Developmental expression of key steroidogenic enzymes in the brain of protandrous black porgy fish, Acanthopagrus schlegeli

The expression profiles of cyp19a1, sf-1, esrs and gths in the brain-pituitary during gonadal sex differentiation in juvenile Japanese eels

Eels are gonochoristic species whose gonadal differentiation initiates at the yellow eel stage and is influenced by environmental factors. We revealed some sex-related genes were sex dimorphically expressed in gonads during gonadal sex differentiation of Japanese eel (Anguilla japonica); however, the expression of sex-related genes in the brain-pituitary during gonadal sex differentiation in eels is still unclear. This study aimed to investigate the sex-related gene expressions in the brain-pituitary and tried to clarify their roles in the brain and gonads during gonadal sex differentiation. Based on our previous histological study, the control eels developed as males, and estradiol-17β (E2) was used for feminization. Our results showed that during testicular differentiation, the brain cyp19a1 transcripts and aromatase proteins were increased significantly; moreover, the cyp19a1, sf-1, foxl2s, and esrs (except gperb) transcripts in the midbrain/pituitary also were increased significantly. Forebrain gnrh1 transcripts increased slightly during gonadal differentiation of both sexes, but the gnrhr1b and gnrhr2 transcripts in the midbrain/pituitary were stable during gonadal differentiation. The expression levels of gths and gh in the midbrain/pituitary were significantly increased during testicular differentiation and were much higher in males than in E2-feminized females. These results implied that endogenous estrogens might play essential roles in the brain/pituitary during testicular differentiation, sf-1, foxl2s, and esrs may have roles in cyp19a1 regulation in the midbrain/pituitary of Japanese eels. For the GnRH-GTH axis, gths, especially fshb, may be regulated by esrs and involved in regulating testicular differentiation and development in Japanese eels.

Triclosan, an antimicrobial drug, induced reproductive impairment in the freshwater fish, Anabas testudineus (Bloch, 1792)

Triclosan (TCS), an antimicrobial drug, is known to occupy different compartments in aquatic ecosystems. The present study focused to evaluate the reproductive toxicity of triclosan, at environmentally relevant (0.009 and 9 μg L-1) and sublethal (176.7 μg L-1) concentrations for 90 days in the pre-spawning phase of the fish, Anabas testudineus. The reproductive biomarkers, namely, gonadal steroidogenic enzymes, expression of aromatic genes, levels of serum gonadotropins, sex hormones, and histology of gonads were analyzed. The weight of the animal, brain weights along with gonadosomatic index decreased while mucus deposition increased significantly at all concentrations of triclosan as the primary defensive mechanism to prevent the entry of toxicants. Triclosan disrupted gonadal steroidogenesis as evidenced by a reduction in the activities of gonadal steroidogenic enzymes. The expressions of cyp19a1a and cyp19a1b genes were up-regulated in the brain of both sexes and testis, while down-regulated in the ovary indicating estrogenic effects of the compound. The endocrine-disrupting effects of triclosan were confirmed. The current results suggest that chronic exposure to triclosan altered reproductive endpoints thereby impairing normal reproductive functions in fish.

Expression and Transcript Localization of star, sf-1, and dax-1 in the Early Brain of the Orange-Spotted Grouper Epinephelus coioides

We investigated the developmental expression and localization of sf-1 and dax-1 transcripts in the brain of the juvenile orange-spotted grouper in response to steroidogenic enzyme gene at various developmental ages in relation to gonadal sex differentiation. The sf-1 transcripts were significantly higher from 110-dah (day after hatching) and gradually increased up to 150-dah. The dax-1 mRNA, on the other hand, showed a decreased expression during this period, in contrast to sf-1 expression. At the same time, the early brain had increased levels of steroidogenic gene (star). sf-1 and star hybridization signals were found to be increased in the ventromedial hypothalamus at 110-dah; however, dax-1 mRNA signals decreased in the early brain toward 150-dah. Furthermore, the exogenous estradiol upregulated star and sf-1 transcripts in the early brain of the grouper. These findings suggest that sf-1 and dax-1 may have an antagonistic expression pattern in the early brain during gonadal sex differentiation. Increased expression of steroidogenic gene together with sf-1 during gonadal differentiation strongly suggests that sf-1 may play an important role in the juvenile grouper brain steroidogenesis and brain development.

Reproductive performance is associated with seasonal plasma reproductive hormone levels, steroidogenic enzymes and sex hormone receptor expression levels in cultured Asian yellow pond turtles (Mauremys mutica)

In order to understand the endocrine mechanism associated with fecundity of seasonally breeding animals, we investigated the plasma reproductive hormones levels and detected the differences in steroidogenic enzymes and sex hormone receptor mRNA levels in female Mauremys mutica. These turtles were divided into higher fecundity (HF) group than those in lower fecundity (LF) group based on paternity identification in our previous research. The plasma estrogen (E2), testosterone (T) and progesterone (P4) levels were significantly higher in pre-breeding season (PBS) than those in non-breeding season (NBS) and were markedly higher in the HF group than those in LF group. In the hypothalamus, there was significantly higher mRNA abundance of P450-cholesterol side-chain cleavage enzyme (P450Scc) encoded by Cyp11α1, aromatase (Cyp19α1) and 5-reductase (5α-R), but significantly lower mRNA levels of follicular stimulating hormone receptor (FSHR) and progesterone receptor (PR) detected in PBS than those in NBS. The pituitary steroidogenic acute regulatory protein (StAR), cytochrome P450-17alpha-hydroxylase (Cyp17α1), 3-hydroxy-steroid dehydrogenase (3βHSD), 17-hydroxy-steroid dehydrogenase 3 (17βHSD3), Cyp19α1, 5α-R, FSHR, estrogen receptor 1 (ESR1), androgen receptor (AR) and PR transcriptional levels in HF group were up-regulated significantly compared with the LF group. In the ovary, Cyp17α1 and 17βHSD3 transcriptional levels were markedly higher in PBS than those in NBS. We detected significantly increased expression levels of all steroidogenic enzymes, but notably lower mRNA levels of FSHR and PR in uterus during the PBS, and the HF group has significantly higher expression levels of StAR, Cyp17α1, 5α-R and AR than LF group. Our work reveals seasonal variations in hormone regulation as well as gene regulation in turtles, providing reliable information to understand the mechanisms underlying the different reproductive capacity of reptiles.

Activation of the brain-pituitary-gonadotropic axis in the black porgy Acanthopagrus schlegelii during gonadal differentiation and testis development and effect of estradiol treatment

Previous studies revealed an estradiol (E2)-dependent peak in brain activity, including neurosteroidogenesis and neurogenesis in the black porgy during the gonadal differentiation period. The brain-pituitary-gonadotropic axis is a key regulator of reproduction and may also be involved in gonadal differentiation, but its activity and potential role in black porgy during the gonadal differentiation period is still unknown. The present study analyzed the expression of regulatory factors involved in the gonadotropic axis at the time of gonadal differentiation (90, 120, 150 days after hatching [dah]) and subsequent testicular development (180, 210, 300 dah). In agreement with previous studies, expression of brain aromatase cyp19a1b peaked at 120 dah, and this was followed by a gradual increase during testicular development. The expression of gonadotropin subunits increased slightly but not significantly during gonadal differentiation and then increased significantly at 300 dah. In contrast, the expression of brain gnrh1 and pituitary gnrh receptor 1 (gnrhr1) exhibited a pattern with two peaks, the first at 120 dah, during the period of gonadal differentiation, and the second peak during testicular development. Gonad fshr and lhcgr increased during gonadal differentiation period with highest transcript level in prespawning season during testicular development. This suggests that the early activation of brain gnrh1, pituitary gnrhr1 and gths, and gonad gthrs might be involved in the control of gonadal differentiation. E2 treatment increased brain cyp19a1b expression at each sampling time, in agreement with previous studies in black porgy and other teleosts. E2 also significantly stimulated the expression of pituitary gonadotropin subunits at all sampling times, indicating potential E2-mediated steroid feedback. In contrast, no significant effect of E2 was observed on gnrh1. Moreover, treatment of AI or E2 had no statistically significant effect on brain gnrh1 transcription levels during gonadal differentiation. This indicated that the early peak of gnrh1 expression during the gonadal differentiation period is E2-independent and therefore not directly related to the E2-dependent peak in brain neurosteroidogenesis and neurogenesis also occurring during this period in black porgy. Both E2-independent and E2-dependent mechanisms are thus involved in the peak expression of various genes in the brain of black porgy at the time of gonadal differentiation.

Aromatase immunolocalization and activity in the lizard's brain: Dynamic changes during the reproductive cycle

The purpose of the present study is to highlight the role of aromatase in the neuroendocrine control of the reproductive cycle of the male lizard Podarcis sicula during the three significant phases, i.e. the pre-reproductive, reproductive, and post-reproductive stages. Using immunohistochemical, biochemical, and hormonal tools, we have determined the localization and the activity of P450 aromatase (P450 aro) in the lizard's brain together with the determination of hormonal profile of sex steroids, i.e. testosterone and 17β-estradiol. The present data demonstrated that the localization of P450 is shown in brain regions involved in the regulation of the reproductive behavior (medial septum, preoptic area, and hypothalamus). Its activity, as well as the intensity of the signal, is modified according to the period of reproduction, resulting in functional dynamic changes. P450 aro activity and signal intensity decrease in the pre-reproductive period and progressively increase during the reproductive stage until it reaches the maximum peak level at the post-reproductive phase. P450 aro determines a local estrogen synthesis, balancing the testosterone and estradiol levels, and therefore its role is crucial, since it plays an important role in the neuroendocrine/behavioral regulation of the reproductive processes in the male lizard P. sicula.

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.

Daily Rhythms of the Expression of Key Genes Involved in Steroidogenesis and Gonadal Function in Zebrafish

Fish present daily and seasonal rhythms in spawning and plasmatic levels of steroids that control reproduction. However, the existence of the rhythms of expression of the genes that underlie the endocrine mechanisms responsible for processes such as steroidogenesis and reproduction in fish have still been poorly explored to date. Here we investigated the daily pattern of the expression of key genes involved in sex steroid production that ultimately set the sex ratio in fish. Adult zebrafish were maintained under a 12:12 h light-dark cycle at a constant temperature of 27°C and were sampled every 4 h during a 24-hour cycle. The expression of key genes in the gonads and brains of female and male individuals were analyzed. In gonads, the expression of aromatase (cyp19a1a, ovarian aromatase) and the antimüllerian hormone (amh, testis) was rhythmic, with almost opposite acrophases: ZT 5:13 h (in the light phase) and ZT 15:39 h (at night), respectively. The expression of foxl2 (forkhead box L2) was also rhythmic in the ovary (acrophase located at ZT 5:02 h) and the expression of dmrt1 (doublesex and mab-3-related transcription factor 1) was rhythmic in testes (acrophase at ZT 18:36 h). In the brain, cyp19a1b (brain aromatase) and cyp11b (11beta-hydroxylase) presented daily differences, especially in males, where the expression peaked at night. These results provide the first evidence for marked time-of-the-day-dependent differences in the expression of the genes involved in sex ratio control, which should be considered when investigating processes such as reproduction, sex differentiation and steroidogenesis in fish.

Comparative aspects of neurosteroidogenesis: From fish to mammals

It is now clearly established that the central and peripheral nervous systems have the ability to synthesize de novo steroids referred to as neurosteroids. The major evidence for biosynthesis of neuroactive steroids by nervous tissues is based on the expression of enzymes implicated in the formation of steroids in neural cells. The aim of the present review is to summarize the current knowledge regarding the presence of steroidogenic enzymes in the brain of vertebrates and to highlight the very considerable contribution of Professor Kazuyoshi Tsutsui in this domain. The data indicate that expression of steroid-producing enzymes in the brain appeared early during vertebrate evolution and has been preserved from fish to mammals.

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.

Neuropeptide Arginine Vasotocin Positively Affects Neurosteroidogenesis in the Early Brain of Grouper, Epinephelus coioides

The neuropeptide arginine vasotocin (AVT) has versatile physiological functions in non-mammalian vertebrates. However, the functional association between AVT and neurosteroidogenesis in the early brain of teleosts remains elusive. We thus studied the developmental expression patterns of the avt gene and their V1 type receptor (avt-rv1 ) at various stages of development [90-150 days after hatching (dah)] in relation to neurosteroidogenesis and oestrogen signalling in the early brain of the orange-spotted grouper (Epinephelus coioides). avt and avt-rv1 mRNAs displayed a significantly increase in expression at 110 dah in the telencephalon and diencephalon. Further, avt mRNAs were localised in three magnocellular neuronal populations of the preoptic area, such as parvocellular, magnocellular and gigantocellular preoptic neurones. Intriguingly, the avt transcripts in those neurones were more abundant in 110 dah compared to other ages. Subsequently, dual fluorescence in situ hybridisation analysis showed that the avt and avt-rv1 genes were highly coexpressed with cyp11a1, hsd3b1, cyp17a1, erα, erβ and gpr30, which indicates their potential for functional association. Cyp19a1b-immunoreactive positive fibres were found in close proximity to avt-expressing neurones. Moreover, our results showed that exogenous Avt caused a significant increase in the cellular and gene levels of steroidogenic enzymes and oestrogen receptors (ers), whereas the administration of an Avt-rv1 antagonist caused a decrease in the expression of both steroidogenic enzymes and ers genes in the brain. Furthermore, exogenous oestradiol (E2 ) strongly up-regulated avt mRNAs in the grouper brain. Taken together, the present studies suggest that avt and steroidogenesis may positively work together to increase both E2 biosynthesis and early brain development.

Activation of brain steroidogenesis and neurogenesis during the gonadal differentiation in protandrous black porgy, Acanthopagrus schlegelii

The early brain development, at the time of gonadal differentiation was investigated using a protandrous teleost, black porgy. This natural model of monosex juvenile fish avoids the potential complexity of sexual dimorphism. Brain neurogenesis was evaluated by histological analyses of the diencephalon, at the time of testicular differentiation (in fish between 90 and 150 days after hatching). Increases in the number of both Nissl-stained total brain cells, and Pcna-immunostained proliferative brain cells were observed in specific area of the diencephalon, such as ventromedialis thalami and posterior preoptic area, revealing brain cell proliferation. qPCR analyses showed significantly higher expression of the radial glial cell marker blbp and neuron marker bdnf. Strong immunohistochemical staining of Blbp and extended cellular projections were observed. A peak expression of aromatase (cyp19a1b), as well as an increase in estradiol (E2 ) content were also detected in the early brain. These data demonstrate that during gonadal differentiation, the early brain exhibits increased E2 synthesis, cell proliferation, and neurogenesis. To investigate the role of E2 in early brain, undifferentiated fish were treated with E2 or aromatase inhibitor (AI). E2 treatment upregulated brain cyp19a1b and blbp expression, and enhanced brain cell proliferation. Conversely, AI reduced brain cell proliferation. Castration experiment did not influence the brain gene expression patterns and the brain cell number. Our data clearly support E2 biosynthesis in the early brain, and that brain E2 induces neurogenesis. These peak activity patterns in the early brain occur at the time of gonad differentiation but are independent of the gonads.

Regulation of local steroidogenesis in the brain and in prostate cancer: lessons learned from interdisciplinary collaboration

Sex steroids play critical roles in the regulation of the brain and many other organs. Traditionally, researchers have focused on sex steroid signaling that involves travel from the gonads via the circulation to intracellular receptors in target tissues. This classic concept has been challenged, however, by the growing number of cases in which steroids are synthesized locally and act locally within diverse tissues. For example, the brain and prostate carcinoma were previously considered targets of gonadal sex steroids, but under certain circumstances, these tissues can upregulate their steroidogenic potential, particularly when circulating sex steroid concentrations are low. We review some of the similarities and differences between local sex steroid synthesis in the brain and prostate cancer. We also share five lessons that we have learned during the course of our interdisciplinary collaboration, which brought together neuroendocrinologists and cancer biologists. These lessons have important implications for future research in both fields.

The sex-specific transcriptome of the hermaphrodite sparid sharpsnout seabream (Diplodus puntazzo)

Background

Teleosts are characterized by a remarkable breadth of sexual mechanisms including various forms of hermaphroditism. Sparidae is a fish family exhibiting gonochorism or hermaphroditism even in closely related species. The sparid Diplodus puntazzo (sharpsnout seabream), exhibits rudimentary hermaphroditism characterized by intersexual immature gonads but single-sex mature ones. Apart from the intriguing reproductive biology, it is economically important with a continuously growing aquaculture in the Mediterranean Sea, but limited available genetic resources. Our aim was to characterize the expressed transcriptome of gonads and brains through RNA-Sequencing and explore the properties of genes that exhibit sex-biased expression profiles.

Results

Through RNA-Sequencing we obtained an assembled transcriptome of 82,331 loci. The expression analysis uncovered remarkable differences between male and female gonads, while male and female brains were almost identical. Focused search for known targets of sex determination and differentiation in vertebrates built the sex-specific expression profile of sharpsnout seabream. Finally, a thorough genetic marker discovery pipeline led to the retrieval of 85,189 SNPs and 29,076 microsatellites enriching the available genetic markers for this species.

Conclusions

We obtained a nearly complete source of transcriptomic sequence as well as marker information for sharpsnout seabream, laying the ground for understanding the complex process of sex differentiation of this economically valuable species. The genes involved include known candidates from other vertebrate species, suggesting a conservation of the toolkit between gonochorists and hermaphrodites.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-655) contains supplementary material, which is available to authorized users.

Increase in estrogen signaling in the early brain of orange-spotted grouper Epinephelus coioides: a mini-review

Despite neurosteroidogenic enzymes are playing important roles in the regulation of brain development and function, the potential link between brain and gonad by the action of steroid hormones during gonadal sex differentiation is still not clear in teleosts. In this mini-review, we summarized our understanding on the early brain development related to the synthesis of neurosteroids and receptor signaling during gonadal sex differentiation in protogynous orange-spotted grouper, Epinephelus coioides (functional females for the first 6 years of life and start to sex change around the age of 7 years) and protandrous black porgy (functional males for the first 2 years of life but begin to change sex during the third year). We found a similar profile in the increased expression of brain aromatase gene (aromatatse B or cyp19a1b), aromatase activity, estradiol (E(2)), and estrogen signaling in the brain of both grouper and black porgy fish during gonadal sex differentiation. In contrast to mammals, teleost fish Cyp19a1b expressed in a unique cell type, a radial glial cell, which is acted as progenitors in the brain of developing and adult fish. In agreement with these pioneer studies, we demonstrated that the grouper cyp19a1b/Cyp19a1b was expressed in radial glial cells. Further, in vivo data in the grouper brain showed that exogenous E(2) upregulated Cyp19a1b immunoreactivity (ir) in radial glial cells. These data suggest the possible roles of Cyp19a1b and E(2) in early brain development which is presumably related to gonadal sex differentiation.

Neurosteroidogenic enzymes and their regulation in the early brain of the protogynous grouper Epinephelus coioides during gonadal sex differentiation

The regulatory role of neurosteroids in the early brain during gonadal sex differentiation is unclear. The aim of this study was to investigate the expression and cellular localization of key steroidogenic enzymes in the early brain of the protogynous orange-spotted grouper Epinephelus coioides and the temporal expressions has been correlated with gonadal sex differentiation. In this study, we showed that peak neurosteroidogenesis occurs in the early brain during gonadal sex differentiation. The temporal expressions of key enzymes, cyp11a1 (cytochrome P450 side chain cleavage), hsd3b1 (3β-hydroxysteroid dehydrogenase) and cyp17a1 (cytochrome P450c17) were studied at different developmental ages (from 90- to 150-dah: days after hatching) using quantitative real-time PCR (q-PCR). q-PCR analysis indicated that the transcript expressions of cyp11a1, hsd3b1 and cyp17a1 were increased in the brain around the period of gonadal sex differentiation. Further, in situ hybridization (ISH) analysis showed that cyp11a1, hsd3b1 and cyp17a1 transcripts were widely expressed in several discrete brain regions, especially the intense expression in the forebrain, with an overall similar expression pattern. High density in the cyp19a1b/Cyp19a1b expression was detected in radial glial cells. Thus, the expression of grouper cyp19a1b/Cyp19a1b is restricted to radial glial cells, suggesting estrogens can modulate their activity. Next, by combining Cyp19a1b immunohistochemistry (IHC) with florescence ISH (FISH) of cyp11a1, hsd3b1 and cyp17a1, we showed that sub-cellular localization of cyp11a1, hsd3b1 and cyp17a1 transcripts, in partial, appeared to be in Cyp19a1b radial glial cell soma. Further, exogenous estradiol (E(2)) increased the expression of cyp17a1 and cyp19a1b/Cyp19a1b in the brain of grouper. Consequently, our results illustrated that the locally synthesized E(2) upregulated neurosteroidogenic enzymes in the early brain and suggest a role for these enzymes in the neurogenic process during gonadal sex differentiation.

Cytochrome P450 (CYP) in fish

Cytochrome P450 (CYP) enzymes are members of the hemoprotein superfamily, and are involved in the mono-oxygenation reactions of a wide range of endogenous and exogenous compounds in mammals and plants. Characterization of CYP genes in fish has been carried out intensively over the last 20 years. In Japanese pufferfish (Takifugu rubripes), 54 genes encoding P450s have been identified. Across all species of fish, 137 genes encoding P450s have been identified. These genes are classified into 18 CYP families: namely, CYP1, CYP2, CYP3, CYP4, CYP5, CYP7, CYP8, CYP11, CYP17, CYP19, CYP20, CYP21, CYP24, CYP26, CYP27, CYP39, CYP46 and CYP51.We pinpointed eight CYP families: namely, CYP1, CYP2, CYP3, CYP4, CYP11, CYP17, CYP19 and CYP26 in this review because these CYP families are studied in detail. Studies of fish P450s have provided insights into the regulation of P450 genes by environmental stresses including water pollution. In this review, we present an overview of the CYP families in fish.

Expression of P450c17 in the human fetal nervous system

P450c17 catalyzes steroid 17α-hydroxylase and 17,20 lyase activities. P450c17 is expressed in human fetal and postnatal adrenals and gonads and in the developing mouse nervous system, but little is known about its expression in the human nervous system. We obtained portions of 9-, 10-, and 11-wk gestation human fetuses and delineated the pattern of expression of P450c17 in their peripheral nervous systems by immunocytochemistry using the P450c17 antiserum previously used to characterize P450c17 in the mouse brain. P450c17 was readily detected in the dorsal root ganglia (DRG) and spinal cord. Neural structures were identified with antisera to the cytoskeletal protein neural cell adhesion molecule; DRG were identified with antisera to the neuronal transcription factor BRN3A and neurotrophin receptor tropomyosin-receptor-kinase B. The identification of P450c17 was confirmed using commercial antisera directed against different domains of P450c17 and by using antisera immunodepleted with authentic human P450c17. We also found expression of the P450 cholesterol side-chain cleavage enzyme (P450scc) in the spinal cord and DRG. Expression of P450scc is limited to cell bodies; unlike P450c17, we never detected P450scc in fiber tracts. Catalysis by P450c17 requires electron donation from P450 oxidoreductase (POR). Dual-label immunohistochemistry detected P450c17 and POR colocalized in DRG bundles, but some fibers containing P450c17 lacked POR. These data suggest that neurosteroids synthesized via these two enzymes may act in the developing human nervous system. The expression of P450c17 in structures lacking POR means that P450c17 may not be steroidogenic in those locations, suggesting that P450c17 may have additional functions that do not require POR.

Neurosteroidogenesis: insights from studies of songbirds

The long-held dogma that the brain is a target of steroids produced by peripheral organs has delayed the widespread acceptance of the functional importance of neurosteroidogenesis. Comparative studies have been vital for establishing the key actions of gonadal and adrenal hormones on brain and behaviour. No doubt, studies across diverse phyla will continue to be crucial for revealing the true significance of neurosteroidogenesis to proper function of the vertebrate brain. Here, we review work carried out in our laboratory, as well as in others, highlighting advances to our understanding of brain steroid synthesis and action using songbirds as animal models. These studies show that steroidogenic transporters and enzymes are present in the songbird brain and that their expression and/or activities are subject to developmental, seasonal or short-term regulation. Our work in a songbird points to synaptic synthesis of neuroactive steroids and fast, perisynaptic membrane actions. Combined with evidence for rapid steroidal control of behaviour, these studies firmly establish a neuromodulatory role for avian neurosteroids. We hope this work will join with that of other species to embolden the acceptance of neurosteroidal signalling as a core property of vertebrate neurobiology.

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.

Developmental expression of genes involved in neural estrogen biosynthesis and signaling in the brain of the orange-spotted grouper Epinephelus coioides during gonadal sex differentiation

In the brain, the synthesis of neurosteroids and receptor activation during gonadal sex differentiation in teleosts are poorly understood. In the present study, the protogynous orange-spotted grouper (Epinephelus coioides) was selected as a model fish, and we hypothesized that de novo synthesis of neural estrogen may play a role in the female grouper brain during gonadal sex differentiation. We investigated the temporal expression of the genes StAR, cyp19a1b and pcna and the sex steroid nuclear receptors for estrogen (ERα, ERβ1 and ERβ2), androgen (AR) and the plasma membrane-associated estrogen receptor (GPR30) in the brain during early developmental ages from 90 days after hatching (dah) to 180dah after gonadal sex differentiation. Our results revealed that mRNA for ERs and GPR30 but not AR was significantly increased at 110dah (a time close to gonadal sex differentiation) in the forebrain and midbrain and for cyp19a1b at 110dah in the forebrain. Brain aromatase activity and estradiol (E2) levels, but not testosterone (T), were increased in the forebrain at 110 and 120dah, respectively. Furthermore, exogenous E2 stimulated cyp19a1b transcripts in the forebrain and hypothalamus and immunoreactive (ir)Cyp19a1b (aromatase enzyme) in the forebrain. irCyp19a1b localized in the glial cells of the forebrain regions. Therefore, we identified a peak of functional aromatase activity and estrogen signaling in the early grouper brain during gonadal sex differentiation. Moreover, pcna transcripts (a marker for cell proliferation activity) were higher in the early brain at 110-150dah. Thus, a peak time of development in the brain is suggested to occur during gonadal sex differentiation in the grouper.

Sexual dimorphism in the brain aromatase expression and activity, and in the central expression of other steroidogenic enzymes during the period of sex differentiation in monosex rainbow trout populations

Using genetic monosex male and female rainbow trout populations, the potential sex differences in the central expression of estrogen receptors (esr1, esr2a, esr2b), brain aromatase (cyp19a1b) and some other steroidogenic enzymes was studied over the period of sex differentiation (from 35 to 63 dpf: days post-fertilization) using quantitative polymerase chain reaction (q-PCR). In addition, aromatase activity was evaluated during this period. The results indicated that brain aromatase (cyp19a1b) expression and activity showed a clear and significant sexually dimorphic pattern with higher levels in male brain between 35 and 53 dpf before the time of gonad morphological differentiation. At that time the expression of a key enzyme involved in the conversion of cholesterol into steroids, the cyp11a1 (p450scc), as well as the estrogen receptors were also sexually dimorphic. The dimorphism was lost from 56 dpf onwards. Transcription factors such as nr5a1b (sf1) and nr0b1 (dax1), but not foxl2a were also higher in males than in females. These results demonstrate that, before or during the early period of morphological gonad differentiation, the brain exhibits a clear sexual dimorphism with respect to the expression and activity of aromatase as well as of certain enzymes and factors involved in steroid synthesis as p450scc and sf1. The results suggest a higher potentiality to produce estrogens by male brains during sex differentiation time.

Neuroendocrine effects of endocrine disruptors in teleost fish

Because a large proportion of potential endocrine disruptors (EDC) end up in surface waters, aquatic species are particularly vulnerable to their potential adverse effects. Recent studies identified a number of brain targets for EDC commonly present in environmentally relevant concentrations in surface waters. Among those neuronal systems disrupted by EDC are the gonadotropin-releasing hormone (GnRH) neurons, the dopaminergic and serotoninergic circuits, and more recently the Kiss/GPR54 system, which regulates gonadotropin release. However, one of the most striking effects of EDC, notably estrogen mimics, is their impact on the cyp19a1b gene that encodes the brain aromatase isoform in fish. Moreover, this is the only example in which the molecular basis of endocrine disruption is fully understood. The aims of this review were to (1) synthesize the most recent discoveries concerning the EDC effects upon neuroendocrine systems of fish and (2) provide, when possible, the underlying molecular basis of disruption for each system concerned. The potential adverse effects of EDC on neurogenesis, puberty, and brain sexualization are also described. It is important to point out the future environmental, social, and economical issues arising from endocrine disruption studies in the context of risk assessment.

Sex differentiation and sex change in the protandrous black porgy, Acanthopagrus schlegeli

Protandrous black porgy fish, Acanthopagrus schlegeli, have a striking life cycle with a male sex differentiation at the juvenile stage and male-to-female sex change at 3 years of age. We had characterized the sex differentiation and sex change in this species by the integrative approaches of histology, endocrine and molecular genetics. The fish differentiated in gonad at the age around 4-months and the gonad further developed with a bisexual gonad for almost for 3 years and sex change at 3 year of age. An antagonistic relationship in the testicular and ovarian tissues was found during the development of the gonadal tissue. Male- (such as sf-1, dmrt1, dax-1 and amh) and female- (such as wnt4, foxl2 and cyp19a1a) promoting genes were associated with testicular and ovarian development, respectively. During gonadal sex differentiation, steroidogenic pathway and estrogen signaling were also highly expressed in the brain. The increased expression of sf-1 and wnt4, cyp19a1a in ovarian tissue and decreased expression of dax-1 in the ovarian tissue may play important roles in sex change from a male-to-female. Endocrine factors such as estradiol and luteinizing hormone may also involve in the natural sex change. Estradiol induced the expression of female-promoting genes and resulted in the precocious sex change in black porgy. Our series of studies shed light on the sex differentiation and sex change in protandrous black porgy and other animals.

Cloning, expression and enzyme activity analysis of testicular 11beta-hydroxysteroid dehydrogenase during seasonal cycle and after hCG induction in air-breathing catfish Clarias gariepinus

A full-length cDNA encoding 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) was cloned from testis of air-breathing catfish, Clarias gariepinus which showed high sequence homology to zebrafish and eel. The open reading frame of 11beta-HSD2 was then transfected to COS-7 cells, which converted 11beta-hydroxytestosterone (11-OHT) to 11-ketotestosterone (11-KT). Using NAD(+), 11beta-HSD2 from testicular microsomes oxidized 11-OHT with apparent K(m) 56+/-4nM and V(max) 55+/-6pmol/h/mgprotein values. Tissue distribution analysis revealed prominent expression in testis, anterior kidney, liver and gills. Expression of 11beta-HSD2 in testis and serum levels of 11-KT were high in the prespawning phase. Administration of human chorionic gonadotropin (hCG) during prespawning and resting phases revealed initial rise in 11beta-HSD2 transcript at 4h followed by gradual increase at 8h, 12h and peaking at 24h, only in testis of prespawning phase. Rate of conversion of 11-OHT to 11-KT by testicular microsomes during different testicular phases and after hCG administration corroborated well with the expression of 11beta-HSD2. Ontogeny study indicated that this enzyme is expressed during testicular development. Thus the spatio-temporal expression supported with putative dehydrogenase activity and circulating 11-KT levels clearly suggest a major role for 11beta-HSD2 during testicular differentiation and seasonal testicular cycle in catfish.

Aromatase in the brain of teleost fish: expression, regulation and putative functions

Unlike that of mammals, the brain of teleost fish exhibits an intense aromatase activity due to the strong expression of one of two aromatase genes (aromatase A or cyp19a1a and aromatase B or cyp19a1b) that arose from a gene duplication event. In situ hybridization, immunohistochemistry and expression of GFP (green fluorescent protein) in transgenic tg(cyp19a1b-GFP) fish demonstrate that aromatase B is only expressed in radial glial cells (RGC) of adult fish. These cells persist throughout life and act as progenitors in the brain of both developing and adult fish. Although aromatase B-positive radial glial cells are most abundant in the preoptic area and the hypothalamus, they are observed throughout the entire central nervous system and spinal cord. In agreement with the fact that brain aromatase activity is correlated to sex steroid levels, the high expression of cyp19a1b is due to an auto-regulatory loop through which estrogens and aromatizable androgens up-regulate aromatase expression. This mechanism involves estrogen receptor binding on an estrogen response element located on the cyp19a1b promoter. Cell specificity is achieved by a mandatory cooperation between estrogen receptors and unidentified glial factors. Given the emerging roles of estrogens in neurogenesis, the unique feature of the adult fish brain suggests that, in addition to classical functions on brain sexual differentiation and sexual behaviour, aromatase expression in radial glial cells could be part of the mechanisms authorizing the maintenance of a high proliferative activity in the brain of fish.

Neurosteroid biosynthesis: enzymatic pathways and neuroendocrine regulation by neurotransmitters and neuropeptides

Neuroactive steroids synthesized in neuronal tissue, referred to as neurosteroids, are implicated in proliferation, differentiation, activity and survival of nerve cells. Neurosteroids are also involved in the control of a number of behavioral, neuroendocrine and metabolic processes such as regulation of food intake, locomotor activity, sexual activity, aggressiveness, anxiety, depression, body temperature and blood pressure. In this article, we summarize the current knowledge regarding the existence, neuroanatomical distribution and biological activity of the enzymes responsible for the biosynthesis of neurosteroids in the brain of vertebrates, and we review the neuronal mechanisms that control the activity of these enzymes. The observation that the activity of key steroidogenic enzymes is finely tuned by various neurotransmitters and neuropeptides strongly suggests that some of the central effects of these neuromodulators may be mediated via the regulation of neurosteroid production.

Salinity effects on the expression of osmoregulatory genes in the euryhaline black porgy Acanthopagrus schlegeli

Black porgy is a marine euryhaline species with a capacity to cope with demands in a wide range of salinities and thus is a perfect model-fish to study osmoregulatory responses to salinity-acclimated processes and their hormonal control. The present study was performed to understand the regulatory changes in hormone, hormone receptors and important osmoregulatory genes in pituitary, gill, intestine and kidney in response to acute salinity stress. Transcript levels were analyzed by quantitative real-time PCR following acute salinity challenge by direct transfer of seawater (SW) acclimatized fish to fresh water (FWBP) and vice versa (SWBP). SW acclimation significantly increased plasma osmolality and intestine Na+/K+-ATPase (NKA) activity while FW acclimation increased plasma cortisol and branchial NKA activity. Plasma osmolality and chloride concentration decreased in FWBP whereas GH levels remained unchanged in both FWBP and SWBP. Comparative analysis of gene profiles between FWBP and SWBP showed that pituitary prolactin transcript increased significantly in FWBP. Prolactin receptor (PRLR) transcripts increased in gill of FWBP while it decreased in gill and kidney of SWBP. NKA transcripts increased in gill of both FWBP and SWBP, while it decreased in intestine of FWBP and increased in intestine and kidney of SWBP. Glucocorticoid receptor (GR) transcripts decreased in intestine and kidney of FWBP while it increased in gill and intestine of SWBP. No significant changes were observed in growth hormone receptor (GHR) transcripts of both FWBP and SWBP in pituitary, gill, intestine and kidney. Our current data demonstrated the correlation between PRLR gene expression in relation to FW adaptation, and GR gene expression in relation to SW adaptation in euryhaline black porgy. The results indicate that black porgy has an excellent osmoregulatory capacity and is capable of withstanding large variations in salinity.

Regulation of P450c17 expression in the early embryo depends on GATA factors

The enzyme P450c17 is required for glucocorticoid, sex steroid, and some neurosteroid biosynthesis. Defective human P450c17 causes sexual infantilism and 46,XY sex reversal but is compatible with life, whereas ablation of the corresponding mouse gene causes embryonic lethality at around E7. Normal mouse embryos express P450c17 protein and activity in the embryonic endoderm at E7. Adult adrenal and gonadal steroidogenesis requires steroidogenic factor-1 (SF-1), but SF-1 is not expressed in the early mouse embryo. We show that P450c17 is expressed in differentiated mouse parietal and visceral endoderm lineages, in cultured mouse F9 embryonic carcinoma stem cells, in mouse embryonic stem cells, and in cultured mouse P19 stem cells. Bases -110 to -55 (which contain an SF-1 site and two potential GATA sites) of the rat cyp17 gene confer promoter activity in F9 cells. Overexpression of SF-1 has no effect, whereas overexpression of GATA4 in F9 cells increases transcription from -110/-55 fused to a reporter and increases endogenous P450c17 mRNA. Chromatin immunoprecipitation assays show that GATA4 binds to -215/+55 of mouse cyp17. Stimulating F9 cells with retinoic acid and cAMP differentiates them into visceral and parietal endoderm. Commensurate with cell differentiation, quantitative PCR showed increased GATA4 and GATA6 mRNAs, temporally followed by increased P450c17 mRNA. Small interfering RNA inhibition of GATA4 or GATA6 in undifferentiated or differentiated F9 cells diminished endogenous cyp17 expression. Thus, P450c17 is expressed in mouse embryonic stem cells, its expression increases upon differentiation to an early embryonic endoderm lineage, and GATA4/6 are responsible for activation of P450c17 gene expression at this early stage of embryonic development.

Steroidogenic enzyme gene expression in the brain of the parthenogenetic whiptail lizard, Cnemidophorus uniparens

The steroidogenic enzyme CYP17 is responsible for catalyzing the production of androgenic precursors, while CYP19 converts testosterone to estradiol. De novo neurosteroidogenesis in specific brain regions influences steroid hormone dependent behaviors. In the all-female lizard species Cnemidophorus uniparens, individuals alternately display both male-like mounting and female-like receptivity. Mounting is associated with high circulating concentrations of progesterone following ovulation (PostOv), while receptivity is correlated with estrogen preceding it (PreOv). At a neuroanatomical level, the preoptic area (POA) and ventromedial nucleus of the hypothalamus (VMN) are the foci of the male-typical mounting and female-typical receptivity, respectively. In this study, we indirectly test the hypothesis that the whiptail lizard brain is capable of de novo neurosteroidogenesis by cloning fragments of the genes encoding two steroidogenic enzymes, CYP17 and CYP19, and examining their expression patterns in the C. uniparens brain. Our data indicate that these genes are expressed in the C. uniparens brain, and more importantly in the POA and VMN. Using radioactive in situ hybridization, we measured higher CYP17 mRNA levels in the POA of PostOv lizards compared to receptive PreOv animals; CYP19 mRNA levels in the VMN did not change across the ovarian cycle. To our knowledge, these are the first data suggesting that the reptilian brain is capable of de novo steroidogenesis. This study also supports the idea that non-gonadal sources of steroid hormones locally produced in behaviorally relevant brain loci are central to the mediation of behavioral output.

Sex- and age-related variation in neurosteroidogenic enzyme mRNA levels during quail embryonic development

Brain can synthesize steroids de novo from cholesterol and this biochemical feature is a conserved property of vertebrates. There is growing evidence indicating that neurosteroids might participate in sexual differentiation of the brain. Therefore, in this study we investigated the presence, the sex differences, and the development-dependent variation of mRNAs coding for key neurosteroidogenic enzymes, namely cytochrome P450 side-chain cleavage enzyme (P450scc), 3beta-hydroxysteroid-dehydrogenase/Delta5-Delta4-isomerase (3beta-HSD), cytochrome P450 17alpha-hydroxylase/c17, 20-lyase (P450c17), and aromatase in embryonic prosencephali. Our results indicated that 3beta-HSD mRNA levels were sexually dimorphic and developmental age-dependent. In particular, 3beta-HSD mRNA levels were higher in females than in males at E7, whereas, this dimorphism was reversed at E9 and E15. In females, the relative levels of 3beta-HSD mRNA were highest at E7, whereas, in males they were significantly higher at E9 and E15 than at E7 and at E11. This sexual dimorphism was a peculiar feature of the prosencephalon, it could not be observed before gonadal sexual differentiation and it was not paralleled by a dimorphism in the brain content of progesterone. The level of mRNA coding for P450scc and for P450c17 did not show obvious developmental- or sex-related variation. Aromatase mRNA varied as a function of the embryonic age but not of the sex. These results, taken together, are suggestive of a potential role of some neurosteroidogenic enzymes in the development of quail brain and suggest that sexual differences in the hormonal environment may occur during brain development.