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

The effects of 17α-methyltestosterone on gonadal histology and gene expression along hypothalamic-pituitary-gonadal axis, germ cells, sex determination, and hypothalamus-pituitary-thyroid axis in zebrafish (Danio rerio)

As a synthetic androgen, 17α-methyltestosterone (MT) is widely used in aquaculture to induce sex reversal and may pose a potential risk to aquatic organisms. This ecological risk has attracted the attention of many scholars, but it is not comprehensive enough. Thus, the adverse effects of MT on zebrafish (Danio rerio) were comprehensively evaluated from gonadal histology, as well as the mRNA expression levels of 47 genes related to hypothalamic-pituitary-gonadal (HPG) axis, germ cell differentiation, sex determination, and hypothalamus-pituitary-thyroid (HPT) axis. Adult zebrafish with a female/male ratio of 5:7 were exposed to a solvent control (0.001% dimethyl sulfoxide) and three measured concentrations of MT (5, 51 and 583 ng/L) for 50 days. The results showed that MT had no significant histological effects on the ovaries of females, but the frequency of late-mature oocytes (LMO) showed a downward trend, indicating that MT could induce ovarian suppression to a certain extent. The transcriptional expression of activating transcription factor 4b1 (atf4b1), activating transcription factor 4b2 (atf4b2), calcium/calmodulin-dependent protein kinase II delta 1 (camk2d1), calcium/calmodulin-dependent protein kinase II delta 2 (camk2d2) and calcium/calmodulin-dependent protein kinase II inhibitor 2 (camk2n2) genes in the brain of females increased significantly at all treatment groups of MT, and the mRNA expression of forkhead box L2a (foxl2) and ovarian cytochrome P450 aromatase (cyp19a1a) genes in the ovaries were down-regulated by 5 and 583 ng/L group, which would translate into inhibition of oocyte development. As compared to females, MT had relatively little effects on the reproductive system of males, and only the transcriptional alterations of synaptonemal complex protein 3 (sycp3) and 17-alpha-hydroxylase/17,20-lyase (cyp17) genes were observed in the testes, not enough to affect testicular histology. In addition, MT at all treatments strongly increased corticotropin-releasing hormone (crh) transcript in the brain of females, as well as deiodinase 2 (dio2) transcript in the brain of males. The paired box protein 8 (pax8) gene was significantly decreased at 51 or 583 ng/L of MT in both female and male brains. The above results suggest that MT can pose potential adverse effects on the reproductive and thyroid endocrine system of fish.

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.

Rxrs and their partner receptor genes inducing masculinization plausibly mediated by endocrine disruption in Paralichthys olivaceus

Retinoid X receptors (RXRs) can form homo- or heterodimers with orphan receptors involved in multiple intertwined signaling pathways. However, there is limited study on the formation of sex phenotypes and the regulation of steroidogenesis by RXRs in fish. Here, in Paralichthys olivaceus, we first indicated that PPARγ::RXRα was predictably a transcription factor for steroidogenesis genes, and Foxl2 and Dmrt1 were also transcription factors for rxrs and their partner receptor genes. When the flounder fry were exposed to LG100268 (LG, RXRs agonist, 50 mg/kg diet), the percentage of males increased from 50% to 71.4%. Before histological differentiation of the flounder ovary (3 cm TL) and testis (6 cm TL), the transcripts of rar β and rar γ (P < 0.05) were activated, and the steroidogenesis gene Hsd3b1 was down-regulated (P < 0.05). The ratios of testosterone (T)/17β-estradiol (E2) were all greatly increased (P < 0.05), and the ratio of 11-ketotestosterone (11-KT)/E2 was elevated at 3 cm TL. Moreover, LG was used to treat the cultured gonads in vitro (10 μM) and the fish with intraperitoneal injection in vivo (12 mg/kg body weight), respectively. LG was able to up-regulate rxr γ, rar γ, and ppar δ, and Hsd3b1 was significantly up-regulated (P < 0.05). The ratios of 11-KT/E2 in the culture medium and in the ovaries of the fish were decreased. Furthermore, the recombinant flounder Foxl2 protein was able to significantly down-regulate ppar γ (P < 0.05) and tr β (P < 0.01) in the ovaries in vitro, and the result of the Dmrt1 in the testes was opposite to that of the Foxl2, probably indicating a feedback loop between RXRs' partner receptors and Foxl2/Dmrt1. These findings introduce for the first time the mode of action of RXRs on the flounder steroidogenesis and provide important data to learn the potential function of RXRs in fish sex differentiation and the potential role of RXRs in aquatic animals in the presence of water pollutants.

Identification and Characterization of Sex-Biased miRNAs in the Golden Pompano (Trachinotus blochii)

The golden pompano (Trachinotus blochii) is a marine fish of considerable commercial importance in China. It shows notable sexual size dimorphism; the growth rate of females is faster than that of males. Therefore, sex-biased research is of great importance in T. blochii breeding. However, there have been few studies on sex differentiation and mechanisms underlying sex determination in T. blochii. MicroRNAs (miRNAs) play crucial roles in sex differentiation and determination in animals. However, limited miRNA data are available on fish. In this study, two small RNA libraries prepared from the gonads of T. blochii were constructed and sequenced. The RNA-seq analysis yielded 1366 known and 69 novel miRNAs with 289 significantly differentially expressed miRNAs (p < 0.05). Gene ontology (GO) analysis confirmed that the TFIIA transcription factor complex (GO: 0005672) was the most significantly enriched GO term. The Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the differentially expressed miRNAs and target genes were mainly related to sex determination and gonadal developmental signaling pathways, specifically the Wnt signaling pathway, MAPK signaling pathway, and steroid biosynthetic pathway. MiRNA-mRNA co-expression network analysis strongly suggested a role for sex-biased miRNAs in sex determination/differentiation and gonadal development. For example, gata4, foxo3, wt1, and sf1 genes were found to be regulated by bta-miR-2898; esr2 and foxo3 by novel_176, and ar by oar-let-7b. Quantitative real-time polymerase chain reaction analysis of selected mRNAs and miRNAs validated the integrated analysis. This study established a set of sex-biased miRNAs that are potential regulatory factors in gonadal development in T. blochii. These results provide new insight into the function of miRNAs in sex differentiation and determination in T. blochii and highlight some key miRNAs for future studies.

Gonadal Soma-Derived Factor Expression is a Potential Biomarker for Predicting the Effects of Endocrine-Disrupting Chemicals on Gonadal Differentiation in Japanese Medaka (Oryzias Latipes)

Chemicals with androgenic or estrogenic activity induce the sex reversal and/or intersex condition in various teleost fish species. Previously, we reported that exposure to 17α-methyltestosterone, bisphenol A, or 4-nonylphenol induces changes in expression of the gonadal soma-derived factor (gsdf) gene accompanied by disruption of gonadal differentiation in Japanese medaka (Oryzias latipes). These findings suggest that gsdf expression might be a useful biomarker for predicting the potential effect of chemicals on gonadal differentiation. We examined the gsdf expression in Japanese medaka exposed to chemicals with estrogenic or androgenic activity. Exposure to the androgenic steroid 17β-trenbolone at 0.5-22.1 μg/L induced the development of ovotestis (presence of ovarian tissue with testicular tissue) and female-to-male sex reversal in XX embryos, and exposure at 6.32 and 22.1 μg/L significantly increased gsdf expression in XX embryos compared with controls at developmental stage 38 (1 day before hatching). In the present study, no statistically significant difference in gsdf mRNA expression was observed after exposure to 17β-estradiol, 17α-ethinylestradiol, and 4-t-octylphenol, which have estrogenic activity. In addition, antiandrogenic chemicals or chemicals without endocrine-disrupting activity did not induce changes in gsdf expression in XX or XY embryos. Thus, an increase in gsdf expression after androgen exposure was observed in XX embryos. Together, these findings indicate that gsdf expression might be useful for predicting the adverse effect of chemicals on gonadal differentiation. Environ Toxicol Chem 2022;41:1875-1884. © 2022 SETAC.

Developmental changes in gene expression and gonad morphology during sex differentiation in Atlantic salmon (Salmo salar)

The Atlantic salmon (Salmo salar) is a globally important species for its value in fisheries and aquaculture, and as a research model. In order to characterise aspects of sex differentiation at the morphological and mRNA level in this species, the present study examined developmental changes in gonad morphology and gene expression in males and females between 0 and 79 days post hatch (dph). Morphological differentiation of the ovary (indicated by the formation of germ cell cysts) became apparent from 52 dph. By 79 dph, ovarian phenotype was evident in 100% of genotypic females. Testes remained in an undifferentiated-like state throughout the experiment, containing germ cells dispersed singularly within the gonadal region distal to the mesentery. There were no significant sex-related differences in gonad cross-section size, germ cell number or germ cell diameter during the experiment. The expression of genes involved in teleost sex differentiation (anti-müllerian hormone (amh), cytochrome P450, family 19, subfamily A, polypeptide 1a (cyp19a1a), forkhead box L2a (foxl2a), gonadal soma-derived factor (gsdf), r-spondin 1 (rspo1), sexually dimorphic on the Y chromosome (sdY)), retinoic acid-signalling (aldehyde dehydrogenase 1a2 (aldh1a2), cytochrome P450 family 26 a1 (cyp26a1), cytochrome P450 family 26 b1 (cyp26b1), t-box transcription factor 1 (tbx1a)) and neuroestrogen production (cytochrome P450, family 19, subfamily A, polypeptide 1b (cyp19a1b)) was investigated. Significant sex-related differences were observed only for the expression of amh, cyp19a1a, gsdf and sdY. In males, amh, gsdf and sdY were upregulated from 34, 59 and 44 dph respectively. In females, cyp19a1a was upregulated from 66 dph. Independent of sex, foxl2a expression was highest at 0 dph and had reduced ∼ 47-fold by the time of morphological sex differentiation at 52 dph. This study provides new insights into the timing and sequence of some physiological changes associated with sex differentiation in Atlantic salmon. These findings also reveal that some aspects of the mRNA sex differentiation pathways in Atlantic salmon are unique compared to other teleost fishes, including other salmonids.

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.

Characterization, expression, and regulatory effects of nr0b1a and nr0b1b in spotted scat (Scatophagus argus)

Nuclear receptor subfamily 0 group B member 1 (Nr0b1) belongs to the nuclear receptor (NR) superfamily. It plays critical roles in sex determination, sex differentiation, and gonadal development in mammals. In this study, the duplicated genes nr0b1a and nr0b1b were identified in spotted scat (Scatophagus argus). Phylogenetic and synteny analyses revealed that, unlike nr0b1a, nr0b1b was retained in several species of teleosts after an nr0b1 gene duplication event but was secondarily lost in other fish species, amphibians, reptiles, birds, and mammals. In a sequence analysis, only 1.5 LXXLL-related repeat motifs were identified in spotted scat Nr0b1a, Nr0b1b, and non-mammalian Nr0b1a/Nr0b1, different from the 3.5 repeat motifs in mammalian Nr0b1. By qPCR, nr0b1a and nr0b1b were highly expressed in testes from stages IV to V and in ovaries from stages II to IV, respectively. Male-to-female sex reversal was induced in XY spotted scat by the administration of exogenous E2. A qPCR analysis showed that nr0b1b mRNA expression was higher in sex-reversed XY fish than in control XY fish, with no difference in nr0b1a. A luciferase assay showed that spotted scat Nr0b1a and Nr0b1b did not individually activate cyp19a1a gene transcription. As in mammals, spotted scat Nr0b1a suppressed Nr5a1-mediated cyp19a1a expression, despite containing only 1.5 LXXLL-related repeat motifs in its N-terminal region, while Nr0b1b stimulated Nr5a1-mediated cyp19a1a transcription. These results demonstrated that nr0b1a and nr0b1b in spotted scat have distinct expression patterns and regulatory effects and further indicate that nr0b1b might be involved in ovarian development by regulating Nr5a1-mediated cyp19a1a expression.

Characteristics and Cryopreservation of Semen of Sex-Reversed Females of Salmonid Fish

Sex reversal has been used as a breeding strategy by salmonid fish to produce genetically and phenotypically single sex populations. Production of all-female fish has great importance for the creation of monosex female triploids of salmonid fish, which are valued for their sterility, lack of female maturation, and larger commercial size. Among salmonids, the majority of rainbow trout (Oncorhynchus mykiss) production is based on all-female production with a high proportion of all-female triploid production in Europe. The main aim of this review is to present the recent knowledge regarding sex-reversed females (SRFs) of salmonid fish. We discuss the methods of sex reversal as well as their effects on the morphology and histology of the reproductive tract. We focus on the characteristics of SRF semen as well as the factors determining semen quality. The lower quality of SRF sperm compared to that of normal males has resulted in the need for the artificial maturation of semen. Most importantly, methods of semen storage-both short-term and long-term (cryopreservation)-that can improve hatchery operations are presented with the special emphasis on recent progress in development of efficient cryopreservation procedures and use of cryopreserved semen in hatchery practice. Moreover, we also address the emerging knowledge concerning the proteomic investigations of salmonid sperm, focusing primarily on the proteomic comparison of normal male and SRF testicular semen and presenting changes in SRF rainbow trout sperm proteome after in vitro incubation in artificial seminal plasma.

The effects of 11-ketotestosterone implants on transcript levels of gonadotropin receptors, and foxl2 and dmrt1 genes in the Previtellogenic ovary of cultured beluga (Huso huso)

The in vivo effect of 11-ketotestosterone (11KT) on transcript levels of the gonadotropin receptors (fshr and lhr) and sex differentiation-related genes (dmrt1 and foxl2) was examined in the ovaries of immature female beluga. For this purpose, six fish were treated with implants containing 2.5 mg 11KT and a placebo group of six females of the same age and gametogenic stage were given a blank implant. The implants were intraperitoneally inserted into 4-year-old females at the previtellogenic stage (mean body weight 5580 ± 165 g) and maintained under culture conditions for 8 weeks. Ovary samples for gene expression analysis of lhr, fshr, dmrt1 and foxl2 were collected by biopsy at 3 and 8 weeks post implantation. Diameters of oocytes increased in response to 11KT treatment, both at 3 and at 8 weeks post implantation, but no obvious changes were evident in cytology. Three weeks of 11KT treatment did not affect target gene expression, but a tendency for a time-dependent decrease of lhr and dmrt1 mRNA levels was observed in both treatment and placebo groups. By 8 weeks of treatment, however, 11KT implants provoked the upregulation of fshr and foxl2 transcript levels. Furthermore, lhr and dmrt1 transcript abundances recovered by 8 weeks of exposure in both blank- and 11KT-implanted beluga. These results suggest that 11KT, either directly or indirectly, may affect gametogenesis and regulate some key components of the reproductive axis in female beluga.

Expression patterns and oestradiol regulation of growth differentiation factor 9 in Schizothorax prenanti

Growth differentiation factor 9 (GDF9) plays pivotal roles in regulating follicular development in many mammalian species. In the present study, the full-length Schizothorax prenanti gdf9 cDNA sequence was isolated and characterized, and its expression pattern in developing gonads and in the gonads of exogenous oestradiol (E₂)-fed fish were analysed. The S. prenanti gdf9 cDNA sequence consisted of 1958 base pairs (bp), encoded a 413 amino acid, and showed high sequence similarity with Carassius gibelio and Cyprinus carpio. The quantitative real-time PCR analysis revealed that gdf9 was mainly expressed in the gonads, with particularly high expression in the cortical alveoli stage ovary and late-spermatogenic stage testis. Immunohistochemical signals for Gdf9 were mainly detected in chromatin nucleolar oocytes, spermatogonia and spermatocytes. Furthermore, the gonadal expression of gdf9 induced by exogenous E₂ was related to the feeding time and dose. Taken together, these findings were helpful to gain a better understanding of the role of Gdf9 in both folliculogenesis and spermatogenesis in S. prenanti.

Developmental Programming: Prenatal Testosterone Excess on Ovarian SF1/DAX1/FOXO3

Prenatal testosterone (T) excess, partly via androgenic programming, enhances follicular recruitment/persistence in sheep as in women with polycystic ovarian syndrome (PCOS). Decreased anti-Mullerian hormone (AMH) in early growing and increased AMH in antral follicles may underlie enhanced recruitment and persistence, respectively. Changes in AMH may be mediated by steroidogenic factor 1 (SF1), an enhancer of AMH, and dosage-sensitive sex reversal, adrenal hypoplasia critical region, on chromosome X, gene 1 (DAX1), that antagonizes SF1. Another mediator could be forkhead box 03 (FOXO3) which regulates follicular recruitment/atresia. To test if androgen-programmed changes in SF1, DAX1, and FOXO3 proteins contribute to follicular defects in prenatal T-treated sheep, ovaries from control, prenatal T-, and dihydrotestosterone (DHT)-treated (days 30-90 of gestation) animals at fetal day (FD) 90, FD140, and 1 and 2 years-of-age were studied. Prenatal T increased DAX1 in granulosa cells of primordial through large preantral and theca cells of large preantral follicles at FD140 and increased SF1 in the granulosa cells of preantral and antral and theca cells of large preantral follicle at 2 years-of-age. Prenatal T increased FOXO3 only in theca cells of preantral (FD140) and antral (2 years-of-age) follicles. Prenatal DHT increased DAX1 in granulosa cells from small preantral follicles at FD140 while increasing SF1 in granulosa cells from antral follicles at 1 year-of-age. These age-dependent changes in DAX1/SF1 partly via androgen-programming are consistent with changes in AMH and may contribute to the enhanced follicular recruitment/persistence, and multifollicular phenotype of prenatal T-treated females and may be of translational relevance to PCOS.

Genotoxic biomarkers and histological changes in marine medaka (Oryzias melastigma) exposed to 17α-ethynylestradiol and 17β-trenbolone

Endocrine-disrupting pollutants in marine environments have aroused great concern for their adverse effects on the reproduction of marine organisms. This study aimed to seek promising biomarkers for estrogenic/androgenic chemicals. First, two possible male-specific genes, SRY-box containing gene 9a2 (sox9a2) and gonadal soma-derived factor (gsdf), were cloned from marine medaka (Oryzias melastigma). Then the responses of sox9a2, gsdf, choriogenin (chgH and chgL), vitellogenin (vtg1 and vtg2), and cytochrome P450 aromatase (cyp19a and cyp19b) were investigated after exposure to 17α-ethynylestradiol (EE₂) and 17β-trenbolone (TB) at 2, 10, and 50 ng/L. The results showed that gsdf was specifically expressed in the testes and easily induced in the ovaries after TB exposure, indicating that gsdf was a potential biomarker of environmental androgens. ChgL was a useful biomarker of weak estrogen pollution for its high sensitivity to low levels of EE₂. In addition, both EE₂ and TB exposure damaged gonadal structures and inhibited gonadal development.

Effects of Temperature on the Expression of Two Ovarian Differentiation-Related Genes foxl2 and cyp19a1a

Exposure to stress induces a series of responses and influences a wide range of biological processes including sex differentiation in fish. The present work investigated the molecular and physiological response to thermal stress throughout the early development stage covering the whole period of sex differentiation of bluegill, Lepomis macrochirus. Larvae were treated using three temperatures, 17, 24, and 32°C from 6 to 90 days posthatching (dph) in 30-L round tanks. There is no significant difference of the sex ratio and survival among the three temperature groups in the geographic population used in this study. Two ovarian differentiation-related genes foxl2 and cyp19a1a were detected at 7 dph suggesting that these genes have already played a role prior to sex differentiation. The expression of foxl2 reached the peak and was thermosensitive just prior to the onset of ovarian differentiation at 27 dph. Histological examination displayed that the proliferation of germ cells and ovarian differentiation were delayed at the low-temperature treatment (17°C) at 97 dph compared with higher temperatures. In conclusion, the water temperature regulates the sex differentiation of bluegill through modulation of the expression of foxl2 and cyp19a1a. A comparative study of the expression profile of sex differentiation-related genes in species will shed light on the evolution of sex-determination mechanisms and the impact of stress on sex differentiation.

Expression pattern of new genes regulating female sex differentiation and in vitro maturational status of oocytes in pigs

The processes underlying maturation of mammalian oocytes are considered crucial for the oocytes ability to undergo monospermic fertilization. The same factors of influence are suggested to impact the development of sex associated characteristics, allowing sex differentiation to progress during embryonic growth. The primary aim of the study was to analyze the gene ontology groups involved in regulation of porcine oocytes' response to endogenous stimuli. The results obtained would indicate potential genes influencing sex differentiation. Additionally, they could help to determine new genetic markers, expression profile of which is substantially regulated during porcine oocytes' in vitro maturation. To achieve that, porcine oocytes were collected for analysis before and after in vitro maturation. Pigs were used as they are a readily available model that presents significant similarity to humans in terms of physiology and anatomy. Microarray analysis of oocytes, before and after in vitro maturation was performed and later validated by RT-qPCR. We have particularly detected and analyzed genes belonging to gene ontology groups associated with hormonal stimulation during maturation of the oocytes, that exhibited significant change in expression (fold change ≥ |2|; p < 0.05) namely "Female sex differentiation" (CCND2, MMP14, VEGFA, FST, INHBA, NR5A1), "Response to endogenous stimulus" (INSR, ESR1, CCND2, TXNIP, TACR3, MMP14, FOS, AR, EGR2, IGFBP7, TGFBR3, BTG2, PLD1, PHIP, UBE2B) and "Response to estrogen stimulus" (INSR, ESR1, CCND2, IHH, TXNIP, TACR3, MMP14). Some of them were characteristic for just one of the described ontologies, while some belonged into multiple ontological terms. The genes were analyzed, with their relation to the processes of interest explained. Overall, the study provides us with a range of genes that might serve as molecular markers of in vitro maturation associated processes of the oocytes. This knowledge might serve as a reference for further studies and, after further validation, as a potentially useful knowledge in assessment of the oocytes during assisted reproduction processes.

Exposure to an anti-androgenic herbicide negatively impacts reproductive physiology and fertility in Xenopus tropicalis

Amphibians are threatened on a global scale and pollutants may be contributing to population declines, but how chemicals impact on their reproduction is poorly understood. We conducted a life cycle analysis to investigate the impacts of early life exposure to two anti-androgens (exposure until completion of metamorphosis;stage 66): flutamide, (50 µg/L)/linuron (9 and 45 µg/L)) on sexual development and breeding competence in Xenopus tropicalis. Our analyses included: mRNA levels of dmrt1, cyp17, amh, cyp19, foxl2 and ar (tadpoles/metamorphs), gonadal histomorphology (metamorphs/adults), mRNA levels of ar/gr (adult male brain/gonad/forelimb), testosterone/corticosterone levels (adult males), secondary sexual characteristics (forelimb width/nuptial pad: adult males) and breeding competence (amplexus/fertility: adult males). Compared to controls, feminised sex ratios and increased number of spermatogonia (adults) were observed after exposure to flutamide and the lower linuron concentration. Exposure to the lower linuron concentration also resulted in demasculinisation of secondary sexual characteristics and reduced male fertility. Flutamide exposure resulted in masculinisation of the nuptial pad and elevated mRNA levels of dmrt1, cyp17, amh and foxl2 in brains (metamorphs). Testosterone levels were higher in all treatment groups, however, overall few effects were observed in response to the higher linuron concentration. Our findings advance understanding of reproductive biology of X. tropicalis and illustrate negative effects of linuron on reproductive processes at a concentration measured in freshwater environments.

Expression of sf1 and dax-1 are regulated by thyroid hormones and androgens during Silurana tropicalis early development

Thyroid hormones (THs) and androgens have been shown to be extensively involved in sexual development; however, relatively little is known with regard to TH-related and androgenic actions in sex determination. We first established expression profiles of three sex-determining genes (sf1, dax-1, and sox9) during the embryonic development of Western clawed frogs (Silurana tropicalis). Transcripts of sf1 and sox9 were detected in embryos before the period in which embryonic transcription commences indicating maternal transfer, whereas dax-1 transcripts were not detected until later in development. To examine whether TH status affects sex-determining gene expression in embryonic S. tropicalis, embryos were exposed to co-treatments of iopanoic acid (IOP), thyroxine (T4), or triiodothyronine (T3) for 96 h. Expression profiles of TH receptors and deiodinases reflect inhibition of peripheral deiodinase activity by IOP and recovery by T3. Relevantly, elevated TH levels significantly increased the expression of sf1 and dax-1 in embryonic S. tropicalis. Further supporting TH-mediated regulation, examination of the presence and frequency of transcription factor binding sites in the putative promoter regions of sex-determining genes in S. tropicalis and rodent and fish models using in silico analysis also identified TH motifs in the putative promoter regions of sf1 and dax-1. Together these findings advocate that TH actions as early as the period of embryogenesis may affect gonadal fate in frogs. Mechanisms of TH and androgenic crosstalk in relation to the regulation of steroid-related gene expression were also investigated.

Piwil1 gene is regulated by hypothalamic-pituitary-gonadal axis in turbot (Scophthalmus maximus): A different effect in ovaries and testes

As constituent factors of Piwi-interacting RNA (piRNA) pathways, Piwi proteins are essential for germline maintenance and gonadal development. Previous studies show that Piwi-piRNA pathways could be regulated by hypothalamic-pituitary-gonadal (HPG) axis, however, related studies have not been reported in marine species. Here we reported the identification of turbot (Scophthalmus maximus) piwil1 gene, which was abundantly expressed in testis and ovary in a tissue-specific manner. Phylogenetic and genomic structure analyses revealed that piwil1 was conserved in its sequence and function during vertebrate evolution. We also investigated the effects of HPG axis hormones, including human chorionic gonadotropin (hCG), estradiol-17β (E2) and 17α-methyltestosterone (MT), on gonadal piwil1 expression via in vivo and in vitro approaches. In ovary, hCG and E2 suppressed piwil1 expression both in vivo and in vitro, and MT increased piwil1 expression in vivo. In testis, hCG had upregulating effects on piwil1 expression in vivo and in vitro, and MT also increased piwil1 expression in vitro. In addition, E2 suppressed expression of piwil1 in vivo. These results indicated that the decreased or increased expression of piwil1 regulated by hormones might play a crucial role during gonadal differentiation and development in S. maximus.

The transcriptomic signature of different sexes in two protogynous hermaphrodites: Insights into the molecular network underlying sex phenotype in fish

Sex differentiation is a puzzling problem in fish due to the variety of reproductive systems and the flexibility of their sex determination mechanisms. The Sparidae, a teleost family, reflects this remarkable diversity of sexual mechanisms found in fish. Our aim was to capture the transcriptomic signature of different sexes in two protogynous hermaphrodite sparids, the common pandora Pagellus erythrinus and the red porgy Pagrus pagrus in order to shed light on the molecular network contributing to either the female or the male phenotype in these organisms. Through RNA sequencing, we investigated sex-specific differences in gene expression in both species' brains and gonads. The analysis revealed common male and female specific genes/pathways between these protogynous fish. Whereas limited sex differences found in the brain indicate a sexually plastic tissue, in contrast, the great amount of sex-biased genes observed in gonads reflects the functional divergence of the transformed tissue to either its male or female character. Α common "crew" of well-known molecular players is acting to preserve either sex identity of the gonad in these fish. Lastly, this study lays the ground for a deeper understanding of the complex process of sex differentiation in two species with an evolutionary significant reproductive system.

Integrated analysis of mRNA-seq and miRNA-seq reveals the potential roles of sex-biased miRNA-mRNA pairs in gonad tissue of dark sleeper (Odontobutis potamophila)

Background

The dark sleeper (Odontobutis potamophila) is an important commercial fish species which shows a sexually dimorphic growth pattern. However, the lack of sex transcriptomic data is hindering further research and genetically selective breeding of the dark sleeper. In this study, integrated analysis of mRNA and miRNA was performed on gonad tissue to elucidate the molecular mechanisms of sex determination and differentiation in the dark sleeper.

Results

A total of 143 differentially expressed miRNAs and 16,540 differentially expressed genes were identified. Of these, 8103 mRNAs and 75 miRNAs were upregulated in testes, and 8437 mRNAs and 68 miRNAs were upregulated in ovaries. Integrated analysis of miRNA and mRNA expression profiles predicted more than 50,000 miRNA-mRNA interaction sites, and among them 27,583 negative miRNA-mRNA interactions. A number of sex related genes were targeted by sex-biased miRNAs. The relationship between 15 sex-biased genes and 15 sex-biased miRNAs verified by using qRT-PCR were described. Additionally, a number of SNPs were revealed through the transcriptome data.

Conclusions

The overall results of this study facilitate our understanding of the molecular mechanism underlying sex determination and differentiation and provide valuable genomic information for selective breeding of the dark sleeper.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3995-9) contains supplementary material, which is available to authorized users.

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.

Sex reversal of brook trout (Salvelinus fontinalis) by 17α-methyltestosterone exposure: A serial experimental approach to determine optimal timing and delivery regimes

Commercial culture of Brook trout (Salvelinus fontinalis) in Tasmania was partly abandoned due to sexual maturation of male fish early on during the estuarine rearing phase. Maturation adversely affects body mass, flesh quality and immunocompetency effectively. Sex reversal techniques such as the in-feed addition of a synthetic androgen have proven difficult to adapt in brook trout. An appropriate timing, duration and delivery vehicle for administration of 17α-methyltestosterone (MT) to produce phenotypic males (neomales) from genotypically female brook trout required further investigation. In this study, groups of brook trout eggs (n=1000) maintained at 9.5±0.15-10±0.14°C, were immersed in MT (400μgL^-1) for four hours on two alternate days (two immersions/group) staggered over a two week period surrounding the hatch of embryos (control groups excluded). The groups were then split and half received MT-supplemented feed for 60days and the other a standard diet. Following an 11 month on-growing period sex phenotypes were determined by gross & histological gonad morphology. The highest proportion of male phenotypes (75%) was found in fish immersed six and four days pre-hatch and subsequently fed a normal diet. Fish fed a MT supplemented diet and immersed in MT showed significantly higher proportions of sterile fish. These data indicate that a pre-hatch immersion-only regime (4-6days pre-hatch at 9.5°C) should be pursued as a target for optimization studies to further refine the effective concentration and duration of exposure to MT for the successful production of neo-male brook trout.

Expression of dmrt1 and vtg genes during gonad formation, differentiation and early maturation in cultured Russian sturgeon Acipenser gueldenstaedtii

Expression of the dmrt1 and vtg genes was described using the real-time PCR (rt-PCR) method from 25 to 1600 days post-hatch (dph) in cultured Russian sturgeon Acipenser gueldenstaedtii. The level of dmrt1 transcription in gonads in subsequent studied periods increased exponentially while vtg expression increased in gonads and livers of A. gueldenstaedtii examined, but in later stages of development. Both dmrt1 and vtg genes showed elevated expression in intersex individuals probably caused by dietary exposure to phyto-oestrogens.

Characterization and Developmental Expression Profile of the Steroidogenic Acute Regulatory Protein (StAR) in the Gonad-Mesonephros Complex of Lithobates sylvaticus

The steroidogenic acute regulatory (StAR) protein is responsible for the movement of cholesterol across mitochondrial membranes and is therefore a key factor in regulating the timing and rate of steroidogenesis. In this study, we characterized the coding region of the star gene in the ranid Lithobates sylvaticus and studied star mRNA levels in steroidogenic tissues during development and under natural conditions. Our results support previous research showing that the StAR sequence is well conserved. We determined that star is expressed in both the interrenal and gonadal tissues of adults and in the tadpole gonad-mesonephros complex (GMC). The mRNA levels of star in the GMC were found to increase during tadpole development, reaching a maximum between Gosner stages (Gs) 32 and 38. We observed a significant drop in star mRNA levels at the end of prometamorphosis (Gs40-41), just before the start of the metamorphic climax. Significant differences in star levels between females and males, with males presenting higher levels than females, were detected at Gs36-38. To our knowledge, this is the first study that reports transitory star sex differences in tadpoles' developing GMC. Our results suggest an involvement of StAR in anuran late male GMC formation and development that requires further investigation.

Simultaneous exposure to estrogen and androgen resulted in feminization and endocrine disruption

Estrogen, which is synthesized earlier in females than androgen in males, is critical for sex determination in non-mammalian vertebrates. However, it remains unknown that what would happen to the gonadal phenotype if estrogen and androgen were administrated simultaneously. In this study, XY and XX tilapia fry were treated with the same dose of 17α-methyltestosterone (MT) and 17β-estradiol (E2) alone and in combination from 0 to 30 days after hatching. Treatment of XY fish with E2 resulted in male to female sex reversal, while treatment of XX fish with MT resulted in female to male sex reversal. In contrast, simultaneous treatment of XX and XY fish with MT and E2 resulted in female, but with cyp11b2 and cyp19a1a co-expressed in the ovary. Serum 11-ketotestosteron level of the MT and E2 simultaneously treated XX and XY female was similar to that of the XY control, while serum E2 level of these two groups was similar to that of the XX control. Transcriptomic cluster analysis revealed that the MT and E2 treated XX and XY gonads clustered into the same branch with the XX control. However a small fraction of genes, which showed disordered expression, may be associated with stress response. These results demonstrated that estrogen could maintain the female phenotype of XX fish and feminize XY fish even in the presence of androgen. Simultaneous treatment with estrogen and androgen up-regulated the endogenous estrogen and androgen synthesis, and resulted in disordered gene expression and endocrine disruption in tilapia.

Morphology, sex steroid level and gene expression analysis in gonadal sex reversal of triploid female (XXX) rainbow trout (Oncorhynchus mykiss)

In non-mammalian vertebrates, estrogens and expressions of cyp19a1 and foxl2 play critical roles in maintaining ovary differentiation and development, while dmrt1 and sox9 are male-specific genes in testicular differentiation and are highly conserved. In order to deeply understand the morphological change, sex steroids level and molecular mechanism of triploid female gonadal reversal in rainbow trout, we studied the ovary morphology, tendency of estradiol-17β (E2) and testosterone (T) levels and the relative expressions of dmrt1, cyp19a1, sox9 and foxl2 in juvenile and adult fish. Our results demonstrated that the development of triploid female gonads in rainbow trout went through arrested development, oocytes dedifferentiation, ovary reconstruction and sex reversal finally. During early gonadal development (154-334 days post-fertilization), the expressions of foxl2 and cyp19a1 increased linearly, while expressions of dmrt1 and sox9 were extremely suppressed, and E2 level was higher, while T level was lower. During the mid-to-late period of triploid female gonadal development (574-964 days post-fertilization), the expressions of dmrt1 and sox9 remained high and were very close to the quantity of diploid male genes, and T levels were even reaching diploid male plasma concentrations, while expressions of cyp19a1 and foxl2 were decreased, leading to decrease in E2 level. We realized that the development model of rainbow trout triploid female gonads was extremely rare, and the regulatory mechanism was very special. Genes involved in gonadal development and endogenous estrogens are pivotal factors in fish natural sex reversal.

Large-scale transcriptome sequencing reveals novel expression patterns for key sex-related genes in a sex-changing fish

Background

Teleost fishes exhibit remarkably diverse and plastic sexual developmental patterns. One of the most astonishing is the rapid socially controlled female-to-male (protogynous) sex change observed in bluehead wrasses (Thalassoma bifasciatum). Such functional sex change is widespread in marine fishes, including species of commercial importance, yet its underlying molecular basis remains poorly explored.

Methods

RNA sequencing was performed to characterize the transcriptomic profiles and identify genes exhibiting sex-biased expression in the brain (forebrain and midbrain) and gonads of bluehead wrasses. Functional annotation and enrichment analysis were carried out for the sex-biased genes in the gonad to detect global differences in gene products and genetic pathways between males and females.

Results

Here we report the first transcriptomic analysis for a protogynous fish. Expression comparison between males and females reveals a large set of genes with sex-biased expression in the gonad, but relatively few such sex-biased genes in the brain. Functional annotation and enrichment analysis suggested that ovaries are mainly enriched for metabolic processes and testes for signal transduction, particularly receptors of neurotransmitters and steroid hormones. When compared to other species, many genes previously implicated in male sex determination and differentiation pathways showed conservation in their gonadal expression patterns in bluehead wrasses. However, some critical female-pathway genes (e.g., rspo1 and wnt4b) exhibited unanticipated expression patterns. In the brain, gene expression patterns suggest that local neurosteroid production and signaling likely contribute to the sex differences observed.

Conclusions

Expression patterns of key sex-related genes suggest that sex-changing fish predominantly use an evolutionarily conserved genetic toolkit, but that subtle variability in the standard sex-determination regulatory network likely contributes to sexual plasticity in these fish. This study not only provides the first molecular data on a system ideally suited to explore the molecular basis of sexual plasticity and tissue re-engineering, but also sheds some light on the evolution of diverse sex determination and differentiation systems.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-015-0044-8) contains supplementary material, which is available to authorized users.

The role of Amh signaling in teleost fish--Multiple functions not restricted to the gonads

This review summarizes the important role of Anti-Müllerian hormone (Amh) during gonad development in fishes. This Tgfβ-domain bearing hormone was named after one of its known functions, the induction of the regression of Müllerian ducts in male mammalian embryos. Later in development it is involved in male and female gonad differentiation and extragonadal expression has been reported in mammals as well. Teleosts lack Müllerian ducts, but they have amh orthologous genes. amh expression is reported from 21 fish species and possible regulatory interactions with further factors like sex steroids and gonadotropic hormones are discussed. The gonadotropin Fsh inhibits amh expression in all fish species studied. Sex steroids show no consistent influence on amh expression. Amh is produced in male Sertoli cells and female granulosa cells and inhibits germ cell proliferation and differentiation as well as steroidogenesis in both sexes. Therefore, Amh might be a central player in gonad development and a target of gonadotropic Fsh. Furthermore, there is evidence that an Amh-type II receptor is involved in germ cell regulation. Amh and its corresponding type II receptor are also present in brain and pituitary, at least in some teleosts, indicating additional roles of Amh effects in the brain-pituitary-gonadal axis. Unraveling Amh signaling is important in stem cell research and for reproduction as well as for aquaculture and in environmental science.

Meta-Analysis of Microarray Data of Rainbow Trout Fry Gonad Differentiation Modulated by Ethynylestradiol

Sex differentiation in fish is a highly labile process easily reversed by the use of exogenous hormonal treatment and has led to environmental concerns since low doses of estrogenic molecules can adversely impact fish reproduction. The goal of this study was to identify pathways altered by treatment with ethynylestradiol (EE2) in developing fish and to find new target genes to be tested further for their possible role in male-to-female sex transdifferentiation. To this end, we have successfully adapted a previously developed bioinformatics workflow to a meta-analysis of two datasets studying sex reversal following exposure to EE2 in juvenile rainbow trout. The meta-analysis consisted of retrieving the intersection of the top gene lists generated for both datasets, performed at different levels of stringency. The intersecting gene lists, enriched in true positive differentially expressed genes (DEGs), were subjected to over-representation analysis (ORA) which allowed identifying several statistically significant enriched pathways altered by EE2 treatment and several new candidate pathways, such as progesterone-mediated oocyte maturation and PPAR signalling. Moreover, several relevant key genes potentially implicated in the early transdifferentiation process were selected. Altogether, the results show that EE2 has a great effect on gene expression in juvenile rainbow trout. The feminization process seems to result from the altered transcription of genes implicated in normal female gonad differentiation, resulting in expression similar to that observed in normal females (i.e. the repression of key testicular markers cyp17a1, cyp11b, tbx1), as well as from other genes (including transcription factors) that respond specifically to the EE2 treatment. The results also showed that the bioinformatics workflow can be applied to different types of microarray platforms and could be generalized to (eco)toxicogenomics studies for environmental risk assessment purposes.

Gonadal development and transcript profiling of steroidogenic enzymes in response to 17α-methyltestosterone in the rare minnow Gobiocypris rarus

It is well known that natural and anthropogenic chemicals interfere with the hormonal system of vertebrate and invertebrate organisms. How these chemicals regulate gonadal steroidogenesis remains to be determined. The main objective of this study was to evaluate the effects of 17α-methyltestosterone (MT), a synthetic model androgen, on gene expression profiles of six key steroidogenic genes in adult rare minnow. The full-length cDNA encoding 11β-hydroxysteroid dehydrogenase-2 (11β-HSD2) was firstly isolated and characterized by RT-PCR and RACE methods. The gonadal transcript changes of StAR, cyp11a1, 3β-HSD, cyp17a1, 11β-HSD2 and cyp19a1a in 6-month adult Gobiocypris rarus exposed to MT and 17α-ethinylestradiol (EE2) for 7, 14 and 21 days were detected by qRT-PCR. To make an effort to connect the transcriptional changes of steroidogenic enzymes with effects on higher levels of biological organization and on VTG, one remarkable sensitive target of steroids, body and gonad weights, histology of gonads, and hepatic vtg mRNA level were measured. MT caused varying degree of abnormalities in ovaries and testes. The hepatic vtg mRNA level was highly inhibited in females and slightly altered in males by MT. Transcripts of several steroidogenic genes including StAR, cyp17a1, and cyp11a1 showed high responsiveness to MT exposure in G. rarus. The gene expression profiles of these steroidogenic genes in MT-treated groups were much distinct with the EE2-treated group.

Molecular cloning of Pcc-dmrt1s and their specific expression patterns in Pengze crucian carp (Carassius auratus var. Pengze) affected by 17α-methyltestosterone

Dmrt1, an important transcription factor associated with testicular differentiation, is conserved among teleost, which could also be detected in ovaries. In the present study, three isoforms of Pcc-dmrt1s (Pcc-dmrt1a, Pcc-dmrt1b and Pcc-dmrt1c) resulting from alternative splicing of the dmrt1 gene were cloned and characterized in the triploid gynogenetic fish, the Pengze crucian carp. Their mRNA expression profiling was investigated in juvenile developmental stages, tissues of the adult fish, and the juveniles under 84.2 ng/L 17α-methyltestosterone (MT) treatments. Results showed that their putative proteins shared high identities to Dmrt1 in cyprinid fish species. Gene expression profiling in the developmental stages showed that all the three target genes had a highest/lowest expression at 56/40 days post-hatching (dph), respectively. The period of 40 dph appeared to be a key time during the process of the ovary development of Pengze crucian carp. The tissue distribution results indicated that Pcc-dmrt1s were predominantly expressed in hepatopancreas, brain, spleen and ovary of the female fish. MT significantly increased the mRNA expression of Pcc-dmrt1a (all 4-week exposures) and Pcc-dmrt1b (except for week 2), while repressed Pcc-dmrt1c transcripts at all exposure period except for week 2. MT extremely significant repressed cyp19a1a transcripts for 1 week. The present study indicated that MT could influence the ovary development of Pengze crucian carp by disturbing gene expressions of Pcc-dmrt1s and cyp19a1a. Furthermore, the present study will be of great significance to broaden the understanding of masculinizing pathway during ovary development in gynogenetic teleost.

Transdifferentiation of differentiated ovary into functional testis by long-term treatment of aromatase inhibitor in Nile tilapia

Females with differentiated ovary of a gonochoristic fish, Nile tilapia, were masculinized by long-term treatment with an aromatase inhibitor (Fadrozole) in the present study. The reversed gonads developed into functional testes with fertile sperm. The longer the fish experienced sex differentiation, the longer treatment time was needed for successful sex reversal. Furthermore, Fadrozole-induced sex reversal, designated as secondary sex reversal (SSR), was successfully rescued by supplement of exogenous 17β-estradiol. Gonadal histology, immunohistochemistry, transcriptome, and serum steroid level were analyzed during SSR. The results indicated that spermatogonia were transformed from oogonia or germline stem cell-like cells distributed in germinal epithelium, whereas Leydig and Sertoli cells probably came from the interstitial cells and granulosa cells of the ovarian tissue, respectively. The transdifferentiation of somatic cells, as indicated by the appearance of doublesex- and Mab-3-related transcription factor 1 (pre-Sertoli cells) and cytochrome P450, family 11, subfamily B, polypeptide 2 (pre-Leydig cells)-positive cells in the ovary, provided microniche for the transdifferentiation of germ cells. Decrease of serum 17β-estradiol was detected earlier than increase of serum 11-ketotestosterone, indicating that decrease of estrogen was the cause, whereas increase of androgen was the consequence of SSR. The sex-reversed gonad displayed more similarity in morphology and histology with a testis, whereas the global gene expression profiles remained closer to the female control. Detailed analysis indicated that transdifferentiation was driven by suppression of female pathway genes and activation of male pathway genes. In short, SSR provides a good model for study of sex reversal in teleosts and for understanding of sex determination and differentiation in nonmammalian vertebrates.

Molecular classification of colorectal cancer: a dream that can become a reality

Despite thousands of studies about colorectal cancer (CRC) as much as extensively usage of prognostic antibodies÷genes and clinical trials that include the newest targeted drugs, this tumor still remains in the top of both incidence and cancer-related mortality. In this review, we intended to correlate our experience in field of colorectal cancer with the literature data and to present our vision about the prognostic and predictive role of some of the most used molecular and immunohistochemical examinations in the field. The prognostic and predictive values of parameters such as microsatellite instability, angiogenesis, Maspin gene/protein, K-ras and BRAF mutations are discussed in relationship to the classical antibodies such as Keratin 7/20, p53 or HER2. At the end, we correlated these informations and tried to realize a molecular classification of colorectal cancer, similar to breast carcinomas, in order to establish targeted groups of patients for targeted therapy.

Antagonistic roles of Dmrt1 and Foxl2 in sex differentiation via estrogen production in tilapia as demonstrated by TALENs

Transcription activator-like effector nucleases (TALENs) are a powerful approach for targeted genome editing and have been proved to be effective in several organisms. In this study, we reported that TALENs can induce somatic mutations in Nile tilapia, an important species for worldwide aquaculture, with reliably high efficiency. Six pairs of TALENs were constructed to target genes related to sex differentiation, including dmrt1, foxl2, cyp19a1a, gsdf, igf3, and nrob1b, and all resulted in indel mutations with maximum efficiencies of up to 81% at the targeted loci. Effects of dmrt1 and foxl2 mutation on gonadal phenotype, sex differentiation, and related gene expression were analyzed by histology, immunohistochemistry, and real-time PCR. In Dmrt1-deficient testes, phenotypes of significant testicular regression, including deformed efferent ducts, degenerated spermatogonia or even a complete loss of germ cells, and proliferation of steroidogenic cells, were observed. In addition, disruption of Dmrt1 in XY fish resulted in increased foxl2 and cyp19a1a expression and serum estradiol-17β and 11-ketotestosterone levels. On the contrary, deficiency of Foxl2 in XX fish exhibited varying degrees of oocyte degeneration and significantly decreased aromatase gene expression and serum estradiol-17β levels. Some Foxl2-deficient fish even exhibited complete sex reversal with high expression of Dmrt1 and Cyp11b2. Furthermore, disruption of Cyp19a1a in XX fish led to partial sex reversal with Dmrt1 and Cyp11b2 expression. Taken together, our data demonstrated that TALENs are an effective tool for targeted gene editing in tilapia genome. Foxl2 and Dmrt1 play antagonistic roles in sex differentiation in Nile tilapia via regulating cyp19a1a expression and estrogen production.

DAX1 regulatory networks unveil conserved and potentially new functions

DAX1 is an orphan nuclear receptor with actions in mammalian sex determination, regulation of steroidogenesis, embryonic development and neural differentiation. Conserved patterns of DAX1 gene expression from mammals to fish have been taken to suggest conserved function. In the present study, the European sea bass, Dicentrarchus labrax, DAX1 promoter was isolated and its conserved features compared to other fish and mammalian DAX1 promoters in order to derive common regulators and functional gene networks. Fish and mammalian DAX1 promoters share common sets of transcription factor frameworks which were also present in the promoter region of another 127 genes. Pathway analysis clustered these into candidate gene networks associated with the fish and mammalian DAX1. The networks identified are concordant with described functions for DAX1 in embryogenesis, regulation of transcription, endocrine development and steroid production. Novel candidate gene network partners were also identified, which implicate DAX1 in ion homeostasis and transport, lipid transport and skeletal development. Experimental evidence is provided supporting roles for DAX1 in steroid signalling and osmoregulation in fish. These results highlight the usefulness of the in silico comparative approach to analyse gene regulation for hypothesis generation. Conserved promoter architecture can be used also to predict potentially new gene functions. The approach reported can be applied to genes from model and non-model species.

Molecular cloning and characterization of amh, dax1 and cyp19a1a genes and their response to 17α-methyltestosterone in Pengze crucian carp

The proteins encoded by amh, dax1 and cyp19a1a play important roles in gonad differentiation. Their functions have been far less studied in teleosts. In this study, the full-length cDNAs of amh, dax1 and cyp19a1a were cloned and characterized in a triploid gynogenic fish, the Pengze crucian carp. Their expression profilings in juvenile development, adult tissues and juveniles exposed to 100 ng/L 17α-methyltestosterone (MT) were investigated. Results showed that their putative proteins shared high identities to their counterparts in cyprinid fish species, respectively. The tissue distribution results indicated that amh and cyp19a1a were predominantly expressed in the ovary and dax1 was dominantly expressed in the liver. Gene profiling in the developmental stages showed that all the three target genes had a consistent highest expression at 48 days post hatching (dph). The period of 48 dph appeared to be a key time during the process of the gonad development of Pengze crucian carp. 100 ng/L MT significantly increased the mRNA expression of amh at 2- and 4-week exposures and enhanced dax1 and cyp19a1a at 6-week exposure. The present study indicated that MT could influence the gonad development in Pengze crucian carp by disturbing sex-differentiation associated gene expression. Furthermore, the present study will be of great significance to broaden the understanding of molecular mechanisms of the physiological processes of reproduction in fish.

Introduction of modern endocrine techniques for the production of monosex population of fishes

Of the techniques available to mass-produce a sterile or monosex population, the hormonal induction of sex reversal is the most widely practiced. This paper presents the synthesis of works done on sex reversal using 17α methyltestosterone (17αMT), 17β estradiol, non-steroidal aromatase inhibitors (AIs) and oestrogen receptor agonist, tamoxifen in commercially important aquaculture species mossambique tilapia Oreochromis mossambicus, Nile tilapia Oreochromis niloticus, common carp Cyprinus carpio, mahseer Tor putitora and African catfish Clarias gariepinus. Results on sex reversal for producing female T. putitora delineated that treatment to fry of T. putitora 60 days post fertilization (60 dpf) with 17β estradiol (150 mg/kg feed) fetched 69.5% female population. Further, raised temperature (23 ± 1 °C) five degrees above ambient temperature brought about 37.5% female populations which was above the control (24.4% females). Feeding tilapia O. mossambicus fry after yolk sac absorption stage (8 dpf) with 17αMT incorporated diet (35 mg/kg feed) under long photoperiod (16L:8D) for 60 days obtained 100% sex reversed males with excellent growth. Treatment with tamoxifen and letrozole (200mg/kg feed) to fingerlings of C. carpio and O. niloticus for 60 days brought about 82.5% and 98.5% masculinization with increased level of testosterone (T). Letrozole treatments to C. gariepinus significantly (p<0.001) increased T level to 1197.76 ± 18.79 pg/ml when treatment was given through feed for 60 days and 1470.5 ± 20.76 pg/ml via intraperitoneal injection. There was significant deviation in sex ratio leading to high level of masculinization in different aquaculture species with treatments of hormones and AIs.

Genomic approaches to study genetic and environmental influences on fish sex determination and differentiation

The embryonic gonad is the only organ that takes two mutually exclusive differentiating pathways and hence gives rise to two different adult organs: testes or ovaries. The recent application of genomic tools including microarrays, next-generation sequencing approaches, and epigenetics can significantly contribute to decipher the molecular mechanisms involved in the processes of sex determination and sex differentiation. However, in fish, these studies are complicated by the fact that these processes depend, perhaps to a larger extent when compared to other vertebrates, on the interplay of genetic and environmental influences. Here, we review the advances made so far, taking into account different experimental approaches, and illustrate some technical complications deriving from the fact that as development progresses it becomes more and more difficult to distinguish whether changes in gene expression or DNA methylation patterns are the cause or the consequence of such developmental events. Finally, we suggest some avenues for further research in both model fish species and fish species facing specific problems within an aquaculture context.

Insulin-like growth factor 3 regulates expression of genes encoding steroidogenic enzymes and key transcription factors in the Nile tilapia gonad

Insulin-like growth factors (Igfs) are implicated in a wide variety of physiological roles in teleost gonadal development and reproduction. In the present study, igf3 mRNA expression in the tilapia ovary was found to be higher than in the testis from 5 to 40 days after hatching (dah) but was lower than that in testis from 50 to 70 dah. Consistently, Igf3 protein signal was detected in the somatic cells of XX and XY gonads from 10 dah until adulthood by immunohistochemistry, using a specific Igf3 polyclonal antibody. Incubation of ovarian and testicular cells in primary culture with recombinant Igf3 significantly increased nr5a1, foxl2, dmrt1, cyp19a1a, cyp11a1, cyp11b2, hsd3b2 , and cyp17a1 expression in a time- and dose-dependent manner. Promoter analysis using luciferase assays in HEK293 cells revealed that igf3 promoter activity was directly activated by Nr5a1 (Sf1) and further enhanced by Foxl2, Nr0b1a (Dax1), and Nr0b1b (Dax2) but repressed by Dmrt1 and estrogen receptor (Esr1, Esr2a, or Esr2b) along with 17beta-estradiol treatment. In addition, igf3 promoter activity was increased slightly by forskolin treatment alone but synergistically up-regulated by transfection with nr5a1. These in vitro results correlated well with the expression profile of igf3 during early gonad differentiation. Our results indicated that igf3 is involved in fish gonad steroidogenesis because of its ability to regulate the expression of foxl2, dmrt1, and nr5a1 and steroidogenic enzymes. The expression of igf3 is in turn regulated by transcription factors Foxl2, Dmrt1, and Nr5a1, as well as by 17beta-estradiol treatment.

Reproductive endocrinology of Syngnathidae

Few studies have examined the underlying hormonal mechanisms that mediate reproductive cyclicity, male pregnancy and reproductive behaviour in syngnathids. Progress in these areas has been hampered by the small size of most species in the family and a lack of validated techniques for assessing endocrine function. Research on a relatively small number of species has suggested that androgens are likely regulators of spermatogenesis and the development of the male brood pouch prior to pregnancy whereas prolactin and corticosteroids synergistically promote brood pouch function during pregnancy. No evidence supports a reversal of reproductive steroid hormone function in sex-role reversed behaviour, but neuropeptides such as arginine vasotocin or isotocin should be examined for their role in regulating parturition and mating behaviour. The diversity of reproductive patterns exhibited by syngnathids suggests that they will provide a unique opportunity to assess how hormonal regulation of integumentary function, gametogenesis and reproductive behaviour have evolved within a teleost lineage. Additionally, their coastal distribution and embryo retention make them potentially important subjects for studies on the effect of endocrine disruption on fitness.

A review of studies on androgen and estrogen exposure in fish early life stages: effects on gene and hormonal control of sexual differentiation

Teleost fish are unique among vertebrates in that phenotypic sex or onset of sex inversion can be easily manipulated by hormonal treatments. In recent years, researchers have begun reporting concentrations of synthetic and natural hormones in the environment. Although concentrations are very low (in the parts per trillion to low parts per billion), they are still of concern because of the high potency of synthetic hormones and the enhanced susceptibility of teleost fishes, especially early life stages, to hormonal exposures. In this review, we will focus on sex differentiation in teleost fishes and how these processes in fish early life stages may be impacted by environmental hormones which are known to contaminate aquatic environments. We will start by reviewing information on sources and concentrations of hormones in the environment and continue by summarizing the state of knowledge of sex differentiation in teleost gonochoristic fishes, including information on genes involved (e.g. cyp19, dmrt1, sox9 and foxl2). We will end our review with a summary of studies that have examined the effects of androgens and estrogens on fish sex differentiation after exposure of fish embryos and larvae and with ideas for future research.

The effects of estrogenic and androgenic endocrine disruptors on the immune system of fish: a review

During the last decade, a number of studies have shown that, in addition to their classically described reproductive function, estrogens and androgens also regulate the immune system in teleosts. Today, several molecules are known to interfere with the sex-steroid signaling. These chemicals are often referred to as endocrine disrupting contaminants (EDCs). We review the growing evidence that these compounds interfere with the fish immune system. These studies encompass a broad range of approaches from field studies to those at the molecular level. This integrative overview improves our understanding of the various endocrine-disrupting processes triggered by these chemicals. Furthermore, the research also explains why fish that have been exposed to EDCs are more sensitive to pathogens during gametogenesis. In this review, we first discuss the primary actions of sex-steroid-like endocrine disruptors in fish and the specificity of the fish immune system in comparison to mammals. Then, we review the known interactions between the immune system and EDCs and interpret the primary effects of sex steroids (estrogens and androgens) and their related endocrine disruptors on immune modulation. The recent literature suggests that immune parameters may be used as biomarkers of contamination by EDCs. However, caution should be used in the assessment of such immunotoxicity. In particular, more attention should be paid to the specificity of these biomarkers, the external/internal factors influencing the response, and the transduction pathways induced by these molecules in fish. The use of the well-known mammalian models provides a useful guide for future research in fish.

Meta-analysis of muscle transcriptome data using the MADMuscle database reveals biologically relevant gene patterns

Background

DNA microarray technology has had a great impact on muscle research and microarray gene expression data has been widely used to identify gene signatures characteristic of the studied conditions. With the rapid accumulation of muscle microarray data, it is of great interest to understand how to compare and combine data across multiple studies. Meta-analysis of transcriptome data is a valuable method to achieve it. It enables to highlight conserved gene signatures between multiple independent studies. However, using it is made difficult by the diversity of the available data: different microarray platforms, different gene nomenclature, different species studied, etc.

Description

We have developed a system tool dedicated to muscle transcriptome data. This system comprises a collection of microarray data as well as a query tool. This latter allows the user to extract similar clusters of co-expressed genes from the database, using an input gene list. Common and relevant gene signatures can thus be searched more easily. The dedicated database consists in a large compendium of public data (more than 500 data sets) related to muscle (skeletal and heart). These studies included seven different animal species from invertebrates (Drosophila melanogaster, Caenorhabditis elegans) and vertebrates (Homo sapiens, Mus musculus, Rattus norvegicus, Canis familiaris, Gallus gallus). After a renormalization step, clusters of co-expressed genes were identified in each dataset. The lists of co-expressed genes were annotated using a unified re-annotation procedure. These gene lists were compared to find significant overlaps between studies.

Conclusions

Applied to this large compendium of data sets, meta-analyses demonstrated that conserved patterns between species could be identified. Focusing on a specific pathology (Duchenne Muscular Dystrophy) we validated results across independent studies and revealed robust biomarkers and new pathways of interest. The meta-analyses performed with MADMuscle show the usefulness of this approach. Our method can be applied to all public transcriptome data.

The duplicated rainbow trout (Oncorhynchus mykiss) T-box transcription factors 1, tbx1a and tbx1b, are up-regulated during testicular development

Tbx1 is a member of the T-box transcription factor gene family involved in embryogenesis and organogenesis. Recently, within a pan-genomic screen using rainbow trout (Oncorhynchus mykiss) cDNA microarrays, we identified a tbx1 homolog with testicular over-expression during sex differentiation. Here, we characterized two very similar rainbow trout tbx1 paralogs, tbx1a and tbx1b. In adult tissues, tbx1a expression is restricted to the gonads, with high expression in the testis, while tbx1b is more widely expressed in gonads, gills, brains, muscle, and skin. During gonadal differentiation, both genes are differentially expressed in favor of testis formation shortly after hatching. These genes are expressed in somatic cells surrounding germ cells of the differentiating testis, while no or only weak expression was observed in the differentiating ovary. tbx1a and tbx1b were also both down-regulated in the differentiating testis during feminization with estrogens and up-regulated in the differentiating ovary during masculinization with an aromatase inhibitor. These results suggest that tbx1a and tbx1b are probably involved in the regulation of testicular differentiation in rainbow trout. Since Tbx1 is known to interact with the retinoic acid (RA) signaling pathway, we also examined the effect of RA on the rainbow trout tbx1 expression pattern. Expression of tbx1a and tbx1b was down-regulated in RA-treated male gonads, suggesting that tbx1 interacts with the RA signaling pathway and thus could be involved in the control of rainbow trout gonadal differentiation.

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

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

Histological study of gonadal development and sex differentiation in Salvelinus fontinalis under Tasmanian climate conditions

This study describes the developmental process of gonads in brook trout from 0 degree days post-hatch (°dph) until completion of sex differentiation (3354°dph). Gonadal development was divided into undifferentiated (0–2013°dph) and differentiated phases (2769–3354°dph). Fertilised eggs (n = 1000) were incubated at 9.5−10°C until hatching at 66 days post-fertilisation (dpf). A total of 20% of alevins sampled on 0°dph were found with unpaired and undifferentiated gonads, indicating that gonadal development commenced before hatch. Initially, undifferentiated gonads contained stromal tissue and few primordial gonadal cells (PGC) (n = 2–5). During the undifferentiated phase, gonads increased in size and proliferative activity of the PGC increased their number (n = 15–22). The differentiated phase commenced with the appearance of sex differentiation at 2769°dph where gonads could be clearly differentiated as ovaries and presumptive testes. Ovaries were identified by the presence of oogonia while presumptive testes contained spermatogonia, vena comittis and a proximal network of cavities. Both ovaries and testes underwent further differentiation until the end of this phase (3354°dph). Oogonia were transformed into primary oocytes while spermatogonial cysts were observed in testes. However, differentiation of steroidogenic cells could not be observed. Direct sex differentiation was found in this study as undifferentiated gonads directly developed into testes and ovaries with anatomical differentiation preceding cytological differentiation. This study confirms previous studies that the prehatch period should be targeted when attempting to produce future monosex populations via indirect sex reversal using androgen treatment.

Sexually dimorphic gene expression in the gonad and liver of shovelnose sturgeon (Scaphirhynchus platorynchus)

The development of a biomarker for rapid detection of intersex is desirable to researchers and fisheries managers alike. The first step is to identify a marker that has a dimorphic expression pattern. With a focus on sex-specific genes, we assessed the use of vitellogenin (vtg), forkhead box L2 (foxl2) and doublesex and mab-3-related transcription factor 1 (dmrt1) as molecular biomarkers for the identification of gender in shovelnose sturgeon (Scaphirhynchus platorynchus), a species known to have intersex individuals. A total of 61 shovelnose sturgeons were sampled from the Wabash River, Indiana, in April 2008. Results from our study indicate that least 7.5% of the non-females had testicular oocytes. Expression level of liver vtg was not higher in females than males, nor was gonad dmrt1 expression found to be higher in males. Only the expression of foxl2 was significantly greater in females and was found to be useful for identifying gender. Variation in expression levels of foxl2 in gonads of intersex fish limited its usefulness as a single biomarker for identifying this condition. Instead, the use of foxl2 to dmrt1 (foxl2 transcript abundance/dmrt1 transcript abundance) may be useful in the identification of intersex fish, as this ratio increased with increased feminization. We conclude that foxl2 can be used to identify sex, but not intersex sturgeon.