Current perspectives on the androgen 5 alpha-dihydrotestosterone (DHT) and 5 alpha-reductases in teleost fishes and amphibians

Species variation in steroid hormone-related gene expression contributes to species diversity in sexually dimorphic communication in electric fishes

Sexually dimorphic behaviors are often regulated by gonadal steroid hormones. Species diversity in behavioral sex differences may arise as expression of genes mediating steroid action in brain regions controlling these behaviors evolves. The electric communication signals of apteronotid knifefishes are an excellent model for comparatively studying neuroendocrine regulation of sexually dimorphic behavior. These fish produce and detect weak electric organ discharges (EODs) for electrolocation and communication. EOD frequency (EODf), controlled by the medullary pacemaker nucleus (Pn), is sexually dimorphic and regulated by androgens and estrogens in some species, but is sexually monomorphic and unaffected by hormones in other species. We quantified expression of genes for steroid receptors, metabolizing enzymes, and cofactors in the Pn of two species with sexually dimorphic EODf (Apteronotus albifrons and Apteronotus leptorhynchus) and two species with sexually monomorphic EODf ("Apteronotus" bonapartii and Parapteronotus hasemani). The "A." bonapartii Pn expressed lower levels of androgen receptor (AR) genes than the Pn of species with sexually dimorphic EODf. In contrast, the P. hasemani Pn robustly expressed AR genes, but expressed lower levels of genes for 5α-reductases, which convert androgens to more potent metabolites, and higher levels of genes for 17β-hydroxysteroid dehydrogenases that oxidize androgens and estrogens to less potent forms. These findings suggest that sexual monomorphism of EODf arose convergently via two different mechanisms. In "A." bonapartii, reduced Pn expression of ARs likely results in insensitivity of EODf to androgens, whereas in P. hasemani, gonadal steroids may be metabolically inactivated in the Pn, reducing their potential to influence EODf.

5 mC modification of steroid hormone biosynthesis-related genes orchestrates feminization of channel catfish induced by high-temperature

To elucidate the mechanism behind channel catfish feminization induced by high temperature, gonad samples were collected from XY pseudo-females and wild-type females and subjected to high-throughput sequencing for Whole-Genome-Bisulfite-Seq (WGBS) and transcriptome sequencing (RNA-Seq). The analysis revealed 50 differentially methylated genes between wild-type females and XY pseudo-females, identified through the analysis of KEGG pathways and GO enrichment in the promoter of the genome and differentially methylated regions (DMRs). Among these genes, multiple differential methylation sites observed within the srd5a2 gene. Repeatability tests confirmed 7 differential methylation sites in the srd5a2 gene in XY pseudo-females compared to normal males, with 1 specific differential methylation site (16608174) distinguishing XY pseudo-females from normal females. Interestingly, the expression of these genes in the transcriptome showed no difference between wild-type females and XY pseudo-females. Our study concluded that methylation of the srd5a2 gene sequence leads to decreased expression, which inhibits testosterone synthesis while promoting the synthesis of 17β-estradiol from testosterone. This underscores the significance of the srd5a2 gene in the sexual differentiation of channel catfish, as indicated by the ipu00140 KEGG pathway analysis.

Dietary steroids promote body weight growth and induce gametogenesis by increasing the expressions of genes related to cell proliferation of sea cucumber (Apostichopus japonicus)

Steroids play a vital role in animal survival, promoting growth and development when administered appropriate concentration exogenously. However, it remains unclear whether steroids can induce gonadal development and the underlying mechanism. This study assessed sea cucumber weights post-culturing, employing paraffin sections and RNA sequencing (RNA-seq) to explore gonadal changes and gene expression in response to exogenous steroid addition. Testosterone and cholesterol, dissolved in absolute ethanol, were incorporated into sea cucumber diets. After 30 days, testosterone and cholesterol significantly increased sea cucumber weights, with the total weight of experimental groups surpassing the control. The testosterone-fed group exhibited significantly higher eviscerated weight than the control group. In addition, dietary steroids influenced gonad morphology and upregulated genes related to cell proliferation，such as RPL35, PC, eLF-1, MPC2, ADCY10 and CYP2C18. Thees upregulated differentially expressed genes were significantly enriched in the organic system, metabolism, genetic information and environmental information categories. These findings imply that steroids may contribute to the growth and the process of genetic information translation and protein synthesis essential for gonadal development and gametogenesis.

Diversity of Androgens; Comparison of Their Significance and Characteristics in Vertebrate Species

Androgen(s) is one of the sex steroids that are involved in many physiological phenomena of vertebrate species. Although androgens were originally identified as male sex hormones, it is well known now that they are also essential in females. As in the case of other steroid hormones, androgen is produced from cholesterol through serial enzymatic reactions. Although testis is a major tissue to produce androgens in all species, androgens are also produced in ovary and adrenal (interrenal tissue). Testosterone is the most common and famous androgen. It represents a major androgen both in males and females of almost vertebrate species. In addition, testosterone is a precursor for producing significant androgens such as11-ketotestosterone, 5α-dihydrotestosterone, 11-ketodihydrotestosterones and 15α-hydroxytestosterone in a species- or sex-dependent manner for their homeostasis. In this article, we will review the significance and characteristics of these androgens, following a description of the history of testosterone discovery and its synthetic pathways.

Exploring the effect of dihydrotestosterone on nucleotide-binding and oligomerization domain-like receptor expression in spotted snakehead Channa punctata (Bloch 1793)

Sex steroids are known to modulate immune responses and as a result many of the immune parameters in seasonally breeding organisms show reproductive-phase dependent variation. Androgens, the male sex steroids, are largely reported to be immunosuppressive. Together with other pattern recognition receptors, the nucleotide-binding and oligomerization domain-like receptors (NLRs) serve as intracellular sentinels and are essential to defense mechanisms. Interestingly, to date the transcriptional modulation of NLRs by androgens has not been explored. In the present study, we investigated the reproductive-phase dependent expression of NLRs in the male spotted snakehead Channa punctata. Furthermore, the effect of dihydrotestosterone (DHT) on NLR expression was studied. The expression of NLRs was observed to be most pronounced during the spawning phase of the fish, which is marked by the highest testosterone level. In vivo as well as in vitro studies showed the diverse effect of DHT on NLR expression depending on the duration and mode of treatment, as well as the immune tissue studied.

BPA disrupted the testis testosterone levels by interfering ER enrichments within StAR 5' flanking region in rare minnow Gobiocypris rarus

Bisphenol A (BPA) is a widely used endocrine disruptor, which has attracted much attention due to its harmful effects on male reproduction. To investigate the interference of BPA on steroid synthesis in males, male rare minnows (Gobiocypris rarus) were exposed to 15 μg L^-1 BPA for 7, 14 and 21 d. Meanwhile, a positive control group was performed with 25 ng L^-1 17α-ethynyl estradiol (EE2). Results showed that BPA exposure induced lower testosterone (T) levels, while affecting the transcripts of steroidogenic gene StAR. Moreover, BPA induced abnormal germ cells proliferation in the testis in rare minnow. Transcriptome analysis showed that 354 transcripts significantly differentially expressed after BPA exposure for 14 d, several of them were enriched in the signaling pathways of cell cycle process, PPAR signaling pathway, the steroid synthesis pathway and estrogen signaling pathway. BPA significantly increased estrogen receptor (ER) levels and induced abnormal protein levels of PPARγ. BPA disrupted the StAR expression by interfering ER enrichments within StAR 5' flanking region. Additionally, our study also revealed that BPA and EE2 might have different mechanisms for interfering with steroid hormone levels and germ cells proliferation in the testis.

Analyzing the gonadal transcriptome of the frog Hoplobatrachus rugulosus to identify genes involved in sex development

BACKGROUND

The tiger frog (Hoplobatrachus rugulosus) is listed as a national Class II protected species in China. In the context of global warming, the sex ratio of amphibians will be affected, and the development of the population will be limited. Therefore, considering the potential for a decrease in the number of amphibians, studying sex evolution and molecular regulation of gonadal development in H. rugulosus, phenomenon that are currently unclear, is of great significance.

RESULTS

Here, H. rugulosus was used to explore the mechanisms regulating gonadal development in amphibians. Illumina HiSeq 3000 was used to sequence the gonadal transcriptome of male and female H. rugulosus at two growth stages to identify genes related to gonadal development and analyze expression differences in the gonads. This analysis indicated that cyp17α, hsd3β, hsd11β1, cyp19α, and hsd17β12 perform vital functions in sex development in amphibians. Specifically, the expression of cyp3α, cyp17α, hsd3β, hsd11β1, sox2, sox9, sox30, soat, cyp19α, hsd17β12, and hspα1s was correlated with gonadal development and differentiation in H. rugulosus, as determined using the quantitative reverse transcriptase-polymerase chain reaction.

CONCLUSION

Significant differences were found in the gonadal gene expression levels in H. rugulosus of both sexes, and we identified a steroid hormone synthesis pathway in this species and analyzed related gene expression, but the changes during sex differentiation were still unclear. To our knowledge, this report presents the first analysis of the H. rugulosus gonadal transcriptome and lays the foundation for future research.

Development of a Liquid Chromatography/Mass Spectrometry-Based Inhibition Assay for the Screening of Steroid 5-α Reductase in Human and Fish Cell Lines

Steroid 5-α reductase (5AR) is responsible for the reduction of steroids to 5-α reduced metabolites, such as the reduction of testosterone to 5-α dihydrotestosterone (DHT). A new adverse outcome pathway (AOP) for 5AR inhibition to reduce female reproduction in fish (AOP 289) is under development to clarify the antiestrogenic effects of 5AR inhibitors in female fish. A sensitive method for the DHT analysis using chemical derivatization and liquid chromatography–tandem mass spectrometry was developed. A cell-based 5AR inhibition assay that utilizes human cell lines, a transient overexpression system, and fish cell lines was developed. The measured IC₅₀ values of two well-known 5AR inhibitors, finasteride and dutasteride, were comparable in the different systems. However, the IC₅₀ of dutasteride in the fish cell lines was lower than that in the human cell lines. Finasteride showed a higher IC₅₀ against the RTG-2 cell line. These results demonstrated that 5ARs inhibition could differ in terms of structural characteristics among species. The assay has high sensitivity and reproducibility and is suitable for the application in 5AR inhibition screening for various endocrine disruption chemicals (EDCs). Future studies will continue to evaluate the quantitative inhibition of 5AR by EDCs to compare the endocrine-disrupting pathway in different species.

Profiles of 5α-Reduced Androgens in Humans and Eels: 5α-Dihydrotestosterone and 11-Ketodihydrotestosterone Are Active Androgens Produced in Eel Gonads

Although 11-ketotestosterone (11KT) and testosterone (T) are major androgens in both teleosts and humans, their 5α-reduced derivatives produced by steroid 5α-reductase (SRD5A/srd5a), i.e., 11-ketodihydrotestosterone (11KDHT) and 5α-dihydrotestosterone (DHT), remains poorly characterized, especially in teleosts. In this study, we compared the presence and production of DHT and 11KDHT in Japanese eels and humans. Plasma 11KT concentrations were similar in both male and female eels, whereas T levels were much higher in females. In accordance with the levels of their precursors, 11KDHT levels did not show sexual dimorphism, whereas DHT levels were much higher in females. It is noteworthy that plasma DHT levels in female eels were higher than those in men. In addition, plasma 11KDHT was undetectable in both sexes in humans, despite the presence of 11KT. Three srd5a genes (srd5a1, srd5a2a and srd5a2b) were cloned from eel gonads. All three srd5a genes were expressed in the ovary, whereas only both srd5a2 genes were expressed in the testis. Human SRD5A1 was expressed in testis, ovary and adrenal, whereas SRD5A2 was expressed only in testis. Human SRD5A1, SRD5A2 and both eel srd5a2 isoforms catalyzed the conversion of T and 11KT into DHT and 11KDHT, respectively, whereas only eel srd5a1 converted T into DHT. DHT and 11KDHT activated eel androgen receptor (ar)α-mediated transactivation as similar fashion to T and 11KT. In contrast, human AR and eel arβ were activated by DHT and11KDHT more strongly than T and 11KT. These results indicate that in teleosts, DHT and 11KDHT may be important 5α-reduced androgens produced in the gonads. In contrast, DHT is the only major 5α-reduced androgens in healthy humans.

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.

Ecotype differences in aggression, neural activity and behaviorally relevant gene expression in cichlid fish

In Lake Malawi, two ecologically distinct lineages of cichlid fishes (rock- vs sand-dwelling ecotypes, each comprised of over 200 species) evolved within the last million years. The rock-dwelling species (Mbuna) are aggressively territorial year-round and males court and spawn with females over rocky substrate. In contrast, males of sand-dwelling species are not territorial and instead aggregate on seasonal breeding leks in which males construct courtship "bowers" in the sand. However, little is known about how phenotypic variation in aggression is produced by the genome. In this study, we first quantify and compare behavior in seven cichlid species, demonstrating substantial ecotype and species differences in unconditioned mirror-elicited aggression. Second, we compare neural activity in mirror-elicited aggression in two representative species, Mchenga conophoros (sand-dwelling) and Petrotilapia chitimba (rock-dwelling). Finally, we compare gene expression patterns between these two species, specifically within neurons activated during mirror aggression. We identified a large number of genes showing differential expression in mirror-elicited aggression, as well as many genes that differ between ecotypes. These genes, which may underly species differences in behavior, include several neuropeptides, genes involved in the synthesis of steroid hormones and neurotransmitter activity. This work lays the foundation for future experiments using this emerging genetic model system to investigate the genomic basis of evolved species differences in both brain and behavior.

Consequences of steroid-5α-reductase deficiency and inhibition in vertebrates

In 1974, a lack of 5α-dihydrotestosterone (5α-DHT), the most potent androgen across species except for fish, was shown to be the origin of a type of pseudohermaphrodism in which boys have female-like external genitalia. This human intersex condition is linked to a mutation in the steroid-5α-reductase type 2 (SRD5α2) gene, which usually produces an important enzyme capable of reducing the Δ⁴-ene of steroid C-19 and C-21 into a 5α-stereoisomer. Seeing the potential of SRD5α2 as a target for androgen synthesis, pharmaceutical companies developed 5α-reductase inhibitors (5ARIs), such as finasteride (FIN) and dutasteride (DUT) to target SRD5α2 in benign prostatic hyperplasia and androgenic alopecia. In addition to human treatment, the development of 5ARIs also enabled further research of SRD5α functions. Therefore, this review details the morphological, physiological, and molecular effects of the lack of SRD5α activity induced by both SRD5α mutations and inhibitor exposures across species. More specifically, data highlights 1) the role of 5α-DHT in the development of male secondary sexual organs in vertebrates and sex determination in non-mammalian vertebrates, 2) the role of SRD5α1 in the synthesis of the neurosteroid allopregnanolone (ALLO) and 5α-androstane-3α,17β-diol (3α-diol), which are involved in anxiety and sexual behavior, respectively, and 3) the role of SRD5α3 in N-glycosylation. This review also features the lesser known functions of SRD5αs in steroid degradation in the uterus during pregnancy and glucocorticoid clearance in the liver. Additionally, the review describes the regulation of SRD5αs by the receptors of androgens, progesterone, estrogen, and thyroid hormones, as well as their differential DNA methylation. Factors known to be involved in their differential methylation are age, inflammation, and mental stimulation. Overall, this review helps shed light on the various essential functions of SRD5αs across species.

The transcriptome of the newt Cynops orientalis provides new insights into evolution and function of sexual gene networks in sarcopterygians

Amphibians evolved in the Devonian period about 400 Mya and represent a transition step in tetrapod evolution. Among amphibians, high-throughput sequencing data are very limited for Caudata, due to their largest genome sizes among terrestrial vertebrates. In this paper we present the transcriptome from the fire bellied newt Cynops orientalis. Data here presented display a high level of completeness, comparable to the fully sequenced genomes available from other amphibians. Moreover, this work focused on genes involved in gametogenesis and sexual development. Surprisingly, the gsdf gene was identified for the first time in a tetrapod species, so far known only from bony fish and basal sarcopterygians. Our analysis failed to isolate fgf24 and foxl3, supporting the possible loss of both genes in the common ancestor of Rhipidistians. In Cynops, the expression analysis of genes described to be sex-related in vertebrates singled out an expected functional role for some genes, while others displayed an unforeseen behavior, confirming the high variability of the sex-related pathway in vertebrates.

The combined effects of temperature and aromatase inhibitor on metamorphosis, growth, locomotion, and sex ratio of tiger frog (Hoplobatrachus rugulosus) tadpoles

Background

The tiger frog (Hoplobatrachus rugulosus) is widely raised by many farms in southern region of China as an economically edible frog. The growth, development, and sexual differentiation of amphibians are influenced by temperature and steroid hormone level. However, the problem of hormone residues is caused by the addition of exogenous hormones in frog breeding, it is worth considering whether non-sterol aromatase inhibitors can be used instead of hormones.

Methods

In our study, H. rugulosus tadpoles were subjected to two water temperatures (29 °C and 34 °C) and three letrozole concentrations in the feed (0, 0.1 and 1 mg/g) to examine the effects of temperature, aromatase inhibitor and their interaction on metamorphosis, locomotion, and sex ratios. A G-test and contingency table were used to analyze the metamorphosis rate of tadpoles and the survival rate of froglets after feeding for 90 days. A G-test was also used to analyze sex ratios in different treatment groups.

Results

Metamorphosis time and body size (snout-vent length, body mass and condition factor) were significantly different between the two temperature treatments. Metamorphosis time was longer and body size was increased at 29 °C compared to those at 34 °C. Letrozole concentration and the temperature × letrozole interaction did not affect these variables. The jumping distance of froglets following metamorphosis was positively associated with the condition factor; when controlling for condition factor, jumping distance was not affected by temperature, letrozole concentration and their interaction. Temperature and letrozole concentration also did not affect metamorphosis and survival rate. Sex ratio of the control group (0 mg/g letrozole) was 1:1 at 29 °C, but there were more males at 34 °C. The sex ratios of H. rugulosus treated with letrozole at 29 °C and 34 °C were significantly biased toward males, and male ratio increased as letrozole concentration increased. Furthermore, more males were produced at 34 °C than at 29 °C at each letrozole concentration.

Prolonged use of finasteride-induced gonadal sex steroids alterations, DNA damage and menstrual bleeding in women

The aim of the present study was to examine the effect of prolonged use of finasteride on serum levels of dihydrotestosterone (DHT), estradiol (E2), progesterone, testosterone and androstenedione in women during the menstrual period. Further, to screen and compare the 5α-reductase activities through the expression of SRD5A1, SRD5A2 and AR gene and to determine the level of VEGF, VKOR and SAA gene expression and DNA damage. A total of 30 Saudi women aged between 25 and 35 years were enrolled in the study. The selected women were divided into two groups. The first group (n = 15) received 5 mg finasteride/day for prolonged period of one year and second group (n = 15) was taken as a healthy control. ELISA technique was used for measuring the serum levels of the targeted hormones, and Comet assay was used for checking the DNA integrity. Our findings revealed significant decrement of DHT, E2, progesterone and androstenedione levels and elevated levels of testosterone in group treated with daily oral doses of 5 mg finasteride/day compared with the control subjects. mRNA expression suggested that finasteride has concrete effects on the gene expression of the selected genes from the treated group in comparison with the control group. In addition, finasteride induced DNA damage, and heavy menstrual bleeding was noted in women treated with finasteride. In conclusion, the present findings revealed that finasteride has adverse health effects in women associated with gonadal sex steroids alterations, DNA damage and heavy menstrual bleeding with no consensus in the treatment of androgenetic alopecia in women.

In vitro exposure of vitellogenic rainbow trout ovarian follicles to endocrine disrupting chemicals can alter basal estradiol-17β production and responsiveness to a gonadotropin challenge

Endogenous estrogens play major roles in many aspects of female reproductive development in fish. In order to develop a relatively high-throughput assay to determine the potential impact on reproductive development, vitellogenic rainbow trout ovarian follicles were exposed to a suite of contaminants in vitro and then assessed for the ability to produce estradiol-17β (E2) after a 500 ng/ml salmon gonadotropin (sGTH) challenge. There was a positive correlation between ovarian follicle size and E2 production, but an inverse correlation between size and responsiveness to sGTH. Significant impacts on E2 levels were observed following treatment with different endocrine disrupting chemicals, such as 17α-ethinylestradiol (EE2), prochloraz, or trenbolone. EE2 was remarkably potent and significantly reduced ovarian follicle responsiveness to sGTH at concentrations as low as 0.1 nM. Of the other contaminants tested, only tamoxifen impacted E2 levels, and only at concentrations near the limits of solubility. Flutamide, fluoxetine, 4-hydroxy tamoxifen, hydroxyflutamide, and norfluoxetine had little or no impact. Quantitative PCR analyses of steroidogenesis-related genes were carried out on EE2 treated ovarian follicles, but significant transcriptional responses to EE2 were not observed. Overall, this study suggests that xenoestrogens and anti-estrogens are more likely to interfere with ovarian E2 synthesis than other classes of EDCs. This also provides a template for further testing of the effects of EDCs on ovarian function.

De novo transcriptome analysis to search for sex-differentiation genes in the Siberian sturgeon

The sturgeon family includes many species that are lucrative for commercial caviar production, some of which face critical conservation problems. The purpose of this study was to identify genes involved in gonadal sex differentiation in sturgeons, contributing to our understanding of the biological cycle of this valuable species. A high-quality de novo Siberian sturgeon gonadal transcriptome was built for this study using gonadal samples from undifferentiated fish at 3, 5, and 6 months of age; recently sex-differentiated fish at 9 months of age; and immature males and females at 14-17 months of age. Undifferentiated fish were sexed after validation of forkhead box L2 (foxl2) and cytochrome P450, family 19, subfamily A, and polypeptide 1a (cyp19a1a) as sex markers, and the transcriptomes of the 3-month-old undifferentiated fish, 5-6-month-old future females, and 5-6-month-old putative males were compared. The ovarian program was associated with strong activation of genes involved in estrogen synthesis (cyp19a1, foxl2, and estradiol 17-beta-dehydrogenase 1), stem-cell niche building and regulation, and sex-specific nerve cell development. The genes related to the stem-cell niche were: (1) the family of iroquois-class homeodomain proteins 3, 4, and 5 (irx3, irx4, irx5-1, irx5-2, and irx5-3), which are essential for somatic-germ cell interaction; (2) extracellular matrix remodeling genes, such as collagen type XXVIII alpha 1 chain and collagen type II alpha 1 chain, matrix metalloproteinases 24-1 and 24-2, and NADPH oxidase organizer 1, which, along with the somatic cells, provide architectural support for the stem-cell niche; and (3) mitogenic factors, such as lim homeobox 2, amphiregulin, G2/M phase-specific E3 ubiquitin-protein ligase, and connector enhancer of kinase suppressor of ras 2, which are up regulated in conjunction with the anti-apoptotic gene G2/M phase-specific E3 ubiquitin-protein ligase suggesting a potential involvement in regulating the number of germ cells. Genes related to sex-specific nerve cell developments were: the neurofilament medium polypeptides, the gene coding for serotonin receptor 7, 5-hydroxytryptamine receptor 7; neurotensin, isoform CRA-a, the neuron-specific transmembrane protein Delta/Notch-like epidermal growth factor-related receptor; and insulinoma-associated protein 1. The putative testicular program was poorly characterized by elements of the immune response. The classic markers of maleness were not specifically activated, indicating that testicular differentiation occurs at a later stage. In sum, the ovarian program, but not the testicular program, is in place by 5-6 months of age in the Siberian sturgeon. The female program is characterized by estrogen-related genes with well-established roles in gonadal differentiation, but also by several genes with no previously-described function in the ovarian development of fish. These newly-reported genes are involved in stem-cell niche building and regulation as well as sex-specific nerve development.

Testis transcriptome alterations in zebrafish (Danio rerio) with reduced fertility due to developmental exposure to 17α-ethinyl estradiol

17α-Ethinylestradiol (EE₂) is a ubiquitous aquatic contaminant shown to decrease fish fertility at low concentrations, especially in fish exposed during development. The mechanisms of the decreased fertility are not fully understood. In this study, we perform transcriptome analysis by RNA sequencing of testes from zebrafish with previously reported lowered fertility due to exposure to low concentrations of EE₂ during development. Fish were exposed to 1.2 and 1.6 ng/L (measured concentration; nominal concentrations 3 and 10 ng/L) of EE₂ from fertilization to 80 days of age, followed by 82 days of remediation in clean water. RNA sequencing analysis revealed 249 and 16 genes to be differentially expressed after exposure to 1.2 and 1.6 ng/L, respectively; a larger inter-sample variation was noted in the latter. Expression of 11 genes were altered by both exposures and in the same direction. The coding sequences most affected could be categorized to the putative functions cell signalling, proteolysis, protein metabolic transport and lipid metabolic process. Several homeobox transcription factors involved in development and differentiation showed increased expression in response to EE₂ and differential expression of genes related to cell death, differentiation and proliferation was observed. In addition, several genes related to steroid synthesis, testis development and function were differentially expressed. A number of genes associated with spermatogenesis in zebrafish and/or mouse were also found to be differentially expressed. Further, differences in non-coding sequences were observed, among them several differentially expressed miRNA that might contribute to testis gene regulation at post-transcriptional level. This study has generated insights of changes in gene expression that accompany fertility alterations in zebrafish males that persist after developmental exposure to environmental relevant concentrations of EE₂ that persist followed by clean water to adulthood. Hopefully, this will generate hypotheses to test in search for mechanistic explanations.

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.

Molecular Analysis of the SRD5A1 and SRD5A2 Genes in Patients with Benign Prostatic Hyperplasia with Regard to Metabolic Parameters and Selected Hormone Levels

Introduction: The etiology of benign prostatic hyperplasia (BPH) has not so far been fully explicated. However, it is assumed that changes in the levels of hormones associated with aging can contribute to the development of prostatic hyperplasia. Dihydrotestosterone combines with the androgen receptor (AR) proteins of the prostate gland. Enzyme activity is based on two isoenzymes: type 1 and type 2. 5α-reductase type 1 is encoded by the SRD5A1 gene, and type 2 is encoded by the SRD5A2 gene. The aim of our study was to determine the frequency of the SRD5A1 (rs6884552, rs3797177) and SRD5A2 (rs523349, rs12470143) genes’ polymorphisms, and to assess the relationships between the genotypes of the tested mutations, and the levels of biochemical and hormonal parameters in patients with BPH. Material and Methods: The study involved 299 men with benign prostatic hyperplasia. We determined the serum levels of particular biochemical parameters—fasting plasma glucose (FPG), total cholesterol (TC), low-density lipoprotein (LDL), high-density lipoprotein (HDL) and triglycerides (TG)—by the spectrophotometric method, using ready reagent kits. The ELISA method was used to determine the levels of the following hormonal parameters and proteins: total testosterone (TT), free testosterone (FT), insulin (I), luteinizing hormone (LH), and sex hormone binding protein (SHBG). Metabolic syndrome was diagnosed. Genotyping was performed by real-time PCR. Results: We analyzed the relationships between the incidence of particular diseases and the genotypes of the SRD5A1 and SRD5A2 polymorphisms among patients with BPH. The BPH patients with the CC genotype of the SRD5A2 rs523349 and rs12470143 polymorphisms were considerably less frequently diagnosed with metabolic syndrome (MetS) (p = 0.022 and p = 0.023 respectively). Our analysis revealed that homozygotes with the CC of the SDR5A2 rs12470143 polymorphism had visibly higher HDL levels than those with the TT and CT genotypes (p = 0.001). Additionally, we found that the patients with the CC genotype of the SDR5A2 rs12470143 polymorphism had considerably higher FT levels (p = 0.001) than the heterozygotes with the CT and the homozygotes with the TT of the genetic variant analyzed in our study. Furthermore, the patients with at least one G allele of the SRD5A2 rs523349 polymorphism had significantly lower SGBG levels (p = 0.022) compared with the homozygotes with the CC genotype. The presence of at least one A allele (AA + AG genotypes) of the SRD5A1 rs3797177 polymorphism entailed notably lower serum insulin levels than those observed in homozygotes with the GG genotype (p = 0.033). Conclusions: The study described in this article shows that selected SRD5A1 and SRD5A2 polymorphisms can alter the levels of metabolic and hormonal parameters in patients with BPH. Special attention should be paid to the SDR5A2 rs12470143 polymorphism, which is associated with a change in lipid profile, as well as with the inheritance and incidence rate of MetS among these patients. An analysis of the frequency of this polymorphism among BPH patients could be useful in estimating the risk of getting ill, and planning therapies of concomitant diseases for BPH patients.

Sex steroids differentially regulate fshb, lhb and gnrhr expression in Atlantic cod (Gadus morhua)

Depending on the stage of gonad maturation, as well as other factors, gonadal steroids can exert either a positive or negative feedback at the brain and pituitary level. While this has been demonstrated in many teleost species, little is known about the nature of steroid feedback in Gadiform fish. Using an optimized in vitro model system of the Atlantic cod pituitary, the present study investigated the potential effects of two physiologically relevant doses of estradiol, testosterone (TS) or dihydrotestosterone (DHTS) on cell viability and gene expression of gonadotropin subunits (fshb/lhb) and two suggested reproduction-relevant gonadotropin-releasing hormone receptors (gnrhr1b/gnrhr2a) during three stages of sexual maturity. In general, all steroids stimulated cell viability in terms of metabolic activity and membrane integrity. Furthermore, all steroids affected fshb expression, with the effect depending on both the specific steroid, dose and maturity status. Conversely, only DHTS exposure affected lhb levels, and this occurred only during the spawning season. Using single-cell qPCR, co-transcription of gnrhr1b and gnrhr2a was confirmed to both fshb- and lhb- expressing gonadotropes, with gnrhr2a being the most prominently expressed isoform. While steroid exposure had no effect on gnrhr1b expression, all steroids affected gnrhr2a transcript levels in at least one maturity stage. These and previous results from our group point to Gnrhr2a as the main modulator of gonadotropin regulation in cod and that regulation of its gene expression level might function as a direct mechanism for steroid feedback at the pituitary level.

Responses of gonadal transcriptome and physiological analysis following exposure to 17α-ethynylestradiol in adult rare minnow Gobiocypris rarus

17α-ethynylestradiol (EE2), a synthetic estrogen commonly used in the oral contraceptive pills, disrupts the sexual differentiation, gonadal development and reproduction in aquatic species. Nowadays aquatic species and even humans still have the potential risks of exposure to EE2. However, the mechanism of EE2 endocrine disruption is still unclear. Aiming to elucidate molecular mechanisms, we analyzed transcriptome profiling of gonads, gonadal histology and the sex steroid hormones in response to EE2 in G. rarus. Through this study, we obtained eight RNA-Seq libraries upon EE2 exposure, and found some key genes and pathways in correlation with the disruption effects of EE2. We found EE2 could disrupt oocyte development and spermatogenesis in adult G. rarus, and EE2 has more obvious disruption effects on male G. rarus than females. Interestingly, EE2 was indicated to be an exogenous DPC-inducing agent and ppp2r3b was suggested to be a spermatogenesis candidate gene in rare minnow. The differential gene expressions of rps30, samp9, ppp2r3b and spartan upon EE2 exposure suggest EE2's disruption effects on gonads could attribute to altered pathways of translation, ribosome biogenesis and cell division.

Non-canonical expression patterns and evolutionary rates of sex-biased genes in a seasonal fish

Sex determination is a highly variable process that utilizes many different mechanisms to initiate the cascade of differentiation processes. The molecular pathways controlling sexual development are less conserved than previously assumed, and appear to require active maintenance in some species; indeed, the developmental decision of gonad phenotype in gonochoristic species is not fixed at an early developmental stage. Much of the knowledge about sex determination mechanisms was derived from research on gonochoristic, non-seasonal breeders. In this study, the transcriptome of resting adult gonads of a seasonal breeder, the endangered Iberian cyprinid fish Squalius pyrenaicus, was analyzed to assess the expression patterns and evolutionary rates of sex-biased genes that could be involved in maintenance of gonad identity as well as in sex determination. Remarkably, some crucial female genes-such as aromatase cyp19a1a, estrogen receptor esr1a, and foxl2-were expressed more abundantly in S. pyrenaicus testis than in ovaries. Moreover, contrary to the higher evolutionary rate changes observed in male-biased genes, higher d_N /d_S ratios were observed for female-biased genes than for male-biased genes in S. pyrenaicus. These results help unravel the impact of seasonality in sex determination mechanisms and the evolution of genes, and highlight the need to study fish at different gonadal maturation states to understand the function of sex-biased genes. Mol. Reprod. Dev. 83: 1102-1115, 2016. © 2016 Wiley Periodicals, Inc.

Metabolite profiles of repeatedly sampled urine from male fathead minnows (Pimephales promelas) contain unique lipid signatures following exposure to anti-androgens

The purpose of this study was twofold. First, we sought to identify candidate markers of exposure to anti-androgens by analyzing endogenous metabolite profiles in the urine of male fathead minnows (mFHM, Pimephales promelas). Based on earlier work, we hypothesized that unidentified lipids in the urine of mFHM were selectively responsive to exposure to androgen receptor antagonists, which is otherwise difficult to confirm using established fish toxicity assays. A second goal was to evaluate the feasibility of non-lethally and repeatedly sampling urine from individual mFHMs over the time course of response to a chemical exposure. Accordingly, we exposed mFHM to the model anti-androgens vinclozolin or flutamide. Urine was collected from each fish at 48hour intervals over the course of a 14day exposure. Parallel experiments were conducted with mFHM exposed to bisphenol A or control water. The frequent handling/sampling regime did not cause apparent adverse effects on the fish. Endogenous metabolite profiling was conducted with gas chromatography-mass spectrometry (GC-MS), which exhibited lower variation for the urinary metabolome than was found in earlier work with nuclear magnetic resonance (NMR) spectroscopy. Specifically, for inter- and intra-individual variations, the median spectrum-wide relative standard deviation (RSD) was 32.6% and 33.3%, respectively, for GC-MS analysis of urine from unexposed mFHM. These results compared favorably with similar measurements of urine from other model species, including the Sprague Dawley rat. In addition, GC-MS allowed us to identify several lipids (e.g., certain saturated fatty acids) in mFHM urine as candidate markers of exposure to androgen receptor antagonists.

Transcriptional networks associated with 5-alpha-dihydrotestosterone in the fathead minnow (Pimephales promelas) ovary

Androgens play a significant role in regulating oogenesis in teleost fishes. The androgen dihydrotestosterone (DHT) is a potent non-aromatizable androgen involved in sexual differentiation in mammals; however, its actions are not well understood in teleost fish. To better characterize the physiological role of DHT in the fathead minnow (FHM) ovary on a temporal scale, in vitro assays for 17β-estradiol (E2) production were conducted in parallel with microarray analysis. Ovarian explants were incubated at different concentrations of DHT (10(-6), 10(-7), and 10(-8)M DHT) in three separate experiments conducted at 6, 9, and 12h. DHT treatment resulted in a rapid and consistent increase in E2 production from the ovary at all three time points. Therefore, DHT may act to shift the balance of metabolites in the steroidogenic pathway within the ovary. Major biological themes affected by DHT in the ovary in one or more of the time points included those related to blood (e.g. vasodilation, blood vessel contraction, clotting), lipids (e.g. lipid storage, cholesterol metabolism, lipid degradation) and reproduction (e.g. hormone and steroid metabolism). Gene networks related to immune responses and calcium signaling were also affected by DHT, suggesting that this androgen may play a role in regulating these processes in the ovary. This study detected no change in mRNA levels of steroidogenic enzymes (cyp19a1, star, 11βhsd, 17βhsd, srd5a isoforms), suggesting that the observed increase in E2 production is likely more dependent on the pre-existing gene or protein complement in the ovary rather than the de novo expression of transcripts. This study increases knowledge regarding the roles of DHT and androgens in general in the teleost ovary and identifies molecular signaling pathways that may be associated with increased E2 production.

Identification of Putative Nuclear Receptors and Steroidogenic Enzymes in Murray-Darling Rainbowfish (Melanotaenia fluviatilis) Using RNA-Seq and De Novo Transcriptome Assembly

Murray-Darling rainbowfish (Melanotaenia fluviatilis [Castelnau, 1878]; Atheriniformes: Melanotaeniidae) is a small-bodied teleost currently under development in Australasia as a test species for aquatic toxicological studies. To date, efforts towards the development of molecular biomarkers of contaminant exposure have been hindered by the lack of available sequence data. To address this, we sequenced messenger RNA from brain, liver and gonads of mature male and female fish and generated a high-quality draft transcriptome using a de novo assembly approach. 149,742 clusters of putative transcripts were obtained, encompassing 43,841 non-redundant protein-coding regions. Deduced amino acid sequences were annotated by functional inference based on similarity with sequences from manually curated protein sequence databases. The draft assembly contained protein-coding regions homologous to 95.7% of the complete cohort of predicted proteins from the taxonomically related species, Oryzias latipes (Japanese medaka). The mean length of rainbowfish protein-coding sequences relative to their medaka homologues was 92.1%, indicating that despite the limited number of tissues sampled a large proportion of the total expected number of protein-coding genes was captured in the study. Because of our interest in the effects of environmental contaminants on endocrine pathways, we manually curated subsets of coding regions for putative nuclear receptors and steroidogenic enzymes in the rainbowfish transcriptome, revealing 61 candidate nuclear receptors encompassing all known subfamilies, and 41 putative steroidogenic enzymes representing all major steroidogenic enzymes occurring in teleosts. The transcriptome presented here will be a valuable resource for researchers interested in biomarker development, protein structure and function, and contaminant-response genomics in Murray-Darling rainbowfish.

Leveraging existing data for prioritization of the ecological risks of human and veterinary pharmaceuticals to aquatic organisms

Medicinal innovation has led to the discovery and use of thousands of human and veterinary drugs. With this comes the potential for unintended effects on non-target organisms exposed to pharmaceuticals inevitably entering the environment. The impracticality of generating whole-organism chronic toxicity data representative of all species in the environment has necessitated prioritization of drugs for focused empirical testing as well as field monitoring. Current prioritization strategies typically emphasize likelihood for exposure (i.e. predicted/measured environmental concentrations), while incorporating only rather limited consideration of potential effects of the drug to non-target organisms. However, substantial mammalian pharmacokinetic and mechanism/mode of action (MOA) data are produced during drug development to understand drug target specificity and efficacy for intended consumers. An integrated prioritization strategy for assessing risks of human and veterinary drugs would leverage available pharmacokinetic and toxicokinetic data for evaluation of the potential for adverse effects to non-target organisms. In this reiview, we demonstrate the utility of read-across approaches to leverage mammalian absorption, distribution, metabolism and elimination data; analyse cross-species molecular target conservation and translate therapeutic MOA to an adverse outcome pathway(s) relevant to aquatic organisms as a means to inform prioritization of drugs for focused toxicity testing and environmental monitoring.

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.

The effects of model androgen 5α-dihydrotestosterone on mummichog (Fundulus heteroclitus) reproduction under different salinities

Endocrine disrupting substances (EDSs) have the potential to disturb sensitive hormone pathways, particularly those involved in development and reproduction. Both fresh and estuarine water bodies receive inputs of EDSs from a variety of sources, including sewage effluent, industrial effluent and agricultural runoff. Based on current literature, freshwater species appear to respond to lower levels of EDSs than estuarine or marine species. Therefore, effects elicited by EDSs in freshwater teleosts may not be an accurate representation of how EDSs affect teleosts in estuarine and marine environments. To address this potential difference, a short-term reproductive bioassay was conducted under conditions of low and high salinity using mummichog (Fundulus heteroclitus), a euryhaline species that is native to the east coast of North America. The goals of this study were to determine the response of mummichog when exposed to an androgenic EDS and whether salinity affected the response. A model androgen, 5α-dihydrotestosterone (DHT), was selected for this experiment. Impacts on reproduction were evaluated at multiple biological levels, including physiological (sex steroid levels), organismal (gonad size and gonad morphology), and functional (egg production) endpoints. Under conditions of high salinity, egg production was significantly reduced at all exposure concentrations. Under conditions of low salinity, there were no significant differences based on DHT treatment; however, egg production in all treatment groups including the control were significantly reduced relative to the high salinity control group. Other reproductive endpoints, such as sex steroid production, showed stronger correlation to fecundity in females than males. This study demonstrates that mummichog fecundity is sensitive to androgenic endocrine disruption while also underscoring the importance of how changes in salinity, an environmental variable, can impact reproduction.

Evaluation of the 5α-reductase inhibitor finasteride on reproduction and gonadal development in medaka, Oryzias latipes

5-α reductase (5αR) inhibitors have an anti-androgenic effect in mammals because they inhibit the conversion of testosterone to the potent androgen, dihydrotestosterone. Finasteride is a type-2 5αR inhibitor that is used as a human pharmaceutical for the treatment of prostate cancer, benign prostate hyperplasia and male pattern baldness. This study evaluated the impacts of finasteride (50, 500 and 5000μg/L) on the development and reproduction of medaka (Oryzias latipes) exposed continuously over multiple generations (F0, F1 and F2). The exposure was initiated with reproductively mature fish (F0 generation) and continued until the hatching of the F2 generation. There were no significant effects on survival, fecundity or fertility in the F0 (50, 500, 5000μg/L) and F1 (50, 500μg/L) generations. The F1 generation exposed to 5000μg/L exhibited significant mortality. Histopathology of the gonads demonstrated that medaka and pre-clinical species respond similarly to finasteride exposure. Intersex condition and maldeveloped gonads were observed in F0 generation males exposed to 5000μg/L and F1 generation males exposed to 500μg/L. F1 generation males exposed to 500μg/L displayed reduced gonadosomatic index with an increased incidence of testicular degeneration. Males in both generations exhibited an increased incidence of Leydig cell hyperplasia at concentrations ⩾500μg/L. F0 generation females exposed to 5000μg/L exhibited increased gonadosomatic index. An increased prevalence of accelerated post-ovulatory follicle involution was observed in females at concentrations ⩾500μg/L in both generations. The gonadal changes induced by finasteride support the idea that 5-α reductase inhibition impacts androgen signaling in fish. Results from this study are discussed in the context of differential expression of the androgen receptor between species of fish.

Food, stress, and circulating testosterone: Cue integration by the testes, not the brain, in male zebra finches (Taeniopygia guttata)

Food abundance is closely associated with reproductive readiness in vertebrates. Food scarcity can activate the hypothalamo-pituitary-adrenal axis, decrease sex steroid secretion, and dampen reproductive behavior. However, the mechanisms underlying these transient effects are unclear. Gonadotropin inhibitory hormone (GnIH), a neuropeptide present in the brain and gonads, is also influenced by glucocorticoids and fasting in some species. We investigated whether fasting stress activated the GnIH system in zebra finches (Taeniopygia guttata), with the potential for downstream effects on reproductive physiology and behavior. We fasted or fed males ad libitum for 10h. Fasting increased corticosterone and decreased testosterone in circulation. To assess whether the decrease in testosterone was mediated by changes in the hypothalamus and/or the gonads, we (1) quantified GnRH- and GnIH-positive neurons in the hypothalamus, (2) assessed hypothalamic gene expression for GnRH and GnIH, and (3) examined gene expression for proteins involved in testosterone synthesis in fasted and control birds. No measure of hypothalamic neuropeptides was related to treatment or circulating steroids. However, birds with higher corticosterone had higher testicular GnIH expression and lower testosterone. StAR and LHR expression were lower in the testes of fasted birds than controls. Thus, the decrease in testosterone was not likely mediated by hypothalamic GnIH, but rather by direct actions of fasting and/or corticosterone on the testes, indicating that the testes can integrate and respond to cues of stress directly. Such local inhibition of testosterone synthesis may allow for rapid and reversible changes in physiology and behavior when conditions are inappropriate for breeding.

Characterization of the annual regulation of reproductive and immune parameters on the testis of European sea bass

The European sea bass, Dicentrarchus labrax L., is a seasonal gonochoristic species, the males of which are generally mature during their second year of life. It has been demonstrated that cytokines and immune cells play a key role in the testicular development. This reproductive-immune interaction might be very important in the sea bass since several pathogens are able to colonise the gonad and persist in this tissue, altering further reproductive functions and spreading disease. This study aims to investigate the reproductive cycle of 1-year European sea bass males by analysing cell proliferation and apoptosis and the expression profile of some reproductive and immune-related genes in the testis, as well as the serum sex steroid levels. Our data demonstrate that, in 1-year-old European sea bass males, the testis undergoes the spermatogenesis process and that the reproductive and immune parameters analysed varied during the reproductive cycle. In the testis, the highest proliferative rates were recorded at the spermatogenesis stage, while the highest apoptotic rates were recorded at the spawning stage. We have also analysed, for the first time in European sea bass males, the serum levels of 17β-estradiol (E2) and dihydrotestosterone and the gene expression profile of the enzymes implied in their production, determining that at least E2 might be involved in the regulation of the reproductive cycle. Some immune relevant genes, including cytokines, lymphocyte receptors, and anti-viral and anti-bacterial molecules were detected in the testis of naïve European sea bass specimens, and their expression profile was related to the stages of the reproductive cycle, suggesting an important role for the defence of the reproductive tissues.

Differential ligand selectivity of androgen receptors α and β from Murray-Darling rainbowfish (Melanotaenia fluviatilis)

Androgen receptors (ARs) mediate the physiological effects of androgens in vertebrates. In fishes, AR-mediated pathways can be modulated by aquatic contaminants, resulting in the masculinisation of female fish or diminished secondary sex characteristics in males. The Murray-Darling rainbowfish (Melanotaenia fluviatilis) is a small-bodied freshwater teleost used in Australia as a test species for environmental toxicology research. We determined concentration-response profiles for selected agonists and antagonists of rainbowfish ARα and ARβ using transient transactivation assays. For both ARα and ARβ, the order of potency of natural agonists was 11-ketotestosterone (11-KT)>5α-dihydrotestosterone>testosterone>androstenedione. Methyltestosterone was a highly potent agonist of both receptors relative to 11-KT. The relative potency of the veterinary growth-promoting androgen, 17β-trenbolone, varied by more than a factor of 5 between ARα and ARβ. The non-steroidal anti-androgen bicalutamide exhibited high inhibitory potency relative to the structurally related model anti-androgen, flutamide. The inhibitory potency of the agricultural fungicide, vinclozolin, was approximately 1.7-fold relative to flutamide for ARα, but over 20-fold in the case of ARβ. Fluorescent protein tagging of ARs showed that the rainbowfish ARα subtype is constitutively localised to the nucleus, while ARβ is cytoplasmic in the absence of ligand, an observation which agrees with the reported subcellular localisation of AR subtypes from other teleost species. Collectively, these data suggest that M. fluviatilis ARα and ARβ respond differently to environmental AR modulators and that in vivo sensitivity to contaminants may depend on the tissue distribution of the AR subtypes at the time of exposure.

Effects of 5α-dihydrotestosterone on expression of genes related to steroidogenesis and spermatogenesis during the sex determination and differentiation periods of the pejerrey, Odontesthes bonariensis

Sex steroid hormones are important players in the control of sex differentiation by regulating gonadal development in teleosts. Although estrogens are clearly associated with the ovarian differentiation in teleosts, the effects of androgens on early gonadal development are still a matter of debate. Traditionally, 11-ketotestosterone (11-KT) is considered the major androgen in fish; however, 5α-dihydrotestosterone (5α-DHT), the most potent androgen in tetrapods, was recently found in fish testis and plasma, but its physiological role is still unknown. In this context, the expression of genes associated with steroidogenesis and spermatogenesis, body growth and sex differentiation were assessed in Odontesthes bonariensis larvae fed with food supplemented with two doses of 5α-DHT (0.1 and 10μg/g of food) from hatching to 6weeks of age. At the lowest dose, 5α-DHT treated larvae showed an estrogenic gene expression pattern, with low hsd11b2 and high cyp19a1a and er2 expression levels with no differences in sex ratio. At the highest dose, 5α-DHT produced a male-shifted sex ratio and the larvae exhibited a gene expression profile characteristic of an advancement of spermatogenesis, with inhibition of amh and stimulation of ndrg3. No differences were observed in somatic growth. These results suggest that in this species, 5α-DHT could have a role on sex differentiation and its effects can differ according to the dose.

Mechanisms of crosstalk between endocrine systems: regulation of sex steroid hormone synthesis and action by thyroid hormones

Thyroid hormones (THs) are well-known regulators of development and metabolism in vertebrates. There is increasing evidence that THs are also involved in gonadal differentiation and reproductive function. Changes in TH status affect sex ratios in developing fish and frogs and reproduction (e.g., fertility), hormone levels, and gonad morphology in adults of species of different vertebrates. In this review, we have summarized and compared the evidence for cross-talk between the steroid hormone and thyroid axes and present a comparative model. We gave special attention to TH regulation of sex steroid synthesis and action in both the brain and gonad, since these are important for gonad development and brain sexual differentiation and have been studied in many species. We also reviewed research showing that there is a TH system, including receptors and enzymes, in the brains and gonads in developing and adult vertebrates. Our analysis shows that THs influences sex steroid hormone synthesis in vertebrates, ranging from fish to pigs. This concept of crosstalk and conserved hormone interaction has implications for our understanding of the role of THs in reproduction, and how these processes may be dysregulated by environmental endocrine disruptors.

Transcriptomics profiling and steroid production in mummichog (Fundulus heteroclitus) testes after treatment with 5α-dihydrotestosterone

5α-Dihydrotestosterone (DHT) is a potent androgen in mammals with multiple roles; however the physiological actions of DHT in male fishes are not well known. To address this knowledge gap, male mummichog (Fundulus heteroclitus) were continuously exposed to 0, 5, and 50 μg/L DHT for 21 days. Following exposure, testes were separated for histology, ex vivo incubation to measure steroidogenic capacity, and gene expression analyses (real-time PCR and microarray). DHT significantly decreased ex vivo 11-ketotestosterone (11KT) production in males exposed to 50 μg/L DHT but not 5 μg/L DHT, and DHT exposure did not affect ex vivo testosterone production. Histological examination revealed that the amount of interlobular and connective tissue present in the testes was increased in the 50 μg/L DHT treatment. Despite reductions in the production of 11KT, DHT did not affect the expression of targeted genes in the steroidogenic pathway such as steroidogenic acute regulatory protein (star), P450 side chain cleavage (cyp11a1) and 11β-hydroxysteroid dehydrogenase (hsd11b3). Microarray analysis in the testes of individuals from control and 50 μg/L DHT revealed that males exposed to 50 μg/L DHT showed regulated transcriptional sub-networks that were related to immunity, regulation of blood flow, lipids and xenobiotic clearance, suggesting that DHT may be involved in the physiological regulation of these processes in the fish testes. A second objective of this study was to determine the feasibility of measuring mRNA levels in tissues used for ex vivo steroid production by comparing RNA integrity and transcript levels in testes of both immediately flash frozen tissue and incubated tissue. There was no significant difference in RNA quality between the two time points, indicating RNA integrity can remain intact for at least 18 h in ex vivo assays, thereby providing a viable option for researchers assessing multi-level biological reproductive endpoints when limited tissue is available. While the gene expression levels of actb, efla, rps12, rps18, star, and hsd11b3 remained unchanged, esr2a (esrba), esr2b (esrbb) and cyp11a1 were significantly lower in incubated tissue compared to flash frozen tissue. Therefore caution must be used as the steady-state levels of select genes may change over time. This study improves our understanding of DHT action in the teleostean testis and generates new hypotheses regarding cell processes that are regulated by this underexplored and potent androgen.

Transcriptomic profiling in Silurana tropicalis testes exposed to finasteride

Investigations of endocrine disrupting chemicals found in aquatic ecosystems with estrogenic and androgenic modes of action have increased over the past two decades due to a surge of evidence of adverse effects in wildlife. Chemicals that disrupt androgen signalling and steroidogenesis can result in an imbalanced conversion of testosterone (T) into 17β-estradiol (E2) and other androgens such as 5α-dihydrotestosterone (5α-DHT). Therefore, a better understanding of how chemicals perturb these pathways is warranted. In this study, the brain, liver, and testes of Silurana tropicalis were exposed ex vivo to the human drug finasteride, a potent steroid 5α-reductase inhibitor and a model compound to study the inhibition of the conversion of T into 5α-DHT. These experiments were conducted (1) to determine organ specific changes in sex steroid production after treatment, and (2) to elucidate the transcriptomic response to finasteride in testicular tissue. Enzyme-linked immunosorbent assays were used to measure hormone levels in media following finasteride incubation for 6 h. Finasteride significantly increased T levels in the media of liver and testis tissue, but did not induce any changes in E2 and 5α-DHT production. Gene expression analysis was performed in frog testes and data revealed that finasteride treatment significantly altered 1,434 gene probes. Gene networks associated with male reproduction such as meiosis, hormone biosynthesis, sperm entry, gonadotropin releasing hormone were affected by finasteride exposure as well as other pathways such as oxysterol synthesis, apoptosis, and epigenetic regulation. For example, this study suggests that the mode of action by which finasteride induces cellular damage in testicular tissue as reported by others, is via oxidative stress in testes. This data also suggests that 5-reductase inhibition disrupts the expression of genes related to reproduction. It is proposed that androgen-disrupting chemicals may mediate their action via 5-reductases and that the effects of environmental pollutants are not limited to the androgen receptor signalling.

Reporter cell lines are useful tools for monitoring biological activity of nuclear receptor ligands

To characterize the specificity of synthetic compounds for nuclear receptors, we established stable cell lines expressing the luciferase gene and different wild-type or chimaeric receptors. MCF-7 cells, which express the oestrogen receptor alpha (ER alpha), and HeLa cells, which do not express the oestrogen receptor, were transfected with a plasmid containing the luciferase gene downstream from a minimum promoter (beta-globin) and an oestrogen-responsive element, generating the MELN and the HELN cell lines, respectively. MELN cells enabled the detection of compounds that bind to the ER alpha or interfere with its pathway. HELN cells were used to establish stable transfectants expressing different nuclear receptors containing the DNA-binding domain of the oestrogen receptors. We thus established ER alpha or ER beta reporter cell lines by transfecting ER alpha or ER beta expression plasmids, and also retinoic acid receptor alpha, beta or gamma reporter cell lines by transfecting the chimaeric RAR gene, in which the DNA-binding domain was replaced by the ER alpha DNA-binding domain.