, no changes were recorded during hormonal treatment, while in ovary expression of both genes decreased during sexual development. These results are a first step in the characterization of ZP in European eel and in the understanding of the mechanism underlying egg envelope formation.

Differential gene expression and biomarkers in zebrafish (Danio rerio) following exposure to produced water components.

The main effluent from oil and gas production is produced water (PW), a waste that contains low to moderate concentrations of oil-derived substances such as polycyclic aromatic hydrocarbons (PAHs) and alkylphenols (APs). PW components may be present in seawater at low concentrations over large areas in the vicinity of oil and gas production facilities. In this study, zebrafish (Danio rerio) were exposed to control and three treatments (high-, pulsed-, low-dose) of a synthetic PW mixture for 1, 7 and 13 weeks. The aim was to investigate the development of transcriptome and biomarker responses as well as relationships between early responses and population-relevant effects. The synthetic PW contained a mixture of low-molecular-weight PAHs (<5 ring) and short-chain APs (C1-C4). The water-borne exposure levels (sum PAH) ranged from 0.54 ppb (low dose) to 5.4 ppb (high dose). Bile pyrene metabolites ranged from 17-133 ng g(-1) bile in the control group to 23-1081 ng g(-1) bile in the high exposure group. Similar levels have been observed in wild fish, confirming an environmentally relevant exposure. The expression of mRNAs of hepatic genes was investigated in the high exposure group using the Zebrafish OligoLibrary from Compugen. Functional clustering analysis revealed effects in the reproductive system, the nervous system, the respiratory system, the immune system, lipid metabolism, connective tissue and in a range of functional categories related to cell cycle and cancer. The majority of differentially expressed mRNAs of genes were down-regulated, suggesting reduction in gene transcription to be as relevant as up-regulation or induction when assessing biological responses to PW exposure. Biomarkers for effects of PAHs (cytochrome P450 1A) and environmental estrogens (vitellogenin) did not appear to be affected by the chronic exposure to low concentration of PW components. Effects at the population level included a reduction in condition factor in male fish from all exposed groups and spinal column deformations in the F1 generation of exposed groups. The different exposure regimes did not produce any significant differences in reproduction or recruitment. The results from this study demonstrate that environmentally relevant concentrations of PW affect gene expression and population-relevant endpoints in zebrafish, although links between the two were not obvious.