Cloning and differential expression of FOXL2 during ovarian development and recrudescence of the catfish, Clarias gariepinus

Determination of the timing of early gonadal differentiation in silver pomfret, Pampus argenteus

Silver pomfret is a species of global significance due to its high nutritional in fisheries sector. To accurately ascertain the timing of sex differentiation mechanism and mRNA level in this species, this study examined gonad morphology and patterns of gene expression related to sex differentiation in males and females from 51 to 180 days post hatch (dph), the temperature of water was maintained at 26 ± 1 ℃. Distinct morphological differentiation of the silver pomfret ovaries, marked by the emergence of primary oocytes, became apparent from 68 dph. By 108 dph, the testes began to differentiate, as evidenced by the appearance of the efferent duct. Early oocytes exhibited a diameter ranged from 0.077 mm to 0.682 mm, with an average diameter of 0.343 ± 0.051 mm. The proportions of various types of germ cells within the testes were subjected to analysis. The localization of Vasa during the early stages of sexual differentiation was a subject to analysis as well. Vasa was predominantly localized within the cytoplasm of gonocyte, peri-nucleolus stage oocytes, primary oocytes and type A spermatogonocytes, indicating that Vasa is involved in the early gonadal differentiation of silver pomfret. The study investigated the expression patterns of dmrt1, gsdf, amh, foxl2, cyp19a1a, cyp11a, sox3 and vasa, all of which are involved in the sex differentiation of teleosts. Among these genes, amh, gsdf, sox3, foxl2, vasa were indentified as crucial contributors to the early gonadal development of silver pomfret. Significant sex-related differences were observed in the expression patterns of amh, dmrt1, gsdf, cyp11a, sox3, cyp19a1a, vasa. This study provides novel insights into the timing of physiological changes associated with the sexual differentiation of silver pomfret. Collectively, the present data indicates that the differentiation of ovaries and testes take place approximately at 68 dph in females and 108 dph in males.

Circular RNA expression profiles and CircSnd1-miR-135b/c-foxl2 axis analysis in gonadal differentiation of protogynous hermaphroditic ricefield eel Monopterus albus

BACKGROUND

The expression and biological functions of circular RNAs (circRNAs) in reproductive organs have been extensively reported. However, it is still unclear whether circRNAs are involved in sex change. To this end, RNA sequencing (RNA-seq) was performed in gonads at 5 sexual stages (ovary, early intersexual stage gonad, middle intersexual stage gonad, late intersexual stage gonad, and testis) of ricefield eel, and the expression profiles and potential functions of circRNAs were studied.

RESULTS

Seven hundred twenty-one circRNAs were identified, and the expression levels of 10 circRNAs were verified by quantitative real-time PCR (qRT-PCR) and found to be in accordance with the RNA-seq data, suggesting that the RNA-seq data were reliable. Then, the sequence length, category, sequence composition and the relationship between the parent genes of the circRNAs were explored. A total of 147 circRNAs were differentially expressed in the sex change process, and GO and KEGG analyses revealed that some differentially expressed (such as novel_circ_0000659, novel_circ_0004005 and novel_circ_0005865) circRNAs were closely involved in sex change. Furthermore, expression pattern analysis demonstrated that both circSnd1 and foxl2 were downregulated in the process of sex change, which was contrary to mal-miR-135b. Finally, dual-luciferase reporter assay and RNA immunoprecipitation showed that circSnd1 and foxl2 can combine with mal-miR-135b and mal-miR-135c. These data revealed that circSnd1 regulates foxl2 expression in the sex change of ricefield eel by acting as a sponge of mal-miR-135b/c.

CONCLUSION

Our results are the first to demonstrate that circRNAs have potential effects on sex change in ricefield eel; and circSnd1 could regulate foxl2 expression in the sex change of ricefield eel by acting as a sponge of mal-miR-135b/c. These data will be useful for enhancing our understanding of sequential hermaphroditism and sex change in ricefield eel or other teleosts.

Function of Foxl2 and Dmrt1 proteins during gonadal differentiation in the olive flounder Paralichthys olivaceus

Study on fish sex differentiation is important both from academic and practical aspects. Foxl2 and Dmrt1 are important transcription factors that should be involved in fish gonadal differentiation, but there is still no direct evidence to clarify their protein functions. Olive flounder Paralichthys olivaceus, an important mariculture fish in China, Japan, and Korea, shows sex-dimorphic growth. In this study, the Foxl2 and Dmrt1 proteins were detected in granulosa cells of the ovary and Sertoli cells of the testis, respectively, showing significant sex-dimorphic expression patterns. Then, bioactive high-purity Foxl2 and Dmrt1 recombinant proteins were obtained in vitro. Furthermore, effects of the recombinant Foxl2 and Dmrt1 during gonadal differentiation period were evaluated by intraperitoneal injection in juvenile fish. Compared with the control group, the male rate in the Dmrt1 group increased from 0 % to 82 %, showing for the first time in fish that the recombinant Dmrt1 could alter the sex phenotype. In addition, transcription levels of cyp19a and its transcription factors also changed after the recombinant Foxl2 and Dmrt1 injection. These findings reveal that Foxl2 and Dmrt1 are vital regulators for fish gonadal differentiation by regulating cyp19a expression, and also provide a new approach for sex control in fish aquaculture.

Feminization of channel catfish with 17β-oestradiol involves methylation and expression of a specific set of genes independent of the sex determination region

Exogenous oestrogen 17β-oestradiol (E2) has been shown to effectively induce feminization in teleosts. However, the molecular mechanisms underlying the process remain unclear. Here, we determined global DNA methylation and gene expression profiles of channel catfish (Ictalurus punctatus) during early sex differentiation after E2 treatment. Overall, the levels of global DNA methylation after E2 treatment were not significantly different from those of controls. However, a specific set of genes were differentially methylated, which included many sex differentiation-related pathways, such as MARK signalling, adrenergic signalling, Wnt signalling, GnRH signalling, ErbB signalling, and ECM-receptor interactions. Many genes involved in these pathways were also differentially expressed after E2 treatment. Specifically, E2 treatments resulted in upregulation of female-related genes and downregulation of male-related genes in genetic males during sex reversal. However, E2-induced sex reversal did not cause sex-specific changes in methylation profiles or gene expression within the sex determination region (SDR) on chromosome 4, suggesting that E2-induced sex reversal was a downstream process independent of the sex determination process that was regulated by sex-specific methylation within the SDR.

Timing of early gonadal differentiation and effects of estradiol-17β treatments on the sex differentiation in Largemouth bass (Micropterus salmoides)

In this study, an efficient estradiol-17β (E₂)-induced feminization method was established based on the timing of early gonadal differentiation in Largemouth bass (Micropterus salmoides). Histological section results showed that from 20 days post-hatch (dph) to 30 dph, the germ cells gradually differentiated into oogonium and spermatic deferent, respectively. Moreover, female-biased genes Foxl2 and Cyp19a1a were up-regulated to the first peak at 20 dph, while the male-biased genes Dmrt1 were up-regulated to the first peak at 30 dph. These results indicated that the timing of early gonadal differentiation in Largemouth bass was between 20 and 30 dph. Therefore, 15 dph Largemouth bass with a body length of 15.10 ± 0.09 mm were chosen, and four E₂-treated diets were set as 0 (E0, control), 50 mg/kg E₂ (E50), 100 mg/kg E₂ (E100), and 200 mg/kg E₂ (E200). After feeding with E₂-treated diets for 60 days, female ratios were 55%, 100%, 100%, and 100% in E0, E50, E100, and E200 groups, respectively. No intersex fish were observed in all the groups. However, 30% of females in the E200 group possessed thinner ovaries, with smaller ovary cavity structures and a decreased number of primary oocyte cells than those in other groups. Besides, the Largemouth bass in the E0 group grew more than those in E50, E100, and E200 groups during the E₂ treatments period (P < 0.05). In conclusion, our study suggested that 50-100 mg/kg E₂-treated diets could effectively induce the feminization of 15 dph Largemouth bass within 60 days duration time, which provided valuable information for the breeding of the all-male Largemouth bass population.

Nr5a homologues in the ricefield eel Monopterus albus: Alternative splicing, tissue-specific expression, and differential roles on the activation of cyp19a1a promoter in vitro

Nr5a (Fushi tarazu factor 1, Ftz-F1) homologues belong to the nuclear receptor superfamily, and are involved in the regulation of reproduction in vertebrates. Four genes encoding Nr5a homologues were present in the genome of ricefield eel, which are designated as nr5a1a, nr5a1b, nr5a2, and nr5a5 in the present study. Alternatively spliced transcripts were identified for nr5a1a and nr5a1b genes. Sequence analysis indicated that nr5a5 is possibly a paralog of nr5a2, and nr5a1b is lost during evolution in some teleosts including tilapia and medaka. Ricefield eel nr5a genes exhibit tissue-specific expression patterns, with nr5a1a and nr5a1b resembling that of the SF-1/Ad4BP (NR5A1) subfamily, and nr5a2 and nr5a5 resembling that of the NR5A2/LRH/FTF subfamily. Transcriptomic analysis revealed parallel expression profiles of nr5a1a, foxl2, and cyp19a1a in ovarian follicles during vitellogenesis, with peak values at the late vitellogenic stage. Real-time PCR indicated that the expression levels of nr5a1a and foxl2 in gonads were decreased significantly during the sexual transition from female to the late intersexual stage. In vitro transient transfection assay showed that Nr5a1a up-regulated ricefield eel cyp19a1a promoter activities synergistically with Foxl2. However, Nr5a1b, Nr5a2, and Nr5a5 could neither activate ricefield eel cyp19a1a promoter alone nor enhance the stimulatory effects of Foxl2 on cyp19a1a promoter activities. Collectively, the above data suggest that Nr5a homologues may have diverse and differential roles in the tissues of ricefield eels. The up-regulation of gonadal nr5a1a and foxl2 during vitellogenesis may be important for the ovarian development whereas their down-regulation during the sexual transition period may be important for the sex change process of ricefield eels, possibly through the regulation of cyp19a1a gene expression.

Common carp pentraxin gene: Evidence for its role in ovarian differentiation and growth

Pentraxins (PTX), belong to an evolutionarily conserved family, containing a PTX protein domain, having role in acute immunological responses and fertility in higher vertebrates. However, information regarding the action of ptx on reproduction is extremely limited in fish. To study this, ptx cDNA was cloned for downstream analysis. Tissue distribution and ontogeny expression analysis indicated the prevalence of ptx in ovary. Varied phase-wise expression during carp ovarian cycle and elevated ptx expression after human chorionic gonadotropin induction, in vitro and in vivo, indicated probable regulation of gonadotropin. In situ hybridization and immunohistochemistry revealed the presence of ptx transcript and protein in the follicular layer of stage-III/IV oocytes indicating a role in ovarian growth. To assess the functional significance of ptx, transient silencing was performed using follicular primary cell culture, in vitro and in common carp, in vivo, through ovary-targeted injection of PEI-siRNA. Transient silencing of ptx-siRNA reduced the expression of various genes/factors related to oogenesis such as transcription factors, several steroidogenic enzymes, and esrs genes. These alterations in expression suggested a plausible role for ptx in ovarian steroidogenesis either, directly or indirectly, which is evident from the changes in the serum estradiol-17β (E₂) and 17α,20β-dihydroxyprogesterone levels. Furthermore, downregulation of aromatase activity was also noticed after transient silencing. Increased ptx expression after E₂ induced sex reversal to juvenile carp showed the correlative role of ptx during ovarian differentiation and development. Taken together, these findings suggest that ptx exerts an important role during ovarian growth, maturation and/or recrudescence of common carp.

Cbx2, a PcG Family Gene, Plays a Regulatory Role in Medaka Gonadal Development

Chromobox homolog 2 (CBX2), a key member of the polycomb group (PcG) family, is essential for gonadal development in mammals. A functional deficiency or genetic mutation in cbx2 can lead to sex reversal in mice and humans. However, little is known about the function of cbx2 in gonadal development in fish. In this study, the cbx2 gene was identified in medaka, which is a model species for the study of gonadal development in fish. Transcription of cbx2 was abundant in the gonads, with testicular levels relatively higher than ovarian levels. In situ hybridization (ISH) revealed that cbx2 mRNA was predominately localized in spermatogonia and spermatocytes, and was also observed in oocytes at stages I, II, and III. Furthermore, cbx2 and vasa (a marker gene) were co-localized in germ cells by fluorescent in situ hybridization (FISH). After cbx2 knockdown in the gonads by RNA interference (RNAi), the sex-related genes, including sox9 and foxl2, were influenced. These results suggest that cbx2 not only plays a positive role in spermatogenesis and oogenesis but is also involved in gonadal differentiation through regulating the expression levels of sex-related genes in fish.

Identification, expression profiling and localization of thoc in common carp ovary: Influence of thoc3-siRNA transient silencing

THO complex is a multisubunit family with a function in transcription and mRNA export. In the present study, transcripts of THO complex (thoc) were identified in developing ovary of common carp and their role during ovarian development and growth has been characterized for the first time in a teleost using expression profiling and transient siRNA silencing. Thoc expression revealed a spatiotemporal pattern in the gonads with high levels at 120 days post-hatch, with moderately high levels thereafter. In situ hybridization and immunohistochemical localization revealed the presence of thoc3 in follicular layer of stage-III/IV oocytes. High levels of thoc3, thoc5, and thoc7 genes in the follicular layer suggest a possible role in ovarian growth. Reduced levels of serum estradiol-17β and 17α, 20β-dihydroxypregn-4-en-3-one after thoc3 transient silencing indicated differential action on steroidogenic enzyme, transcription factor, and growth factor genes. Furthermore, transient silencing of thoc3, in vivo and in vitro, downregulated ad4bp/sf1, amh, cyp19a1a, foxl2, hsd3b, hsd11b1, hsd20b, hsd17b1, rspo1, and vtg. Incidentally, gdf9 and igf1 were upregulated, while no change was seen in esr1/2, nanos, and vasa. These observations imply that thoc3 seems to regulate ovarian function including steroidogenesis, either directly or indirectly.

FoxL2 combined with Cyp19a1a regulate the spawning upstream migration in Coilia nasus

FoxL2 is a member of the forkhead/HNF-3-related family of transcription factors which provides tissue specific gene regulation. It is known to regulate ovarian aromatase, which plays a crucial role in ovarian development and mature. To understand the role of FoxL2/ovarian aromatase encoded gene Cyp19a1a during ovarian development and recrudescence, we identified cDNA characteristics of FoxL2 and Cyp19a1a, analyzed its temporal expression both at transcript and protein levels in the anadromous fish, Coilia nasus. Tissue distribution pattern revealed that FoxL2 mRNA expression level was highest in ovary, while Cyp19a1a mRNA was highest in brain. During the upstream migration cycle, in ovary, the FoxL2 mRNA temporal expression peaked at the multiplication stage (stage III in May), the Cyp19a1a mRNA expression peaked at the onset stage (stage I in March). It was found that their mRNA transcripts were maintained at high level during the migration stage (from stage I in March to stage VI in July). Additionally, the strongest immunolabeling positive signals of Cyp19a1a and FoxL2 proteins were mainly found in the cytoplasm of olfactory bulb cell, stratum granulare and neurogliocyte cells and development stage oocytes. Data indicated that FoxL2 and Cyp19a1a were inducible and functional in the C. nasus ovary development and migration process. Therefore, the present results can be regarded as evidence for indispensable roles of FoxL2 and Cyp19a1a in the ovary development and migratory behavior at gene expression patterns and encoded protein distribution level.

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.

Alteration in molecular markers of oocyte development and intersex condition in mullets impacted by wastewater treatment plant effluents

Wastewater Treatment Plant (WWTP) discharges are an important source of endocrine disrupting chemicals (EDCs) into the aquatic environment. Fish populations inhabiting downstream of WWTP effluents show alterations in gonad and gamete development such as intersex condition, together with xenoestrogenic effects such as vitellogenin up-regulation. However, the molecular mechanisms participating in the development of intersex condition in fish are not elucidated. The aim of this study was to assess the impact of two WWTPs effluents (Gernika and Bilbao-Galindo situated in the South East Bay of Biscay) with different contaminant loads, in thicklip grey mullet (Chelon labrosus) populations inhabiting downstream, examining the presence and severity of intersex condition, during two seasons. Molecular markers of xenoestrogenicity and oocyte differentiation and development (vtgAa, cyp19a1a, cyp19a1b, cyp11b, foxl2, dmrt1 and gtf3a) were also studied. Intersex mullets were identified downstream of both WWTPs and vtgAa was upregulated in intersex and non intersex males. Sex dependent differential transcription levels of target genes were detected in mullets from Galindo. However, no such pattern was observed in mullets from Gernika, suggesting an attenuating effect over studied genes caused by a higher presence of EDCs in this site, as indicated by the elevated prevalence of intersex mullets in this population. In conclusion, no direct association between xenoestrogenic responses and intersex condition was established. Mullets from Gernika showed signs of severe EDC exposure compared to those from Galindo, as demonstrated by the higher prevalence of intersex males and the reduction in transcription profile differences between sexes of gametogenic gene markers.

Sequential, Divergent, and Cooperative Requirements of Foxl2a and Foxl2b in Ovary Development and Maintenance of Zebrafish

Foxl2 is essential for mammalian ovary maintenance. Although sexually dimorphic expression of foxl2 was observed in many teleosts, its role and regulative mechanism in fish remained largely unclear. In this study, we first identified two transcript variants of foxl2a and its homologous gene foxl2b in zebrafish, and revealed their specific expression in follicular layer cells in a sequential and divergent fashion during ovary differentiation, maturation, and maintenance. Then, homozygous foxl2a mutants (foxl2a-/-) and foxl2b mutants (foxl2b-/-) were constructed and detailed comparisons, such as sex ratio, gonadal histological structure, transcriptome profiling, and dynamic expression of gonadal development-related genes, were carried out. Initial ovarian differentiation and oocyte development occur normally both in foxl2a-/- and foxl2b-/- mutants, but foxl2a and foxl2b disruptions result in premature ovarian failure and partial sex reversal, respectively, in adult females. In foxl2a-/- female mutants, sox9a-amh/cyp19a1a signaling was upregulated at 150 days postfertilization (dpf) and subsequently oocyte apoptosis was triggered after 180 dpf. In contrast, dmrt1 expression was greater at 105 dpf and increased several 100-fold in foxl2b-/- mutated ovaries at 270 dpf, along with other testis-related genes. Finally, homozygous foxl2a-/-/foxl2b-/- double mutants were constructed in which complete sex reversal occurs early and testis-differentiation genes robustly increase at 60 dpf. Given mutual compensation between foxl2a and foxl2b in foxl2b-/- and foxl2a-/- mutants, we proposed a model in which foxl2a and foxl2b cooperate to regulate zebrafish ovary development and maintenance, with foxl2b potentially having a dominant role in preventing the ovary from differentiating as testis, as compared to foxl2a.

Involvement of pax2 in ovarian development and recrudescence of catfish: a role in steroidogenesis

PAX2, a member of paired box family, is an essential transcription factor for the organ development in vertebrates including teleosts, yet no evidence has been shown for its involvement in reproduction. To study this, partial- and/or full-length cDNA of pax2 was isolated from the ovary of catfish, Clarias batrachus, along with its other Pax family members, pax1 and pax9 Tissue distribution and ontogeny expression analysis indicated the prevalence of pax2 but not pax1 and pax9 in ovary. Varied phase-wise expression during ovarian cycle and elevation of pax2 after human chorionic gonadotropin induction showed probable regulation by gonadotropins. Pax2 could be localized in various stages of oocytes and in follicular layer of vitellogenic and post-vitellogenic oocytes. To assess the functional significance of pax2, transient RNA silencing was performed using primary catfish ovarian follicle culture, in vitro, and in catfish, in vivo, through ovary-targeted injection of PEI-esiRNA. Pax2 siRNA treatment reduced the expression of various transcripts related to ovarian development like signaling molecules such as wnt4 and wnt5, estrogen receptors, several steroidogenic enzymes and transcription factors. These transitions in transcript levels might have been mediated by Pax2 acting upstream of wnt4/5 that may play a role in steroidogenesis and/or ovarian development along with ad4bp/sf-1 or by direct or indirect interaction with steroidogenic enzyme genes, which is evident from the change in the levels of serum estradiol-17β but not 17α,20β-dihydroxy-4-pregnen-3-one. Taken together, it seems that pax2 has a plausible role during ovarian development and/or recrudescence of catfish either directly or indirectly through Wnt signaling pathway.

Foxl2 and Its Relatives Are Evolutionary Conserved Players in Gonadal Sex Differentiation

Foxl2 is a member of the large family of Forkhead Box (Fox) domain transcription factors. It emerged during the last 15 years as a key player in ovarian differentiation and oogenesis in vertebrates and especially mammals. This review focuses on Foxl2 genes in light of recent findings on their evolution, expression, and implication in sex differentiation in animals in general. Homologs of Foxl2 and its paralog Foxl3 are found in all metazoans, but their gene evolution is complex, with multiple gains and losses following successive whole genome duplication events in vertebrates. This review aims to decipher the evolutionary forces that drove Foxl2/3 gene specialization through sub- and neo-functionalization during evolution. Expression data in metazoans suggests that Foxl2/3 progressively acquired a role in both somatic and germ cell gonad differentiation and that a certain degree of sub-functionalization occurred after its duplication in vertebrates. This generated a scenario where Foxl2 is predominantly expressed in ovarian somatic cells and Foxl3 in male germ cells. To support this hypothesis, we provide original results showing that in the pea aphid (insects) foxl2/3 is predominantly expressed in sexual females and showing that in bovine ovaries FOXL2 is specifically expressed in granulosa cells. Overall, current results suggest that Foxl2 and Foxl3 are evolutionarily conserved players involved in somatic and germinal differentiation of gonadal sex.

Molecular cloning, computational analysis and expression pattern of forkhead box l2 (Foxl2) gene in catfish

Foxl2 belongs to forkhead/HNF-3-related family of transcription factors which is involved in ovarian differentiation and development. In present study, the Foxl2 mRNA was cloned from ovary of C. batrachus. The full length cDNA sequence of the Foxl2 was 1056bp which consists of 5' (41bp) and 3' (106bp) non-coding regions, as well as a 909bp of open reading frame (ORF) that encodes 302 amino acids. The putative protein was having the theoretical molecular weight (MW) of 34.018kD and a calculated isoelectric point (pI) of 9.38. There were 11 serine (Ser), 5 threonine (Thr), and 5 tyrosine (Tyr) phosphorylation sites and 2 putative N-glycosylation sites on the predicted protein. The ligand binding sites were predicted to be present on amino acids 42, 49, 50, 91, 92 and 95 respectively. The signal peptide analysis predicted that C. batrachus Foxl2 is a non-secretory protein. The hydropathy profile of Foxl2 protein revealed that this protein is hydrophilic in nature. Protein-protein interaction demonstrated that Foxl2 protein chiefly interacts with cytochrome P450 protein family. The mRNA transcript analysis of various tissues indicated that the C. batrachus Foxl2 mRNA was more expressed in the brain, pituitary and ovary in female while, the former two tissues and testis showed low expression in male. This study provides a basis for further structural and functional exploration of the Foxl2 from C. batrachus, including its deduced protein and its signal transduction function.

Molecular identification and expression of the Foxl2 gene during gonadal sex differentiation in northern snakehead Channa argus

Channa argus is one of the most commercially important fish species in China. Studies show that males of C. argus grow faster than females at the same age. In order to explore the sex differentiation mechanism of C. argus, we isolated the full length of the sex-related gene Foxl2 cDNA and analysed its expression patterns during gonadal sex differentiation. Alignment of known Foxl2 amino acid sequences from vertebrates confirmed the conservation of the Foxl2 open reading frame, especially the forkhead domain and C-terminal region. Quantitative RT-PCR revealed that Foxl2 is predominantly expressed in brain, pituitary, gill and ovary, with its highest level in ovary but low levels in testis and other tissues, reflecting a potential role for Foxl2 in the brain-pituitary-gonad axis in C. argus. Our ontogenetic stage data showed that C. argus Foxl2 expression was significantly upregulated from 1 to 11 days posthatching (dph) and that the initiation of expression preceded the first anatomical ovarian differentiation (27 dph), suggesting that Foxl2 might play a potential role in early gonadal sex differentiation in C. argus. In addition, the Foxl2 protein was primarily located in granulosa cells surrounding the oocytes of mature C. argus, implying that Foxl2 may have a basic function in granulosa cell differentiation and the maintenance of oocytes.

Association of novel polymorphisms of forkhead box L2 and growth differentiation factor-9 genes with egg production traits in local Chinese Dagu hens

Transcription factor forkhead box L2 (FOXL2) and growth differentiation factor-9 (GDF9) genes have critical roles in the regulation of hen ovarian development. In the present study, these genes were explored as possible molecular markers associated with BW, hen-housed egg production, and egg weight in Chinese Dagu hens. Samples were analyzed using the PCR-single strand conformation polymorphism (PCR-SSCP) technique followed by sequencing analysis, and two novel single nucleotide polymorphisms (SNPs) were identified within these candidate genes. Among them, an A/G transition at base position 238 in the coding region of the FOXL2 gene and a G/T transversion at base position 1609 in exon 2 of the GDF9 gene were found to be polymorphic and named SNPs A238G and G1609T, respectively. The SNP A238G (FOXL2) leads to a nonsynonymous substitution (isoleucine77-to-valine), and when the 360 Dagu hen samples were divided into genotypes AA and AB, allele A was found to be present at a higher frequency. Furthermore, the AA genotype correlated with significantly higher hen-housed egg production at 30, 43, 57, and 66 wk of age and with a higher egg weight at 43 wk (P<0.05). For the SNP G1609T (GDF9), the hens were typed into TT and TC genotypes, with the T allele shown to be dominant. The TC genotype was also markedly correlated with higher hen-housed egg production and a higher egg weight (P<0.05). Moreover, four haplotypes were reconstructed based on these two SNPs, with the AATC haplotype found to be correlated with the highest hen-housed egg production at 30 to 66 wk of age and with higher egg weights at 43 wk (P<0.05). Collectively, the two SNPs identified in this study might be used as possible genetic molecular markers to aid in the improvement of egg production traits in chicken breeding.

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.

Early exposure of 17α-ethynylestradiol and diethylstilbestrol induces morphological changes and alters ovarian steroidogenic pathway enzyme gene expression in catfish, Clarias gariepinus

Environmental estrogens are major cause of endocrine disruption in vertebrates, including aquatic organisms. Teleosts are valuable and popular models for studying the effects of endocrine disrupting chemicals (EDCs) in the environment. In the present study, we investigated the changes caused by exposure to the synthetic estrogens 17α-ethynylestradiol (EE2 ) and diethylstilbesterol (DES) during early stages of growth and sex differentiation of air-breathing catfish, Clarias gariepinus, at the morphological, histological, and molecular levels. Catfish hatchlings, 0 day post hatch (dph) were exposed continuously to sublethal doses of EE2 (50 ng/L) and DES (10 ng/L) until 50 dph and subsequently monitored for ovarian structural changes and alteration in the gene expression of steroidogenic enzymes till adulthood. Treated fish exhibited morphological deformities such as spinal curvature, stunted growth, and yolk-sac fluid retention. In addition to ovarian atrophy, DES-treated fish showed either rudimentary or malformed ovaries. Detailed histological studies revealed precocious oocyte development as well as follicular atresia. Further, transcript levels of various steroidogenic enzyme and transcription factor genes were altered in response to EE2 and DES. Activity of the rate-limiting enzyme of estrogen biosynthesis, aromatase, in the ovary as well as the brain of treated fish was in accordance with transcript level changes. These developmental and molecular effects imparted by EE2 and DES during early life stages of catfish could demonstrate the deleterious effects of estrogen exposure and provide reliable markers for estrogenic EDCs exposure in the environment.

Characterization and gonadal expression of FOXL2 relative to Cyp19a genes in spotted scat Scatophagus argus

In the present study, we cloned the full-length cDNAs of FOXL2, Cyp19a1a and Cyp19a1b and analyzed their expression patterns during gonadal development in spotted scat, Scatophagus argus. All three genes were expressed in ovaries and testes but showed sexual dimorphism. At early stages of gonadal development, the expression of FOXL2 in ovaries was higher than testes. FOXL2 expression deceased gradually as gonadal development continued, and reached the lowest level at the mature stage. Cyp19a1a and Cyp19a1b were expressed coordinately with FOXL2, except at the early vitellogenic stage in the ovary. The expression of FOXL2, Cyp19a1a and Cyp19a1b was mainly localized in granulosa cells of ovaries. In S. argus testes, strong expression of FOXL2 gene was observed in the interstitial cells including tubules and Leydig cells, while Cyp19a1a and Cyp19a1b were mainly expressed in Sertoli cells throughout gametogenesis. These results show that FOXL2 plays an essential role in sexual development, and imply that it may regulate Cyp19a1a and Cyp19a1b expression in S. argus.

Molecular cloning and analysis of gonadal expression of Foxl2 in the rice-field eel Monopterus albus

We isolated the complete Foxl2 (Foxl2a) cDNA from the Monopterus albus ovary. An alignment of known Foxl2 amino-acid sequences confirmed the conservation of the Foxl2 open reading frame, especially the forkhead domain and C-terminal region. The expression of Foxl2 was detected in the brain, eyes, and gonads. A high level of Foxl2 expression in the ovary before sex reversal, but its transcripts decreased sharply when the gonad developed into the ovotestis and testis. The correlation between the Foxl2 expression and the process of sex development revealed the important function of Foxl2 during the sex reversal of M. albus. Immunohistochemical analysis showed that Foxl2 was expressed abundantly in granulosa cells and in the interstitial cells of the ovotestis and testis. These results suggest that Foxl2 plays a pivotal role in the development and maintenance of ovarian function. Foxl2 may be also involved in the early development of testis and the development of ocular structures of M. albus.

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

Background

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

Results

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

Conclusions

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

Electronic supplementary material

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

Molecular players involved in temperature-dependent sex determination and sex differentiation in Teleost fish

The molecular mechanisms that underlie sex determination and differentiation are conserved and diversified. In fish species, temperature-dependent sex determination and differentiation seem to be ubiquitous and molecular players involved in these mechanisms may be conserved. Although how the ambient temperature transduces signals to the undifferentiated gonads remains to be elucidated, the genes downstream in the sex differentiation pathway are shared between sex-determining mechanisms. In this paper, we review recent advances on the molecular players that participate in the sex determination and differentiation in fish species, by putting emphasis on temperature-dependent sex determination and differentiation, which include temperature-dependent sex determination and genetic sex determination plus temperature effects. Application of temperature-dependent sex differentiation in farmed fish and the consequences of temperature-induced sex reversal are discussed.

Cloning and expression analysis of Foxl2 during the reproductive cycle in Korean rockfish, Sebastes schlegeli

Foxl2 is a member of the winged helix/forkhead family of transcription factors and is known to regulate ovarian aromatase, which plays a crucial role in ovarian differentiation. To address the role of Foxl2 in gonads and brain during gonadal development, we isolated the full-length cDNA of Foxl2 and analyzed its spatiotemporal expression patterns in the viviparous teleost Korean rockfish, Sebastes schlegeli. Tissue distribution pattern revealed that the Foxl2 was detected in the liver, fat, gill, brain, and ovary, but could hardly be found in the testis. Reverse transcriptase PCR suggested that Foxl2 in Korean rockfish may involve in ovary development in the study of expression level during gonads development. It also revealed that the stage of highest expression level for Foxl2 was almost much earlier than cyp19a1a and cyp19a1b during the gonadal development stage in gonads and brain except for cyp19a1a in brain. Furthermore, the expression pattern of Foxl2 as well as aromatases may imply the role of Foxl2 in the up-regulation of aromatases not only in the female fish but also in male.

foxl2 and foxl3 are two ancient paralogs that remain fully functional in teleosts

FOXL2 is a forkhead transcription factor involved in mammalian development and regulation of reproduction. Two foxl2 paralogs, foxl2a and foxl2b, have been described in various teleost species and were considered as fish-specific duplicates. Here, we report the isolation and characterization of foxl2a (foxl2) and foxl2b (foxl3) in European sea bass (Dicentrarchus labrax), together with the identification of these two genes in non-teleost genomes. Phylogenetic and synteny analyses indicate that these paralogs originated from an ancient genome duplication event that happened long before the teleost specific duplication. While foxl2/foxl2a has been maintained in most vertebrate lineages, foxl2b, which we propose to rename as foxl3, was repeatedly lost in tetrapods. Gonadal expression patterns of the sea bass genes point to a strong sexual dimorphism, and the mRNA levels of foxl2 in ovary and foxl3 in testis vary significantly during the reproductive cycle. When overexpressed in cultured ovarian follicular cells, foxl2 and foxl3 produced functional transcription factors able to control the expression of reproduction-related genes. Taken together, these data suggest that Foxl2 may play a conserved role in ovarian maturation, while Foxl3 could be involved in testis physiology.

Endosulfan and flutamide, alone and in combination, target ovarian growth in juvenile catfish, Clarias batrachus

Juvenile Catfish(es), Clarias batrachus of 50 days post hatch (dph) were exposed to endosulfan (2.5 parts per billion [ppb]) and flutamide (33 ppb), alone and in combination for 50 days to access their impact on ovarian development. The doses used in this study were nominal considering pervious reports. Sampling was done at 100 dph to perform histology and measurement of various transcripts, estradiol-17β and aromatase activity. In general, treatments enhanced expression of ovary-specific transcription factors, steroidogenic enzymes steroidogenic acute regulatory protein and aromatases while transcripts of tryptophan hydroxylase2 (tph2) and catfish gonadotropin-releasing hormone declined in the brain of all treated groups with maximum reduction in the endosulfan group. Significant reduction of tph2 immunoreactivity in the forebrain/telencephalon-preoptic area endorsed our results. Increased number of pre-vitellogenic and less immature oocytes in the treated groups indicated hastened ovarian growth. Elevated ovarian aromatase activity and plasma estradiol-17β levels were noticed in the treated groups with maximum being in the endosulfan group. These data together demonstrate that the exposure of endosulfan causes synchronous precocious ovarian development better than flutamide, alone or in combination. Our results suggest that both endosulfan and flutamide alter ovarian growth by triggering precocious development in catfish.

Molecular cloning and expression analysis of fushi tarazu factor 1 in the brain of air-breathing catfish, Clarias gariepinus

Background

Fushi tarazu factor 1 (FTZ-F1) encodes an orphan nuclear receptor belonging to the nuclear receptor family 5A (NR5A) which includes adrenal 4-binding protein or steroidogenic factor-1 (Ad4BP/SF-1) and liver receptor homologue 1 (LRH-1) and plays a pivotal role in the regulation of aromatases.

Methodology/Principal Findings

Present study was aimed to understand the importance of FTZ-F1 in relation to brain aromatase (cyp19a1b) during development, recrudescence and after human chorionic gonadotropin (hCG) induction. Initially, we cloned FTZ-F1 from the brain of air-breathing catfish, Clarias gariepinus through degenerate primer RT-PCR and RACE. Its sequence analysis revealed high homology with other NR5A1 group members Ad4BP/SF-1 and LRH-1, and also analogous to the spatial expression pattern of the latter. In order to draw functional correlation of cyp19a1b and FTZ-F1, we analyzed the expression pattern of the latter in brain during gonadal ontogeny, which revealed early expression during gonadal differentiation. The tissue distribution both at transcript and protein levels revealed its prominent expression in brain along with liver, kidney and testis. The expression pattern of brain FTZ-F1 during reproductive cycle and after hCG induction, in vivo was analogous to that of cyp19a1b shown in our earlier study indicating its involvement in recrudescence.

Conclusions/Significance

Based on our previous results on cyp19a1b and the present data, it is plausible to implicate potential roles for brain FTZ-F1 in ovarian differentiation and recrudescence process probably through regulation of cyp19a1b in teleosts. Nevertheless, these interactions would require primary coordinated response from ovarian aromatase and its related transcription factors.

FTZ-F1 and FOXL2 up-regulate catfish brain aromatase gene transcription by specific binding to the promoter motifs

Cytochrome P450 aromatase (cyp19) catalyzes the conversion of androgens into estrogens. Teleosts have distinct, ovarian specific (cyp19a1a) and brain specific (cyp19a1b) cyp19 genes. Previous studies in teleosts demonstrated regulation of cyp19a1a expression by the NR5A nuclear receptor subfamily as well as a fork head transcription factor, FOXL2. In the present study, we investigated the involvement of fushi tarazu factor 1, FTZ-F1, a NR5A subfamily member, and FOXL2 in the regulation of cyp19a1b expression in brain of the air-breathing catfish, Clarias gariepinus. Based on the synchronous expression pattern of cyp19a1b, FTZ-F1 and FOXL2 in the brain, we isolated the 5' upstream region of cyp19a1b to analyse regulatory motifs. Promoter motif analysis revealed FTZ-F1/NR5A1 and FOXL2 binding nucleotide sequences. Transient transfection studies showed that FTZ-F1 and FOXL2 together enhanced the transcriptional activity of cyp19a1b gene in mammalian cell lines. Mutation in either of their putative binding sites within the cyp19a1b promoter abolished this effect. Electrophoretic gel mobility shift experiments indicated that FTZ-F1 and FOXL2 proteins bind to the synthesized radio-labelled oligomers used as probes and mobility shifted upon addition of their respective antibodies. Chromatin immunoprecipitation assay confirmed the binding of both these transcription factors to their corresponding cis-acting elements in the upstream region of cyp19a1b. To our knowledge, this study is the first report on the transcriptional regulation of cyp19a1b by FTZ-F1 and FOXL2 in a teleost fish.