Previtellogenic oocyte growth and transcriptional changes of steroidogenic enzyme genes in immature female Atlantic cod (Gadus morhua L.) after exposure to the androgens 11-ketotestosterone and testosterone

Sex- and time-specific parental effects of warming on reproduction and offspring quality in a coral reef fish

Global warming can disrupt reproduction or lead to fewer and poorer quality offspring, owing to the thermally sensitive nature of reproductive physiology. However, phenotypic plasticity may enable some animals to adjust the thermal sensitivity of reproduction to maintain performance in warmer conditions. Whether elevated temperature affects reproduction may depend on the timing of exposure to warming and the sex of the parent exposed. We exposed male and female coral reef damselfish (Acanthochromis polyacanthus) during development, reproduction or both life stages to an elevated temperature (+1.5°C) consistent with projected ocean warming and measured reproductive output and newly hatched offspring performance relative to pairs reared in a present-day control temperature. We found female development in elevated temperature increased the probability of breeding, but reproduction ceased if warming continued to the reproductive stage, irrespective of the male's developmental experience. Females that developed in warmer conditions, but reproduced in control conditions, also produced larger eggs and hatchlings with greater yolk reserves. By contrast, male development or pairs reproducing in higher temperature produced fewer and poorer quality offspring. Such changes may be due to alterations in sex hormones or an endocrine stress response. In nature, this could mean female fish developing during a marine heatwave may have enhanced reproduction and produce higher quality offspring compared with females developing in a year of usual thermal conditions. However, male development during a heatwave would likely result in reduced reproductive output. Furthermore, the lack of reproduction from an average increase in temperature could lead to population decline. Our results demonstrate how the timing of exposure differentially influences females and males and how this translates to effects on reproduction and population sustainability in a warming world.

Disruption of classical estrogenic targets in brown trout primary hepatocytes by the model androgens testosterone and dihydrotestosterone

Estrogenic effects triggered by androgens have been previously shown in a few studies. Aromatization and direct binding to estrogen receptors (ERs) are the most proposed mechanisms. For example, previously, a modulation of vitellogenin A (VtgA) by testosterone (T), an aromatizable androgen, was reported in brown trout primary hepatocytes. The effect was reversed by an ER antagonist. In this study, using the same model the disruption caused by T and by the non-aromatizable androgen - dihydrotestosterone (DHT), was assessed in selected estrogenic targets. Hepatocytes were exposed (96 h) to six concentrations of each androgen. The estrogenic targets were VtgA, ERα, ERβ1 and two zona pellucida genes, ZP2.5 and ZP3a.2. The aromatase CYP19a1 gene and the androgen receptor (AR) were also included. Modulation of estrogenic targets was studied by quantitative real-time PCR and immunohistochemistry, using an HScore system. VtgA and ERα were up-regulated by DHT (1, 10, 100 μM) and T (10, 100 μM). In contrast, ERβ1 was down-regulated by DHT (10, 100 μM), and T (100 μM). ZP2.5 mRNA levels were increased by DHT and T (1, 10, 100 μM), while ZP3a.2 was up-regulated by DHT (100 μM) and T (10, 100 μM). Positive correlations were found between VtgA and ERα mRNA levels and ZPs and ERα, after exposure to both androgens. The mRNA levels of CYP19a1 were not changed, while AR expression tended to increase after micromolar DHT exposures. HScores for Vtg and ZPs corroborated the molecular findings. Both androgens triggered estrogen signaling through direct binding to ERs, most probably ERα.

Androgens regulate follicle stage-dependent pro- and anti-apoptosis in teleost ovaries through ZIP9 activation of different G proteins†

Androgens mediate a number of processes in mammalian and teleost ovaries in a follicle-stage dependent manner, including follicle growth, survival, and apoptosis. We recently reported that the membrane androgen receptor ZIP9 mediates apoptosis in Atlantic croaker granulosa/theca (G/T) cells from mature ovarian follicles, but the effects of androgens on early stage G/T cells in this model remains unknown. Here we show that testosterone mediates pro- and anti-apoptotic responses in a follicle stage-dependent manner in croaker ovarian follicle cells. Testosterone treatment decreased the incidence of apoptosis in G/T cells from early stage follicles (diameter <300 μm) but increased apoptosis in G/T cells from late stage follicles (diameter >400 μm). Small interfering RNA targeting ZIP9, but not the nuclear androgen receptor, blocked the anti-apoptotic response, indicating ZIP9 mediates anti-apoptotic in addition to pro-apoptotic responses. Testosterone treatment of early stage G/T cells resulted in opposite signaling outcomes from those previously characterized for the ZIP9-mediated apoptotic response including decreased cAMP and intracellular free zinc levels, and downregulation of pro-apoptotic member mRNA expression. While ZIP9-mediated apoptosis involves activation of a stimulatory G protein (Gs), activators of Gs signaling antagonized the anti-apoptotic response. Proximity ligation and G protein activation assays indicated that in G/T cells from early stage follicles ZIP9 is in close proximity and activates an inhibitory G protein, while in G/T cells from late stage follicles ZIP9 is in close proximity and activates Gs. This study demonstrates that ZIP9 mediates opposite survival responses of croaker G/T cells by activating different G proteins in a follicle stage-dependent manner.

The zinc transporter ZIP9 (Slc39a9) regulates zinc dynamics essential to egg activation in zebrafish

The zinc transporter ZIP9 (SLC39A9) was recently characterized as a membrane androgen receptor in various teleost and mammalian cell models. ZIP9 shows the highest expression in ovaries of teleosts, a tissue in which both androgen signaling and zinc dynamics have significant roles. To examine the role of ZIP9 in ovarian physiology, we generated a ZIP9-mutant zebrafish strain using a CRISPR/Cas9 system. zip9^-/- females showed significant reductions in fecundity, embryo viability, and growth of their offspring compared to wildtype (WT) fish. Furthermore, a high proportion of zip9^-/- eggs failed to undergo normal chorion elevation during activation. In WT eggs, zinc was detected in cortically-localized vesicles which underwent exocytosis upon activation. zip9^-/- eggs showed abnormal cortical vesicle development and had a significantly depressed activation-induced zinc release compared to WT eggs. Moreover, pharmacologically sustained elevation of zinc in WT eggs prior to activation resulted in abnormal chorion elevation similar to that observed in zip9^-/- eggs. These results indicate that ZIP9 is essential for proper zinc modulation during zebrafish egg activation and presents the first evidence of zinc modulation during egg activation in a non-mammalian species.

The effects of 11-ketotestosterone implants on transcript levels of gonadotropin receptors, and foxl2 and dmrt1 genes in the Previtellogenic ovary of cultured beluga (Huso huso)

The in vivo effect of 11-ketotestosterone (11KT) on transcript levels of the gonadotropin receptors (fshr and lhr) and sex differentiation-related genes (dmrt1 and foxl2) was examined in the ovaries of immature female beluga. For this purpose, six fish were treated with implants containing 2.5 mg 11KT and a placebo group of six females of the same age and gametogenic stage were given a blank implant. The implants were intraperitoneally inserted into 4-year-old females at the previtellogenic stage (mean body weight 5580 ± 165 g) and maintained under culture conditions for 8 weeks. Ovary samples for gene expression analysis of lhr, fshr, dmrt1 and foxl2 were collected by biopsy at 3 and 8 weeks post implantation. Diameters of oocytes increased in response to 11KT treatment, both at 3 and at 8 weeks post implantation, but no obvious changes were evident in cytology. Three weeks of 11KT treatment did not affect target gene expression, but a tendency for a time-dependent decrease of lhr and dmrt1 mRNA levels was observed in both treatment and placebo groups. By 8 weeks of treatment, however, 11KT implants provoked the upregulation of fshr and foxl2 transcript levels. Furthermore, lhr and dmrt1 transcript abundances recovered by 8 weeks of exposure in both blank- and 11KT-implanted beluga. These results suggest that 11KT, either directly or indirectly, may affect gametogenesis and regulate some key components of the reproductive axis in female beluga.

Gonad development and reproductive hormones of invasive silver carp (Hypophthalmichthys molitrix) in the Illinois River

Reproduction is a major component of an animal's life history strategy. Species with plasticity in their reproductive biology are likely to be successful as an invasive species, as they can adapt their reproductive effort during various phases of a biological invasion. Silver carp (Hypophthalmicthys molitrix), an invasive cyprinid in North America, display wide variation in reproductive strategies across both their native and introduced ranges, though the specifics of silver carp reproduction in the Illinois River have not been established. We assessed reproductive status using histological and endocrinological methods in silver carp between April and October 2018, with additional histological data from August to October 2017. Here, we show that female silver carp are batch spawners with asynchronous, indeterminate oocyte recruitment, while male silver carp utilize a determinate pattern of spermatogenesis which ceases in the early summer. High plasma testosterone levels in females could be responsible for regulating oocyte development. Our results suggest that silver carp have high spawning activity in the early summer (May-June), but outside of the peak spawning period, female silver carp can maintain spawning-capable status by adjusting rates of gametogenesis and atresia in response to environmental conditions, while males regress their gonads as early as July. The results of this study are compared to reports of silver carp reproduction in other North American rivers as well as in Asia.

Steroidogenic acute regulatory protein transcription is regulated by estrogen receptor signaling in largemouth bass ovary

Estrogenic contaminants in the environment are linked to the occurrence of reproductive abnormalities in many aquatic species, including largemouth bass (Micropterus salmoides; LMB). Previous work has shown that many different types of xenoestrogens regulate expression of the Steroidogenic Acute Regulatory protein (StAR), a cholesterol-transporting protein vital to steroid hormone biosynthesis; however, the regulatory mechanisms of StAR are incompletely characterized in fish. To learn more about endogenous expression patterns of StAR in the ovary, LMB were collected from the St. John's River (Florida, USA) over an entire breeding season to investigate StAR expression. Plasma 17β-estradiol (E2) and StAR mRNA levels were positively correlated in females, and StAR mRNA levels displayed ~ 100-fold increase between primary oocyte growth stages and final maturation. To further study the regulation of StAR, female LMB in the laboratory were fed at ≃2% of their weight on a diet laden with 17α-ethinylestradiol (EE2, 70 or 200 ng EE2 per gram feed). Diets were designed to achieve a physiologically-relevant exposure to EE2, and StAR expression was assessed in vivo. We observed a dose-dependent suppression of StAR mRNA levels, however both diets led to high, pharmacological levels in the blood and do not represent normal physiological ranges of estrogens. In the 200 ng EE2/gm feed group, ovarian StAR mRNA levels were suppressed to approximately 5% of that of the LMB control group. These investigations suggest that LMB StAR increases in expression during oocyte maturation and that it is suppressed by E2 feedback when estrogen levels are high, through the HPG axis. A 2.9 kb segment of the LMB StAR promoter was examined for putative E2 response elements using in silico software, and a putative estrogen receptor binding element (ERE/-1745) was predicted in the promoter. The functionality of the ERE was examined using MA-10 mouse Leydig cells transfected with the LMB StAR promoter. Estrogen receptor (ER) interaction with ERE/-1745 was evaluated under basal and human chorionic gonadotropin (hCG)-treated conditions in the presence and absence of E2. Chromatin immunoprecipitation (ChIP) experiments revealed that ESR1 binding to the promoter was enriched under basal conditions and E2 exposure elicited an increase in enrichment (4-fold) above that observed under basal conditions. ESR2 was not strongly enriched at the ERE/-1745 site, suggesting that StAR may be preferentially regulated by LMB estrogen receptor 1 (esr1). Taken together, these different experiments provide evidence that LMB StAR is under the control of estrogens and that ESR1 binds directly to the LMB StAR promoter in an E2-responsive manner.

Anti-masculinization induced by aromatase inhibitors in adult female zebrafish

Background

Early sex differentiation genes of zebrafish remain an unsolved mystery due to the difficulty to distinguish the sex of juvenile zebrafish. However, aromatase inhibitors (AIs) could direct juvenile zebrafish sex differentiation to male and even induce ovary-to-testis reversal in adult zebrafish.

Results

In order to determine the transcriptomic changes of sex differentiation in juvenile zebrafish and early sex-reversal in adult zebrafish, we sequenced the transcriptomes of juvenile and adult zebrafish treated with AI exemestane (EM) for 32 days, when juvenile zebrafish sex differentiation finished. EM treatment in females up-regulated the expression of genes involved in estrogen metabolic process, female gamete generation and oogenesis, including gsdf, macf1a and paqr5a, while down-regulated the expression of vitellogenin (vtg) genes, including vtg6, vtg2, vtg4, and vtg7 due to the lower level of Estradiol (E2). Furthermore, EM-juveniles showed up-regulation in genes related to cell death and apoptosis, such as bcl2l16 and anax1c, while the control-juveniles exhibited up-regulation of genes involved in positive regulation of reproductive process and oocyte differentiation such as zar1 and zpcx. Moreover, EM-females showed higher enrichment than control females in genes involved in VEGF signaling pathway, glycosaminoglycan degradation, hedgehog signaling pathway, GnRH signaling pathway and steroid hormone biosynthesis.

Conclusions

Our study shows anti-masculinization in EM-treated adult females but not in EM-treated juveniles. This may be responsible for the lower sex plasticity in adults than juveniles.

Effects of 11-Ketotestosterone on Development of the Previtellogenic Ovary in the Sterlet, Acipenser ruthenus

11-ketotestosterone (11-KT) is a non-aromatizable and the most potent androgen in a few teleost. It has been reported that 11-KT in serum had a high concentration and increased sharply before the period of yolk deposition in females of few fishes. The aim of this study was to analyze the role of 11-KT both in vivo and in vitro on ovarian development, related gene expression levels, Vitellogenin (Vtg) synthesis, and serum sex steroid concentrations in previtellogenic cultured sterlet (Acipenser ruthenus). Silastic strips embedded with 11-KT (5 or 25 mg/kg) were implanted in vivo for 30 days. Ovarian masculinization or sex reversal was not observed. Histological analysis showed that 11-KT promoted sterlet ovarian development in a dose-dependent manner. Vtg and testosterone (T) increased significantly, while 17β-estradiol (E2) decreased with no significant difference among groups. The expression of genes androgen receptor (ar), vtg and lipoprotein lipase (lpl) were significantly increased in liver. However, 11-KT had no effect on the expression of foxl2 and cyp19a1 in ovary. In vitro, after incubation with 11-KT (10 and 100 μM) for 5 days, both T and E2 concentrations increased in both hepatic explants and ovarian explants culture medium; the concentration of Vtg also increased in hepatic explants culture medium. The expression of ar, era, vtg, and lpl increased significantly in hepatic explants. However, only the expression of era significantly increased in cultured ovarian explants. Altogether, these results suggest that 11-KT induced ovarian development, as well as Vtg and lipid synthesis, and could be an important factor facilitating the initiation of Vtg synthesis in the liver of the previtellogenic sterlet.

Ultrasound as a noninvasive tool for monitoring reproductive physiology in female Atlantic salmon (Salmo salar)

Aiming to explore ultrasound technology as a noninvasive method for maturation monitoring, we compared ultrasound observations and measurements in female Atlantic salmon (Salmo salar) during the last year before ovulation with standard, invasive methods such as gonadosomatic index (GSI), gonad histology and sex hormone analysis. Ultrasound measurements of ovaries correlated strongly (R > 0.9, P < 0.01) with ovary weight and GSI, and could be used as a noninvasive tool for GSI estimation. Using ultrasound, we were able to identify females with advanced oocyte development and elevated sex hormone and GSI levels earlier than previously observed. Histological studies confirmed these observations showing oocyte yolk accumulation 10 months before ovulation and 8 months before significant increase in sex hormones. Levels of the sex hormone 11‐keto testosterone (11‐KT) indicated a new role of this hormone at final maturation in salmon females. We propose the use of ultrasound as an alternative method to traditionally used invasive methods during sexual maturation monitoring in wild and farmed Atlantic salmon broodstock populations. Eliminating sacrifice of valuable broodfish, and reducing handling stress, would improve animal welfare in present‐day broodstock management.

11-Ketotestosterone induces oocyte growth, but does not affect oocyte cytology in pre-vitellogenic captive beluga, Huso huso L

An effect of 11-ketotestosterone (11-KT) on growth of previtellogenic (PV) ovaries of eel, salmon and Atlantic cod has been demonstrated. The purpose of this study was to investigate the effects of 11-KT treatment (in vivo) on ovarian growth, on hormonal and biochemical changes in blood, and on ovarian mRNA levels of lipidation-related genes in captive beluga with PV oocytes. In addition, the potential involvement of lipoprotein lipase (Lpl), an important enzyme for extracellular hydrolysis of lipoprotein-associated lipids, was evaluated. Twelve beluga (4-year olds) were treated with an intraperitoneal slow-release implant of either 11-KT (2.5 mg) or a compressed matrix (control). Ovarian biopsy was done to obtain pre- (day 0: T0) and post-treatment (day 21: T21) data on histology and target gene expression. Three weeks of exposure resulted in an increase in serum 11-KT levels from 2.2 ng/mL to 83 ng/mL but did not yield significant changes in serum levels of triacylglycerides and cholesterol. Furthermore, 11-KT implantation increased oocyte diameters from 259 μm (T0) to 309 μm by T21. Regardless of the increase in oocyte size, ovaries remained in the PV stage, mostly as late perinucleolar oocytes. Meanwhile, at the molecular level, the expression of lipidation-related transcripts [lpl, apolipoprotein E (apoe), very low density lipoprotein receptors (vldlr), low-density lipoprotein receptor-related protein 8-like (lrp8)] was significantly up-regulated after three weeks. Immunostaining for Lpl by Western blotting indicated three immunoreactive bands (70, 58 and 37 kDa) in ovarian homogenates from beluga, but signal intensity was not affected by treatment. Altogether, the administration of 11-KT increased 11-KT serum levels, oocyte size, and the expression of genes associated with lipid uptake. However, this treatment did not advance ovarian development beyond the PV stage.

Expression of sf1 and dax-1 are regulated by thyroid hormones and androgens during Silurana tropicalis early development

Thyroid hormones (THs) and androgens have been shown to be extensively involved in sexual development; however, relatively little is known with regard to TH-related and androgenic actions in sex determination. We first established expression profiles of three sex-determining genes (sf1, dax-1, and sox9) during the embryonic development of Western clawed frogs (Silurana tropicalis). Transcripts of sf1 and sox9 were detected in embryos before the period in which embryonic transcription commences indicating maternal transfer, whereas dax-1 transcripts were not detected until later in development. To examine whether TH status affects sex-determining gene expression in embryonic S. tropicalis, embryos were exposed to co-treatments of iopanoic acid (IOP), thyroxine (T4), or triiodothyronine (T3) for 96 h. Expression profiles of TH receptors and deiodinases reflect inhibition of peripheral deiodinase activity by IOP and recovery by T3. Relevantly, elevated TH levels significantly increased the expression of sf1 and dax-1 in embryonic S. tropicalis. Further supporting TH-mediated regulation, examination of the presence and frequency of transcription factor binding sites in the putative promoter regions of sex-determining genes in S. tropicalis and rodent and fish models using in silico analysis also identified TH motifs in the putative promoter regions of sf1 and dax-1. Together these findings advocate that TH actions as early as the period of embryogenesis may affect gonadal fate in frogs. Mechanisms of TH and androgenic crosstalk in relation to the regulation of steroid-related gene expression were also investigated.

Ovarian aromatase loss-of-function mutant medaka undergo ovary degeneration and partial female-to-male sex reversal after puberty

Although estrogens have been generally considered to play a critical role in ovarian differentiation in non-mammalian vertebrates, the specific functions of estrogens during ovarian differentiation remain unclear. We isolated two mutants with premature stops in the ovarian aromatase (cyp19a1) gene from an N-ethyl-N-nitrosourea-based gene-driven mutagenesis library of the medaka, Oryzias latipes. In XX mutants, gonads first differentiated into normal ovaries containing many ovarian follicles that failed to accumulate yolk. Subsequently, ovarian tissues underwent extensive degeneration, followed by the appearance of testicular tissues on the dorsal side of ovaries. In the newly formed testicular tissue, strong expression of gsdf was detected in sox9a2-positive somatic cells surrounding germline stem cells suggesting that gsdf plays an important role in testicular differentiation during estrogen-depleted female-to-male sex reversal. We conclude that endogenous estrogens synthesized after fertilization are not essential for early ovarian differentiation but are critical for the maintenance of adult ovaries.

Transcriptomic Analysis for Differentially Expressed Genes in Ovarian Follicle Activation in the Zebrafish

In teleosts, the onset of puberty in females is marked by the appearance of the first wave of pre-vitellogenic (PV) follicles from the pool of primary growth (PG) follicles (follicle activation) in the ovary during sexual maturation. To understand the mechanisms underlying follicle activation and therefore puberty onset, we undertook this transcriptomic study to investigate gene expression profiles in the event. Our analysis revealed a total of 2,027 up-regulated and 859 down-regulated genes during the PG-PV transition. Gene Ontology (GO) analysis showed that in addition to basic cellular functions such as gene transcription, cell differentiation, and cell migration, other biological processes such as steroidogenesis, cell signaling and angiogenesis were also enriched in up-regulated genes; by comparison, some processes were down-regulated including piRNA metabolism, gene silencing and proteolysis. Further Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis identified a variety of signaling pathways that might play pivotal roles in PG-PV transition, including MAPK, TGF-β, Hedgehog, FoxO, VEGF, Jak-STAT, and phosphatidylinositol signaling pathways. Other pathways of particular interest included endocytosis and glycosaminoglycan biosynthesis. We also analyzed expression changes of genes expressed in different compartments viz. oocytes and follicle cells. Interestingly, most oocyte-specific genes remained unchanged in expression during follicle activation whereas a great number of genes specifically expressed in the follicle cells showed significant changes in expression. Overall, this study reported a comprehensive analysis for genes, biological processes and pathways involved in follicle activation, which also marks female puberty onset in the zebrafish when occurring for the first time in sexual maturation.

Effects of dietary arachidonic acid on the reproductive physiology of female Atlantic cod (Gadus morhua L.)

The present study was designed to investigate potential effects of arachidonic acid (ARA) on the reproductive physiology of female Atlantic cod (Gadus morhua L.). Two-year old Atlantic cod of both sexes were equally distributed into eight sea cages after completion of their first spawning in May 2005. Four experimental groups were established and fed diets with different levels of ARA corresponding to 0.5, 1, 2 and 4% of total fatty acid. Ovarian growth and development was documented every month. Fatty acid composition was analysed in ovaries, liver and plasma at the beginning of the experiment, one month prior to spawning, and in spent fish, one month after spawning was completed. Plasma concentrations of estradiol-17β, testosterone and vitellogenin, and ovarian gene transcript levels of steroidogenic acute regulatory protein (star), P450aromatase (cyp19a1a) and 20β-hydroxy steroid dehydrogenase (20bhsd/cbr1) were monitored every month in fish fed the experimental diets and related to oocyte stage. Potential fecundity was calculated based on ovarian samples taken one month before onset of spawning. Ovarian and plasma ARA levels were highly correlated to dietary ARA levels. There was a net accumulation of ARA compared to other essential fatty acids in ovarian tissue that was reflected in a decrease in EPA:ARA ratio. Plasma concentrations of vitellogenin, estradiol-17β and testosterone and key gene transcript levels were affected by dietary ARA and stage of maturation. The results show that ARA has a significant influence on the reproductive physiology of female Atlantic cod.

Timecourse of oocyte development in saithe Pollachius virens

Wild caught North Sea saithe Pollachius virens were monitored for growth, sex steroid profiles and oocyte development pre-spawning and measured for egg size and group fecundity during the spawning season in the laboratory. Vitellogenesis commenced in late October-early November, at a leading cohort size (C_L ) of c. 250 µm, after which oocytes grew rapidly in size until spawning started in February. Notably, a distinct cortical alveoli stage was virtually absent with yolk granules observed in developing oocytes at the very beginning of vitellogenesis. Little atresia was observed pre-spawning, but atretic re-absorption of remnant oocytes containing yolk granules was found in all females immediately post-spawning. As expected, concentrations of sex steroids, oestradiol-17β (females), testosterone (both sexes) and 11-ketotestosterone (both sexes), increased pre-spawning before dropping post-spawning. The present experiment provides the first validation of sex steroid levels in P. virens. Post-ovulatory follicles were visible in histological sections from female gonads 9-11 months post-spawning, but then disappeared. Spawning commenced around a C_L of c. 750 µm (700-800 µm). Hydrated oocytes (eggs) measured between 1·04 and 1·31 mm (mean = 1·18 mm) with decreasing sizes towards the end of spawning. The average estimated realized fecundity was c. 0·84 million eggs (median female total length, L_T = 60 cm). Spawning lasted from 13 February to 29 March.

Molecular mechanism of endocrine system impairment by 17α-methyltestosterone in gynogenic Pengze crucian carp offspring

The effects of synthetic androgen 17α-methyltestosterone (MT) on endocrine impairment were examined in crucian carp. Immature 7-month old mono-female Pengze crucian carp (Pcc) F2 offspring were exposed to 50 and 100 μg/L of MT (week 2, 4, and 8). Gonadosomatic index, hepatosomatic index and intestine weight altered considerably and oocyte development was repressed. In the treatment groups, ovarian 11-ketotestosterone decreased, whereas 17β-estradiol and testosterone increased, and ovarian aromatase activities increased at week 4. However, in the brain tissue, those values significantly decreased. Quantitative RT-PCR analysis demonstrated changes in steroid receptor genes and upregulation of steroidogenic genes (Pcc-3bhsd, Pcc-11bhsd2 Pcc-cyp11a1), while the other three steroidogenic genes (Pcc-cyp17a1, Pcc-cyp19a1a and Pcc-star) decreased from week 4 to week 8. Ovarian, hepatic Pcc-vtg B and vitellogenin concentration increased in both 50 and 100 μg/L of MT exposure groups. This study adds further information regarding the effects of androgens on the development of previtellogenic oocytes, which suggests that MT could directly target estrogen signaling pathway, or indirectly affect steroidogenesis and vitellogenesis.

Triacylglyceride physiology in the short-finned eel, Anguilla australis--the effects of androgen

The importance of androgens (especially 11-ketotestosterone) during previtellogenesis in eels is well established. In wild pubertal migrants, circulating 11-ketotestosterone levels correlate with a number of morphological and molecular changes. Here, we test the prediction that this correlation represents a causal relationship by artificially raising the levels of circulating 11-ketotestosterone in prepubertal nonmigratory female and pubertal, migratory male short-finned eels (Anguilla australis) using sustained-release hormone implants. In females, increases in hepatosomatic index and transcript copy numbers of hepatic apolipoprotein B and microsomal triacylglyceride transfer protein indicated increased repackaging of endogenously sourced triacylglycerides. These changes in liver measures were reflected in increased concentrations of serum triacylglycerides. However, despite a small increase in gonadosomatic index, ovarian lipoprotein receptor transcript abundances were not affected by 11-ketotestosterone. Interestingly, no such changes in hepatic gene expression were detected in a dose-response experiment using males. We propose that the androgens are inducing the observed changes in previtellogenic females, although it remains unclear to what extent these effects are direct or indirect.

Non-monotonic dose-response effect of bisphenol A on rare minnow Gobiocypris rarus ovarian development

Bisphenol A (BPA) is widely spread in the environment, and can cause various reproductive disrupting effects on different organisms, including fish. Our previous published study showed that BPA has non-monotonic (inverted U-shaped) dose-response effect on rare minnow Gobiocypris rarus ovarian weight at different concentrations. To investigate the potential mechanism, we exposed female rare minnow to 1, 15 and 225 µg L(-1) BPA for 7 days in the present study. The levels of vitellogenin (Vtg), sex hormones, hydrogen peroxide (H2O2), glutathione (GSH) and triglyceride (TG) were measured. RNA-seq of ovary tissues was also performed. Result showed that Vtg, sex hormone and TG levels showed an inverted U-shaped increased response, while H2O2 and GSH levels showed a U-shaped inhibited response. RNA-seq data showed that many genes involved in lipid metabolism, oxidative stress, and proteolysis processes were altered. The change of Vtg, H2O2, GSH and TG levels was possibly related to the altered sex hormone levels. Sex hormone's direct effect, Vtg accumulation, TG accumulation and oxidative stress induced proteolysis may contribute to the change of ovary weight.

Does anti-androgen, flutamide cancel out the in vivo effects of the androgen, dihydrotestosterone on sexual development in juvenile Murray rainbowfish (Melanotaenia fluviatilis)?

The aim of the present study was to investigate if the effects of the androgen, dihydrotestosterone (DHT) on the sexual development in juvenile Murray rainbowfish (Melanotaenia fluviatilis) are canceled out by the anti-androgen, flutamide. Fish (60 days post hatch) were exposed to 250ng/L of DHT, 25μg/L of flutamide (Flu-low), 250μg/L of flutamide (Flu-high), DHT+Flu low and DHT+Flu high. After 35 days of exposure, lengths and weights of the fish were measured and the condition factor (CF) calculated; vitellogenin (VTG) concentrations were measured in tail tissue; sex steroid hormones (17β-estradiol [E2] and 11-keto testosterone [11-KT]) were measured in the head tissue and abdominal regions were used in histological investigation of the gonads. Treatment with DHT reduced the body-length of both male and female fish, an effect which was canceled out by low and high concentrations of flutamide. However, flutamide (low or high) could not nullify the DHT-induced reduction in the CF in either sex. The E2 levels were reduced only in female fish after exposure to DHT but returned to normal after treatment with Flu-high. DHT increased the levels of 11-KT and decreased the E2/11-KT ratio in both sexes. Flu-high, but not Flu-low, could nullify these effects. Both DHT and flutamide (low or high) induced VTG production and this effect persisted when both chemicals were co-administered. Treatment with DHT did not affect gonadal cell development in the testes. However, the female fish treated with DHT contained ovaries in early-vitellogenic stage in comparison to the pre-vitellogenic ovaries in control fish. Co-treatment with flutamide (low or high) resulted in oocyte atresia. The results from the present study suggest that treatment with Flu-high could cancel out DHT-induced effects only on the hormonal profile and body-length in both male and female fish. Juvenile fish co-treated with DHT and flutamide (low or high) had high VTG levels and low CF. In addition, the ovaries in female fish were atretic. These data represent potential adverse effects on the ability of the fish to reproduce successfully.

Steroids in teleost fishes: A functional point of view

Steroid hormones are involved in the regulation of a variety of processes like embryonic development, sex differentiation, metabolism, immune responses, circadian rhythms, stress response, and reproduction in vertebrates. Teleost fishes and humans show a remarkable conservation in many developmental and physiological aspects, including the endocrine system in general and the steroid hormone related processes in particular. This review provides an overview of the current knowledge about steroid hormone biosynthesis and the steroid hormone receptors in teleost fishes and compares the findings to the human system. The impact of the duplicated genome in teleost fishes on steroid hormone biosynthesis and perception is addressed. Additionally, important processes in fish physiology regulated by steroid hormones, which are most dissimilar to humans, are described. We also give a short overview on the influence of anthropogenic endocrine disrupting compounds on steroid hormone signaling and the resulting adverse physiological effects for teleost fishes. By this approach, we show that the steroidogenesis, hormone receptors, and function of the steroid hormones are reasonably well understood when summarizing the available data of all teleost species analyzed to date. However, on the level of a single species or a certain fish-specific aspect of physiology, further research is needed.

Juvenile exposure to vinclozolin shifts sex ratios and impairs reproductive capacity of zebrafish

Exposure to endocrine disruptors during critical periods of development can impact the sustainability of wild fish populations. Anti-androgenic compounds have received less attention, but are capable of modulating gonad differentiation and maturation, and impairing reproduction in fish. The fungicide vinclozolin (VZ) has been shown to impair reproduction in adult fish, but less is known about its effects following exposure earlier in development. Here we show that waterborne exposure to 400μg VZ/L during critical periods of sex differentiation (21-35 days post fertilization) permanently shifts sex ratios towards females, and alters the maturation of the gonad. Both fecundity and fertility were reduced, even when oogenesis and spermatogenesis recover and sperm motility is not altered. These results demonstrate the need to better understand the impacts of early exposure to anti-androgenic compounds on fish.

Study on the zona pellucida 4 (ZP4) gene sequence and its expression in the ovaries of patients with polycystic ovary syndrome

BACKGROUND

Polycystic ovary syndrome (PCOS) is a common endocrine disorder of unknown pathology, involving reproductive and metabolic abnormalities. Oocyte-specific genes are a group of genes expressed exclusively in ovarian tissue; therefore, they can play an important role in ovarian pathologies such as PCOS. The zona pellucida 4 (ZP4) gene encodes glycoprotein which is a part of the extracellular matrix of oocyte.

MATERIALS AND METHODS

We analyzed 87 patients with PCOS, which were divided into four groups depending on their phenotype. In each patient, we performed profound clinical and biochemical analysis, including the measurement of serum androgens. The ovarian tissue samples were used to perform a real-time polymerase chain reaction and immunohistochemical staining using anti-ZP4 monoclonal antibodies. The ZP4 gene was sequenced from peripheral lymphocytes.

RESULTS

The expression of ZP4 was present in early antral follicles and was stronger in mature follicles. The subgroup of patients with eumenorrhea and without hyperandrogenism presented the highest expression of ZP4 in ovarian tissue. In one case, we found a mutation of the ZP4 gene. No correlations were found between the ZP4 expression level and biochemical or clinical indices.

CONCLUSIONS

Data from this and animal studies suggest a possible relationship between androgens and ZP4 expression. ZP4 expression is highest among patients with PCOS and a regular cycle, and this is a consequence of the presence of mature follicles in this group. In some patients with PCOS and infertility, ZP4 mutation can be found.

Effects of model aromatizable (17α-methyltestosterone) and non-aromatizable (5α-dihydrotestosterone) androgens on the adult mummichog (Fundulus heteroclitus) in a short-term reproductive endocrine bioassay

Androgens originating from pulp mill processing, sewage treatment facilities and agricultural activities have the potential for discharge into aquatic receiving environments. To assess androgen effects on reproductive endocrine status in fish in estuarine environments, male and female adult northern mummichog (Fundulus heteroclitus macrolepidotus) were exposed to an aromatizable androgen (17α-methyltestosterone; MT) and a non-aromatizable androgen (5α-dihydrotestosterone; DHT) in a short-term reproductive endocrine bioassay. Fish were nominally exposed to 10 μg/L or 100 μg/L DHT, or 0.1 μg/L or 1 μg/L MT for 14 days during gonadal recrudescence. Actual concentrations of androgens, as measured by enzyme immunoassay (EIA), were 10-49% of nominal MT 0.1, 3-6% of nominal MT 1, 5-10% of nominal DHT 10 and 3-25% of nominal DHT 100. Female mummichog were impacted to a greater degree by androgen exposure, with increased plasma testosterone (T) at 100 μg/L DHT, depressed plasma 17β-estradiol (E2) at both DHT concentrations and at 1 μg/L MT, as well as depressed in vitro E2 at both MT concentrations and 100 μg/L DHT. Males had depressed plasma T in the 10 μg/L DHT treatment and depressed in vitro 11-ketotestosterone production for both MT concentrations and 10 μg/L DHT. Ovarian aromatase gene expression was induced in females exposed to 1 μg/L MT. DHT at 100 μg/L increased hepatic vitellogenin-1 (VTG1) expression in males and depressed VTG1 expression in females. The range of responses between sexes and among species provides evidence for modes of actions and potential impacts of androgens in aquatic receiving environments.

Effects of short-term exposure to the model anti-androgen, flutamide on reproductive function based endpoints in female Murray rainbowfish (Melanotaenia fluviatilis)

The aim of the present study was to evaluate the responses of female Murray rainbowfish (Melanotaenia fluviatilis) to the model anti-androgen, flutamide in a short-term exposure. Adult female Murray rainbowfish were exposed to nominal (measured) concentrations of 125 (104), 250 (163), 500 (378) and 1000 (769) µg/L of flutamide for seven days in a semi-static set-up. Plasma vitellogenin (VTG), 11-keto testosterone (11-KT) and 17β-estradiol (E2) concentrations, brain aromatase activity and ovarian histology were assessed following the exposure. No treatment-related mortality was found in rainbowfish and there was no effect of flutamide on the developmental stage of the ovaries. Histological investigation revealed absence of mature oocytes in flutamide-treated fish. In addition, a significant reduction in the sizes of the vitellogenic oocytes was found after treatment with 500 and 1000 µg/L flutamide. The circulating levels of VTG and the activity of aromatase in the brain were also significantly reduced in fish treated with 500 and 1000 µg/L flutamide. Treatment with higher concentrations of flutamide reduced the levels of 11-KT and E2 in plasma. The results from this study demonstrate that a short-term exposure to the model anti-androgen, flutamide can adversely affect the reproductive function based on end-points such as plasma VTG, 11-KT and E2; brain aromatase activity and sizes of the oocytes in female Murray rainbowfish. Further, a positive correlation between these experimental variables suggests hormonal imbalance.

Effects of elevated dissolved carbon dioxide and perfluorooctane sulfonic acid, given singly and in combination, on steroidogenic and biotransformation pathways of Atlantic cod

In the aquatic environments, the predicted changes in water temperature, pO2 and pCO2 could result in hypercapnic and hypoxic conditions for aquatic animals. These conditions are thought to affect several basic cellular and physiological mechanisms. Yet, possible adverse effects of elevated CO2 (hypercapnia) on teleost fish, as well as combined effects with emerging and legacy environmental contaminants are poorly investigated. In this study, juvenile Atlantic cod (Gadus morhua) were divided into groups and exposed to three different water bath PFOS exposure regimes (0 (control), 100 and 200 μg L(-1)) for 5 days at 1h/day, followed by three different CO2-levels (normocapnia, moderate (0.3%) and high (0.9%)). The moderate CO2 level is the predicted near future (within year 2300) level, while 0.9% represent severe hypercapnia. Tissue samples were collected at 3, 6 and 9 days after initiated CO2 exposure. Effects on the endocrine and biotransformation systems were examined by analyzing levels of sex steroid hormones (E2, T, 11-KT) and transcript expression of estrogen responsive genes (ERα, Vtg-α, Vtg-β, ZP2 and ZP3). In addition, transcripts for genes encoding xenobiotic metabolizing enzymes (cyp1a and cyp3a) and hypoxia-inducible factor (HIF-1α) were analyzed. Hypercapnia alone produced increased levels of sex steroid hormones (E2, T, 11-KT) with concomitant mRNA level increase of estrogen responsive genes, while PFOS produced weak and time-dependent effects on E2-inducible gene transcription. Combined PFOS and hypercapnia exposure produced increased effects on sex steroid levels as compared to hypercapnia alone, with transcript expression patterns that are indicative of time-dependent interactive effects. Exposure to hypercapnia singly or in combination with PFOS produced modulations of the biotransformation and hypoxic responses that were apparently concentration- and time-dependent. Loading plots of principal component analysis (PCA) produced a significant grouping of individual scores according to the exposure scenarios at day 6 and 9. Overall, the PCA analysis produced a unique clustering of variables that signifies a positive correlation between exposure to high PFOS concentration and mRNA expression of E2 responsive genes. Notably, this pattern was not evident for individuals exposed to PFOS concentrations in combination with elevated CO2 scenarios. To our knowledge, the present study is the first of its kind, to evaluate such effects using combined exposure to a perfluoroalkyl sulfonate and elevated levels of CO2 saturation, representative of future oceanic climate change, in any fish species or lower vertebrate.

Plasma nesfatin-1 is not affected by long-term food restriction and does not predict rematuration among iteroparous female rainbow trout (Oncorhynchus mykiss)

The metabolic peptide hormone nesfatin-1 has been linked to the reproductive axis in fishes. The purpose of this study was to determine how energy availability after spawning affects plasma levels of nesfatin-1, the metabolic peptide hormone ghrelin, and sex steroid hormones in rematuring female rainbow trout (Oncorhynchus mykiss). To limit reproductive maturation, a group of female trout was food-restricted after spawning and compared with a control group that was fed a standard broodstock ration. The experiment was conducted twice, once using two-year-old trout (second-time spawners) and once using three-year-old trout (third-time spawners). During monthly sampling, blood was collected from all fish, and a subset of fish from each treatment was sacrificed for pituitaries. Pituitary follicle-stimulating hormone-beta (fsh-β) mRNA expression was analyzed with q-RT-PCR; plasma hormone levels were quantified by radioimmunoassay (17β-estradiol and ghrelin) and enzyme-linked immunosorbent assay (11-keto-testosterone and nesfatin-1). Although plasma nesfatin-1 levels increased significantly in the months immediately after spawning within both feeding treatments, plasma nesfatin-1 did not differ significantly between the two treatments at any point. Similarly, plasma ghrelin levels did not differ significantly between the two treatments at any point. Food restriction arrested ovarian development by 15–20 weeks after spawning, shown by significantly lower plasma E2 levels among restricted-ration fish. Pituitary fsh-β mRNA levels were higher among control-ration fish than restricted-ration fish starting at 20 weeks, but did not differ significantly between treatment groups until 30 weeks after spawning. Within both treatment groups, plasma 11-KT was elevated immediately after spawning and rapidly decreased to and persisted at low levels; starting between 20 and 25 weeks after spawning, plasma 11-KT was higher among control-ration fish than restricted-ration fish. The results from these experiments do not provide support for plasma nesfatin-1 as a signal for the initiation of reproductive development in rematuring female rainbow trout.

Monthly variations in the profile of sex steroids and gonadal development of brook trout (Salvelinus fontinalis Mitchill) during puberty in Tasmania

Puberty is an important reproductive event that has not been studied in brook trout in the Southern Hemisphere. The present study describes the histological development of gonads and variations in the levels of oestradiol-17β (E2), testosterone (T) and 11-ketotestosterone (11-KT) during the first year of male and female brook trout. The study started when the trout were at an age of 8 months (n = 10) and continued until they were 15 months. Of the males, 60% attained puberty at an age of 14 months. The peak of the gonadosomatic index in males was observed at 15 months of age (3.0 ± 0.9%). Female fish did not achieve maturation during their first year and ovarian development did not progress beyond the vesicular oocyte stage within the study period.

Molecular characterization and quantification of sablefish (Anoplopoma fimbria) gonadotropins and their receptors: reproductive dysfunction in female captive broodstock

Efforts to establish an aquaculture industry for sablefish (Anoplopoma fimbria) are constrained by reproductive dysfunction in wild-caught fish and by lack of reproduction of F1 females. Toward a better understanding of the reproductive dysfunction of captive broodstock, full-length cDNAs encoding the sablefish gonadotropin subunits (fshb, lhb and cga) and their receptors (fshr and lhcgr) were cloned, sequenced and quantitative real-time PCR assays developed. Sablefish gonadotropin subunits display some unique features, such as two additional Cys residues in the N-terminal region of Fshb and a lack of potential N-glycosylation sites in Fshb and Lhb, whereas Fshr and Lhcgr possess conserved structural characteristics described in other vertebrates. Wild females captured in fall completed gametogenesis in captivity the next spawning season, whereas females captured three months earlier, during summer, failed to mature. Interestingly, these wild non-maturing females exhibited similar reproductive features as prepubertal F1 females, including low levels of pituitary gonadotropin and ovarian receptor mRNAs and plasma sex steroids, and ovarian follicles arrested at the perinucleolus stage. In conclusion, this study described the cloning, molecular characterization and development of qPCRs for sablefish gonadotropins and their receptors. Rearing conditions may impair vitellogenic growth of ovarian follicles in sablefish, compromising the reproductive success of broodstock.

The effects of 11-ketotestosterone on ovarian physiology of previtellogenic captive hapuku (Polyprion oxygeneios)

The present study investigated, for the first time in a perciform teleost, the effects of in vivo 11-ketotestosterone (11-KT) treatment using slow-release implants on ovarian development and gonadotropin receptor mRNA levels in captive previtellogenic females of hapuku (Polyprion oxygeneios). At the cellular/functional level, ovarian development and ovarian and hepatic total lipid levels were examined. At the molecular level, transcript abundance of ovarian follicle-stimulating hormone receptor (FSH-R) and luteinizing hormone receptor (LH-R) was measured. Additionally, cyclic adenosine monophosphate (cAMP) levels in ovarian fragments from placebo and 11-KT implanted fish incubated with or without human chorionic gonadotropin (hCG) in vitro were compared between groups. There were no significant differences between treatments with regard to oocyte size and lipid contents of liver and ovary. Messenger RNA levels of FSH-R and LH-R were significantly lower in the treated females. Similarly, cAMP levels were significantly lower in the ovarian fragments of the 11-KT implanted females. These results suggest that 11-KT specifically, but possibly androgens in general, may not have an important function in regulating gonadal development of previtellogenic female hapuku; indeed, if anything, 11-KT appeared to have a detrimental effect and its use will not be beneficial in advancing sexual maturity of hapuku in aquaculture.

The effects of 17-α-ethinylestradiol (EE2) on molecular signaling cascades in mummichog (Fundulus heteroclitus)

Exposures to ≤10 ng/L of 17-α-ethinylestradiol (EE2) will reduce or shut down egg production in freshwater fish models, while mummichog (Fundulus heteroclitus), an estuarine species, are able to produce eggs at EE2 concentrations >3000 ng/L. The objective of this study was to gain mechanistic insight into how mummichog are able to produce eggs during exposures to high EE2. Mummichog were exposed to 0, 50 or 250 ng/L of EE2 for 14 d. There were no changes in gonadosomatic index, liversomatic index, gonad development, or plasma estradiol levels after exposure to EE2. However, testosterone significantly decreased with EE2 exposures (50, 250 ng/L). Microarray analysis in the liver revealed that cell processes associated with lipids were affected by EE2 at the transcriptome level. Based on the transcriptomics data, we hypothesize that mummichog are able to maintain lipid transport and uptake into the ovary and this may be associated with apolipoproteins, facilitating normal oocyte development. Novel gene regulatory networks for protein modification targets were also constructed to learn more about the potential roles of estrogens in the teleost liver. Although post-translational modifications (PTMs) are important regulatory mechanisms, the roles of PTMs in protein regulation in fish and the susceptibility of PTMs to aquatic pollutants are largely unexplored and may offer novel insight into mechanisms of endocrine disruption.

Molecular cloning and characterization of amh, dax1 and cyp19a1a genes and their response to 17α-methyltestosterone in Pengze crucian carp

The proteins encoded by amh, dax1 and cyp19a1a play important roles in gonad differentiation. Their functions have been far less studied in teleosts. In this study, the full-length cDNAs of amh, dax1 and cyp19a1a were cloned and characterized in a triploid gynogenic fish, the Pengze crucian carp. Their expression profilings in juvenile development, adult tissues and juveniles exposed to 100 ng/L 17α-methyltestosterone (MT) were investigated. Results showed that their putative proteins shared high identities to their counterparts in cyprinid fish species, respectively. The tissue distribution results indicated that amh and cyp19a1a were predominantly expressed in the ovary and dax1 was dominantly expressed in the liver. Gene profiling in the developmental stages showed that all the three target genes had a consistent highest expression at 48 days post hatching (dph). The period of 48 dph appeared to be a key time during the process of the gonad development of Pengze crucian carp. 100 ng/L MT significantly increased the mRNA expression of amh at 2- and 4-week exposures and enhanced dax1 and cyp19a1a at 6-week exposure. The present study indicated that MT could influence the gonad development in Pengze crucian carp by disturbing sex-differentiation associated gene expression. Furthermore, the present study will be of great significance to broaden the understanding of molecular mechanisms of the physiological processes of reproduction in fish.

Up-regulation of gonadotropin mRNA-expression at the onset of gametogenesis in the roach (Rutilus rutilus): evidence for an important role of brain-type aromatase (cyp19a1b) in the pituitary

The present study characterized changes in key parameters of reproduction in adult roach (Rutilus rutilus) from Lake Grosser Mueggelsee (Berlin, Germany) during natural gametogenesis. Fish of both sexes were sampled in monthly intervals between April and August in order to cover the onset of gametogenesis. Investigated parameters included gonad histology, plasma levels of 17β-oestradiol (E2), testosterone (T), 11-ketotestosterone (11-KT), and 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) as well as the expression of gonadotropin subunits in the pituitary. Furthermore, the mRNA-expression of brain-type aromatase (cyp19a1b), androgen receptor (ar), and estrogen receptor isoforms was studied at the pituitary level. The onset of gametogenesis - as indicated by follicles with cortical alveoli in females and first spermatogonia B in males - was observed in July, accompanied by a significant up-regulation of follicle-stimulating hormone β (fshβ) mRNA in the pituitary in both sexes. On the other hand, luteinizing hormone β (lhβ) mRNA increased later on in August. In males, the increase of fshβ mRNA in July coincided with a rise in plasma 11-KT concentrations. In females, E2 in plasma increased later, not until August, shortly before true vitellogenesis (late cortical alveoli stage). Expression of sex steroid receptors in the pituitary revealed only minor seasonal fluctuations. Most pronounced, ar mRNA displayed the highest level pre-spawning in both sexes. Interestingly, cyp19a1b mRNA-expression in the pituitary increased in parallel with fshβ already before any changes in plasma E2 or T occurred. These data suggest an important role of pituitary FSH and aromatase at the onset of gametogenesis in the roach.

Identification and transcriptional modulation of the largemouth bass, Micropterus salmoides, vitellogenin receptor during oocyte development by insulin and sex steroids

Fish vitellogenin synthesized and released from the liver of oviparous animals is taken up into oocytes by the vitellogenin receptor. This is an essential process in providing nutrient yolk to developing embryos to ensure successful reproduction. Here we disclose the full length vtgr cDNA sequence for largemouth bass (LMB) that reveals greater than 90% sequence homology with other fish vtgr sequences. We classify LMB Vtgr as a member of the low density lipoprotein receptor superfamily based on conserved domains and categorize as the short variant that is devoid of the O-glycan segment. Phylogenetic analysis places LMB Vtgr sequence into a well-supported monophyletic group of fish Vtgr. Real-time PCR showed that the greatest levels of LMB vtgr mRNA expression occurred in previtellogenic ovarian tissues. In addition, we reveal the effects of insulin, 17beta-estradiol (E(2)), and 11-ketotestosterone (11-KT) in modulation of vtgr, esr, and ar mRNAs in previtellogenic oocytes. Insulin increased vtgr expression levels in follicles ex vivo while exposure to E(2) or 11-KT did not result in modulation of expression. However, both steroids were able to repress insulin-induced vtgr transcript levels. Coexposure with insulin and E(2) or of insulin and 11-KT increased ovarian esr2b and ar mRNA levels, respectively, which suggest a role for these nuclear receptors in insulin-mediated signaling pathways. These data provide the first evidence for the ordered stage-specific expression of LMB vtgr during the normal reproductive process and the hormonal influence of insulin and sex steroids on controlling vtgr transcript levels in ovarian tissues.

Carbonyl reductase mRNA abundance and enzymatic activity as potential biomarkers of oxidative stress in marine fish

Carbonyl reductase (CBR) is an enzyme involved in protection from oxidative stress. In rainbow trout (Oncorhynchus mykiss), the hepatic mRNA abundance of the two isoforms (A and B) is increased after exposure to treated sewage effluents, as well as after exposure with β-naphthoflavone (β-NF) and the pro-oxidant paraquat. In this study, we show that the same chemicals similarly increase the single known hepatic CBR mRNA level and CBR catalytic activity in the coastal living eelpout (Zoarces viviparus). Hepatic CBR mRNA abundance and catalytic activity were also compared between eelpout collected at contaminated and reference sites on the Swedish west coast, but no differences were observed. In conclusion, CBR is a potential biomarker candidate for monitoring the exposure and effects of AhR agonists and/or pro-oxidants in the marine environment, but more research is needed to investigate temporal regulation as well as dose dependency for different chemicals. The mRNA and enzymatic assays presented in this study provide two additional tools for researchers interested in expanding their biomarker battery.

Androgen-specific regulation of FSH signalling in the previtellogenic ovary and pituitary of the New Zealand shortfinned eel, Anguilla australis

The evidence for androgens having a pivotal role in the functioning of the female reproductive axis--such as initiating puberty or vitellogenesis--is mounting. However, the use of aromatizable androgens and the tissue-specific focus of most studies often make it unclear if androgenic effects throughout the axis proceed via androgen or estrogen signalling mechanisms. In this study, we assessed the effects of 11-ketotestosterone (11KT, a non-aromatizable androgen) on the pituitary and ovary of previtellogenic (PV) freshwater eels Anguilla australis, comparing them with eels naturally undergoing early vitellogenesis (EV). We found that 11KT treatment produces molecular and morpho-physiological phenotypes that were generally intermediate between PV and EV. Most notably, we demonstrated that 11KT induces effects on follicle-stimulating hormone (FSH) signalling in the pituitary and ovaries that are in opposition to each other. Thus, 11KT significantly reduced fshβ subunit expression in the pituitary. At the same time, 11KT dramatically increased mRNA levels of ovarian FSH receptor and plasma levels of estradiol-17β, very likely sensitizing the previtellogenic follicle to the FSH signal. Androgens therefore may be important in facilitating puberty in the eel.

The effects of estrogenic and androgenic endocrine disruptors on the immune system of fish: a review

During the last decade, a number of studies have shown that, in addition to their classically described reproductive function, estrogens and androgens also regulate the immune system in teleosts. Today, several molecules are known to interfere with the sex-steroid signaling. These chemicals are often referred to as endocrine disrupting contaminants (EDCs). We review the growing evidence that these compounds interfere with the fish immune system. These studies encompass a broad range of approaches from field studies to those at the molecular level. This integrative overview improves our understanding of the various endocrine-disrupting processes triggered by these chemicals. Furthermore, the research also explains why fish that have been exposed to EDCs are more sensitive to pathogens during gametogenesis. In this review, we first discuss the primary actions of sex-steroid-like endocrine disruptors in fish and the specificity of the fish immune system in comparison to mammals. Then, we review the known interactions between the immune system and EDCs and interpret the primary effects of sex steroids (estrogens and androgens) and their related endocrine disruptors on immune modulation. The recent literature suggests that immune parameters may be used as biomarkers of contamination by EDCs. However, caution should be used in the assessment of such immunotoxicity. In particular, more attention should be paid to the specificity of these biomarkers, the external/internal factors influencing the response, and the transduction pathways induced by these molecules in fish. The use of the well-known mammalian models provides a useful guide for future research in fish.

Expression of androgen receptor mRNA in the ovary of Japanese eel, Anguilla japonica, during artificially induced ovarian development

In order to elucidate how androgens may mediate their effects on ovarian growth, we investigated the mRNA levels of two subtypes of androgen receptor (ara and arb) in the ovary of feminized Japanese eel (Anguilla japonica) during artificially induced ovarian development by quantitative real-time reverse transcriptase polymerase chain reaction and in situ hybridization. Ara mRNA levels were high from the late oil droplet stage to the late vitellogenic stage, whereas arb mRNA levels were high from the late oil droplet stage to the midvitellogenic stage. Both ar mRNAs were predominantly observed in the follicle cells and the epithelial cells of the ovigerous lamellae in all stages. In the oil droplet stage, oogonia exhibited intense signals for ar mRNAs. There was no obvious difference in localization pattern between ara and arb in all ovaries examined, irrespective of maturational stage. It was difficult to identify the follicle cell types that were positive for ar mRNA during ovarian development. Only in post-ovulatory follicles could theca and granulosa cells be clearly identified, and ar signals were observed in both layers. The predominant localization of ar mRNA in the follicle cells suggests that androgens play important roles in oocyte growth by acting on these cells in this species. We have shown the expression profile and localization of ar mRNA during ovarian development for the first time in an oviparous vertebrate.

Induction of hepatic carbonyl reductase/20beta-hydroxysteroid dehydrogenase mRNA in rainbow trout downstream from sewage treatment works--possible roles of aryl hydrocarbon receptor agonists and oxidative stress

Carbonyl reductase/20beta-hydroxysteroid dehydrogenase (CR/20beta-HSD) serves both as a key enzyme in the gonadal synthesis of maturing-inducing hormone in salmonids, and as an enzyme protecting against certain reactive oxygen species. We have previously shown that mRNA of the hepatic CR/20beta-HSD B isoform is increased in rainbow trout caged downstream from a Swedish sewage treatment plant. Here, we report an increase of both the A as well as B form in fish kept downstream from a second sewage treatment plant. The two mRNAs were also induced in fish hepatoma cells in vitro after exposure to effluent extract. This indicates that the effects observed in vivo could be a direct effect on the liver, i.e. the mRNA induction does not require a signal from any other organ. When fish were exposed in vivo to several effluents treated with more advanced methods (ozone, moving bed biofilm reactor or membrane bioreactor) the expression of hepatic mRNA CR/20beta-HSD A and B was significantly reduced. Their abundance did not parallel the reduction of estrogen-responsive transcripts, in agreement with our previous observations that ethinylestradiol is not a potent inducer. Treatment with norethisterone, methyltestosterone or hydrocortisone in vivo did not induce the hepatic CR/20beta-HSD A and B mRNA expression. In contrast, both isoforms were markedly induced by the aryl hydrocarbon receptor agonist beta-naphthoflavone as well as by the pro-oxidant herbicide paraquat. We hypothesize that the induction of CR/20beta-HSD A and B by sewage effluents could be due to anthropogenic contaminants stimulating the aryl hydrocarbon receptor and/or causing oxidative stress.

Naturally-induced endocrine disruption by the parasite Ligula intestinalis (Cestoda) in roach (Rutilus rutilus)

Fish represent the most frequently used vertebrate class for the investigation of endocrine disruption (ED) in wildlife. However, field studies are complicated by exposure scenarios involving a variety of anthropogenic and natural influences interfering with the endocrine system. One natural aspect rarely considered in ecotoxicological studies is how parasites modulate host physiology. Therefore, investigations were carried out to characterise the impacts of the parasitic tapeworm Ligula intestinalis on plasma sex steroid levels and expression of key genes associated with the reproduction in roach (Rutilus rutilus), a sentinel species for wildlife ED research. Parasitisation by L. intestinalis suppressed gonadal development in both genders of roach and analysis of plasma sex steroids revealed substantially lower levels of 17beta-oestradiol (E2) and 11-ketotestosterone (11-KT) in infected females as well as E2, 11-KT, and testosterone in infected males. Consistently, in both, infected females and males, expression of the oestrogen dependent genes such as vitellogenin and brain-type aromatase in liver and brain was reduced. Furthermore, parasitisation differentially modulated mRNA expression of the oestrogen and androgen receptors in brain and liver. Most prominently, liver expression of oestrogen receptor 1 was reduced in infected females but not in males, whereas expression of oestrogen receptor 2a was up-regulated in both genders. Further, insulin-like growth factor 1 mRNA in the liver was increased in infected females but not in males. Despite severe impacts on plasma sex steroids and pituitary gonadotropin expression, brain mRNA levels of gonadotropin-releasing hormone (GnRH) precursors encoding GnRH2 and GnRH3 were not affected by L. intestinalis-infection. In summary, the present results provide basic knowledge of the endocrine system in L. intestinalis-infected roach and clearly demonstrate that parasites can cause ED in fish.

Oogenesis in teleosts: how eggs are formed

One of the major objectives of the aquaculture industry is the production of a large number of viable eggs with high survival. Major achievements have been made in recent years in improving protocols for higher efficiency of egg production and viability of progeny. Main gaps remain, however, in understanding the dynamic processes associated with oogenesis, the formation of an egg, from the time that germ cells turn into oogonia, until the release of ova during spawning in teleosts. Recent studies on primordial germ-cells, yolk protein precursors and their processing within the developing oocyte, the deposition of vitamins in eggs, structure and function of egg envelopes and oocyte maturation processes, further reveal the complexity of oogenesis. Moreover, numerous circulating endocrine and locally-acting paracrine and autocrine factors regulate the various stages of oocyte development and maturation. Though it is clear that the major regulators during vitellogenesis and oocyte maturation are the pituitary gonadotropins (LH and FSH) and sex steroids, the picture emerging from recent studies is of complex hormonal cross-talk at all stages between the developing oocyte and its surrounding follicle layers to ensure coordination of the various processes that are involved in the production of a fertilizable egg. In this review we aim at highlighting recent advances on teleost fish oocyte differentiation, maturation and ovulation, including those involved in the degeneration and reabsorption of ovarian follicles (atresia). The role of blood-borne and local ovarian factors in the regulation of the key steps of development reveal new aspects associated with egg formation.

Comparative transcriptomic analysis of follicle-enclosed oocyte maturational and developmental competence acquisition in two non-mammalian vertebrates

BACKGROUND

In vertebrates, late oogenesis is a key period during which the oocyte acquires its ability to resume meiosis (i.e. maturational competence) and to develop, once fertilized, into a normal embryo (i.e. developmental competence). However, the molecular mechanisms involved in these key biological processes are far from being fully understood. In order to identify key mechanisms conserved among teleosts and amphibians, we performed a comparative analysis using ovarian tissue sampled at successive steps of the maturational competence acquisition process in the rainbow trout (Oncorhynchus mykiss) and in the clawed toad (Xenopus laevis). Our study aimed at identifying common differentially expressed genes during late oogenesis in both species. Using an existing transcriptomic analysis that had previously been carried out in rainbow trout, candidate genes were selected for subsequent quantitative PCR-based comparative analysis.

RESULTS

Among the 1200 differentially expressed clones in rainbow trout, twenty-six candidate genes were selected for further analysis by real-time PCR in both species during late oogenesis. Among these genes, eight had similar expression profiles in trout and Xenopus. Six genes were down-regulated during oocyte maturation (cyp19a1, cyp17a1, tescalcin, tfr1, cmah, hsd11b3) while two genes exhibited an opposite pattern (apoc1, star). In order to document possibly conserved molecular mechanisms, four genes (star, cyp19a1, cyp17a1 and hsd11b3) were further studied due to their known or suspected role in steroidogenesis after characterization of the orthology relationships between rainbow trout and Xenopus genes. Apoc1 was also selected for further analysis because of its reported function in cholesterol transport, which may modulate steroidogenesis by regulating cholesterol bioavailability in the steroidogenic cells.

CONCLUSIONS

We have successfully identified orthologous genes exhibiting conserved expression profiles in the ovarian follicle during late oogenesis in both trout and Xenopus. While some identified genes were previously uncharacterized during Xenopus late oogenesis, the nature of these genes has pointed out molecular mechanisms possibly conserved in amphibians and teleosts. It should also be stressed that in addition to the already suspected importance of steroidogenesis in maturational competence acquisition, our approach has shed light on other regulatory pathways which may be involved in maturational and developmental competence acquisitions that will require further studies.

Neural aromatase transcript and protein levels in Atlantic salmon (Salmo salar) are modulated by the ubiquitous water pollutant, 4-nonylphenol

At present, there are no known direct occurrences of nonylphenol (NP) in nature. Therefore, its presence in nature is solely a consequence of human activities. NP is generated through degradation of alkylphenol ethoxylates released mainly from textile, metal working, institutional cleansing and laundry cleaning, but few data on the amount of the release is available. These compounds have been shown to affect several biological processes, including the endocrine systems, in a wide number of species. The cytochrome P450 aromatase (Cyp19) is the rate-limiting step in estrogen production, and is known to be a potential target for endocrine-disrupting chemicals (EDCs) such as NP. Teleost fish generally have a high brain aromatase activity, and the effects of EDCs in fish brain is not thoroughly investigated. In this study, juvenile Atlantic salmon (Salmo salar) were exposed to waterborne concentrations of the synthetic pharmaceutical and xenoestrogen 17alpha-ethynylestradiol (EE2; 5ng/L) and the xenoestrogen 4-nonylphenol (NP; 5 and 50microg/L) for 72h. Brain tissue and blood were sampled from individual fish. Gene expression patterns of Cyp19 isoforms were determined by quantitative PCR, aromatase protein immunoreactivity in the brain was evaluated by immunohistochemistry and immunoblotting, and aromatase activity was analyzed using the tritiated water-release assay. Plasma estradiol (E2) and testosterone (T) levels were measured by EIA. In the brain, EE2 increased the mRNA expression of Cyp19b almost threefold compared to the solvent control, whereas Cyp19a levels were unaffected by EE2 treatment. In contrast, both NP concentrations produced significant reduction of Cyp19a expression. Immunohistochemical aromatase protein reactivity was localized in several brain regions, but no apparent quantitative effects of the exposures were observed. Immunoblotting analysis showed that EE2 and NP produced a slight increase in brain immunoreactive aromatase protein band, compared with controls. Plasma levels of E2 increased twofold when treated with EE2 and 5microg NP/L, and threefold when exposed to 50microg NP/L. In general, the present study shows that the parallel biochemical, transcriptional and cellular detection of neural aromatase for endocrine-disrupting effects from EE2 and NP may be observed at specific levels of the biological organization.