Two distinct isoforms of cDNA encoding rainbow trout androgen receptors

Human and fish differences in steroid receptors activation: A review

Steroid receptors (SRs) are transcription factors activated by steroid hormones (SHs) that belong to the nuclear receptors (NRs) superfamily. Several studies have shown that SRs are targets of endocrine disrupting chemicals (EDCs), widespread substances in the environment capable of interfering with the endogenous hormonal pathways and causing adverse health effects in living organisms and/or their progeny. Cell lines with SRs reporter gene are currently used for in vitro screening of large quantities of chemicals with suspected endocrine-disrupting activities. However, most of these cell lines express human SRs and therefore the toxicological data obtained are also extrapolated to non-mammalian species. In parallel, in vivo tests have recently been developed on fish species whose data are also extrapolated to mammalian species. As some species-specific differences in SRs activation by natural and synthetic chemicals have been recently reported, the aim of this review is to summarize those between human and fish SRs, as representatives of mammalian and non-mammalian toxicology, respectively. Overall, this literature study aims to improve inter-species extrapolation of toxicological data on EDCs and to understand which reporter gene cell lines expressing human SRs are relevant for the assessment of effects in fish and whether in vivo tests on fish can be properly used in the assessment of adverse effects on human health.

A phylogenetics-based nomenclature system for steroid receptors in teleost fishes

Teleost fishes have emerged as tractable models for studying the neuroendocrine regulation of social behavior via molecular genetic techniques, such as CRISPR/Cas9 gene editing. Moreover, teleosts provide an opportunity to investigate the evolution of steroid receptors and their functions, as species within this lineage possess novel steroid receptor paralogs that resulted from a teleost-specific whole genome duplication. Although teleost fishes have grown in popularity as models for behavioral neuroendocrinology, there is not a consistent nomenclature system for steroid receptors and their genes, which may impede a clear understanding of steroid receptor paralogs and their functions. Here, we used a phylogenetic approach to assess the relatedness of protein sequences encoding steroid receptor paralogs in 18 species from 12 different orders of the Infraclass Teleostei. While most similarly named sequences grouped based on the established phylogeny of the teleost lineage, our analysis revealed several inconsistencies in the nomenclature of steroid receptor paralogs, particularly for sequences encoding estrogen receptor beta (ERβ). Based on our results, we propose a nomenclature system for teleosts in which Greek symbols refer to proteins and numbers refer to genes encoding different subtypes of steroid receptors within the five major groups of this nuclear receptor subfamily. Collectively, our results bridge a critical gap by providing a cohesive naming system for steroid receptors in teleost fishes, which will serve to improve communication, promote collaboration, and enhance our understanding of the evolution and function of steroid receptors across vertebrates.

Gene Duplication of Androgen Receptor As An Evolutionary Driving Force Underlying the Diversity of Sexual Characteristics in Teleost Fishes

Sexual dimorphism allows species to meet their fitness optima based on the physiological availability of each sex. Although intralocus sexual conflict appears to be a genetic constraint for the evolution of sex-specific traits, sex-linked genes and the regulation of sex steroid hormones contribute to resolving this conflict by allowing sex-specific developments. Androgens and their receptor, androgen receptor (Ar), regulate male-biased phenotypes. In teleost fish, ar ohnologs have emerged as a result of teleost-specific whole genome duplication (TSGD). Recent studies have highlighted the evolutionary differentiation of ar ohnologs responsible for the development of sexual characteristics, which sheds light on the need for comparative studies on androgen regulation among different species. In this review, we discuss the importance of ar signaling as a regulator of male-specific traits in teleost species because teleost species are suitable experimental models for comparative studies owing to their great diversity in male-biased morphological and physiological traits. To date, both in vivo and in vitro studies on teleost ar ohnologs have shown a substantial influence of ars as a regulator of male-specific reproductive traits such as fin elongation, courtship behavior, and nuptial coloration. In addition to these sexual characteristics, ar substantially influences immunity, inducing a sex-biased immune response. This review aims to provide a comprehensive understanding of the current state of teleost ar studies and emphasizes the potential of teleost fishes, given their availability, to find molecular evidence about what gives rise to the spectacular diversity among fish species.

Developmental regulation of the male urogenital papilla in the male marine teleost black rockfish, Sebastes schlegelii (Hilgendorf, 1880)†

The male external genitalia of the black rockfish (Sebastes schlegelii Hilgendorf, 1880) is a fleshy protrusion known as the urogenital papilla (UGP), which functions to deliver sperm into the female reproductive tract for internal fertilization. It is not known which genes regulate the development of the UGP. The aim of this study was to identify key genes that regulate the development of the UGP in black rockfish and to determine the distribution of androgen receptor gene (ar) in the UGP. A total of 26 adult males and 560 juvenile fish were used in the experiment, in which we divided all normally developing juveniles into normal development and androgen groups. We added methyltestosterone solution (100 μg/l) to the androgen group-treated fish tank, soaked for 2 h per day for 38 days, and sampled 5~10 samples each time every 5 days during the culture process. Gene expression changes related to UGP were analyzed with tissue specificity between control and androgen groups during sex differentiation, adult male maturation, and the copulation stage (September to December) using real-time quantitative polymerase chain reaction. The expression of ar was also localized by two-color in situ hybridization in the UGP region of juvenile fish. Androgen treatment enhanced ar expression levels and the ar signal was stronger in the UGP region of both adult breeding fish and androgen-treated juvenile fish. This study provides insights into the regulation of the external genitalia of black rockfish and presents vital information for the artificial breeding of viviparous fish.

Detection of anti-androgenic activity of chemicals in fish studies: a data review

A systematic review was conducted on the sensitivity of fish testing guidelines to detect the anti-androgenic activity of substances. Sequence Alignment to Predict Across Species Susceptibility (SeqAPASS) was used to investigate the conservation of the androgen receptor (AR) between humans and fish, and among fish species recommended in test guidelines. The AR is conserved between fish species and humans (i.e. ligand binding domain [LBD] homology ≥70%) and among the recommended fish species (LBD homology >85%). For model anti-androgens, we evaluated literature data on in vitro anti-androgenic activity in fish-specific receptor-based assays and changes in endpoints indicative of endocrine modulation from in vivo studies. Anti-androgenic activity was most consistently and reliably detected in in vitro and in vivo mechanistic studies with co-exposure to an androgen (spiggin in vitro assay, Rapid Androgen Disruption Activity Reporter [RADAR] Assay, and Androgenised Female Stickleback Screen). Regardless of study design (Fish Short-Term Reproduction Assay [FSTRA], Fish Sexual Development Test [FSDT], partial or full life-cycle tests), or endpoint (vitellogenin, secondary sexual characteristics, gonadal histopathology, sex ratio), there was no consistent evidence for detecting anti-androgenic activity in studies without androgen co-exposure, even for the most potent substances (while less potent substances may induce no (clear) response). Therefore, based on studies without androgen co-exposure (35 FSTRAs and 22 other studies), the other studies (including the FSDT) do not outperform the FSTRA for detecting potent anti-androgenic activity, which if suspected, would be best addressed with a RADAR assay. Overall, fish do not appear particularly sensitive to mammalian anti-androgens.

Genetic dissection of steroid-hormone modulated social behavior: Novel paralogous genes are a boon for discovery

Research across species has led to important discoveries on the functions of steroid hormones in the regulation of behavior. However, like in many fields, advancements in transgenic and mutagenic technology allowed mice to become the premier genetic model for conducting many experiments to understand how steroids control social behavior. Since there has been a general lack of parallel methodological developments in other species, many of the findings cannot be generalized. This is especially the case for teleost fish, in which a whole-genome duplication produced novel paralogs for key steroid hormone signaling genes. In this review, we summarize technical advancements over the history of the field of neuroendocrinology that have led to important insights in our understanding of the control of social behavior by steroids. We demonstrate that early mouse genetic models to understand these mechanisms suffered from several issues that were remedied by more precise transgenic technological advancements. We then highlight the importance of CRISPR/Cas9 gene editing tools that will in time bridge the gap between mice and non-traditional model species for understanding principles of steroid hormone action in the modulation of social behavior. We specifically highlight the role of teleost fish in bridging this gap because they are 1) highly genetically tractable and 2) provide a novel advantage in achieving precise genetic control. The field of neuroendocrinology is entering a new "gene editing revolution" that will lead to novel discoveries about the roles of steroid hormones in the regulation and evolutionary trajectories of social behavior.

Role of sex steroids in fish sex determination and differentiation as revealed by gene editing

The involvement of sex steroids in sex determination and differentiation is relatively conserved among non-mammalian vertebrates, especially in fish. Thanks to the advances in genome sequencing and genome editing, significant progresses have been made in the understanding of steroidogenic pathway and hormonal regulation of sex determination and differentiation in fish. It seems that loss of function study of single gene challenges the traditional views that estrogen is required for ovarian differentiation and androgen is needed for testicular development, but it is not so in essence. Steroidogenic enzymes can be classified into two categories based on expression and enzyme activities in fish. One type, encoded by star2, cyp17a1 and cyp19a1a, is involved in estrogen production and exclusively expressed in the gonads. Mutation of these genes results in the up-regulation of male pathway genes and sex reversal from genetic female to male. The other type, encoded by the duplicated paralogs of the above genes, including star1, cyp11a1, cyp17a2 and cyp19a1b, as well as cyp11c1 gene, is dominantly expressed both in gonads and extra-gonadal tissues. Mutation of these genes alters the steroids (androgen, DHP and cortisol) production and spermatogenesis, fertility, secondary sexual characteristics and sexual behavior, but usually does not affect the sex differentiation. For the estrogen receptors (esr1, esr2a and esr2b), single mutation failed to, but double and triple mutation leads to sex reversal from female to male, indicating that at least Esr2a and Esr2b are required to mediate the role of estrogen in sex determination proved by gene editing experiments. Taken together, results from gene editing enrich our understanding of steroid synthesis pathways and further confirm the critical role of estrogen in female sex determination by antagonizing the male pathway in fish.

Control of testes mass by androgen receptor paralogs in a cichlid

Steroid hormones play numerous important and diverse roles in the differentiation and development of vertebrate primary and secondary reproductive characteristics. However, the exact role of androgen receptors-which bind circulating androgens-in this regulatory pathway is unclear. Teleost fishes further complicate this question by having two paralogs of the androgen receptor (ARα and ARβ) resulting from a duplication of their ancestral genome. We investigated the functional role of these two ARs on adult testes mass, by eliminating receptor function of one or both paralogs using CRISPR/Cas9 genome edited Astatotilapia burtoni, an African cichlid fish. Fish with two or more functional AR alleles were more likely to be male compared to fish with one or fewer, suggesting that the two paralogs may play redundant roles in the A. burtoni sex determination system. We replicated previous work showing that fish lacking functional ARβ possess testes smaller than wild-type fish, while fish lacking ARα possess testes larger than wild-type fish. However, we found novel evidence supporting a complex relationship between the two AR paralogs in the regulation of testes mass. For instance, the effects of ARα mutation on testes mass are eliminated in homozygous ARβ mutants but the reverse is not true. These results suggest a dynamic relationship between these two AR paralogs where ARβ functions may be permissive to ARα functions in the control of testes mass. This mechanism may contribute to the robust physiological plasticity displayed by A. burtoni and other social teleost fishes.

Salinity-dependent expression of calcium-sensing receptors in Atlantic salmon (Salmo salar) tissues

Multiple reports suggest that calcium-sensing receptors (CaSRs) are involved in calcium homeostasis, osmoregulation, and/or salinity sensing in fish (Loretz 2008, Herberger and Loretz 2013). We have isolated three unique full-length CaSR cDNAs from Atlantic salmon (Salmo salar) kidney that share many features with other reported CaSRs. Using anti-CaSR antibodies and PCR primers specific for individual salmon CaSR transcripts we show expression in osmoregulatory, neuroendocrine and sensory tissues. Furthermore, CaSRs are expressed in different patterns in salmon tissues where mRNA and protein expression are modified by freshwater or seawater acclimation. For example, in seawater, CaSR mRNA and protein expression is increased significantly in kidney as compared to freshwater. Electrophysiological recordings of olfactory responses produced upon exposure of salmon olfactory epithelium to CaSR agonists suggest a role for CaSRs in chemoreception in this species consistent with other freshwater, anadromous, and marine species where similar olfactory responses to divalent and polyvalent cations have been reported. These data provide further support for a role of CaSR proteins in osmoregulatory and sensory functions in Atlantic salmon, an anadromous species that experiences a broad range of environmental salinities in its life history.

The intersection of stress, sex and immunity in fishes

While sexual dimorphism in immune responses has been documented in other vertebrates, evidence for a similar phenomenon in fish is lacking. Here, we review the relationship between immunity, stress, spawning, and sex hormones in fish to gain a better understanding of sex-based differences in fish immune responses and its consequences for aquaculture. It is well known that there is a strong link between the stress response and immune function in fish. In addition, research to date has demonstrated that sexual dimorphism in the stress response exists in many species; yet, the relationship between the sexual dimorphic stress responses and immune function has rarely been explored together. Aside from stress, spawning is also known to trigger changes in fish immune responses. Estrogens and androgens have been shown to modulate the immune system which could account for differences between the two sexes of fish when spawning; however, evidence regarding the sexual dimorphism of these changes varies between fishes and is likely related to the spawning strategy employed by a given species. Sex hormones are also used in aquaculture practices to produce monosex populations, and exposure to these hormones early in development has been shown to impact the development of immune organs in several fishes. While female fish are generally thought to be more robust than males, aquaculture practices should also consider the role that maternal stress has on the immune function of the offspring and what role this plays in compromising the immune response of farmed fish.

Binding specificities of estrogen receptor with perfluorinated compounds: A cross species comparison

BACKGROUND

Perfluorinated compounds (PFCs) were reported to result in the endocrine disruption by activating the estrogen receptor (ER) and inducing ER-mediated transcriptions.

OBJECTIVE

The aim of the present work was to perform cross-species comparisons on the characteristics of eight PFCs binding to humans ERα and to rats ERα.

METHODS

In the present work, in vivo tests, including serum estradiol level assay and immunohistochemical staining, fluorescence assay and molecular models were applied.

RESULTS

Based on the in vivo experiments, the exposure of PFOA and PFOS to female rats was proved to increase the ERα expression in the terus, suggesting that PFCs may act as estrogenic compounds to activate ERα in vivo. The further fluorescence assay presented that these eight PFCs have stronger binding abilities to human ERα than to rat ERα. In addition, the differences in binding specificities between human ERα and rat ERα were identified in the process of molecular dynamics modeling with the term of helix position and the ability of coregulator recruitment. It can be found that more and stronger charge clamps could form between PFCs with human ERα than with rat ERα. Also, the eight PFCs presented lower binding energies in human ERα systems, which proved that eight PFCs presented much stronger binding abilities with human ERα.

DISCUSSION

In all, it can be concluded that PFCs might be more sensitive to human ERα than to that of rats, which also suggested the greater susceptibility to adverse effects on humans. The present work was a beginning assessment of a cross-species comparison, providing important information on health impacts of PFCs in humans.

Androgen signaling in male fishes: Examples of anti-androgenic chemicals that cause reproductive disorders

Similar to other vertebrates, androgens regulate spermatogenesis in fishes. In teleosts, the main androgen is 11-Ketotestosterone (11-KT), which is oxidized testosterone (T) at the C₁₁ position. Compared to T, 11-KT is a nonaromatizable steroid, and does not convert to 17β-estradiol. However, circulatory levels of both T and 11-KT undergo seasonal variations along with testicular development. Physiological functions of androgens are mediated via androgen receptor (Ar). So far, nuclear Ar and membrane Ar have been identified in fishes. In the present study, we reviewed androgen biosynthesis in fishes, compared molecular structure of nuclear Ar in models of mammals and fishes, and investigated the mechanisms of action of environmental contaminants that differentially disrupt androgen signaling in fish reproduction. In the latter case, the adverse effects of vinclozolin (VZ) and bis(2-ethylhexyl) phthalate (DEHP) are compared. Both VZ and DEHP are capable of decreasing sperm quality in males. Vinclozolin causes an increase in 11-KT production associated with increases in kisspeptin (kiss-1) and salmon gonadotropin-releasing hormone (gnrh3) mRNA levels as well as circulatory levels of luteinizing hormone (Lh). In contrast, DEHP inhibits 11-KT production associated with a decrease in circulatory Lh levels. However, DEHP-inhibited 11-KT production is not associated with changes in kiss-1 and gnrh3 mRNA levels. Studies also show that VZ alters ar mRNA levels, while DEHP is without effect. These suggest that VZ and DEHP act differentially to cause androgen-dependent reproductive disorder in male fishes. Molecular analyses of the nuclear AR show that both DNA and ligand binding domains (DBD and LBD, respectively) are highly conserved within models of mammals and fishes. A phylogeny tree of the AR shows distinct clusters between mammals and fishes. In fishes, subtypes of Arα and Arβ are also separated in distinct clusters. Thus, further studies need to generate ar knockout fish model to better elucidate androgen regulation of reproduction in fishes via Ar.

Fertility impairment with defective spermatogenesis and steroidogenesis in male zebrafish lacking androgen receptor

The pivotal role of androgen receptor (AR) in regulating male fertility has attracted much research attention in the past two decades. Previous studies have shown that total AR knockout would lead to incomplete spermatogenesis and lowered serum testosterone levels in mice, resulting in azoospermia and infertility. However, the precise physiological role of ar in controlling fertility of male fish is still poorly understood. In this study, we have established an ar knockout zebrafish line by transcription activator-like effectors nucleases. Homozygous ar mutant male fish with smaller testis size were found to be infertile when tested by natural mating. Intriguingly, a small amount of mature spermatozoa was observed in the ar mutant fish. These mature spermatozoa could fertilize healthy oocytes, albeit with a lower fertilization rate, by in vitro fertilization. Moreover, the expression levels of most steroidogenic genes in the testes were significantly elevated in the ar mutants. In contrast, the levels of estradiol and 11-ketotestosterone (11-KT) were significantly decreased in the ar mutants, indicating that steroidogenesis was defective in the mutants. Furthermore, the protein level of LHβ in the serum decreased markedly in the ar mutants when compared with wild-type fish, probably due to the positive feedback from the diminished steroid hormone levels.

Characterization and expression of androgen receptors in olive flounder

Androgens are critical hormones that regulate sex differentiation, sexual maturation, and spermatogenesis in vertebrates, which is mainly mediated by androgen receptors (ARs). Reports on transcript variants of ar (AR encoding gene) in human are almost always associated with cancers and androgen insensitivity syndrome. However, the knowledge of ar variants in teleosts is scarce. In this study, arβ and two transcript variants of arα (arα1 and arα2) in olive flounder (Paralichthys olivaceus) were cloned and analyzed. Their expression patterns were investigated in 16 adult female and male tissues by RT-PCR, respectively. arα1 was expressed in the majority of tissues excluding male liver, medulla oblongata and female cerebellum, with higher levels in male gonad, kidney, head kidney, intestine, stomach, spleen, heart and gill than in female. arα2 had similar expression patterns as arα1, with lower levels in general. arβ was also widely expressed in various tissues excluding male spleen, female spleen and gill, with higher levels in male gonad, kidney, head kidney, intestine and lower levels in hypothalamus than in female. Compared with arβ, much lower expression levels of arα1 and arα2 were detected in different brain areas. The real-time quantitative PCR (qPCR) results showed that the total arα expression level was relatively higher during olive flounder gonadal differentiation and before the onset of testis differentiation, whereas arβ was expressed significantly higher during male gonadal differentiation period than female gonadal differentiation period. The in vitro transient transfection assays showed that ARα1, ARα2 and ARβ could all suppress the activity of cyp19a (p450arom aromatase gene) promoter, and the inhibitory effect of ARα1 was dose dependent. Our results imply that arα1, arα2 and arβ are sex-related genes and they might play important roles in gonadal differentiation in flounder.

Functional distinctions associated with the diversity of sex steroid hormone receptors ESR and AR

Sex steroid hormones including estrogens and androgens play fundamental roles in regulating reproductive activities and they act through estrogen and androgen receptors (ESR and AR). These steroid receptors have evolved from a common ancestor in association with several gene duplications. In most vertebrates, this has resulted in two ESR subtypes (ESR1 and ESR2) and one AR, whereas in teleost fish there are at least three ESRs (ESR1, ESR2a and ESR2b) and two ARs (ARα and ARβ) due to a lineage-specific whole genome duplication. Functional distinctions have been suggested among these receptors, but to date their roles have only been characterized in a limited number of species. Sexual differentiation and the development of reproductive organs are indispensable for all animal species and in vertebrates these events depend on the action of sex steroid hormones. Here we review the recent progress in understanding of the functions of the ESRs and ARs in the development and expression of sexually dimorphic characteristics associated with steroid hormone signaling in vertebrates, with representative fish, amphibians, reptiles, birds and mammals.

Involvement of 11-ketotestosterone in hooknose formation in male pink salmon (Oncorhynchus gorbuscha) jaws

Mature male Pacific salmon (Oncorhynchus spp.) develop a hooknose, as a secondary male sexual characteristic, during the spawning period. It is likely that androgens regulate hooknose formation. However, endocrinological and histochemical details about the relationship between androgens and hooknose formation are poorly understood. In this study, we performed assays of serum androgens, detection of androgen receptor (AR) in hooknose tissues, external morphological measurement of hooknose-related lengths, and microscopic observation of hooknose tissues of pink salmon (O. gorbuscha) at different stages of sexual maturation. Expression of the arβ gene was detected in hooknose tissues of males but not females. The elongation of these tissues was mediated directly via androgens. Serum 11-ketotestosterone (11-KT) concentrations indicated a significant positive correlation with both jaw lengths during sexual maturation of males. In the upper jaw, cartilage tissue developed during hooknose formation, and AR-immunoreactive chondrocytes were located in the rostal-vetral regions of hooknose cartilage in maturing male. The chondrocytes in maturing males before entering into rivers exhibited rich-cytoplasm with high cell activity than at other sexual development stages. On the other hand, in the lower jaw, the development of the spongiosa-like bone meshworks. AR-immunoreactivity was detected in a proportion of the osteocytes and osteoblast-like cells in the spongiosa-like bone meshworks. These results indicate that hooknose formation in pink salmon, which is associated with the buildup of a structure with sufficient strength that it can be used to attack other males on the spawning ground, is regulated by 11-KT.

Steroid Transport, Local Synthesis, and Signaling within the Brain: Roles in Neurogenesis, Neuroprotection, and Sexual Behaviors

Sex steroid hormones are synthesized from cholesterol and exert pleiotropic effects notably in the central nervous system. Pioneering studies from Baulieu and colleagues have suggested that steroids are also locally-synthesized in the brain. Such steroids, called neurosteroids, can rapidly modulate neuronal excitability and functions, brain plasticity, and behavior. Accumulating data obtained on a wide variety of species demonstrate that neurosteroidogenesis is an evolutionary conserved feature across fish, birds, and mammals. In this review, we will first document neurosteroidogenesis and steroid signaling for estrogens, progestagens, and androgens in the brain of teleost fish, birds, and mammals. We will next consider the effects of sex steroids in homeostatic and regenerative neurogenesis, in neuroprotection, and in sexual behaviors. In a last part, we will discuss the transport of steroids and lipoproteins from the periphery within the brain (and vice-versa) and document their effects on the blood-brain barrier (BBB) permeability and on neuroprotection. We will emphasize the potential interaction between lipoproteins and sex steroids, addressing the beneficial effects of steroids and lipoproteins, particularly HDL-cholesterol, against the breakdown of the BBB reported to occur during brain ischemic stroke. We will consequently highlight the potential anti-inflammatory, anti-oxidant, and neuroprotective properties of sex steroid and lipoproteins, these latest improving cholesterol and steroid ester transport within the brain after insults.

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.

Neofunctionalization of Androgen Receptor by Gain-of-Function Mutations in Teleost Fish Lineage

Steroid hormone receptor family provides an example of evolution of diverse transcription factors through whole-genome duplication (WGD). However, little is known about how their functions have been evolved after the duplication. Teleosts present a good model to investigate an accurate evolutionary history of protein function after WGD, because a teleost-specific WGD (TSGD) resulted in a variety of duplicated genes in modern fishes. This study focused on the evolution of androgen receptor (AR) gene, as two distinct paralogs, ARα and ARβ, have evolved in teleost lineage after TSGD. ARα showed a unique intracellular localization with a higher transactivation response than that of ARβ. Using site-directed mutagenesis and computational prediction of protein-ligand interactions, we identified two key substitutions generating a new functionality of euteleost ARα. The substitution in the hinge region contributes to the unique intracellular localization of ARα. The substitution on helices 10/11 in the ligand-binding domain possibly modulates hydrogen bonds that stabilize the receptor-ligand complex leading to the higher transactivation response of ARα. These substitutions were conserved in Acanthomorpha (spiny-rayed fish) ARαs, but not in an earlier branching lineage among teleosts, Japanese eel. Insertion of these substitutions into ARs from Japanese eel recapitulates the evolutionary novelty of euteleost ARα. These findings together indicate that the substitutions generating a new functionality of teleost ARα were fixed in teleost genome after the divergence of the Elopomorpha lineage. Our findings provide a molecular explanation for an adaptation process leading to generation of the hyperactive AR subtype after TSGD.

Sex steroids stimulate leptin gene expression in Atlantic salmon parr hepatocytes in vitro

In mammals, leptin plays an important role in puberty and reproduction and leptin is regulated by sex steroids. Elevated leptin levels have been associated with sexual maturation in some teleosts such as Atlantic salmon. In the present study, primary cultures of Atlantic salmon hepatocytes were used to investigate the direct effects of different sex steroids on expression of the two salmon leptin-a genes, lepa1 and lepa2. Testosterone (T) stimulated both lepa1 and lepa2 in a dose dependent manner after four days of incubation. The stimulatory effect of T on leptin expression was not prevented by co-incubation with the aromatase inhibitor fadrozole, indicating a direct androgen effect on transcription. The non-aromatizable androgen 11-ketotestosterone (11-KT), which is the main androgen in fish, was generally slightly less potent than T in stimulating lepa1 and lepa2. The strongest stimulatory response was seen for 17β-estradiol (E2). E2 treatment significantly up-regulated lepa1 and lepa2 gene expression at doses of 10nM and 1nM for each gene, respectively. Lepa1, but not lepa2, was stimulated by T and 11-KT in immature male and immature female parr, while E2 stimulated expression of both genes. The sensitivity to sex steroid stimulation differed in maturing males compared to immature. In maturing males, the androgens and E2 stimulated lepa2 but not lepa1, while in immature males, the androgens and E2 stimulated lepa1, but only E2 stimulated lepa2. The differential response of the two leptin paralogues to the sex steroids suggests differences in regulation of the two leptin genes during maturation. Altogether, these results indicate that leptin expression in Atlantic salmon hepatocytes is directly regulated at the transcriptional level by the main teleost androgens and an estrogen, and that the response might depend on the developmental stage of the fish.

Molecular aspects of bovine cystic ovarian disease pathogenesis

Cystic ovarian disease (COD) is one of the main causes of reproductive failure in cattle and causes severe economic loss to the dairy farm industry because it increases both days open in the post partum period and replacement rates due to infertility. This disease is the consequence of the failure of a mature follicle to ovulate at the time of ovulation in the estrous cycle. This review examines the evidence for the role of altered steroid and gonadotropin signaling systems and the proliferation/apoptosis balance in the ovary with cystic structures. This evidence suggests that changes in the expression of ovarian molecular components associated with these cellular mechanisms could play a fundamental role in the pathogenesis of COD. The evidence also shows that gonadotropin receptor expression in bovine cystic follicles is altered, which suggests that changes in the signaling system of gonadotropins could play a fundamental role in the pathogenesis of conditions characterized by altered ovulation, such as COD. Ovaries from animals with COD exhibit a disrupted steroid receptor pattern with modifications in the expression of coregulatory proteins. These changes in the pathways of endocrine action would trigger the changes in proliferation and apoptosis underlying the aberrant persistence of follicular cysts.

Free Spanish abstract: A Spanish translation of this abstract is freely available at http://www.reproduction-online.org/content/149/6/R251/suppl/DC1.

Molecular cloning, characterization, and gene expression of the androgen receptor in the large yellow croaker, Larimichthys crocea

Androgens mediate a wide range of physiological responses and developmental processes in vertebrates, involving both reproductive and nonreproductive systems. The activity of androgens is mediated by the androgen receptor (AR), a member of the nuclear receptor superfamily. In this study, an AR gene was cloned from the large yellow croaker (Larimichthys crocea) for the first time. qRT-PCR revealed ubiquitous expression of AR in all adult tissues examined, with higher expression in the gonad and liver of both sexes and highest expression in the blastula stage of embryonic development. Using in situ hybridization, we detected positive signals of AR in the spermatogonium, spermatocyte, spermatid, and spermatozoon during spermatogenesis, in the cytoplasm of all oocytes during oogenesis and in the follicle cells of stage IV oocytes. Our findings support the important role that AR plays in gametogenesis, gonadal development, and the early stages of embryonic development.

A combined strategy involving Sanger and 454 pyrosequencing increases genomic resources to aid in the management of reproduction, disease control and genetic selection in the turbot (Scophthalmus maximus)

Background

Genomic resources for plant and animal species that are under exploitation primarily for human consumption are increasingly important, among other things, for understanding physiological processes and for establishing adequate genetic selection programs. Current available techniques for high-throughput sequencing have been implemented in a number of species, including fish, to obtain a proper description of the transcriptome. The objective of this study was to generate a comprehensive transcriptomic database in turbot, a highly priced farmed fish species in Europe, with potential expansion to other areas of the world, for which there are unsolved production bottlenecks, to understand better reproductive- and immune-related functions. This information is essential to implement marker assisted selection programs useful for the turbot industry.

Results

Expressed sequence tags were generated by Sanger sequencing of cDNA libraries from different immune-related tissues after several parasitic challenges. The resulting database (“Turbot 2 database”) was enlarged with sequences generated from a 454 sequencing run of brain-hypophysis-gonadal axis-derived RNA obtained from turbot at different development stages. The assembly of Sanger and 454 sequences generated 52,427 consensus sequences (“Turbot 3 database”), of which 23,661 were successfully annotated. A total of 1,410 sequences were confirmed to be related to reproduction and key genes involved in sex differentiation and maturation were identified for the first time in turbot (AR, AMH, SRY-related genes, CYP19A, ZPGs, STAR FSHR, etc.). Similarly, 2,241 sequences were related to the immune system and several novel key immune genes were identified (BCL, TRAF, NCK, CD28 and TOLLIP, among others). The number of genes of many relevant reproduction- and immune-related pathways present in the database was 50–90% of the total gene count of each pathway. In addition, 1,237 microsatellites and 7,362 single nucleotide polymorphisms (SNPs) were also compiled. Further, 2,976 putative natural antisense transcripts (NATs) including microRNAs were also identified.

Conclusions

The combined sequencing strategies employed here significantly increased the turbot genomic resources available, including 34,400 novel sequences. The generated database contains a larger number of genes relevant for reproduction- and immune-associated studies, with an excellent coverage of most genes present in many relevant physiological pathways. This database also allowed the identification of many microsatellites and SNP markers that will be very useful for population and genome screening and a valuable aid in marker assisted selection programs.

Profiling of androgen response in rainbow trout pubertal testis: relevance to male gonad development and spermatogenesis

The capacity of testicular somatic cells to promote and sustain germ cell differentiation is largely regulated by sexual steroids and notably androgens. In fish species the importance of androgens is emphasized by their ability to induce sex reversal of the developing fries and to trigger spermatogenesis. Here we studied the influence of androgens on testicular gene expression in trout testis using microarrays. Following treatment of immature males with physiological doses of testosterone or 11-ketotestosterone, 418 genes that exhibit changes in expression were identified. Interestingly, the activity of testosterone appeared stronger than that of 11-ketotestosterone. Expression profiles of responsive genes throughout testis development and in isolated germ cells confirmed androgens to mainly affect gene expression in somatic cells. Furthermore, specific clusters of genes that exhibit regulation coincidently with changes in the natural circulating levels of androgens during the reproductive cycle were highlighted, reinforcing the physiological significance of these data. Among somatic genes, a phylogenetic footprinting study identified putative androgen response elements within the proximal promoter regions of 42 potential direct androgen target genes. Finally, androgens were also found to alter the germ line towards meiotic expression profiles, supporting the hypothesis of a role for the somatic responsive genes in driving germ cell fate. This study significantly increases our understanding of molecular pathways regulated by androgens in vertebrates. The highly cyclic testicular development in trout together with functions associated with regulated genes reveal potential mechanisms for androgen actions in tubule formation, steroid production, germ cell development and sperm secretion.

Specific and non-overlapping functions of testosterone and 11-ketotestosterone in the regulation of professional phagocyte responses in the teleost fish gilthead seabream

Sex hormones, both estrogens and androgens, have a strong impact on immunity in mammals. In fish, the role of androgens in immunity has received little attention and contradictory conclusions have been obtained. However, it is well known that sex steroids are involved in fish growth, osmoregulation and gonad remodelation. In this study, we examine the in vitro effects of testosterone and 11-ketotestosterone, the two main fish androgens, on the professional phagocytes of the teleost fish gilthead seabream (Sparus aurata L.). Although both testosterone and 11-ketotestosterone failed to modulate the respiratory burst of seabream phagocytes, testosterone but not 11-ketotestosterone was able to increase the phagocytic ability of non-activated phagocytes. Curiously, 11-ketotestosterone was more powerful than testosterone at inducing the expression of its own receptor, namely androgen receptor b (ARb), in acidophilic granulocytes (AGs), but none of them affected the basal ARb expression levels in macrophages (MØ). Furthermore, although physiological concentrations of testosterone exerted a pro-inflammatory effect on both AGs and MØs, 11-ketotestosterone showed an anti-inflammatory effect in AGs and a strong pro-inflammatory effect in MØs. Interestingly, both androgens modulated the expression of toll-like receptors in these two immune cell types, suggesting that androgens might regulate the sensitivity of phagocytes to pathogens and damage signals. Testosterone and 11-ketotestosterone have a competitive effect, at least, on the modulation of the expression of some genes. Therefore, our results show for the first time a non-overlapping role for testosterone and 11-ketotestosterone in the regulation of professional phagocyte functions in fish.

Androgen receptor-beta mRNA levels in different tissues in breeding and post-breeding male and female sticklebacks, Gasterosteus aculeatus

BACKGROUND

Androgens induce male characters by activating androgen receptors (AR). Previous quantitative studies on AR in fishes have been limited to few tissues and/or a single season/reproductive state. The aim of this investigation was to study the possible role of AR-beta expression levels in the control of male traits in the three-spined stickleback. To that end, AR-beta expression levels in major tissues in breeding and post-breeding male and female sticklebacks were examined.

METHODS

AR-beta mRNA levels were quantified in ten tissues; eye, liver, axial muscle, heart, brain, intestine, ovary, testis, kidney and pectoral muscle in six breeding and post-breeding males and females using reverse transcription quantitative PCR.

RESULTS

Breeding in contrast to post-breeding males built nests and showed secondary sexual characters (e.g. kidney hypertrophy) and elevated androgen levels. Post-breeding females had lower ovarian weights and testosterone levels than breeding females. AR-beta was expressed in all studied tissues in both sexes and reproductive states with the highest expression in the gonads and in the kidneys. The kidney is an androgen target organ in sticklebacks, from which breeding males produce the protein spiggin, which is used in nest-building. There was also high AR-beta expression in the intestine, an organ that appears to take over hyperosmo-regulation in fresh water when the kidney hypertrophies in mature males and largely loses this function. The only tissue that showed effects of sex or reproductive state on AR-beta mRNA levels was the kidneys, where post-breeding males displayed higher AR-beta mRNA levels than breeding males.

CONCLUSION

The results indicate that changes in AR-beta mRNA levels play no or little role in changes in androgen dependent traits in the male stickleback.

The brain of teleost fish, a source, and a target of sexual steroids

Neurosteroids are defined as steroids de novo synthesized in the central nervous system. While the production of neurosteroids is well documented in mammals and amphibians, there is less information about teleosts, the largest group of fish. Teleosts have long been known for their high brain aromatase and 5α-reductase activities, but recent data now document the capacity of the fish brain to produce a large variety of sex steroids. This article aims at reviewing the available information regarding expression and/or activity of the main steroidogenic enzymes in the brain of fish. In addition, the distribution of estrogen, androgen, and progesterone nuclear receptors is documented in relation with the potential sites of production of neurosteroids. Interestingly, radial glial cells acting as neuronal progenitors, appear to be a potential source of neurosteroids, but also a target for centrally and/or peripherally produced steroids.

Disruption of androgen receptor signaling in males by environmental chemicals

Androgen-disruptors are environmental chemicals in that interfere with the biosynthesis, metabolism or action of endogenous androgens resulting in a deflection from normal male developmental programming and reproductive tract growth and function. Since male sexual differentiation is entirely androgen-dependent, it is highly susceptible to androgen-disruptors. Animal models and epidemiological evidence link exposure to androgen disrupting chemicals with reduced sperm counts, increased infertility, testicular dysgenesis syndrome, and testicular and prostate cancers. Further, there appears to be increased sensitivity to these agents during critical developmental windows when male differentiation is at its peak. A variety of in vitro and in silico approaches have been used to identify broad classes of androgen disrupting molecules that include organochlorinated pesticides, industrial chemicals, and plasticizers with capacity to ligand the androgen receptor. The vast majority of these synthetic molecules act as anti-androgens. This review will highlight the evidence for androgen disrupting chemicals that act through interference with the androgen receptor, discussing specific compounds for which there is documented in vivo evidence for male reproductive tract perturbations. This article is part of a Special Issue entitled 'Endocrine disruptors'.

Isolation, sequence analysis, and characterization of androgen receptor in Southern catfish, Silurus meridionalis

Androgen receptor (AR), the mediator of androgen, plays important roles in the androgen signal pathway. In the present study, we isolated and analyzed the cDNA sequence and tissue distribution of androgen receptor in Southern catfish (scAR). The full-length cDNA of scAR contains 3,116 bp with an open reading frame (ORF) of 2,415 bp, encoding a protein of 804 amino acids (aa). Tissue distribution analysis of scAR revealed that it was expressed in all tissues examined, with no sexual dimorphism in the ovary and testis. Phylogenetic analysis and multiple amino acids sequence alignment indicated the close relationship and high similarity of scAR with ARs from cypriniform species. In addition, partial sequences of ARs from 7 other siluriform species were also isolated. Comparison of catfish ARs with those from other vertebrates revealed that an extra C-terminal tail of about 20aa exists in all the ARs from siluriform fishes investigated, but not in other ARs. The extra sequence was resulted from a 4-bp insertion before the stop codon of other vertebrate ARs, and it was identical in ARs from siluriform species of the same genus but different among ARs from species of different genera. We report here for the first time that the ARs from siluriform species are longer in C-terminal than those from other vertebrates and it might be useful in reconstruction of the phylogenetic relationship among siluriform fishes. The significance of the extra C-terminal tail for AR function remains elusive.

Characterization of androgen receptor structure and nucleocytoplasmic shuttling of the rice field eel

Androgen receptor (AR) plays a critical role in prostate cancer and male sexual differentiation. We have identified AR from a primitive vertebrate with a sex reversal characteristic, the rice field eel. AR of this species (eAR) is distinct from human AR, especially in the ligand binding domain (LBD), and its expression in gonads shows an increasing tendency during gonadal transformation from ovary via ovotestis to testis. eAR has a restricted androgen-dependent transactivation function after a nuclear translocation upon dihydrotestosterone exposure. A functional nuclear localization signal was further identified in the DNA binding domain and hinge region. Although nuclear export is CRM1-independent, eAR has a novel nuclear export signal, which is negatively charged, indicating that a nuclear export pathway may be mediated by electrostatic interaction. Further, our studies have identified critical sequences for ligand binding in the C terminus. A structure of three α-helices in the LBD has been conserved from eels to humans during vertebrate evolution, despite a distinct amino acid sequence. Mutation analysis confirmed that the LBD is essential for dihydrotestosterone-induced nuclear import of eAR and following transactivation function in the nucleus. In addition, eAR interacts with both Sox9a1 and Sox9a2, and their interaction regulates transactivation of eAR. Our data suggest that the primitive species conserves and especially acquires key novel domains, the nuclear export signal and LBD, for the eAR function in spite of a rapid sequence evolution.

Neuroendocrinology of sexual plasticity in teleost fishes

The study of sex differences has produced major insights into the organization of animal phenotypes and the regulatory mechanisms generating phenotypic variation from similar genetic templates. Teleost fishes display the greatest diversity of sexual expression among vertebrate animals. This diversity appears to arise from diversity in the timing of sex determination and less functional interdependence among the components of sexuality relative to tetrapod vertebrates. Teleost model systems therefore provide powerful models for understanding gonadal and non-gonadal influences on behavioral and physiological variation. This review addresses socially-controlled sex change and alternate male phenotypes in fishes. These sexual patterns are informative natural experiments that illustrate how variation in conserved neuroendocrine pathways can give rise to a wide range of reproductive adaptations. Key regulatory factors underlying sex change and alternative male phenotypes that have been identified to date include steroid hormones and the neuropeptides GnRH and arginine vasotocin, but genomic approaches are now implicating a diversity of other influences as well.

Zebrafish (Danio rerio) androgen receptor: sequence homology and up-regulation by the fungicide vinclozolin

Steroid hormones regulate gene expression in organisms by binding to receptor proteins. These hormones include the androgens, which signal through androgen receptors (ARs). Endocrine disrupters (EDCs) are chemicals in the environment that adversely affect organisms by binding to nuclear receptors, including ARs. Vinclozolin, a fungicide used on fruit and vegetable crops, is a known anti-androgen, a type of EDC that blocks signals from testosterone and its derivatives. In order to better understand the effects of EDCs, further research on androgen receptors and other hormone signaling pathways is necessary. In this study, we demonstrate the evolutionary conservation between the genomic structure of the human and zebrafish ar genes and find that ar mRNA expression increases in zebrafish embryos exposed to vinclozolin, which may be evolutionarily conserved as well. At 48 and 72 h post-fertilization, vinclozolin-treated embryos express ar mRNA 8-fold higher than the control level. These findings suggest that zebrafish embryos attempt to compensate for the presence of an anti-androgen by increasing the number of androgen receptors available.

Spermatogenesis in fish

Spermatogenesis is a developmental process during which a small number of diploid spermatogonial stem cells produce a large number of highly differentiated spermatozoa carrying a haploid, recombined genome. We characterise morphologically the different germ cell stages with particular attention for the spermatogonial generations, including the stem cells and their specific capacity to colonise a recipient's testis after transplantation. We propose a nomenclature for fish germ cells to improve the comparability among different teleost fish but also to higher vertebrates. Survival and development of germ cells depends on their continuous and close contact to Sertoli cells, and we review their multiple roles in the cystic mode of spermatogenesis seen in fish. We then discuss gene expression patterns associated with testis maturation. The endocrine system of vertebrates has evolved as master control system over spermatogenesis. In fish, both pituitary gonadotropins LH and FSH stimulate gonadal sex steroid hormone production directly by activating Leydig cells. Information is reviewed on the effects of progestin, androgens, and estrogens on global testicular gene expression patterns (microarray analysis), and on the molecular mechanisms by which steroids regulate specific candidate genes (identified by subtractive hybridization approaches) during early stages of testis maturation. Moreover, progestin and androgen effects on spermiation and milt hydration are discussed. Sex steroids mainly act via receptors expressed by Sertoli cells. One type of response is that Sertoli cells change growth factor expression, which subsequently modulates germ cell proliferation/differentiation via mechanisms yet to be characterised. Finally, we review data on germ cell autonomous processes, mainly derived from loss-of-function mutant fish lines, before identifying a number of focus areas for future research activities.

Evolutionary history and functional characterization of androgen receptor genes in jawed vertebrates

Vertebrates show diverse sexual characters in sexually attractive and reproductive organs, which are regulated by steroid hormones, particularly androgens. However, the evolutionary history of androgen receptor (AR) gene remains largely unknown on the basis of phylogenic and functional analyses. To elucidate the evolutionary history and functional diversification of AR genes in vertebrates, we cloned the AR cDNAs from a shark, basal ray-finned fishes (Actinopterygii), namely bichir and sturgeon (Acipenseriformes), and teleosts including a basal teleost, arowana (Osteoglossiformes). Molecular phylogenetic analysis revealed that the gene duplication event that gave rise to two different teleost ARs (alpha and beta) likely occurred in the actinopterygian lineage leading to teleosts after the divergence of Acipenseriformes but before the split of Osteoglossiformes, which is compatible with the phylogenetic timing of teleost-specific genome duplication. Searching for AR genes in the medaka genome indicated that the teleost AR gene duplication has been associated with the duplication between chromosomes 10 and 14. Our functional analysis revealed that the shark AR activates the target gene via androgen response element by classical androgens. The teleost ARalpha showed the unique intracellular localization with a significantly higher transactivating capacity than that by teleost ARbeta. These findings indicate that the most ancient type of AR, as activated by the classical androgens as ligands, emerged before the Chondrichthyes-Osteichthyes split, and the AR gene was duplicated during the teleost-specific genome duplication event. We report here for the first time the accurate evolutionary history of AR gene and functional characterization of AR duplicates in teleost lineage.

Androgens enhance plasticity of an electric communication signal in female knifefish, Brachyhypopomus pinnicaudatus

Sex steroids were initially defined by their actions shaping sexually dimorphic behavioral patterns. More recently scientists have begun exploring the role of steroids in determining sex differences in behavioral plasticity. We investigated the role of androgens in potentiating circadian, pharmacological, and socially-induced plasticity in the amplitude and duration of electric organ discharges (EODs) of female gymnotiform fish. We first challenged female fish with injections of serotonin (5-HT) and adrenocorticotropic hormone (ACTH), and with social encounters with female and male conspecifics to characterize females' pre-implant responses to each treatment. Each individual was then implanted with a pellet containing dihydrotestosterone (DHT) concentrations of 0.0, 0.03, 0.1, 0.3, or 1.0 mg 10 g(-1) body weight. We then repeated all challenges and compared each female's pre- and post-implant responses. The highest implant dose enhanced EOD duration modulations in response to all challenge types, responses to male challenge were also greater at the second highest dose, and responses to ACTH challenge were enhanced in females receiving all but the smallest dose (and blank) implants. Alternatively, amplitude modulations were enhanced only during female challenges and only when females received the highest DHT dose. Our results highlight the differential regulation of EOD duration and amplitude, and suggest that DHT enhanced the intrinsic plasticity of the electrogenic cells that produce the EOD rather than modifying behavioral phenotypes. The relative failure of DHT to enhance EOD amplitude plasticity also implies that factors other than androgens are involved in regulating/promoting male-typical EOD circadian rhythms and waveform modulations displayed in social contexts.

SEX STEROIDS AND SPERMATOGENESIS IN THE AFRICAN CATFISH (CLARIAS GARIEPINUS)

Little is known about the physiological regulations of spermatogenesis of the African catfish (Clarias gariepinus), a species used as an experimental model for two decades. After a brief introduction to the cystic type of spermatogenesis in fish, the role of androgens and estrogens will be discussed, leading to a conclusion that androgens are required for spermatogenesis while their mode of action is poorly understood. In the cystic mode of spermatogenesis in fish, the Sertoli cells are formed cystic, in the somniferous lobules enclosing a single germ cell clone, providing suitable experimental models to address questions of relevance for vertebrate spermatogenesis in general.

Seasonal variations in testicular connexin levels and their regulation in the brook trout, Salvelinus fontinalis

Spermatogenesis requires coordinated intercellular communication mediated by gap junctions. Gap junctions are composed of connexons that are themselves composed of connexins (Cxs). The present objective was to determine the regulation of testicular Cxs in a seasonal breeder, the brook trout. To assess seasonal variations in testicular Cxs, trout were sampled monthly throughout spermatogenesis (June-November). Circulating levels of testosterone (T) and 11-ketotestosterone (11-KT) as well as mRNA levels for testicular androgen receptors (ar-alpha, ar-beta), thyroid hormone receptors (tr-alpha, tr-beta) and gonadotropin I receptor (rgthI) were measured. Plasma T levels peaked in October, one month prior to spawning, while 11-KT levels peaked at spawning. ar-alpha and ar-beta mRNA levels increased during spermatogenesis and peaked in November while tr-alpha, tr-beta mRNA levels stayed constant throughout spermatogenesis and increased dramatically in November. rgthI mRNA levels decreased progressively during spermatogenesis. Cx43 and Cx30 levels were constant during spermatogenesis and decreased in November. Cx31 levels were also constant during spermatogenesis but decreased dramatically in October and November. Cx43.4 levels peaked in July then decreased in September and levels were undetectable thereafter. Using in vitro cultures of testicular fragments we demonstrated that cx43 mRNA levels were regulated in a dose-response manner by 3,5,3'-triiodo-l-thyronine (0-370 nM) and cAMP (0-100 ng/ml) but levels were not regulated by 11-KT. These results indicate that testicular Cxs vary as a function of spermatogenesis and that the expression of cx43 in the trout testis is regulated by both cAMP and TH.

The fate of the duplicated androgen receptor in fishes: a late neofunctionalization event?

BACKGROUND

Based on the observation of an increased number of paralogous genes in teleost fishes compared with other vertebrates and on the conserved synteny between duplicated copies, it has been shown that a whole genome duplication (WGD) occurred during the evolution of Actinopterygian fish. Comparative phylogenetic dating of this duplication event suggests that it occurred early on, specifically in teleosts. It has been proposed that this event might have facilitated the evolutionary radiation and the phenotypic diversification of the teleost fish, notably by allowing the sub- or neo-functionalization of many duplicated genes.

RESULTS

In this paper, we studied in a wide range of Actinopterygians the duplication and fate of the androgen receptor (AR, NR3C4), a nuclear receptor known to play a key role in sex-determination in vertebrates. The pattern of AR gene duplication is consistent with an early WGD event: it has been duplicated into two genes AR-A and AR-B after the split of the Acipenseriformes from the lineage leading to teleost fish but before the divergence of Osteoglossiformes. Genomic and syntenic analyses in addition to lack of PCR amplification show that one of the duplicated copies, AR-B, was lost in several basal Clupeocephala such as Cypriniformes (including the model species zebrafish), Siluriformes, Characiformes and Salmoniformes. Interestingly, we also found that, in basal teleost fish (Osteoglossiformes and Anguilliformes), the two copies remain very similar, whereas, specifically in Percomorphs, one of the copies, AR-B, has accumulated substitutions in both the ligand binding domain (LBD) and the DNA binding domain (DBD).

CONCLUSION

The comparison of the mutations present in these divergent AR-B with those known in human to be implicated in complete, partial or mild androgen insensitivity syndrome suggests that the existence of two distinct AR duplicates may be correlated to specific functional differences that may be connected to the well-known plasticity of sex determination in fish. This suggests that three specific events have shaped the present diversity of ARs in Actinopterygians: (i) early WGD, (ii) parallel loss of one duplicate in several lineages and (iii) putative neofunctionalization of the same duplicate in percomorphs, which occurred a long time after the WGD.

Simultaneous determination of androgenic and estrogenic endpoints in the threespine stickleback (Gasterosteus aculeatus) using quantitative RT-PCR

A method to evaluate the expression of three hormone responsive genes, vitellogenin (estrogens), spiggin (androgens), and an androgen receptor (ARbeta) using real-time PCR in threespine stickleback is presented. Primers were designed from previously characterised spiggin and ARbeta sequences, while a homology cloning strategy was used to isolate a partial gene sequence for stickleback vitellogenin (Vtg). Spiggin mRNA was significantly higher in kidneys of field-caught males compared to females by greater than five orders of magnitude while ARbeta levels were only 1.4-fold higher in males. Female fish had four order of magnitude higher liver Vtg expression than wild-captured males. To determine the sensitivity of these genes to induction by hormones, male and female sticklebacks were exposed to 1, 10 and 100 ng/L of methyltestosterone (MT) or estradiol (E2) in a flow-through exposure system for 7 days. Spiggin induction in females, and Vtg induction in males were both detectable at 10 ng/L of MT and E2, respectively. MT exposure did not induce ARbeta expression in the kidneys of female stickleback. In vitro gonadal steroid hormones production was measured in testes and ovaries of exposed stickleback to compare gene expression endpoints to an endpoint of hormonal reproductive alteration. Reduction in testosterone production in ovaries at all three MT exposure concentrations, and ovarian estradiol synthesis at the 100 ng/L exposure were the only effects observed in the in vitro steroidogenesis for either hormone exposure. Application of these methods to assess both androgenic, estrogenic, and anti-steroidogenic properties of environmental contaminants in a single fish species will be a valuable tool for identifying compounds causing reproductive dysfunction in fishes.

Expression profiling of candidate genes during ovary-to-testis trans-differentiation in rainbow trout masculinized by androgens

Fish gonadal phenotype is very sensitive to sex steroid and functional masculinizations can be obtained in most species using androgen treatments. To gain insight into the molecular effects of androgen-induced masculinization we characterized, in the rainbow trout, the gonadal expression profiles of 103 candidate genes involved in sex differentiation and early gametogenesis. The androgen treatment (11beta-hydroxyandrostenedione, 10 mg/kg of food for 3 months) was administered in a genetic all-female population. Gonads were sampled at different time points in genetic all-male and all-female control populations and in the androgen-treated group. Gene expression profiles were recorded by real-time RT-PCR and biological samples and gene expressions were compared using a global clustering analysis. This analysis revealed that masculinization with androgens acts firstly by repressing granulosa cell related genes, including genes involved in ovarian differentiation (foxl2a, fst, cyp19a1a), and subsequently by repressing genes important for early oogenesis (gdf9, bcl2lb, fancl, gcl, fshb, lhb, sox23, sox24, nup62 and vtgr). However, this masculinizing treatment did not induce a testicular differentiation similar to what was observed in the control male population. This was especially noticeable for many Leydig cell genes encoding proteins involved in steroidogenesis or its control (hsd3b1, star, cyp17a1, cyp11b2.1 and nr5a1b) that were down-regulated in the androgen-treated group. Concomitantly some Sertoli cells marker genes were up-regulated by the androgen treatment (sox9a.1, nr0b1, cldn11, dmrt1) whereas others were down-regulated (amh, sox9a.2), suggesting a partial differentiation of the Sertoli cell lineage. Overall, this suggests that the crucial step of this masculinization process is the de-differentiation of the granulosa cells.

Androgens modulate testicular androgen production in African catfish (Clarias gariepinus) depending on the stage of maturity and type of androgen

Previous work showed that androgen treatment suppressed testicular steroidogenesis in juvenile African catfish Clarias gariepinus. Similar to other vertebrates, however, circulating androgen levels increase during puberty in catfish. We therefore studied if androgen-induced inhibition of androgen production decreases during sexual maturation. As in other vertebrates, testosterone (T) is found in the circulation in fish but typically, 11-ketotestosterone (11-KT) is the quantitatively dominating androgen. In previous studies with juvenile catfish, these two androgens showed different biological activities as regards spermatogenesis or pituitary hormone production, but were equally effective in suppressing testicular steroidogenesis. Hence, the second question we studied was if the two types of androgens show distinct effects on the steroidogenic system in pubertal or adult males. The inhibitory effect of 11-KT on the testicular steroidogenic capacity waned with progressing sexual maturation, while T-mediated inhibition remained strong until adulthood reducing the in vitro steroid production 4- to 10-fold. However, the gonadotropin responsiveness of testicular tissue was not compromised and expression of testicular gonadotropin receptors did not respond differently to the two androgens. We conclude that the selective disappearance of the inhibitory effect of 11-KT contributes to allowing the pubertal increase of the plasma level of this androgen.

Fifteen years after "Wingspread"--environmental endocrine disrupters and human and wildlife health: where we are today and where we need to go

In 1991, a group of expert scientists at a Wingspread work session on endocrine-disrupting chemicals (EDCs) concluded that "Many compounds introduced into the environment by human activity are capable of disrupting the endocrine system of animals, including fish, wildlife, and humans. Endocrine disruption can be profound because of the crucial role hormones play in controlling development." Since that time, there have been numerous documented examples of adverse effects of EDCs in invertebrates, fish, wildlife, domestic animals, and humans. Hormonal systems can be disrupted by numerous different anthropogenic chemicals including antiandrogens, androgens, estrogens, AhR agonists, inhibitors of steroid hormone synthesis, antithyroid substances, and retinoid agonists. In addition, pathways and targets for endocrine disruption extend beyond the traditional estrogen/androgen/thyroid receptor-mediated reproductive and developmental systems. For example, scientists have expressed concern about the potential role of EDCs in increasing trends in early puberty in girls, obesity and type II diabetes in the United States and other populations. New concerns include complex endocrine alterations induced by mixtures of chemicals, an issue broadened due to the growing awareness that EDCs present in the environment include a variety of potent human and veterinary pharmaceutical products, personal care products, nutraceuticals and phytosterols. In this review we (1) address what have we learned about the effects of EDCs on fish, wildlife, and human health, (2) discuss representative animal studies on (anti)androgens, estrogens and 2,3,7,8-tetrachlorodibenzo-p-dioxin-like chemicals, and (3) evaluate regulatory proposals being considered for screening and testing these chemicals.

Sexual maturation modulates expression of nuclear receptor types in laser-captured single cells of the cichlid (Oreochromis niloticus) pituitary

The role of steroid/thyroid hormones in the regulation of endocrine cells at the level of the pituitary has remained unclear. Therefore, using single-cell quantitative real-time PCR, we examined absolute amounts of transcripts for nuclear receptors [estrogen receptors (ERs) alpha, beta, and gamma; androgen receptors (ARs) a and b; glucocorticoid receptors (GRs) 1, 2a, and 2b; and thyroid hormone receptors (TRs) alpha1, alpha2, and beta] in pituitary cells of immature (IM) and mature (M) male tilapia, Oreochromis niloticus. In the two reproductive stages, ACTH cells expressed only ERbeta, whereas all other pituitary cell types expressed ERalpha + beta, and a subpopulation coexpressed ARa, ARb, GR1, GR2b, and TRbeta but lacked ERgamma, GR2a, TRalpha1, and TRalpha2. IM males had high percentages of LH cells (IM 46.0% vs. M 10.0%), GH cells (IM 23.3% vs. M 7.9%), and prolactin cells (IM 68.8% vs. M 6.0%) with ERbeta, and TSH cells (IM 19.2% vs. M 0.0%) and MSH cells (IM 25.6% vs. M 0.0%) with ERalpha + TRbeta. A high percentage of FSH cells in IM males expressed ERbeta (IM 46.9% vs. M 18.8%), and FSH cells in M males showed significantly high GR1 transcripts (IM 76.0 +/- 5.0 vs. M 195.0 +/- 10.7 copies per cell; P < 0.05), suggesting that FSH cells are regulated differently in the two reproductive stages. Coexpression of ERalpha + beta in high percentages of cells of the GH family (GH, IM 43.8% vs. M 14.3%; prolactin, IM 8.3% vs. M 59.7%; somatolactin, IM 22.2% vs. M 42.2%) suggests that the expression of both ERs is important for functionality. Thus, differential coexpression of genes for nuclear receptors in subpopulations of pituitary cell types suggests multiple steroid/thyroid hormone regulatory pathways at the level of the pituitary during the two reproductive stages.