Molecular cloning and expression during spermatogenesis of a cDNA encoding testicular 11beta-hydroxylase (P45011beta) in rainbow trout (Oncorhynchus mykiss)

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

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

De Novo Assembly, Characterization and Comparative Transcriptome Analysis of the Gonads of Jade Perch (Scortum barcoo)

Due to the high meat yield and rich nutritional content, jade perch (Scortum barcoo) has become an important commercial aquaculture species in China. Jade perch has a slow growth rate, taking 3-4 years to reach sexual maturity, and has almost no difference in body size between males and females. However, the study of its gonad development and reproduction regulation is still blank, which limited the yield increase. Herein, the gonad transcriptomes of juvenile males and females of S. barcoo were identified for the first time. A total of 107,060 unigenes were successfully annotated. By comparing male and female gonad transcriptomes, a total of 23,849 differentially expressed genes (DEGs) were identified, of which 9517 were downregulated, and 14,332 were upregulated in the testis. In addition, a large number of DEGs involved in sex differentiation, gonadal development and differentiation and gametogenesis were identified, and the differential expression patterns of some genes were further verified using real-time fluorescence quantitative PCR. The results of this study will provide a valuable resource for further studies on sex determination and gonadal development of S. barcoo.

Steroidogenic Effects of Salinity Change on the Hypothalamus-Pituitary-Gonad (HPG) Axis of Male Chinese Sea Bass (Lateolabrax maculatus)

As lower vertebrates, teleost species could be affected by dynamic aquatic environments and may respond to environmental changes through the hypothalamus–pituitary–gonad (HPG) axis to ensure their normal growth and sexual development. Chinese sea bass (Lateolabrax maculatus), euryhaline marine teleosts, have an extraordinary ability to deal with a wide range of salinity changes, whereas the salinity decrease during their sex-maturation season may interfere with the HPG axis and affect their steroid hormone metabolism, resulting in abnormal reproductive functioning. To this end, in this study, 40 HPG axis genes in the L. maculatus genome were systematically characterized and their copy numbers, phylogenies, gene structures, and expression patterns were investigated, revealing the conservation of the HPG axis among teleost lineages. In addition, freshwater acclimation was carried out with maturing male L. maculatus, and their serum cortisol and 11-ketotestosterone (11-KT) levels were both increased significantly after the salinity change, while their testes were found to be partially degraded. After salinity reduction, the expression of genes involved in cortisol and 11-KT synthesis (cyp17a, hsd3b1, cyp21a, cyp11c, hsd11b2, and hsd17b3) showed generally upregulated expression in the head kidneys and testes, respectively. Moreover, cyp11c and hsd11b2 were involved in the synthesis and metabolism of both cortisol and 11-KT, and after salinity change their putative interaction may contribute to steroid hormone homeostasis. Our results proved the effects of salinity change on the HPG axis and steroidogenic pathway in L. maculatus and revealed the gene interactions involved in the regulation of steroid hormone levels. The coordinated interaction of steroidogenic genes provides comprehensive insights into steroidogenic pathway regulation, as well as sexual development, in teleost species.

Establishment of a Spermatogonial Stem Cell Line with Potential of Meiosis in a Hermaphroditic Fish, Epinephelus coioides

Spermatogonial stem cells (SSCs) are unique adult stem cells capable of self-renewal and differentiation into sperm. Grouper is a protogynous hermaphroditic fish farmed widely in the tropical and subtropical seas. In this study, we established an SSC line derived from adult testis of orange-spotted grouper, Epinephelus coioides. In the presence of basic fibroblast growth factor (bFGF) and leukemia inhibitory factor (LIF), the cells could be maintained with proliferation and self-renewal over 20 months and 120 passages under in vitro culture conditions. The cells exhibited strong alkaline phosphatase activity and the characteristics of SSCs with the expression of germ cell markers, including Vasa, Dazl, and Plzf, as well as the stem cell markers Nanog, Oct4, and Ssea1. Furthermore, the cultured cells could be induced by 11-ketotestosterone treatment to highly express the meiotic markers Rec8, Sycp3, and Dmc1, and produce some spherical cells, and even sperm-like cells with a tail. The findings of this study suggested that the cultured grouper SSC line would serve as an excellent tool to study the molecular mechanisms behind SSCs self-renewal and differentiation, meiosis during spermatogenesis, and sex reversal in hermaphroditic vertebrates. Moreover, this SSC line has great application value in grouper fish aquaculture, such as germ cell transplantation, genetic manipulation, and disease research.

Cyp17a1 is Required for Female Sex Determination and Male Fertility by Regulating Sex Steroid Biosynthesis in Fish

In teleost fish, sex steroids are involved in sex determination, sex differentiation, and fertility. Cyp17a1 (Cytochrome P450 family 17 subfamily A member 1) is thought to play essential roles in fish steroidogenesis. Therefore, to further understand its roles in steroidogenesis, sex determination, and fertility in fish, we constructed a cyp17a1 gene mutant in Nile tilapia (Oreochromis niloticus). In XX fish, mutation of the cyp17a1 gene led to a female-to-male sex reversal with a significant decline in 17β-estradiol (E2) and testosterone (T) production, and ectopic expression of male-biased markers (Dmrt1 and Gsdf) in gonads from the critical window of sex determination. Sex reversal was successfully rescued via T or E2 administration, and ovarian characteristics were maintained after termination of E2 supplementation in the absence of endogenous estrogen production in cyp17a1-/- XX fish. Likewise, deficiencies in T and 11-ketotestosterone (11-KT) production in both cyp17a1-/- XX sex-reversed males and cyp17a1-/- XY mutants resulted in meiotic initiation delays, vas deferens obstruction and sterility due to excessive apoptosis and abnormal mitochondrial morphology. However, 11-KT treatment successfully rescued the dysspermia to produce normal sperm in cyp17a1-/- male fish. Significant increases in gonadotropic hormone (gth) and gth receptors in cyp17a1-/- mutants may excessively upregulate steroidogenic gene expression in Leydig cells through a feedback loop. Taken together, our findings demonstrate that Cyp17a1 is indispensable for E2 production, which is fundamental for female sex determination and differentiation in XX tilapia. Additionally, Cyp17a1 is essential for T and 11-KT production, which further promotes spermatogenesis and fertility in XY males.

Gene Expression of Takifugu rubripes Gonads During AI- or MT-induced Masculinization and E2-induced Feminization

Elucidating the global molecular changes that occur during aromatase inhibitor (AI)- or 17α-methyltestosterone (MT)-induced masculinization and estradiol-17β (E2)-induced feminization is critical to understanding the roles that endocrine and genetic factors play in regulating the process of sex differentiation in fish. Here, fugu larvae were treated with AI (letrozole), MT, or E2 from 25 to 80 days after hatching (dah), and gonadal transcriptomic analysis at 80 dah was performed. The expression of dmrt1, gsdf, foxl2, and other key genes (star, hsd3b1, cyp11c1, cyp19a1a, etc.) involved in the steroid hormone biosynthesis pathway were found be altered. The expression of dmrt1, gsdf, cyp19a1a, and foxl2 was further verified by quantitative polymerase chain reaction. In the control group, the expression of dmrt1 and gsdf was significantly higher in XY larvae than in XX larvae, while the expression of foxl2 and cyp19a1a was significantly higher in XX larvae than in XY larvae (P < .05). AI treatment suppressed the expression of foxl2 and cyp19a1a, and induced the expression of dmrt1 and gsdf in XX larvae. MT treatment suppressed the expression of foxl2, cyp19a1a, dmrt1, and gsdf in XX larvae. E2 treatment suppressed the expression of dmrt1 and gsdf, but did not restore the expression of foxl2 and cyp19a1a in XY larvae. The shared response following AI, MT, and E2 treatment suggested that these genes are essential for sex differentiation. This finding offers some insight into AI or MT-induced masculinization, and E2-induced femininization in fugu.

Effects of the Thyroid Endocrine System on Gonadal Sex Ratios and Sex-Related Gene Expression in the Pufferfish Takifugu rubripes

To examine the effect and mechanism of thyroid hormone on gonadal sex differentiation, Takifugu rubripes larvae were treated with goitrogen (methimazole, MET, 1000 g/g), and thyroxine (T4, 2nM) from 25 to 80 days after hatching (dah). Gonadal histology and sex ratios of fish were then determined at 80 dah. MET treatment induced masculinization, but T4 treatment did not induce feminization in T. rubripes larvae. Transcriptomic analysis of gonads at 80 dah was then conducted. Among the large number of differentially expressed genes between the groups, the expression of foxl2, cyp19a1a, and dmrt1 was altered. The expression of foxl2, cyp19a1a, dmrt1 and gsdf at 25, 40, 55 days after treatment (dat) was further analyzed by qPCR. MET treatment suppressed the expression of foxl2 and cyp19a1a, and induced the expression of dmrt1 in genetic females (p < 0.05). Additionally, T4 treatment induced an increase in the expression of cyp19a1a in genetic XY gonads only at 25 dat. However, the increase in cyp19a1a expression did not continue to 40 and 55 dat. This may explain why feminization of larvae was not found in the T4-treated group. Thus, the present study provides the first evidence that MET treatment causes masculinization in teleost fish. The effects of MET-induced masculinization in T. rubripes may act primarily via suppression of the expression of foxl2 and cyp19a1a, and stimulation of the expression of dmrt1. Moreover, the effects of higher concentrations of T4 or different concentrations of T3, on sex differentiation require further testing.

Identification of sex differences in zebrafish (Danio rerio) brains during early sexual differentiation and masculinization using 17α-methyltestoterone

Sexual behavior in teleost fish is highly plastic. It can be attributed to the relatively few sex differences found in adult brain transcriptomes. Environmental and hormonal factors can influence sex-specific behavior. Androgen treatment stimulates behavioral masculinization. Sex dimorphic gene expression in developing teleost brains and the molecular basis for androgen-induced behavioral masculinization are poorly understood. In this study, juvenile zebrafish (Danio rerio) were treated with 100 ng/L of 17 alpha-methyltestosterone (MT) during sexual development from 20 days post fertilization to 40 days and 60 days post fertilization. We compared brain gene expression patterns in MT-treated zebrafish with control males and females using RNA-Seq to shed light on the dynamic changes in brain gene expression during sexual development and how androgens affect brain gene expression leading to behavior masculinization. We found modest differences in gene expression between juvenile male and female zebrafish brains. Brain aromatase (cyp19a1b), prostaglandin 3a synthase (ptges3a), and prostaglandin reductase 1 (ptgr1) were among the genes with sexually dimorphic expression patterns. MT treatment significantly altered gene expression relative to both male and female brains. Fewer differences were found among MT-treated brains and male brains compared to female brains, particularly at 60 dpf. MT treatment upregulated the expression of hydroxysteroid 11-beta dehydrogenase 2 (hsd11b2), deiodinase, iodothyronine, type II (dio2), and gonadotrophin releasing hormones (GnRH) 2 and 3 (gnrh2 and gnrh3) suggesting local synthesis of 11-ketotestosterone, triiodothyronine, and GnRHs in zebrafish brains which are influenced by androgens. Androgen, estrogen, prostaglandin, thyroid hormone, and GnRH signaling pathways likely interact to modulate teleost sexual behavior.

Expressional regulation of gonadotropin receptor genes and androgen receptor genes in the eel testis

Receptors for follicle-stimulating hormone (Fshr), luteinizing hormone (Lhcgr1 and Lhcgr2) and androgens (Ara and Arb) transduce the hormonal signals that coordinate spermatogenesis, but the factors that regulate the abundance of these transducers in fish testes remain little-understood. To mend this paucity of information, we first determined changes in transcript abundance for these receptors (fshr, lhcgr1, ara and arb) during spermatogenesis induced by human chorionic gonadotropin (hCG) injection in the eel, Anguilla australis. We related our findings to testicular production of the fish androgen, 11-ketotestosterone (11-KT), and to the levels of the transcripts encoding steroidogenic acute regulatory protein (star) and 11β-hydroxylase (cyp11b), and subsequently evaluated the effects of hCG or 11-KT on mRNA levels of these target genes in vitro. Testicular 11-KT production was greatly increased by hCG treatment, both in vivo and in vitro, and associated with up-regulation of star and cyp11b transcripts. In situ hybridization indicated that testicular fshr mRNA levels were higher in the early stages of hCG-induced spermatogenesis, while lhcgr1 transcripts were most abundant later, once spermatids were observed. In vitro experiments further showed that hCG and its steroidal mediator 11-KT significantly increased fshr transcript abundance. These data provide new angles on the interactions between gonadotropin and androgen signaling during early spermatogenesis. Increases in levels of 11-KT following hCG injection elevated testicular fshr mRNA levels augmenting Fsh sensitivity in the testis. This evidence is suggestive of a positive feedback loop between gonadotropins and 11-KT that may be key to regulating early spermatogenesis in fish.

Toxic effects of bisphenol A on goldfish gonad development and the possible pathway of BPA disturbance in female and male fish reproduction

Bisphenol A (BPA) is an abundant endocrine-disrupting compound that is found in the aquatic environment and has adverse effects on fish reproduction; however, the exact pathway of these impacts is unclear. In this study, the different effects of BPA on ovarian and testis development in goldfish (Carassius auratus) and the different mechanisms underlying these effects were investigated. The gonadosomatic index (GSI) and gonadal histology demonstrated that BPA diminished ovarian maturation in goldfish, which recovered after BPA treatment withdrawal. In males, BPA disrupted testis maturation, but this disruption could not be recovered after BPA treatment withdrawal. The hypothalamic-pituitary-gonad (HPG) axis-related genes sgnrh, fshβ and lhβ were significantly decreased in BPA-treated female fish, while no changes in sex steroid hormone levels and no TUNEL and PCNA staining were found in the ovary, suggesting that BPA may reduce ovarian maturation through the HPG axis. In male fish, TUNEL staining was found in 1 μg L^-1 BPA-exposed germ cells and 50 and 500 μg L^-1 BPA-exposed Leydig cells. Decreases in 11-KT levels were also found in 50 and 500 μg L^-1 BPA-exposed fish, but BPA did not affect genes associated with the HPG axes. This result shows that BPA disrupts testis maturation through apoptosis of germ cells and Leydig cells, thus inducing decreases in 11-KT levels that disrupt spermatogenesis. Collectively, our findings provide insights into the molecular and cellular mechanisms underlying BPA disturbance of goldfish reproduction.

Expression of gonadotropin subunit and gonadotropin receptor genes in wild female New Zealand shortfinned eel (Anguilla australis) during yellow and silver stages

Despite tremendous importance of follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh) as primary controllers of reproductive development, information on the expression profiles of the genes encoding gonadotropin subunits and gonadotropin receptors (Fshr and Lhr) in wild eels are essentially non-existent. This study investigated pituitary fshb and lhb mRNA levels and ovarian fshr and lhr mRNA levels of wild shortfinned eels, Anguilla australis at different stages of oogenesis. Protein expression of Fsh in the pituitary was also quantified and visualized using slot blot and immunohistochemistry. Pituitary fshb and lhb mRNA levels showed a differential expression pattern, fshb mRNA levels increasing significantly from the perinucleolus (PN) to the oil droplet stage (OD) before slightly decreasing (not significantly) in the early vitellogenic stage (EV). A similar trend was observed in relative Fsh protein levels analyzed by slot blot and immunohistochemistry, but this trend was not reflected in the plasma levels of sex steroids. In contrast, pituitary lhb mRNA levels increased significantly from the PN to EV stage. A higher expression of Fsh at both mRNA and protein levels in the pituitary of eels at the OD stage compared to other investigated stages suggests that synthesis of Fsh production in the pituitary may reach a peak at the OD stage. In the ovary, transcript abundances of fshr and lhr gradually increased during previtellogenic follicle growth, but markedly and significantly increased thereafter. Taken together, our data suggest i) that Fsh release may be very limited, or absent, prior to onset of puberty in shortfinned eels and ii) that Lh is not functionally important in this fish during the EV stage.

Histological and transcriptomic effects of 17α-methyltestosterone on zebrafish gonad development

BACKGROUND

Sex hormones play important roles in teleost ovarian and testicular development. In zebrafish, ovarian differentiation appears to be dictated by an oocyte-derived signal via Cyp19a1a aromatase-mediated estrogen production. Androgens and aromatase inhibitors can induce female-to-male sex reversal, however, the mechanisms underlying gonadal masculinisation are poorly understood. We used histological analyses together with RNA sequencing to characterise zebrafish gonadal transcriptomes and investigate the effects of 17α-methyltestosterone on gonadal differentiation.

RESULTS

At a morphological level, 17α-methyltestosterone (MT) masculinised gonads and accelerated spermatogenesis, and these changes were paralleled in masculinisation and de-feminisation of gonadal transcriptomes. MT treatment upregulated expression of genes involved in male sex determination and differentiation (amh, dmrt1, gsdf and wt1a) and those involved in 11-oxygenated androgen production (cyp11c1 and hsd11b2). It also repressed expression of ovarian development and folliculogenesis genes (bmp15, gdf9, figla, zp2.1 and zp3b). Furthermore, MT treatment altered epigenetic modification of histones in zebrafish gonads. Contrary to expectations, higher levels of cyp19a1a or foxl2 expression in control ovaries compared to MT-treated testes and control testes were not statistically significant during early gonad development (40 dpf).

CONCLUSION

Our study suggests that both androgen production and aromatase inhibition are important for androgen-induced gonadal masculinisation and natural testicular differentiation in zebrafish.

Early-life glucocorticoids programme behaviour and metabolism in adulthood in zebrafish

Glucocorticoids (GCs) in utero influence embryonic development with consequent programmed effects on adult physiology and pathophysiology and altered susceptibility to cardiovascular disease. However, in viviparous species, studies of these processes are compromised by secondary maternal influences. The zebrafish, being fertilised externally, avoids this problem and has been used here to investigate the effects of transient alterations in GC activity during early development. Embryonic fish were treated either with dexamethasone (a synthetic GC), an antisense GC receptor (GR) morpholino (GR Mo), or hypoxia for the first 120h post fertilisation (hpf); responses were measured during embryonic treatment or later, post treatment, in adults. All treatments reduced cortisol levels in embryonic fish to similar levels. However, morpholino- and hypoxia-treated embryos showed delayed physical development (slower hatching and straightening of head-trunk angle, shorter body length), less locomotor activity, reduced tactile responses and anxiogenic activity. In contrast, dexamethasone-treated embryos showed advanced development and thigmotaxis but no change in locomotor activity or tactile responses. Gene expression changes were consistent with increased (dexamethasone) and decreased (hypoxia, GR Mo) GC activity. In adults, stressed cortisol values were increased with dexamethasone and decreased by GR Mo and hypoxia pre-treatments. Other responses were similarly differentially affected. In three separate tests of behaviour, dexamethasone-programmed fish appeared 'bolder' than matched controls, whereas Mo and hypoxia pre-treated fish were unaffected or more reserved. Similarly, the dexamethasone group but not the Mo or hypoxia groups were heavier, longer and had a greater girth than controls. Hyperglycaemia and expression of GC responsive gene (pepck) were also increased in the dexamethasone group. We conclude that GC activity controls many aspects of early-life growth and development in the zebrafish and that, like other species, manipulating GC status pharmacologically, physiologically or genetically in early life leads to programmable metabolic and behavioural traits in adulthood.

A comparative study of vitellogenesis in Echinodermata: Lessons from the sea star

The provision of yolk precursor proteins to the oviparous egg is crucial for normal embryo development. In Echinodermata, a transferrin-like yolk component termed major yolk protein (MYP) is a major precursor protein in Echinoidea and Holothuroidea. In contrast, in Asteroidea a single vitellogenin (Vtg) was recently identified, but its role as primary yolk protein remains unclear. To resolve the apparent MYP-Vtg dichotomy in sea stars and to understand the dynamics of candidate yolk protein gene expression during the reproductive cycle, we investigated the molecular structures of sea star Vtg and MYP and quantified their transcript levels during oogenesis. By combining protein sequencing of the predominant proteins in ovulated eggs of Patiriella regularis with ovarian transcriptome sequencing and molecular cloning, we characterized two cDNAs encoding two bona fide Vtgs (PrVtg1 and PrVtg2) and a partial cDNA encoding MYP (PrMYP). PrMYP mRNA was found in low abundance in growing oocytes, possibly as maternal transcripts for translation after ovulation. In contrast, PrVtg transcripts, whose levels varied during the reproductive cycle, were not found in developing oocytes - rather, they were detected in ovarian follicle cells and pyloric caeca, indicating an extra-oocytic origin. Vtg accumulating in oocytes was stored in the form of cleaved products, which constituted the most abundant yolk polypeptides in ovulated sea star eggs; their levels decreased during early embryonic and larval development. Together, these traits are the hallmarks of a classical yolk protein - and hence, we contend that Vtg, and not MYP, is the main yolk protein in asteroids.

Production of germ cell-deficient salmonids by dead end gene knockdown, and their use as recipients for germ cell transplantation

We previously established a spermatogonial transplantation model in fish using triploid recipients. Although triploid salmonids are sterile, they carry a limited number of immature triploid germ cells that potentially compete with the donor-derived germ cells for their niche. We therefore assessed the biological characteristics of germ cell-deficient gonads in rainbow trout for their suitability as recipients for germ cell transplantation in this study. Antisense morpholino oligonucleotides against the dead end gene were microinjected into the fertilized eggs of rainbow trout to eliminate endogenous germ cells, leaving only their supporting cells. Unlike similar approaches performed in zebrafish and medaka, these germ cell-deficient rainbow trout did not show a male-biased sex ratio. Approximately 30,000 spermatogonia were then transplanted into the body cavities of both germ cell-deficient and control recipients. The donor-derived germ cells showed significantly higher proliferation in the gonads of germ cell-deficient recipients than those in the gonads of the control recipients. Finally, the applicability of the germ cell-deficient recipients for xenogeneic transplantation was evaluated by transplanting rainbow trout spermatogonia into germ cell-deficient masu salmon recipients. The resulting recipient salmon matured normally and produced trout gametes, and early survival of the resulting trout offspring was as high as that of the control offspring. Thus, dead end-knockdown salmonids appear to be ideal recipients for the intraperitoneal transplantation of spermatogonia.

Gonadal Transcriptome Analysis in Sterile Double Haploid Japanese Flounder

Sterility is a serious problem that can affect all bionts. In teleosts, double haploids (DHs) induced by mitogynogenesis are often sterile. This sterility severely restricts the further application of DHs for production of clones, genetic analysis, and breeding. However, sterile DH individuals are good source materials for investigation of the molecular mechanisms of gonad development, especially for studies into the role of genes that are indispensable for fish reproduction. Here, we used the Illumina sequencing platform to analyze the transcriptome of sterile female DH Japanese flounder in order to identify major genes that cause sterility and to provide a molecular basis for an intensive study of gonadal development in teleosts. Through sequencing, assembly, and annotation, we obtained 52,474 contigs and found that 60.7% of these shared homologies with existing sequences. A total of 1225 differentially expressed unigenes were found, including 492 upregulated and 733 downregulated genes. Gene Ontology and KEGG analyses showed that genes showing significant upregulation, such as CYP11A1, CYP11B2, CYP17, CYP21, HSD3β, bcl2l1, and PRLR, principally correlated with sterol metabolic process, steroid biosynthetic process, and the Jak-stat signaling pathway. The significantly downregulated genes were primarily associated with immune response, antigen processing and presentation, cytokine–cytokine receptor interaction, and protein digestion and absorption. Using a co-expression network analysis, we conducted a comprehensive comparison of gene expression in the gonads of fertile and sterile female DH Japanese flounder. Identification of genes showing significantly different expression will provide further insights into DH reproductive dysfunction and oocyte maturation processes in teleosts.

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.

Steroidogenesis and phase II conjugation during the gametogenesis of thicklip grey mullet (Chelon labrosus) from a population showing intersex condition

Steroidogenesis, the process by which steroid hormones are synthesized, involves a vast number of enzymes and biochemical pathways that are susceptible to chemical modulation. Endocrine disrupting compounds (EDCs) are of special concern since they can alter hormone homeostasis by interfering with synthesis, transport and elimination of hormones. It is important to understand gender differences and the natural variation in steroid balance through gamete development in fish exposed to EDCs. The aim of this study was to determine mRNA levels of genes encoding for Steroidogenic Acute Regulatory (star) protein; the steroidogenic enzymes P450 11β hydroxylase (cyp11b1) and P450 aromatase (cyp19a1a); as well as the phase II conjugation enzymes sulfotransferase (sult) and UDP-glucuronosyltransferase (ugt), together with the activity of P450 aromatase and plasma levels of 17β-estradiol (E2) and 11-ketotestosterone (11-KT), at different gametogenic stages and in intersex individuals of the thicklip grey mullet Chelon labrosus. Results demonstrated that the transcription levels of star, sult and ugt and levels of E2 and 11-KT in plasma significantly changed with the interaction between gender and reproductive stage. Cyp11b1 and cyp19a1a transcription levels were significantly different between genders while the activity of P450 aromatase varied significantly between genders and reproductive stages. Results from a multivariate assessment demonstrated that measured endpoints distinguished male, female and intersex mullets at immature gametogenic stage. Intersex distinction was based on sult, ugt and cyp19a1a transcript levels and P450 aromatase activity. The present work provides data to be used in future experimental designs with C. labrosus species, and gives new clues about the molecular events that lead to intersex occurrence in mullets.

Localization of steroidogenic enzymes and Foxl2a in the gonads of mature zebrafish (Danio rerio)

In zebrafish, the identification of the cells expressing steroidogenic enzymes and their regulators is far from completely fulfilled though it could provide crucial information on the elucidation of the role of these enzymes. The aim of this study was to better characterize the expression pattern of steroidogenic enzymes involved in estrogen and androgen production (Cyp17-I, Cyp11c1, Cyp19a1a and Cyp19a1b) and one of their regulators (Foxl2a) in zebrafish gonads. By using immunohistochemistry, we localized the steroid-producing cells in mature zebrafish gonads and determined different expression patterns between males and females. All these steroidogenic enzymes and Foxl2a were detected both in the testis and ovary. In the testis, they were all localized both in Leydig and germ cells except Cyp19a1b which was only detected in germ cells. In the ovary, Cyp17-I, Cyp19a1a and Foxl2a were immunolocalized in both somatic and germ cells while Cyp19a1b was only detected in germ cells and Cyp11c1 in somatic cells. Moreover, Cyp19a1a and Foxl2a did not display exactly the same patterns of spatial localization but their expressions were correlated suggesting a possible regulation of cyp19a1a gene by Foxl2a in zebrafish. Comparative analysis revealed a dimorphic expression of Cyp11c1, Cyp19a1a, Cyp19a1b and Foxl2a between males and females. Overall, our study provides a detailed description of the expression of proteins involved in the biosynthesis of steroidal hormones at the cellular scale within gonads, which is critical to further elucidating the intimate roles of the enzymes and the use of the zebrafish as a model in the field of endocrinology.

Changes in Plasma Sex Steroid and Cortisol Levels during Annual Reproductive Cycle of Ribbed Gunnel, Dictyosoma burgeri

We investigated the changes in plasma sex steroid hormones, testosterone (T), estradiol-17β (E₂), 17,20β -dihydroxy-4-pregnen-3-one (17α20βP), 11-ketotestosterone (11KT) and cortisol levels from ribbed gunnel, Dictyosoma burgeri in associated with annual reproductive cycle. The gonadosomatic index (GSI) of females increased from November, peaked in February and decreased rapidly from March. The GSI of males also increased from November, peaked in January and then decreased gradually. In females, E₂ levels increased and remained high from December to February. The levels of T showed a similar tendency and correlated (r_s=0.898, p<0.01) with E₂ levels. The levels of 17α20βP increased rapidly in February (4.78±1.01 ng/ml) and peaked in July (5.08±0.65 ng/ml). Cortisol level was peaked in March and correlated with 17α20βP levels (r_s=0.696, p<0.01). In males, the levels of T was peaked in January and then decreased rapidly. The levels of 11KT were remained high from October to January. On the other hand, the levels of 17α20βP fluctuated during reproductive cycle. These results suggest that plasma sex steroids in ribbed gunnels have annual periodicity, and that cortisol may involve in maturation of females.

Dynamic expression of 11β-hydroxylase during testicular development, recrudescence and after hCG induction, in vivo and in vitro in catfish, Clarias batrachus

Cytochrome P450 11β-hydroxylase (11β-h), is involved in the production of 11-hydroxytestosterone, an immediate precursor for 11-ketotestosterone (11-KT), a potent androgen in teleosts. To understand the role of 11β-h in gonadal development, maturation, function and recrudescence in an annually reproducing teleost, the present study was conducted using Clarias batrachus. Four forms of 11β-h cDNA, regular type (2.253 kb), variant 1 (1.290 kb), variant 2 (1.223 kb) and variant 3 (1.978 kb) were identified from the testis of catfish which expressed ubiquitously with high levels in testis. 11β-h transcripts were detected as early as 0 days post hatch further, stage- and sex-dependent increase in the 11β-h transcripts were seen during gonadal differentiation/development. In addition, high expression of 11β-h (regular type) in pre-spawning phase was detected. Corroboratively, levels of 11-KT in serum and testicular tissue was high during pre-spawning and spawning phases, which might facilitate initiation and normal progression of spermatogenesis. The expression of 11β-h was high after human chorionic gonadotropin induction in vivo (all forms), and in vitro (regular type). Immunohistochemical and immunofluorescence localization showed the presence of 11β-h in Sertoli and interstitial/Leydig cells of the testis. These results suggest that 11β-h is involved in late stages of testicular development, together with the regulation of seasonal reproductive cycle in catfish.

The acute salinity changes activate the dual pathways of endocrine responses in the brain and pituitary of tilapia

To analyze and compare the stress and osmoregulatory hormones and receptors in pituitary during acute salinity changes, the expression patterns of corticotropin releasing hormone (crh) in hypothalamus, prolactin (prl) releasing peptide (pRrp) in telencephalon and diencephalon, glucocorticoid receptors 2 (gr2), and mineralocorticoid receptor (mr), crh-r, pro-opiomelanocorticotropin (pomc), pRrp, prl, dopamine 2 receptor (d2-r), growth hormone (gh), gh-receptor (gh-r) and insulin-like growth hormone (igf-1) transcripts in pituitary were characterized in euryhaline tilapia. The results indicate that the crh transcripts increased in the hypothalamus and rostral pars distalis of the pituitary after the transfer of fish to SW. Similarly, the pRrp transcripts were more abundant in SW acclimated tilapia forebrain and hypothalamus. The crh-r, gr2 and mr transcripts were more expressed in rostral pars distalis and pars intermedia of pituitary at SW than FW tilapia. The data indicate that the SW acclimation stimulates these transcripts in the specific regions of the brain and pituitary which may be related to the activation of the hypothalamic-pituitary-interrenal (HPI)-axis. The results of dual in situ hybridization reveal that the transcripts of crh-r, gr2 and mr with pomc are highly co-localized in corticotrophs of pituitary. Furthermore, we demonstrate high expression of pRrp in the brain and low expression of pRrp and prl transcripts in the pituitary of SW fish. No crh-r and corticosteroid receptors were co-localized with prl transcripts in the pituitary. The gh-r and igf-1 mRNA levels were significantly increased in SW acclimated tilapia pituitary whereas there was no difference in the gh mRNA levels. The data suggest that the locally produced pRrp and d2-r may control and regulate the expression of prl mRNA in pituitary. Therefore, the dual roles of pRrp are involved in the stress (via brain-pituitary) and osmoregulatory (via pituitary) pathways in tilapia exposed to acute salinity changes.

Relaxin-related gene expression differs between anadromous and stream-resident stickleback (Gasterosteus aculeatus) following seawater transfer

Relaxin (RLN) is a hormone that was originally identified as a regulator of pregnancy and reproduction. However, recent mammalian studies have demonstrated that relaxins also have potent osmoregulatory actions. In mammals, six relaxin family peptides have been identified: RLN1/2, RLN3, insulin-like peptide (INSL) 3, INSL4, INSL5, and INSL6. Previous genome database searches have revealed that teleosts also possess multiple relaxin family genes. However, the functions of these relaxin family peptides in teleosts remain unclear. In order to gain insight into the osmoregulatory functions of teleost relaxins, we studied the relaxin family peptides in euryhaline three-spined sticklebacks (Gasterosteus aculeatus), which have diversified into a variety of ecotypes. Rln3a, rln3b, and rln transcripts were abundant in the stickleback brain, whereas insl5b transcript levels were highest in the intestine among tissues. Seawater challenge experiments showed that transcript levels of rln3a, rln3b, and rln in the brain changed significantly after seawater transfer. Particularly, rln3b showed different patterns of temporal changes between anadromous and stream-resident morphs. The transcript levels of relaxin family peptide receptors, rxfp1, rxfp2b, rxfp3-2a, and rxfp3-2b, did not exhibit substantial changes in the brain, although these were constantly higher in the anadromous morph than the stream-resident morph. These results suggest that stickleback relaxin systems are differentially regulated by salinity signals, at least at the transcriptional level, and anadromous and stream-resident morphs differ in relaxin signaling pathways. The differences in the expression of relaxin-related genes between these two morphs provide a foundation for further exploration of the osmoregulatory function of relaxins in teleosts.

Identification of a gonad-expression differential gene insulin-like growth factor-1 receptor (Igf1r) in the swamp eel (Monopterus albus)

In vertebrate species, the biopotential embryonic gonad differentiation is affected by many key genes and key steroidogenic enzymes. Insulin-like growth factor-1 receptor (Igf1r) has been considered as an important sex-differentiation gene in mammals and could mediate the biological action of Igf1, an important regulator of key steroidogenic enzymes. However, Igf1r gene is still unknown in the swamp eel, an economically important fish. In our study, we identified Igf1r gene in the swamp eel, which was a 2,148-bp open-reading frame encoding a protein of 716 amino acids. The alignment and the phylogenetic tree showed that Igf1r of the swamp eel had a conservative sequence with other vertebrates, especial fishes. Western blotting of Igf1r showed that Igf1r expressed much more in ovotestis and testis than in ovary, indicating an important role of Igf1r during gonad differentiation. We analyzed ubiquitination of Igf1r by co-immunoprecipitation and found the amount of ubiquitinated Igf1r was increased from ovary, ovotestis to testis, which was reversely to the trend of Hsp10 expression during gonadal transformation. It was possible that Hsp10 could suppress Igf1r ubiquitination during gonadal development of the swamp eel.

Characterization of two paralogous StAR genes in a teleost, Nile tilapia (Oreochromis niloticus)

Steroidogenic acute regulatory protein (StAR) transports cholesterol, the substrate for steroid synthesis, to the inner membranes of mitochondria. It is well known that estrogen is essential for female sex determination/differentiation in fish. However, no reports showed that the conventional StAR, which was supposed to be essential for estrogen production, was expressed in female gonads during the critical timing of sex determination/differentiation. In this study, two different StAR isoforms, named as StAR1 and StAR2, were characterized from the gonads of Nile tilapia (Oreochromis niloticus). Phylogenetic and synteny analysis revealed that two StAR genes existed in teleosts, Xenopus and chicken indicating that the duplication event occurred before the divergence of teleosts and tetrapods. Real-time PCR revealed that StAR1 was dominantly expressed in the testis, head kidney and kidney; while StAR2 was expressed exclusively in the gonads. In situ hybridization and immunohistochemistry demonstrated that StAR1 was expressed in the interrenal cells of the head kidney and Leydig cells of the testis; while StAR2 was expressed in the Leydig cells of the testis and the interstitial cells of the ovary. Ontogenic analysis demonstrated that StAR2 was expressed abundantly from 5 days after hatching (dah) in the somatic cells in XX gonads, whereas in XY gonads, both StARs could be detected from 30 dah until adulthood. Intraperitoneal injection of human chorionic gonadotropin experiments showed that expression of StAR1 and 2 was significantly elevated at 8h and persisted until 24h after injection in the testis. Taken together, our data suggested that StAR1 is likely to be required for cortisol production in the head kidney, and StAR2 is probably involved in estrogen production during early sex differentiation in XX gonads. In contrast, both StARs might be required for androgen production in testes. For the first time, our data demonstrated that two fish StARs might be involved in steroidogenesis in a tissue and developmental stage dependent manner.

The cytochrome P450 genes of channel catfish: their involvement in disease defense responses as revealed by meta-analysis of RNA-Seq data sets

BACKGROUND

Cytochrome P450s (CYPs) encode one of the most diverse enzyme superfamily in nature. They catalyze oxidative reactions of endogenous molecules and exogenous chemicals.

METHODS

We identified CYPs genes through in silico analysis using EST, RNA-Seq and genome databases of channel catfish. Phylogenetic analyses and conserved syntenic analyses were conducted to determine their identities and orthologies. Meta-analysis of RNA-Seq databases was conducted to analyze expression profile of CYP genes following bacterial infection.

RESULTS

A full set of 61 CYP genes was identified and characterized in channel catfish. Phylogenetic tree and conserved synteny provided strong evidence of their identities and orthorlogy. Lineage-specific gene duplication was evident in a number of clans in channel catfish. CYP46A1 is missing in the catfish genome as observed with syntenic analysis and RT-PCR analysis. Thirty CYPs were found up- or down-regulated in liver, while seven and eight CYPs were observed regulated in intestine and gill following bacterial infection.

CONCLUSION

We systematically identified and characterized a full set of 61 CYP genes in channel catfish and studied their expression profiles after bacterial infection. While bacterial challenge altered the expression of large numbers of CYP genes, the mechanisms and significance of these changes are not known.

GENERAL SIGNIFICANCE

This work provides an example to systematically study CYP genes in non-model species. Moreover, it provides a basis for further toxicological and physiological studies in channel catfish.

Steroidogenic acute regulatory protein transcript abundance in the eel, Anguilla australis: changes during the induced reproductive cycle and effects of follicle-stimulating hormone during previtellogenesis

Steroidogenic acute regulatory protein (StAR) mRNA levels in the eel ovary were assayed by quantitative PCR and related to plasma steroid levels throughout oogenesis in order to shed light on the previously considered 'aberrant' prematurational increase in plasma levels of estradiol-17β (E2). Total ovarian StAR transcript abundance mirrored circulating levels of E2, but not of 11-ketotestosterone (11KT). The study was complemented by evaluation of in vitro effects of follicle-stimulating hormone (FSH) on ovarian StAR transcript abundance and on short-term ('acute') radiolabelled pregnenolone-supported steroid metabolism by ovarian fragments to understand how the production of steroids during previtellogenic oocyte growth is regulated. We observed a significant effect of FSH on StAR mRNA levels within 24h of incubation, but these were no longer evident by 4 days of culture. Unexpectedly, FSH had no effect on substrate-supported steroidogenesis, as comparable yields of steroid products were detected using semi-quantitative HPLC and scintillation counting. We conclude that the eel ovarian follicle can respond to FSH from a very early stage of development (early oil droplet stage) by increasing StAR mRNA levels, but that there is no evidence for acute effects of FSH on bioactive steroid production downstream of cytochrome P450 side-chain cleavage. Furthermore, the prematurational increase in StAR mRNA in vivo is in keeping with general teleost models and is likely to be a 'normal' response to reaching advanced stages of development.

Evaluation of reproductive endocrine status in hornyhead turbot sampled from Southern California's urbanized coastal environments

As part of a regionwide collaboration to determine the occurrence of contaminants and biological effects in coastal ecosystems offshore of urban southern California, the present study characterized the reproductive endocrinology of an indigenous flatfish, the hornyhead turbot (Pleuronichthys verticalis), and compared groups sampled from different study sites representing varying degrees of pollution to screen for potential endocrine disruptive effects. Turbot were sampled from locations near the coastal discharge sites of four large municipal wastewater treatment plants (WWTPs) located between Los Angeles and San Diego, California, USA, and were compared with fish sampled from three far-field reference locations in the region. Despite environmental presence of both legacy contaminants and contaminants of emerging concern and evidence for fish exposure to several classes of contaminants, both males and females generally exhibited coordinated seasonal reproductive cycles at all study sites. Patterns observed included peaks in sex steroids (17β-estradiol, testosterone, 11-ketotestosterone) in the spring and low levels in the fall, changes corresponding to similarly timed gonadal changes and plasma vitellogenin concentrations in females. Comparisons between fish captured at the different study sites demonstrated some regional differences in plasma levels of estrogens and androgens, indicative of location-associated effects on the endocrine system. The observed differences, however, could not be linked to the ocean discharge locations of four of the largest WWTPs in the world.

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.

Divergence in sex steroid hormone signaling between sympatric species of Japanese threespine stickleback

Sex steroids mediate the expression of sexually dimorphic or sex-specific traits that are important both for mate choice within species and for behavioral isolation between species. We investigated divergence in sex steroid signaling between two sympatric species of threespine stickleback (Gasterosteus aculeatus): the Japan Sea form and the Pacific Ocean form. These sympatric forms diverge in both male display traits and female mate choice behaviors, which together contribute to asymmetric behavioral isolation in sympatry. Here, we found that plasma levels of testosterone and 17β-estradiol differed between spawning females of the two sympatric forms. Transcript levels of follicle-stimulating hormone-β (FSHβ) gene were also higher in the pituitary gland of spawning Japan Sea females than in the pituitary gland of spawning Pacific Ocean females. By contrast, none of the sex steroids examined were significantly different between nesting males of the two forms. However, combining the plasma sex steroid data with testis transcriptome data suggested that the efficiency of the conversion of testosterone into 11-ketotestosterone has likely diverged between forms. Within forms, plasma testosterone levels in males were significantly correlated with male body size, a trait important for female mate choice in the two sympatric species. These results demonstrate that substantial divergence in sex steroid signaling can occur between incipient sympatric species. We suggest that investigation of the genetic and ecological mechanisms underlying divergence in hormonal signaling between incipient sympatric species will provide a better understanding of the mechanisms of speciation in animals.

Cloning and expression of the translocator protein (18 kDa), voltage-dependent anion channel, and diazepam binding inhibitor in the gonad of largemouth bass (Micropterus salmoides) across the reproductive cycle

Cholesterol transport across the mitochondrial membrane is rate-limiting for steroidogenesis in vertebrates. Previous studies in fish have characterized expression of the steroidogenic acute regulatory protein, however the function and regulation of other genes and proteins involved in piscine cholesterol transport have not been evaluated. In the current study, mRNA sequences of the 18 kDa translocator protein (tspo; formerly peripheral benzodiazepine receptor), voltage-dependent anion channel (vdac), and diazepam binding inhibitor (dbi; also acyl-CoA binding protein) were cloned from largemouth bass. Gonadal expression was examined across reproductive stages to determine if expression is correlated with changes in steroid levels and with indicators of reproductive maturation. In testis, transcript abundance of tspo and dbi increased with reproductive maturation (6- and 23-fold maximal increase, respectively) and expression of tspo and dbi was positively correlated with reproductive stage, gonadosomatic index (GSI), and circulating levels of testosterone. Testis vdac expression was positively correlated with reproductive stage and GSI. In females, gonadal tspo and vdac expression was negatively correlated with GSI and levels of plasma testosterone and 17β-estradiol. Ovarian dbi expression was not correlated with indicators of reproductive maturation. These studies represent the first investigation of the steroidogenic role of tspo, vdac, and dbi in fish. Findings suggest that cholesterol transport in largemouth bass testis, but not in ovary, may be transcriptionally-regulated, however further investigation will be necessary to fully elucidate the role of these genes in largemouth bass steroidogenesis.

Localization of diversified relaxin gene transcripts in the brain of eels

Relaxin 3 (RLN3) is a newly-discovered member of the insulin superfamily. We isolated three RLN3-like cDNAs from the brain of the Japanese eel (Anguilla japonica). The deduced amino acid sequences of the RLN3-like cDNAs contained the two-chain structure common to relaxin including a RXXXRXXI/V motif in the B-chain. Phylogenetic analysis assigned the two prepropeptides into teleost/mammalian RLN3 group, which are a pair of duplicates generated by the teleost-specific third-round whole genome duplication, and the other one into teleost RLN group. Therefore, they have been named eel rln3a, rln3b and rln. rln3a transcripts were abundant in the middle-posterior region of the brain and detected at lower levels in the gills, head kidney and kidney. rln3b transcripts were also detected in the middle-posterior region of the brain, but the expression levels were lower than those of rln3a. Low levels of rln transcripts were detected in all brain areas, pituitary, digestive tract and gonad. Quantitative PCR analysis did not detect differences in expression of any rln3 or rln gene between freshwater- and seawater-acclimated eels. In situ hybridization showed that rln3a was expressed in neurons of the lateral lemniscus of the midbrain and of the griseum centrale (GC) of the hindbrain, while low amounts of rln transcripts were found in neurons of the periventricular nucleus of the posterior tuberculum of the diencephalon and the GC. These results suggest that the multiple RLN3-like peptides may play regulatory roles in the brain of euryhaline fish.

Cloning, pharmacological characterization, and expression analysis of Atlantic salmon (Salmo salar L.) nuclear progesterone receptor

To better understand the role(s) of progestogens during early stages of spermatogenesis, we carried out studies on the nuclear progesterone receptor (Pgr) of the Atlantic salmon. Its open-reading frame shows the highest similarity with other piscine Pgr proteins. When expressed in mammalian cells, salmon Pgr exhibited progestogen-specific, dose-dependent induction of reporter gene expression, with 17α,20β-dihydroxy-4-pregnen-3-one (DHP) showing the highest potency. We then analyzed testicular pgr mRNA and DHP plasma levels in animals during the onset of spermatogenesis, which were exposed to natural light or to constant light, to induce significant differences in testis growth. Grouping of the animals according to their progress through spermatogenesis showed that testicular pgr mRNA levels as well as DHP plasma levels first increased when germ cells had reached the stage of late type B spermatogonia and further increased when entered meiosis, i.e. when spermatocytes were present. However, in situ hybridization studies revealed that pgr mRNA expression was restricted to Sertoli cells, with a strong signal in Sertoli cells contacting type A/early type B spermatogonia, while Sertoli cells contacting larger germ cell clones with further differentiated stages (e.g. late type B spermatogonia) were less intensely/not stained. We conclude that the increase in pgr mRNA levels per pair of testis reflects, at least in part, the increased number of Sertoli cells enveloping type A and early type B spermatogonia. We propose that Sertoli cell-expressed Pgr may mediate DHP-stimulated early steps in spermatogenesis in Atlantic salmon, such as an increase in the number of new spermatogonial cysts.

Evaluation of Sycp3, Plzf and Cyclin B3 expression and suitability as spermatogonia and spermatocyte markers in zebrafish

Recent studies in mammals have revealed the heterogeneity of spermatogonial populations which contain differentiated and undifferentiated cells that further divide into actual stem cells and potential stem cells. In fish however, there are no functional definitions, and very few molecular markers, for germ cells. In our present study, specific antibodies were raised against Sycp3, Plzf and Cyclin B3 in zebrafish and then used to determine the localization of these proteins in the testis. We wished to confirm whether these molecules were potential markers for spermatocytes and spermatogonia. Immunohistochemical observations revealed that Sycp3 is specifically localized in spermatocytes in typical nuclear patterns at each meiotic stage. Plzf was found to be localized in the nucleus of both type A and type B spermatogonia until the 8-cell clone, similar to the pattern in Plzf-positive A(single)-A(aligned) undifferentiated spermatogonia in rodents. In addition to Plzf, the localization of Cyclin B3 was predominantly detected in the nuclei of type A and early type B spermatogonia until the 16-cell clone. Additionally, Cyclin B3 protein signals were detected in germ cells in large cysts, possibly corresponding to spermatocytes at the preleptotene stage. Our present data thus show that these molecules have properties that will enable their use as markers of spermatocytes and early spermatogonia in zebrafish.

Effects of reproductive stage and 11-ketotestosterone on LPL mRNA levels in the ovary of the shortfinned eel

To understand the dynamics of lipid uptake into the ovary and the potential role that lipoprotein lipase plays in this event, changes in LPL transcript abundance during oogenesis were measured in both wild-caught and pituitary homogenate-induced artificially maturing eels. Also, the effects of 11-ketotestosterone (11-KT) on LPL mRNA levels were investigated in vivo and in vitro. Normalized ovarian LPL transcript abundance increased as oogenesis advanced, and it rose particularly rapidly during midvitellogenesis, corresponding to pronounced increases in ovarian lipid deposits and LPL activity. Furthermore, LPL mRNA levels were dramatically increased following 11-KT treatment in vivo, findings that were reinforced as trends in ovarian tissue incubated in vitro. Ovarian LPL appears to be directly involved in the uptake of lipids into the eel ovary, an involvement that appears to be controlled, at least in part, by the androgen 11-KT.

Effects of reproductive stage, GH, and 11-ketotestosterone on expression of growth differentiation factor-9 in the ovary of the eel, Anguilla australis

In order to study the regulation of the growth differentiation factor-9 (gdf9) gene in a primitive teleost with semelparous life history, we cloned a cDNA encoding shortfinned eel Gdf9, expressed a partial peptide in Escherichia coli, and raised an antiserum to evaluate changes in Gdf9 expression during its pituitary homogenate-induced reproductive cycle. The effects of in vivo and in vitro exposure to the androgen 11-ketotestosterone (11-KT), known to affect previtellogenic (PV) oocyte growth, were also determined. Furthermore, we investigated whether Gdf9 expression was metabolically gated by treating PV fish with recombinant GH in vivo. Immunoreactive proteins of ca. 52 and 55 kDa were identified by western blot analysis. Gdf9 message and protein were most abundant in PV oocytes, and peaked slightly earlier for mRNA than for protein. Captivity resulted in reduced gdf9 mRNA levels, which were restored following pituitary homogenate treatment. As oocytes progressed through induced oogenesis, Gdf9 expression decreased. Neither 11-KT nor GH treatment affected gdf9 mRNA levels in PV fish, although GH could partially restore handling- or captivity-induced decreases in gdf9 mRNA levels. Semelparous eels thus show an expression pattern of Gdf9 during oogenesis that is similar to that seen in other vertebrates, that appears responsive to handling or captivity stress, and whose control remains to be elucidated.

Effects of tributyltin on salmon interrenal CYP11β, steroidogenic factor-1 and glucocorticoid receptor transcripts in the presence and absence of second messenger activator, forskolin

The mechanisms by which TBT produces modulations of the endocrine systems are not fully described. In this study, juvenile salmon were force-fed diet containing TBT (0: solvent control, 0.1, 1 and 10 mg/kg fish) for 72 h. Subsequently, fish exposed to solvent control and 10 mg/kg TBT were exposed to waterborne concentration of the adenyl cyclase stimulator forskolin (200 μg/L) for 2 and 4 h. Tissue and blood were sampled from individual fish (n=6). Gene expression patterns of CYP11β, steroidogenic factor-1 (SF-1), and glucocorticoid receptor (GlucR) were determined by qPCR. TBT generally decreased mRNA levels of CYP11β, GlucR and SF-1, compared to the solvent control and these effects were differentially modulated by the presence of forskolin. This study suggests that TBT may exert broader endocrine disrupting effects through possible modulation of cAMP/PKA second messenger systems.

Molecular characterization of cyp11a1 and cyp11b1 and their gene expression profile in pejerrey (Odontesthes bonariensis) during early gonadal development

Sex steroids are known to be involved in gonadal differentiation in fish, but whether androgens are early mediators of testis differentiation remains unclear. We studied the sex-related developmental variations in the gene expression of two key enzymes involved in steroids and androgen synthesis (cyp11a1 and cyp11b1) in trunks and isolated gonads of pejerrey (Odontesthes bonariensis) larvae during and after the sex determination period. Also, and in order to have a better characterization of this process we studied the expression of Sertoli (dmrt1, amh, sox9) and Leydig (nr5a1 or sf-1) cell markers as well as a gene with higher expression in females (cyp19a1a). No clear differences were observed in the expression of cyp11a1 and cyp11b1 during the temperature-sensitive window in the trunk of pejerrey larvae. Nevertheless, a clear increase of cyp11b1 was observed in isolated gonads taken from fish reared at the male producing temperature. In these gonads we also confirmed the trends of genes with higher expression in males (dmrt1, amh) and females (cyp19a1a) as previously described in larval trunks of pejerrey. Our results showed that the expression of cyp11b1 was positively associated with the morphological differentiation of the testis. Nevertheless the involvement of 11-oxygenated androgens during the temperature-sensitive window could not be clearly established.

Molecular cloning of two isoforms of 11beta-hydroxylase and their expressions in the Nile tilapia, Oreochromis niloticus

P450 11beta-hydroxylase, encoded by P450(11beta) gene, is a key mitochondrial enzyme to produce 11beta-hydroxy testosterone, substrate for the production of 11-ketotestosterone (11-KT), which has been shown to be potent androgen in several fish species. In the present work, two alternative splicing isoforms i.e. P450(11beta)-1 and P450(11beta)-2 cDNAs were cloned from the Nile tilapia, Oreochromis niloticus. They were 1614 and 1227bp in length with open reading frames encoding proteins of 537 and 408 amino acids, respectively. In contrast to P450(11beta)-1, which derived from 9 exons of the P450(11beta) gene, the 7th and 8th exons were absent in P450(11beta)-2. Tilapia P450(11beta)-1 shares the highest homology with that of medaka, Oryzias latipes. Expressions of P450(11beta)-1 and -2 were detected in the kidney and head kidney of both sexes, and in the testis but not in the ovary, with P450(11beta)-2 lower than P450(11beta)-1. Ontogenic expressions of both isoforms were detected in testis from 50dah onwards. P450(11beta)-1 and -2 were strongly expressed in sex reversed XX testis after fadrozole and tamoxifen treatment, but completely inhibited in 17beta-estradiol induced XY ovary. The existence of two alternatively spliced isoforms and the sexual dimorphic expression of P450(11beta)s were further confirmed by Northern blot. Strong expression signals in Leydig cells and weak signals in spermatogonia were detected by in situ hybridization and immunohistochemistry. Taken together, our data suggest a role for P450(11beta) in the spermatogenesis of tilapia through the production of 11-KT in testis, in addition to cortisol production in head kidney.

Expression and gonadotropin regulation of membrane progestin receptor alpha in Atlantic croaker (Micropogonias undulatus) gonads: role in gamete maturation

Recent results suggest that membrane progestin receptor alpha (mPRalpha) mediates nongenomic actions of progestin hormones to induce oocyte maturation and sperm hypermotility in several teleost species. The role of mPRalpha in gamete and gonadal physiology was further evaluated in the present study by examining gonadal expression of mPRalpha during gamete maturation in Atlantic croaker (Micropogonias undulatus), a well-characterized teleost model of oocyte maturation and sperm motility. Sequencing of the croaker mPRalpha gene isolated from croaker ovaries showed it is 98% homologous at the nucleotide level to spotted seatrout mPRalpha. The mPRalpha mRNA and protein were detected in both somatic and gonadal tissues. In croaker ovaries, the mPRalpha protein was present throughout the gonadal cycle and was upregulated by gonadotropin in vitro, coincident with the acquisition of oocyte maturational competence (i.e., ability to respond to progestin hormones and complete oocyte maturation). Both mPRalpha mRNA and protein were also expressed in croaker testes throughout the gonadal cycle. Expression of mPRalpha protein was weakly upregulated in testes after 18 h of in vitro gonadotropin treatment. Immunocytochemical staining showed mPRalpha was localized to both germ and interstitial cells. Finally, elevated levels of mPRalpha protein in croaker sperm were associated with high sperm motility. Taken together, these data strongly support the hypothesis that mPRalpha mediates progestin induction of oocyte maturation and upregulation of sperm motility in teleosts.

Modulation of salmon ovarian steroidogenesis and growth factor responses by the xenoestrogen, 4-nonylphenol

Endocrine-disrupting chemicals are known to influence organismal reproductive processes, including the production and regulation of gonadal steroids. This study evaluated the effects of a xenoestrogen (nonylphenol: NP) on salmon ovarian steroidogenesis and growth factors using an in vitro organ culture system. Ovarian tissues were cultivated for 3 and 7d with different concentrations of NP (0 (control), 1, 10 and 50 microM) dissolved in ethanol (0.1%). The mRNA expressions of steroidogenic acute regulatory (StAR) protein, P450-mediated cholesterol side-chain cleavage (P450scc), aromatase isoforms, 3beta-hydroxysteroid dehydrogenase (3beta-HSD), Cyp11beta-, Cyp17 and 21-hydroxylase, and insulin-like growth factors (IGF-1 and IGF-2) and IGF1-receptor (IGF1-R) were quantified by real-time PCR. Tissue levels of estradiol-17beta (E2), testosterone (T) and 11-ketotestosterone (11-KT) were quantified using enzyme immunoassays. Our data show that nominal NP levels produced time- and concentration-specific effects on the expression of steroidogenesis- and IGF-related transcripts in salmon ovarian tissues. Tissue levels of ovarian E2, T and 11-KT were significantly modulated after NP exposure. Interestingly, elevated ovarian E2 levels after 10 microM NP exposure at day 3 paralleled P450Arom isoforms mRNA expression at the same time interval. The expression patterns of other steroidogenic protein and enzyme genes, such as StAR, P450scc, 3beta-HSD and Cyp17 inversely paralleled this pattern, displaying consistent decreased transcript levels. These findings show that NP (an ubiquitous environmental pollutant) can produce variations in gonadal steroidogenesis and growth regulating responses with potential consequences for overt fecundity in teleosts.

Aromatase (P450arom) and 11beta-hydroxylase (P45011beta) genes are differentially expressed during the sex change process of the protogynous rice field eel, Monopterus albus

Steroids are known to play a crucial role in gonadal sex differentiation in many non-mammalian vertebrates, but also in the gonadal sex change of hermaphroditic teleosts. We investigated the expression of two genes encoding key steroidogenic enzymes, i.e., cytochrome P450 aromatase (P450arom) and cytochrome P45011beta-hydroxylase (P45011beta), during the sex change of the protogynous rice field eel, Monopterus albus. Using RT-PCR with degenerate primers, we cloned rice field eel homologous fragments for both genes (rcP450arom and rcP45011beta) as indicated by the high level of homology with P450arom and P45011beta sequences from various vertebrates. Gonadal expression of rcP450arom and rcP45011beta mRNA levels were then assessed during the sex change by semi-quantitative RT-PCR and a real-time RT-PCR. rcP450arom was predominantly expressed in ovary, much less in ovotestis, and barely in testis. Conversely, P45011beta was markedly up-regulated at the onset of testicular development. These findings underline that regulation of steroidogenesis is an important process in the sex change of protogynous rice field eel, and they clearly indicate that the concomitant down-regulation of P450arom and up-regulation of P45011beta are of pivotal importance to the sex change of this species.

Adaptive evolution of mammalian aromatases: lessons from Suiformes

Estrogen synthesis evolved in chordates to control reproduction. The terminal enzyme in the cascade directly responsible for estrogen synthesis is aromatase cytochrome P450 (P450arom) encoded by the CYP19 gene. Mammals typically have a single CYP19 gene but pigs, peccaries and other Suiformes have two or more resulting from duplication in a common ancestor. Duplication of CYP genes in the steroid synthetic cascade has occurred for only one other enzyme, also terminal, 11beta-hydroxylase P450 (P450c11). P450arom and P450c11 share common substrates and even physiological functions as possible remnants from a common P450 progenitor, perhaps an ancestral P450arom, which is supported by phylogenetic analysis. Conserved tissue-specific expression patterns of P450arom paralogs in placenta and gonads of pigs and peccaries suggest how functional adaptation may have proceeded divergently and influenced adopted reproductive strategies including ovulation rate and litter size. Data suggest that the porcine placental paralog evolved catalytically to protect female conceptuses from testosterone produced by male siblings; the gonadal paralog to synthesize a novel, nonaromatizable testosterone metabolite (1OH-testosterone) that may increase ovulation rate. This would represent a coevolution facilitating litter bearing as pigs diverged from peccaries. Evidence of convergence between the peccary CYP19 genes and lower tissue expression may therefore represent initiation of loss of the functional paralogs. Studies on the Suiforme aromatases provide insights into the evolution of the steroidogenic cascade and metabolic pathways in general, how it translates into physiological adaptations (altered reproductive strategies for instance), and how duplicated genes become stabilized or disappear from genomes.

Steroidogenic acute regulatory protein in white sturgeon (Acipenser transmontanus): cDNA cloning, sites of expression and transcript abundance in corticosteroidogenic tissue after an acute stressor

The white sturgeon, Acipenser transmontanus, is a primitive bony fish that is recognized as an important emerging species for aquaculture. However, many aspects of its stress and reproductive physiology remain unclear. These processes are controlled by various steroid hormones. In order to investigate the regulation of steroidogenesis associated with acute stress in sturgeon, a cDNA-encoding steroidogenic acute regulatory protein (StAR) was isolated from white sturgeon. The putative amino acid sequence of sturgeon StAR shares high homology (over 60%) with other vertebrates. Phylogenetic analysis grouped sturgeon StAR within Actinopterygii, but it was clearly segregated from teleost StARs. RT-PCR analysis revealed that transcripts were most abundant in yellow corpuscles found throughout the kidney and weaker signals were detected in gonad and kidney. Very weak signals were also detected in brain and spleen by quantitative real-time PCR. In situ hybridization revealed that StAR is expressed in the cells of yellow corpuscles. No significant changes in StAR gene expression were detected in response to an acute handling stress. These results suggest that StAR is highly conserved throughout vertebrates, but the expression of the functional protein during the stress response may be partially regulated post-transcriptionally.

Gene expression profiling during spermatogenesis in early maturing male Atlantic salmon parr testes

The initiation of sexual maturation and spermatogenesis are complex processes that require the highly coordinated regulation of a number of key genes. The endocrine system plays crucial roles in these processes, but the precise mechanisms involved in sexual maturation of fish are poorly understood. We investigated the expression of genes encoding proteins involved in sex steroid biosynthesis (Ff1b (FTZ-F1 homolog), steroidogenic acute regulatory protein (StAR), cytochrome P450 cholesterol side-chain cleavage enzyme (P450scc), 3beta-hydroxysteroid dehydrogenase/Delta(5)-Delta(4)-isomerase (3beta-HSD), cytochrome P450 17alpha-hydroxylase/17,20-lyase (P450c17), cytochrome P450 11beta-hydroxylase (P45011beta) and 11beta-hydroxysteroid dehydrogenase (11beta-HSD)) and the anti-Müllerian hormone (AMH) homolog during early sexual maturation of one-summer-old male Atlantic salmon parr by RT-PCR. Genes encoding Ff1b, StAR, 3beta-HSD, P450c17 and 11beta-HSD were upregulated during spermatogonial proliferation. During the course of spermatogenesis expression profiles of Ff1b, StAR, 3beta-HSD, P450scc, P450c17, P45011beta, and 11beta-HSD were similar; transcript levels being low during early stages, then strongly increasing during spermiogenesis. These results indicate that coordinated de novo transcription of genes encoding StAR as well as 3beta-HSD, P450c17 and 11beta-HSD might be required for sex steroids production during the initiation of spermatogenesis in salmon. In contrast, transcription levels of AMH were comparatively high in immature testes, decreased when spermatogenesis was initiated, and were lowest during spermiogenesis, suggesting that AMH suppression plays a crucial role in the process of spermatogenesis in salmonids. Correlation analyses show that FSH and LH might be differentially involved in the regulation of several of these genes studied.

Plasma 11-deoxycorticosterone (DOC) and mineralocorticoid receptor testicular expression during rainbow trout Oncorhynchus mykiss spermiation: implication with 17alpha, 20beta-dihydroxyprogesterone on the milt fluidity?

BACKGROUND

In rainbow trout (Oncorhynchus mykiss), the endocrine control of spermiation is not fully understood. Besides 11ketotestosterone (11KT) and 17alpha, 20beta-dihydroxyprogesterone (MIS), the potential physiological ligand of the mineralocorticoid receptor (MR) 11-deoxycorticosterone (DOC), is a credible candidate in O. mykiss spermiation regulation as spermiation is accompanied with changes in aqueous and ionic flows.

METHODS

In this study, we investigated potential roles of DOC during spermiation 1) by describing changes in blood plasma DOC level, MR mRNA abundance during the reproductive cycle and MR localization in the reproductive tract 2) by investigating and comparing the effects of DOC (10 mg/kg) and MIS (5 mg/kg) supplementations on sperm parameters 3) by measuring the in vitro effect of DOC on testis MIS production.

RESULTS

The plasma concentration of DOC increased rapidly at the end of the reproductive cycle to reach levels that were 10-50 fold higher in mature males than in immature fish. MR mRNA relative abundance was lower in maturing testes when compared to immature testes, but increased rapidly during the spermiation period, immediately after the plasma rise in DOC. At this stage, immunohistochemistry localized MR protein to cells situated at the periphery of the seminiferous tubules and in the efferent ducts. Neither DOC nor MIS had significant effects on the mean sperm volume, although MIS treatment significantly increased the percentage of males producing milt. However, a significant reduction in the spermatocrit was observed when DOC and MIS were administrated together. Finally, we detected an inhibitory effect of DOC on testis MIS production in vitro.

CONCLUSION

These results are in agreement with potential roles of DOC and MR during spermiation and support the hypothesis that DOC and MIS mechanisms of action are linked during this reproductive stage, maybe controlling milt fluidity. They also confirm that in O. mykiss MIS is involved in spermiation induction.