Changes in localization of cytochrome P450 cholesterol side-chain cleavage (P450scc) in Japanese eel testis and ovary during gonadal development

Differential tissue expression of sex steroid-synthesizing enzyme CYP11A1 in male Tibetan sheep (Ovis aries)

Steroid metabolism is a fundament to testicular development and function. The cytochrome P450, family 11, subfamily A, polypeptide 1 (CYP11A1) is a key rate-limiting enzyme for catalyzing the conversion of cholesterol to pregnenolone. However, despite its importance, what expression and roles of CYP11A1 possesses and how it regulates the testicular development and spermatogenesis in Tibetan sheep remains largely unknown. Based on this, we evaluated the expression and localization patterns of CYP11A1 in testes and epididymides of Tibetan sheep at three developmental stages (three-month-old, pre-puberty; one-year-old, sexual maturity and three-year-old, adult) by quantitative real-time PCR (qPCR), western blot and immunofluorescence. The results showed that CYP11A1 mRNA and protein were expressed in testes and epididymides throughout the development stages and obviously more intense in one- and three-year-old groups than three-month-old group (except for the caput epididymidis). Immunofluorescence assay showed that the CYP11A1 protein was mainly located in Leydig cells and epididymal epithelial cells. In addition, positive signals of CYP11A1 protein were observed in germ cells, epididymal connective tissue and sperms stored in the epididymal lumen. Collectively, these results suggested that the CYP11A1 gene might be mainly involved in regulating spermatogenesis and androgen synthesis in developmental Tibetan sheep testis and epididymis.

Characterization of CYP11A1 and its potential role in sex asynchronous gonadal development of viviparous black rockfish Sebastes schlegelii (Sebastidae)

Mitochondrial cytochrome P450 side-chain cleavage (P450scc), encoded by the cyp11a1 gene, initiates the first step of steroid biosynthesis. In this study, a 1554-bp open reading frame (ORF) of black rockfish (Sebastes schlegelii) cyp11a1 was cloned. The cyp11a1 gene is located on chromosome 5 and has 9 exons. The ORF encodes a putative precursor protein of 517 amino acids, and the predicted cleavable mitochondrial targeting peptide is located at amino acids 1-39. P450scc shares homology with other teleosts and tetrapods, which have relatively conserved binding regions with heme, cholesterol and adrenodoxin. Tissue distribution analysis revealed that the highest expression levels of cyp11a1 were detected in mature gonads and head kidney but that low levels were detected in gestational/regressed ovaries, regressed testes and other tissues. Immunostaining of P450scc was observed in testicular Leydig cells, ovarian theca cells, interrenal glands of head kidney, pituitary and multiple regions of brain. Particularly, two kinds of fish-specific P450scc-positive cells, including coronet cells of brain saccus vasculosus and hypophyseal somatolactin cells, were identified in black rockfish. Our results provide novel evidence for the potential role played by P450scc in reproduction behavior by mediating steroidogenesis in viviparous teleost.

17β-Hydroxysteroid dehydrogenase type 12a responsible for testicular 11-ketotestosterone synthesis in the Japanese eel, Anguilla japonica

The production of 11-ketotestosterone (11KT), an important steroid hormone in piscine spermatogenesis, is regulated by the pituitary gonadotropins [Gths: follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh)] and it is synthesized by catalytic reactions involving several steroidogenic enzymes. Among these enzymes, the role of 17β-hydroxysteroid dehydrogenases (Hsd17bs) that exhibited 17-ketosteroid reducing activity (17KSR activity) responsible for 11KT synthesis is still poorly understood. In the present study, for the deeper understanding of testicular 11KT biosynthesis, we first investigated the steroidogenic pathway to produce 11KT in Japanese eel testis. In vitro incubation of the testis with androstenedione (A4) and the subsequent analysis of the metabolites by thin-layer chromatography indicated that 11KT was synthesized from A4 via 11β-hydroxyandrostenedione (11OHA4) and 11-ketoandrostenedione (11KA4), which indicated that the steroidogenic enzyme exhibiting the 17KSR activity responsible for converting 11KA4 to 11KT is crucial for 11KT production. Subsequently, cDNAs encoding three candidate enzymes, Hsd17b type3 (Hsd17b3), Hsd17b type12a (Hsd17b12a), and 20β-hydroxysteroid dehydrogenase type2 (Hsd20b2), potentially with the 17KSR activity were isolated and characterized in the Japanese eel. The isolated hsd17b3, hsd17b12a, and hsd20b2 cDNAs putatively encoded 308, 314, and 327 amino acid residues with high homology to those of other vertebrate counterparts, respectively. The Hsd17b3, Hsd17b12a, and Hsd20b2 expressed either in HEK293T or in Hepa-E1 converted 11KA4 to 11KT. Tissue-distribution analysis by quantitative real time PCR revealed that hsd17b12a and hsd20b2 mRNAs were detected in the testis, while hsd17b3 mRNA was not detectable. Furthermore, we examined the effects of Gths on the 17KSR activity and the expression of the candidate genes in the immature testis. The 17KSR activity was upregulated by administration of Gths. Furthermore, only expression of hsd17b12a among three candidates was upregulated by Gths as well as the 17KSR activity. These findings strongly suggested that Hsd17b12a is one of the enzymes with 17KSR activity responsible for 11KT synthesis in the testis of Japanese eel.

Action of the Metalloproteinases in Gonadal Remodeling during Sex Reversal in the Sequential Hermaphroditism of the Teleostei Fish Synbranchus marmoratus (Synbranchiformes: Synbranchidae)

Teleostei present great plasticity regarding sex change. During sex reversal, the whole gonad including the germinal epithelium undergoes significant changes, remodeling, and neoformation. However, there is no information on the changes that occur within the interstitial compartment. Considering the lack of information, especially on the role played by metalloproteinases (MMPs) in fish gonadal remodeling, the aim of this study was to evaluate the action of MMPs on gonads of sex reversed females of Synbranchus marmoratus, a fresh water protogynic diandric fish. Gonads were processed for light microscopy and blood samples were used for the determination of plasma sex steroid levels. During sex reversal, degeneration of the ovaries occurred and were gradually replaced by the germinal tissue of the male. The action of the MMPs induces significant changes in the interstitial compartment, allowing the reorganization of germinal epithelium. Leydig cells also showed an important role in female to male reversion. The gonadal transition coincides with changes in circulating sex steroid levels throughout sex reversion. The action of the MMPs, in the gonadal remodeling, especially on the basement membrane, is essential for the establishment of a new functional germinal epithelium.

Effects of Fluoride on Expression of P450, CREM and ACT Proteins in Rat Testes

Fluoride (F) is an essential trace element that humans and animals ingest from water, air, and fluoride-containing products; however, excessive fluoride absorption can damage a variety of organs and tissues, including the male reproductive system. Our previous studies found that fluoride exposure lowered sperm quality and interfered with spermatogenesis; however, the exact mechanism remained unclear. Proteins cytochrome P450 (P450), cAMP-responsive element modulator (CREM), and activator of CREM in testis (ACT) play the key roles in spermatogenesis and sperm motility. To investigate whether fluoride affects the expression of P450, CREM, and ACT, we used immunohistochemical techniques to determine expression levels of these proteins in testes of rats administered 100 mg NaF/L for 2 weeks via drinking water. The results showed that P450 expression was decreased while CREM and ACT expression was increased in the fluoride group, compared to the control. These data suggest that fluoride can impair male reproduction by affecting expression of P450, CREM, and ACT in the testes.

Regulation of sex steroid production and mRNAs encoding gonadotropin receptors and steroidogenic proteins by gonadotropins, cyclic AMP and insulin-like growth factor-I in ovarian follicles of rainbow trout (Oncorhynchus mykiss) at two stages of vitellogenesis

At the completion of vitellogenesis, the steroid biosynthetic pathway in teleost ovarian follicles switches from estradiol-17β (E2) to maturational progestin production, associated with decreased follicle stimulating hormone (Fsh) and increased luteinizing hormone (Lh) signaling. This study compared effects of gonadotropins, human insulin-like growth factor-I (IGF1), and cAMP/protein kinase A signaling (forskolin) on E2 production and levels of mRNAs encoding steroidogenic proteins and gonadotropin receptors using midvitellogenic (MV) and late/postvitellogenic (L/PV) ovarian follicles of rainbow trout. Fsh, Lh and forskolin, but not IGF1, increased testosterone and E2 production in MV and L/PV follicles. Fsh increased steroidogenic acute regulatory protein (star; MV), 3β-hydroxysteroid dehydrogenase/Δ(5-4) isomerase (hsd3b; MV) and P450 aromatase (cyp19a1a; MV) transcript levels. Lh increased star mRNA levels (MV, L/PV) but reduced cyp19a1a transcripts in L/PV follicles. At both follicle stages, IGF1 reduced levels of hsd3b transcripts. In MV follicles, IGF1 decreased P450 side-chain cleavage enzyme (cyp11a1) transcripts but increased cyp19a1a transcripts. In MV follicles only, forskolin increased star and hsd3b transcripts. Forskolin reduced MV follicle cyp11a1 transcripts and reduced cyp19a1a transcripts in follicles at both stages. Fsh and Lh reduced fshr transcripts in L/PV follicles. Lh also reduced lhcgr transcripts (L/PV). IGF1 had no effect on gonadotropin receptor transcripts. Forskolin reduced MV follicle fshr transcript levels and reduced lhcgr transcripts in L/PV follicles. These results reveal hormone- and stage-specific transcriptional regulation of steroidogenic protein and gonadotropin receptor genes and suggest that the steroidogenic shift at the completion of vitellogenesis involves loss of stimulatory effects of Fsh and Igfs on cyp19a1a expression and inhibition of cyp19a1a transcription by Lh.

Gonadal soma-derived factor (gsdf), a TGF-beta superfamily gene, induces testis differentiation in the teleost fish Oreochromis niloticus

The Nile tilapia, Oreochromis niloticus, is a gonochoristic teleost fish with an XX/XY genetic system and is an excellent model for gonadal sex differentiation. In the present study, we screened novel genes that were expressed predominantly in either XY or XX undifferentiated gonads during the critical period for differentiation of gonads into ovaries or testes using microarray screening. We focused on one of the isolated 12 candidate genes, #9475, which was an ortholog of gsdf (gonadal soma-derived factor), a member of the transforming growth factor-beta superfamily. #9475/gsdf showed sexual dimorphism in expression in XY gonads before any other testis differentiation-related genes identified in this species thus far. We also overexpressed the #9475/gsdf gene in XX tilapia, and XX tilapia bearing the #9475/gsdf gene showed normal testis development, which suggests that #9475/gsdf plays an important role in male determination and/or differentiation in tilapia.

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.

Molecular cloning of cytochrome P450 side-chain cleavage and changes in its mRNA expression during gonadal development of brown hagfish, Paramyxine atami

Since hagfishes are considered the most primitive vertebrate known, extant or extinct, studies on their reproduction are indispensable for understanding phylogenetic aspects of vertebrate reproduction. However, little information is available on the endocrine regulation of the gonadal function in the hagfish. Based on EST analysis of the testis of the brown hagfish (Paramyxine atami), P450 side chain cleavage (CYP11A), which is the first and essential enzyme for steroidogenesis in jawed vertebrates, was cloned. The deduced amino acid sequence of hagfish CYP11A shows high identity to other animal forms especially in two functional domains, adrenodoxin binding domain and heme-binding domain. In the phylogenetic analysis, hagfish CYP11A forms a clade with the vertebrate CYP11A. Following the real-time PCR analysis, CYP11A mRNA expression levels were clearly correlated to the developmental stages of gonads in both sexes of the brown hagfish. By in situ hybridization, CYP11A mRNA signals were found in the theca cells of the ovarian follicles and Leydig cells and the tubule-boundary cells of the testis. These molecular and histological evidences are suggesting that CYP11A plays functional roles as a steroidogenic enzyme in gonadal development. Moreover, native GTH purified from hagfish pituitary stimulated the transcriptional levels of CYP11A in the organ-cultured testis in vitro, clearly suggesting that the steroidogenic activity of the hagfish is under the control of the pituitary GTH. It is suggested that vertebrates, during their early evolution, have established the pituitary-gonadal reproductive system.

Inhibitory effects of β-endorphin on cortisol release from goldfish (Carassius auratus) head kidney: an in vitro study

β-Endorphin (β-END) is an endogenous opioid peptide derived from the common precursor proopiomelanocortin, together with adrenocorticotropic hormone (ACTH) and melanocyte-stimulating hormone (MSH). Although the roles of ACTH and MSH in fish are well known, the roles of circulating β-END have not been elucidated. In the present study, we evaluated the biological roles of β-END in the goldfish. First, we cloned the cDNAs of the delta opioid receptor (DOR), kappa opioid receptor (KOR), and mu opioid receptor (MOR) from the brain of the goldfish. Second, we analyzed the tissues that expressed these genes by using reverse transcription polymerase chain reaction. Among the several tissues that contained the opioid gene transcripts, the mRNAs of DOR, KOR, and MOR were detected in interrenal cells of the head kidney, which produce cortisol. On the basis of these results, the effects of β-END on cortisol release were examined in vitro. β-END alone suppressed the basal release of cortisol in a dose-dependent manner. Moreover, β-END inhibited the cortisol-releasing activity of ACTH1-24. Therefore, it is probable that the role of β-END in the interrenal cells is the suppression of cortisol release. Interestingly, the suppression of cortisol release was not observed with N-acetyl-β-END, indicating that acetylation decreases the activity of β-END in interrenal cells.

Salinity-dependent in vitro effects of homologous natriuretic peptides on the pituitary-interrenal axis in eels

We examined the effects of atrial, B-type, ventricular and C-type natriuretic peptides (ANP, BNP, VNP and CNP1, 3, 4) on cortisol secretion from interrenal tissue in vitro in both freshwater (FW) and seawater (SW)-acclimated eels. We first localized the interrenal and chromaffin cells in the eel head kidney using cell specific markers (cholesterol side-chain cleavage enzyme (P450ssc) and tyrosine hydroxylase (TH), respectively) and established the in vitro incubation system for eel interrenal tissue. Unexpectedly, none of the NPs given alone to the interrenal tissue of FW and SW eels stimulated cortisol secretion. However, ANP and VNP, but not BNP and three CNPs, enhanced the steroidogenic action of ACTH in SW interrenal preparations, while CNP1 and CNP4, but not ANP, BNP, VNP and CNP3, potentiated the ACTH action in FW preparations. These salinity dependent effects of NPs are consistent with the previous in vivo study in the eel where endogenous ACTH can act with the injected NPs. 8-Br-cGMP also enhanced the ACTH action in both FW and SW eel preparations, suggesting that the NP actions were mediated by the guanylyl cyclase-coupled NP receptors (GC-A and B) that were localized in the eel interrenal. Further, ANP and CNP1 stimulated ACTH secretion from isolated pituitary glands of SW and/or FW eels. In summary, the present study revealed complex mechanisms of NP action on corticosteroidogenesis through the pituitary-interrenal axis in eels, thereby providing a deeper insight into the role of the NP family in the acclimation of this euryhaline teleost to diverse salinity environments.

Follicle-stimulating hormone regulation of ovarian transcripts for steroidogenesis-related proteins and cell survival, growth and differentiation factors in vitro during early secondary oocyte growth in coho salmon

Little is known about follicle-stimulating hormone (FSH) function during oocyte growth in fishes. The goal of this study was to gain a fundamental understanding of FSH action on ovarian follicles during early secondary oocyte growth by examining changes in ovarian gene expression and steroidogenesis in response to FSH. Coho salmon (Oncorhynchus kisutch) mid to late cortical alveolus stage follicles were incubated with or without salmon FSH in time-course and concentration-response experiments. Steroid levels were determined in the culture medium by immunoassay and levels of target ovarian mRNAs were determined by quantitative RT-PCR. Medium estradiol-17β (E2) levels increased in response to FSH and plateaued by 36h, while testosterone levels increased similarly but were lower and more variable than E2. Gonadotropin receptor transcripts were differentially regulated, with fshr and lhcgr being down- and up- regulated, respectively. Transcripts encoding proteins involved in steroidogenesis, such as star and hsd3b were significantly upregulated by FSH, whereas aromatase (cyp19a1a) mRNA was unaffected by FSH and declined over time in culture. A recently identified teleost gene, bmp16, was suppressed by FSH and an anti-apoptotic factor, clusterin 1 (clu1), was upregulated by FSH. Lesser FSH effects were observed on igf2, cyp11a1 and cyp17a1, which were stimulated, and igf1ra, inhbb, amh and apoe, which were suppressed. As evident by the significant increases in steroid production and transcripts for specific steroidogenesis-related proteins, FSH influences steroidogenesis during early secondary growth and may be a critical signal for puberty onset. Effects of FSH on ovarian anti-apoptotic and growth factor genes suggest roles for FSH in cell survival, growth and differentiation in teleosts.

In situ hybridization to detect spatial gene expression in medaka

A whole-animal tissue section in situ hybridization (ISH) system with radio-labeled probes was developed to detect differential gene expression among tissues of the small, oviparous teleost fish, Japanese medaka (Oryzias latipes). Because of its tissue- and gender-specific expression, gonadal aromatase (CYP19a) was selected as a model gene to demonstrate the potential of the system. The ISH system was validated with a 7d exposure to the model aromatase inhibitor, fadrozole. Fadrozole did not affect the magnitude of gene expression in testes, but significantly up-regulated CYP19a gene expression in ovaries. These results were confirmed with quantitative real-time-polymerase chain reaction (RT-PCR). Histological evaluation revealed that females exposed to 100microg/L fadrozole lacked mature oocytes. Male gonadal morphology was normal in all treatments. The ISH method developed in this study allowed tissue-specific resolution of gene expression in a whole animal model, as well as the ability to analyze cellular morphological detail in the same organism.

Japanese eel follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh): production of biologically active recombinant Fsh and Lh by Drosophila S2 cells and their differential actions on the reproductive biology

Two gonadotropins (Gths), follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh), control gonadal steroidogenesis and gametogenesis in vertebrates, including teleost fish. Here, we report on the production of biologically active recombinant Fsh (rec-Fsh) and Lh (rec-Lh) in Japanese eel using Drosophila S2 cells. The three subunits composing Gths, i.e., glycoprotein hormone, alpha polypeptide (Cga), follicle-stimulating hormone, beta polypeptide (Fshb), and luteinizing hormone, beta polypeptide (Lhb), were at first independently produced and were proven to be glycosylated and secreted as the mature peptides. Each beta subunit, along with its Cga, was simultaneously coexpressed to produce heterodimeric rec-Fsh and rec-Lh that were subsequently highly purified. The biological activity of rec-Gths was demonstrated in various in vitro assays. The rec-Gths differentially activated their receptors, which resulted in an increase in 11-ketotestosterone (11KT) secretion, a differential alteration of gene expression of steroidogenic enzymes in immature testis, and the induction of the complete process of spermatogenesis in vitro. The data strongly suggest that Fsh and Lh differentially play important roles in the reproductive physiology of the Japanese eel. By contrast, these rec-Gths exhibited little activity in the gonad when administered in vivo. This difference between in vitro and in vivo bioactivity is probably due to the qualitative nature of glycosylation in S2 cells, which resulted in degradation of the recombinant protein in vivo. These differences in the carbohydrate moieties need to be elucidated and ameliorated.

Fluorescence in situ hybridization techniques (FISH) to detect changes in CYP19a gene expression of Japanese medaka (Oryzias latipes)

The aim of this study was to develop a sensitive in situ hybridization methodology using fluorescence-labeled riboprobes (FISH) that allows for the evaluation of gene expression profiles simultaneously in multiple target tissues of whole fish sections of Japanese medaka (Oryzias latipes). To date FISH methods have been limited in their application due to autofluorescence of tissues, fixatives or other components of the hybridization procedure. An optimized FISH method, based on confocal fluorescence microscopy was developed to reduce the autofluorescence signal. Because of its tissue- and gender-specific expression and relevance in studies of endocrine disruption, gonadal aromatase (CYP19a) was used as a model gene. The in situ hybridization (ISH) system was validated in a test exposure with the aromatase inhibitor fadrozole. The optimized FISH method revealed tissue-specific expression of the CYP19a gene. Furthermore, the assay could differentiate the abundance of CYP19a mRNA among cell types. Expression of CYP19a was primarily associated with early stage oocytes, and expression gradually decreased with increasing maturation. No expression of CYP19a mRNA was observed in other tissues such as brain, liver, or testes. Fadrozole (100 microg/L) caused up-regulation of CYP19a expression, a trend that was confirmed by RT-PCR analysis on excised tissues. In a combination approach with gonad histology, it could be shown that the increase in CYP19a expression as measured by RT-PCR on a whole tissue basis was due to a combination of both increases in numbers of CYP19a-containing cells and an increase in the amount of CYP19a mRNA present in the cells.