Differential expression and dynamic changes of SOX3 during gametogenesis and sex reversal in protogynous hermaphroditic fish

Role of Sox3 in Estradiol-Induced Sex Reversal in Pelodiscus sinensis

The Chinese soft-shelled turtle Pelodiscus sinensis, an economically important species in China, exhibits significant sexual dimorphism. Males are more valuable than females owing to their wider calipash and faster growth. Estradiol (E2)-induced sex reversal is used to achieve all-male breeding of turtles; however, the mechanism of this sex reversal remains unclear. In this study, we characterized the Sox3 gene, whose expression level was high in the gonads and brain and exhibited significant sexual dimorphism in the ovary. During embryonic development, Sox3 was highly expressed at the initiation of ovarian differentiation. E2 and Sox3-RNAi treatment before sexual differentiation led to 1352, 908, 990, 1011, and 975 differentially expressed genes in five developmental stages, respectively, compared with only E2 treatment. The differentially expressed genes were clustered into 20 classes. The continuously downregulated and upregulated genes during gonadal differentiation were categorized into Class 0 (n = 271) and Class 19 (n = 606), respectively. KEGG enrichment analysis showed that Sox3 significantly affected sexual differentiation via the Wnt, TGF-β, and TNF signaling pathways and mRNA surveillance pathway. The expression of genes involved in these signaling pathways, such as Dkk4, Nog, Msi1, and Krt14, changed significantly during gonadal differentiation. In conclusion, the deletion of Sox3 may lead to significant upregulation of the mRNA surveillance pathway and TNF and Ras signaling pathways and downregulation of the Wnt and TGF-β signaling pathways, inhibiting E2-induced sex reversal. These findings suggest that Sox3 may play a certain promoting effect during E2-induced sex reversal in P. sinensis.

Characterization of ddx4 and dnd Homologs in Snakeskin Gourami (Trichopodus pectoralis) and Their Expression Levels during Larval Development and in Gonads of Males and Females

The purpose of this study was to clone and characterize ddx4 and dnd1 homologs in snakeskin gourami (Trichopodus pectoralis) and to determine their expression levels during larval development and in the gonads of males and females. Both cDNAs contained predicted regions that shared consensus motifs with the ddx4 family in teleosts and the dnd family in vertebrates. Phylogenetic tree construction analysis confirmed that these two genes were clustered in the families of teleosts. Both ddx4 and dnd1 mRNAs were detectable only in the gonads, particularly in germ cells. These two genes were expressed during early larval development. The expression of ddx4 was high during early larval development and decreased with increasing developmental age, whereas dnd1 expression increased with developmental age. In adult fish, the expression levels of both genes were higher in the ovary than in the testis. Overall, these findings provide valuable molecular information on ddx4 and dnd, and can be applied in future reproductive biological studies relating to sex dimorphism in snakeskin gourami.

Comparative transcriptome provides insights into differentially expressed genes between testis and ovary of Onychostoma macrolepis in reproduction period

The Onychostoma macrolepis (O. macrolepis) is a rare and endangered fishery species inhabiting the river of Qinling Mountains and some flowing freshwaters in China. The declining population of O. macrolepis caused by asynchrony of male and female development prompted us to focus on genetic regulation of its reproduction. In this study, high-throughput RNA-sequencing technology was applied to assemble and annotate the transcriptome of O. macrolepis testis and ovary. The results showed that a number of 338089335 (ovary:163216500, testis:174872835) raw sequences were obtained. After non-redundant analysis, a number of 207826065 (ovary:102334008, testis:105492057) high quality reads were obtained and predicted as unigenes, in which 201,038,682 unigenes were annotated with multiple databases. Taking the ovarian transcriptome as a control, comparative transcriptome analysis showed that 9918 differentially expressed genes (DEGs) up-regulated in the testis and 13,095 DEGs down-regulated. Many DEGs were involved with sex-related GO terms and KEGG pathways, such as oocyte maturation, gonadal development, steroid biosynthesis pathways, MAPK signaling pathway and Wnt signaling pathway. Finally, the expression patterns of 19 unigenes were validated by using quantitative real-time polymerase chain reaction (qRT-PCR). This study illustrates a potential molecular mechanism on the unsynchronized male and female development of the O. macrolepis during the reproduction period in June and provides a theoretical basis for future artificial reproduction.

Unraveling the genotype by environment interaction in a thermosensitive fish with a polygenic sex determination system

In most animals, sex determination occurs at conception, when sex chromosomes are segregated following Mendelian laws. However, in multiple reptiles and fishes, this genetic sex can be overridden by external factors after fertilization or birth. In some species, the genetic sex may also be governed by multiple genes, further limiting our understanding of sex determination in such species. We used the European sea bass (Dicentrarchus labrax) as a model and combined genomic (using a single nucleotide polymorphism chip) and transcriptomic (RNA-Sequencing) approaches to thoroughly depict this polygenic sex determination system and its interaction with temperature. We estimated genetic sex tendency (eGST), defined as the estimated genetic liability to become a given sex under a liability threshold model for sex determination, which accurately predicts the future phenotypic sex. We found evidence that energetic pathways, concerning the regulation of lipids and glucose, are involved in sex determination and could explain why females tend to exhibit higher energy levels and improved growth compared to males. Besides, early exposure to high-temperature up-regulated sox3, followed by sox9a in individuals with intermediate eGST, but not in individuals showing highly female-biased eGST, providing the most parsimonious explanation for temperature-induced masculinization. This gonadal state was maintained likely by DNA methylation and the up-regulation of several genes involved in histone modifications, including jmjd1c Overall, we describe a sex determination system resulting from continuous genetic and environmental influences in an animal. Our results provide significant progress in our understanding of the mechanisms underlying temperature-induced masculinization in fish.

Systematic identification and expression analysis of the Sox gene family in spotted sea bass (Lateolabrax maculatus)

The Sox gene family encodes a set of transcription factors characterized by a conserved Sry-related high mobility group (HMG)-box domain, which performs a series of essential biological functions in diverse tissues and developmental processes. In this study, the Sox gene family was systematically characterized in spotted sea bass (Lateolabrax maculatus). A total of 26 Sox genes were identified and classified into eight subfamilies, namely, SoxB1, SoxB2, SoxC, SoxD, SoxE, SoxF, SoxH and SoxK. The phylogenetic relationship, exon-intron and domain structure analyses supported their annotation and classification. Comparison of gene copy numbers and chromosome locations among different species indicated that except tandem duplicated paralogs of Sox17/Sox32, duplicated Sox genes in spotted sea bass were generated from teleost-specific whole genome duplication during evolution. In addition, qRT-PCR was performed to detect the expression profiles of Sox genes during development and adulthood. The results showed that the expression of 16 out of 26 Sox genes was induced dramatically at different starting points after the multicellular stage, which is consistent with embryogenesis. At the early stage of sex differentiation, 9 Sox genes exhibited sexually dimorphic expression patterns, among which Sox3, Sox19 and Sox6b showed the most significant ovary-biased expression. Moreover, the distinct expression pattern of Sox genes was observed in different adult tissues. Our results provide a fundamental resource for further investigating the functions of Sox genes in embryonic processes, sex determination and differentiation as well as controlling the homeostasis of adult tissues in spotted sea bass.

Transcriptional changes of mouse ovary during follicle initial or cyclic recruitment mediated by extra hormone treatment

AIMS

Folliculogenesis contains gonadotropin-independent and -dependent stage. Disruption in any of this process would induce failure in retrieving capable oocytes during clinical treatment. However, there is still limited understanding of the molecular components specifically regulating this process.

MATERIAL AND METHODS

Ovaries of P3, P20 and exogenous gonadotropin-treated P22 mice were sampled and underwent RNA-seq to investigate the transcriptome variance during mouse folliculogenesis.

KEY FINDINGS

In our dataset, 1883 and 626 DEGs were captured for each stage respectively, which were further clustered into eight expression patterns. Pathway enrichment analysis identified distinct biological processes enriched in two stages, with the most prominent being the pathways related to metabolism, gene expression, cell cycle, immune system and DNA methylation. Transcriptional regulator inference yielded eight master transcription factors (i.e. Runx1, Stat3, Sox3, Pou5f1, Gata4, Foxl2, Cebpb, and Esr1) driving folliculogenesis.

SIGNIFICANCE

Our study revealed the temporal transcriptional reprogramming and gene expression dynamics during folliculogenesis mediated by extra hormone treatment, which could provide novel insights to controlled ovarian stimulation in future infertility treatment.

Gonad-Specific Transcriptomes Reveal Differential Expression of Gene and miRNA Between Male and Female of the Discus Fish (Symphysodon aequifasciatus)

The discus fish (Symphysodon aequifasciatus) is an ornamental fish that is well-known around the world. In artificial reproduction, they must be matched by one male and one female, whereas phenotype investigation indicated that there are no significant differences in appearance between males and females, which causes great difficulties in the mating during artificial reproduction. So, it is of great importance to establish artificial sex identification methods for the discus fish. The molecular mechanism of the sexual dimorphism of the discus fish was previously unknown. In this study, we constructed six cDNA libraries from three adult testes and three adult ovaries and performed RNA sequencing for identifying sex-biased candidate genes and microRNAs (miRNAs). A total of 50,082 non-redundant genes (unigenes) were identified, of which 18,570 unigenes were significantly overexpressed in testes, and 11,182 unigenes were significantly overexpressed in ovaries. A total of 551 miRNAs were identified, of which 47 miRNAs were differentially expressed between testes and ovaries. Eight differentially expressed unigenes, seven differentially expressed miRNAs and one non-differential miRNA were validated by quantitative real-time polymerase chain reaction. Twenty-four of these differentially expressed miRNAs and their 15 predicted target genes constituted 41 miRNA–mRNA interaction pairs, and some of vital sex-related metabolic pathways were also identified. These results revealed these differentially expressed genes and miRNAs between ovary and testis might be involved in regulating gonadal development, sex determination, gametogenesis, and physiological function maintenance, and there are complex regulatory networks between genes and miRNAs. It can help us understand the molecular mechanism of the sexual dimorphism and obtain a high-efficiency sex identification method in the artificial reproduction process of the discus fish.

Gonadal Transcriptome Analysis of Sex-Related Genes in the Protandrous Yellowfin Seabream (Acanthopagrus latus)

Yellowfin seabream (Acanthopagrus latus), a protandrous hermaphroditic fish, is a good model for studying the mechanism of sex reversal. However, limited knowledge is known about the genetic information related to reproduction and sex differentiation in this species. Here, we performed de novo transcriptome sequencing analysis of the testis, ovotestis, and ovary to identify sex-related genes in yellowfin seabream. The results assembled 71,765 unigenes in which 16,126 and 17,560 unigenes were differentially expressed in the ovotestis and ovary compared to the testis, respectively. The most differentially expressed gene (DEG)-enriched Kyoto Encyclopedia of Genes and Genomes and GO pathways were closely associated with the synthesis of sex steroid hormones. Functional analyses identified 55 important sex-related DEGs, including 32 testis-biased DEGs (dmrt1, amh, and sox9, etc.), 20 ovary-biased DEGs (cyp19a, foxl2, and wnt4, etc.), and 3 ovotestis-biased DEGs (lhb, dmrt2, and foxh1). Furthermore, the testis-specific expression of dmrt1 and the brain-pituitary-ovary axis expression of foxl2 were characterized, suggesting that they might play important roles in sex differentiation in yellowfin seabream. Our present work provided an important molecular basis for elucidating the mechanisms underlying sexual transition and reproductional regulation in yellowfin seabream.

Characterization of the European Sea Bass (Dicentrarchus labrax) Gonadal Transcriptome During Sexual Development

The European sea bass is one of the most important cultured fish in Europe and has a marked sexual growth dimorphism in favor of females. It is a gonochoristic species with polygenic sex determination, where a combination between still undifferentiated genetic factors and environmental temperature determines sex ratios. The molecular mechanisms responsible for gonadal sex differentiation are still unknown. Here, we sampled fish during the gonadal developmental period (110 to 350 days post fertilization, dpf), and performed a comprehensive transcriptomic study by using a species-specific microarray. This analysis uncovered sex-specific gonadal transcriptomic profiles at each stage of development, identifying larger number of differentially expressed genes in ovaries when compared to testis. The expression patterns of 54 reproduction-related genes were analyzed. We found that hsd17β10 is a reliable marker of early ovarian differentiation. Further, three genes, pdgfb, snx1, and nfy, not previously related to fish sex differentiation, were tightly associated with testis development in the sea bass. Regarding signaling pathways, lysine degradation, bladder cancer, and NOD-like receptor signaling were enriched for ovarian development while eight pathways including basal transcription factors and steroid biosynthesis were enriched for testis development. Analysis of the transcription factor abundance showed an earlier increase in females than in males. Our results show that, although many players in the sex differentiation pathways are conserved among species, there are peculiarities in gene expression worth exploring. The genes identified in this study illustrate the diversity of players involved in fish sex differentiation and can become potential biomarkers for the management of sex ratios in the European sea bass and perhaps other cultured species.

Loss-of-function of sox3 causes follicle development retardation and reduces fecundity in zebrafish

Folliculogenesis is essential for production of female gametes in vertebrates. However, the molecular mechanisms underlying follicle development, particularly apoptosis regulation in ovary, remain elusive. Here, we generated sox3 knockout zebrafish lines using CRISPR/Cas9. sox3 knockout led to follicle development retardation and a reduced fecundity in females. Comparative analysis of transcriptome between sox3^−/− and wild-type ovaries revealed that Sox3 was involved in pathways of ovarian steroidogenesis and apoptosis. Knockout of sox3 promoted follicle apoptosis and obvious apoptosis signals were detected in somatic cells of stages III and IV follicles of sox3^−/− ovaries. Moreover, Sox3 can bind to and activate the promoter of cyp19a1a. Up-regulation of Cyp19a1a expression promoted 17β-estradiol synthesis, which inhibited apoptosis in follicle development. Thus, Sox3 functions as a regulator of Cyp19a1a expression, via 17β-E2 linking apoptosis suppression, which is implicated in improving female fecundity.

Divergent Expression Patterns and Function of Two cxcr4 Paralogs in Hermaphroditic Epinephelus coioides

Chemokine receptor Cxcr4 evolved two paralogs in the teleost lineage. However, cxcr4a and cxcr4b have been characterized only in a few species. In this study, we identified two cxcr4 paralogs from the orange-spotted grouper, Epinephelus coioides. The phylogenetic relationship and gene structure and synteny suggest that the duplicated cxcr4a/b should result from the teleost-specific genome duplication (Ts3R). The teleost cxcr4 gene clusters in two paralogous chromosomes exhibit a complementary gene loss/retention pattern. Ec_cxcr4a and Ec_cxcr4b show differential and biased expression patterns in grouper adult tissue, gonads, and embryos at different stages. During embryogenesis, Ec_cxcr4a/b are abundantly transcribed from the neurula stage and mainly expressed in the neural plate and sensory organs, indicating their roles in neurogenesis. Ec_Cxcr4a and Ec_Cxcr4b possess different chemotactic migratory abilities from the human SDF-1α, Ec_Cxcl12a, and Ec_Cxcl12b. Moreover, we uncovered the N-terminus and TM5 domain as the key elements for specific ligand⁻receptor recognition of Ec_Cxcr4a-Ec_Cxcl12b and Ec_Cxcr4b-Ec_Cxcl12a. Based on the biased and divergent expression patterns of Eccxcr4a/b, and specific ligand⁻receptor recognition of Ec_Cxcl12a/b⁻Ec_Cxcr4b/a, the current study provides a paradigm of sub-functionalization of two teleost paralogs after Ts3R.

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.

Gonadal development and expression of sex-specific genes during sex differentiation in the Japanese eel

The process of gonadal development and mechanism involved in sex differentiation in eels are still unclear. The objectives were to investigate the gonadal development and expression pattern of sex-related genes during sex differentiation in the Japanese eel, Anguilla japonica. For control group, the elvers of 8-10cm were reared for 8months; and for feminization, estradiol-17β (E2) was orally administered to the elvers of 8-10cm for 6months. Only males were found in the control group, suggesting a possible role of environmental factors in eel sex determination. In contrast, all differentiated eels in E2-treated group were female. Gonad histology revealed that control male eels seem to differentiate through an intersexual stage, while female eels (E2-treated) would differentiate directly from an undifferentiated gonad. Tissue distribution and sex-related genes expression during gonadal development were analyzed by qPCR. The vasa, figla and sox3 transcripts in gonads were significantly increased during sex differentiation. High vasa expression occurred in males; figla and sox3 were related to ovarian differentiation. The transcripts of dmrt1 and sox9a were significantly increased in males during testicular differentiation and development. The cyp19a1 transcripts were significantly increased in differentiating and differentiated gonads, but did not show a differential expression between the control and E2-treated eels. This suggests that cyp19a1 is involved both in testicular differentiation and development in control males, and in the early stage of ovarian differentiation in E2-treated eels. Importantly, these results also reveal that cyp19a1 is not a direct target for E2 during gonad differentiation in the eel.

Divergent Expression Patterns and Function Implications of Four nanos Genes in a Hermaphroditic Fish, Epinephelus coioides

Multiple nanos genes have been characterized in several fishes, but the functional implications of their various expression patterns remain unclear. In this study, we identified and characterized four nanos genes from a hermaphroditic fish orange-spotted grouper, Epinephelus coioides. Ecnanos1a and Ecnanos1b show divergent expression patterns, and the dynamic expression change of Ecnanos1a in pituitaries during sex change is associated with testis differentiation and spermatogenesis. Ecnanos2 and Ecnanos3 might be germline stem cells (GSCs) and primordial germ cells (PGCs)-specific markers, respectively. Significantly, Ecnanos3 3'-untranslated region (UTR) is necessary for PGC specific expression, where a non-canonical "GCACGTTT" sequence is required for miR-430-mediated repression of Ecnanos3 RNA. Furthermore, grouper Dead end (Dnd) can relieve miR-430 repression in PGCs by associating with a 23 bp U-rich region (URR) in Ecnanos3 3'-UTR. The current study revealed the functional association of multiple nanos genes with PGC formation and germ cell development in orange-spotted grouper, and opened up new possibilities for developing biotechnologies through utilizing the associations between Ecnanos3 and PGCs or between Ecnanos2 and GSCs in the hermaphroditic fish.

Sox3 binds to 11β-hydroxysteroid dehydrogenase gene promoter suggesting transcriptional interaction in catfish

In fishes, the expression of steroidogenic enzyme genes and their related transcription factors (TFs) are critical for the regulation of steroidogenesis and gonadal development. 11-KT is the potent androgen and hence, 11β-hsd, enzyme involved in 11-KT production is important. Regulation of 11β-hsd gene was never studied in any fishes. At first 11β-hsd was cloned and recombinant protein was tested for enzyme activity prior to expression and promoter motif analysis. Expression changes revealed stage- and sex-dependent increase in the ontogenic studies. Further, 11β-hsd expression was higher during spawning phase of reproductive cycle and was found to be gonadotropin inducible both in vivo and in vitro. ∼2kb of 5' upstream region of 11β-hsd, was cloned from catfish genomic DNA library and in silico promoter analysis revealed putative TF binding sites such as Sox3, Wt1, Pax2, Dmrt1 and Ad4BP/SF-1. Luciferase reporter assay using the sequential deletion constructs in human embryonic kidney and Chinese hamster ovary cells revealed considerable promoter activity of the constructs containing Sox3, but not with other motifs largely. Site-directed mutagenesis, Sox3 over expression, electrophoretic mobility shift and chromatin immunoprecipitation assays further substantiated the binding of Sox3 to its corresponding cis-acting element in the upstream promoter motif of 11β-hsd. This is the first report to show that Sox3 binds to the 11β-hsd gene promoter and transactivates to regulate male reproduction in a teleost.

Genome-Wide Identification and Transcriptome-Based Expression Profiling of the Sox Gene Family in the Nile Tilapia (Oreochromis niloticus)

The Sox transcription factor family is characterized with the presence of a Sry-related high-mobility group (HMG) box and plays important roles in various biological processes in animals, including sex determination and differentiation, and the development of multiple organs. In this study, 27 Sox genes were identified in the genome of the Nile tilapia (Oreochromis niloticus), and were classified into seven groups. The members of each group of the tilapia Sox genes exhibited a relatively conserved exon-intron structure. Comparative analysis showed that the Sox gene family has undergone an expansion in tilapia and other teleost fishes following their whole genome duplication, and group K only exists in teleosts. Transcriptome-based analysis demonstrated that most of the tilapia Sox genes presented stage-specific and/or sex-dimorphic expressions during gonadal development, and six of the group B Sox genes were specifically expressed in the adult brain. Our results provide a better understanding of gene structure and spatio-temporal expression of the Sox gene family in tilapia, and will be useful for further deciphering the roles of the Sox genes during sex determination and gonadal development in teleosts.

Molecular Cloning, Promoter Analysis and Expression Profiles of the sox3 Gene in Japanese Flounder, Paralichthys olivaceus

Sox3, which belongs to the SoxB1 subgroup, plays major roles in neural and gonadal development. In the present study, Japanese flounder Paralichthys olivaceus sox3 gene (Posox3) and its promoter sequence were isolated and characterized. The deduced PoSox3 protein contained 298 amino acids with a characteristic HMG-box domain. Alignment and phylogenetic analyses indicated that PoSox3 shares highly identical sequence with Sox3 homologues from different species. The promoter region of Posox3 has many potential transcription factor (TF) binding sites. The expression profiles of Posox3 in different developmental stages and diverse adult tissues were analyzed by quantitative real-time RT-PCR (qRT-PCR). Posox3 mRNA was maternally inherited, and maintained at a considerably high expression level between the blastula stage and the hatching stage during embryonic development. Posox3 was abundantly expressed in the adult brain and showed sexually dimorphic expression pattern. In situ hybridization (ISH) was carried out to investigate the cellular distribution of Posox3 in the ovary, and results showed the uniform distribution of Posox3 throughout the cytoplasm of oogonia and stage I–III oocytes. These results indicate that Posox3 has potentially vital roles in embryonic and neural development and may be involved in the oogenesis process. Our work provides a fundamental understanding of the structure and potential functions of Sox3 in Paralichthys olivaceus.

Genetic basis and biotechnological manipulation of sexual dimorphism and sex determination in fish

Aquaculture has made an enormous contribution to the world food production, especially to the sustainable supply of animal proteins. The utility of diverse reproduction strategies in fish, such as the exploiting use of unisexual gynogenesis, has created a typical case of fish genetic breeding. A number of fish species show substantial sexual dimorphism that is closely linked to multiple economic traits including growth rate and body size, and the efficient development of sex-linked genetic markers and sex control biotechnologies has provided significant approaches to increase the production and value for commercial purposes. Along with the rapid development of genomics and molecular genetic techniques, the genetic basis of sexual dimorphism has been gradually deciphered, and great progress has been made in the mechanisms of fish sex determination and identification of sex-determining genes. This review summarizes the progress to provide some directive and objective thinking for further research in this field.

Expression analysis of sox3 during testicular development, recrudescence, and after hCG induction in catfish, Clarias batrachus

In teleosts, the expression of steroidogenic enzymes and related transcription factor genes occurs in a stage- and tissue-specific manner causing sexual development. The role of sox3, an evolutionary ancestor of SRY, has not been studied in detail. Therefore, the full-length cDNA of sox3 (1,197 kb) was cloned from catfish testis, and mRNA expression was analyzed during gonadal development, during the seasonal reproductive cycle, and after human chorionic gonadotropin (hCG) induction. Tissue distribution analysis showed that sox3 expression was higher in testis, ovary, and brain compared to other tissues analyzed. Developing and mature testis showed higher sox3 expression than ovary of corresponding stages, and more sox3 transcripts were found during the spawning phase of the seasonal reproductive cycle. Expression of sox3 was upregulated by hCG after in vivo and in vitro induction, suggesting that gonadotropins might stimulate it. In situ hybridization and immunohistochemistry showed the presence of sox3 mRNA and protein in somatic and interstitial cell layers of the testis. Sox3 could also be found in the zona radiata of developing and mature oocytes. Exposure of methyltestosterone (1 µg/l) and ethinylestradiol (1 µg/l) for 21 days during testicular development showed lower sox3 expression levels in the testis and brain, indicating a certain feedback intervention. These results suggest a possible role for Sox3 in the regulation of testicular development and function.

Zebrafish Noxa promotes mitosis in early embryonic development and regulates apoptosis in subsequent embryogenesis

Noxa functions in apoptosis and immune system of vertebrates, but its activities in embryo development remain unclear. In this study, we have studied the role of zebrafish Noxa (zNoxa) by using zNoxa-specifc morpholino knockdown and overexpression approaches in developing zebrafish embryos. Expression pattern analysis indicates that zNoxa transcript is of maternal origin, which displays a uniform distribution in early embryonic development until shield stage, and the zygote zNoxa transcription is initiated from this stage and mainly localized in YSL of the embryos. The zNoxa expression alterations result in strong embryonic development defects, demonstrating that zNoxa regulates apoptosis from 75% epiboly stage of development onward, in which zNoxa firstly induces the expression of zBik, and then cooperates with zBik to regulate apoptosis. Moreover, zNoxa knockdown also causes a reduction in number of mitotic cells before 8 h.p.f., suggesting that zNoxa also promotes mitosis before 75% epiboly stage. The effect of zNoxa on mitosis is mediated by zWnt4b in early embryos, whereas zMcl1a and zMcl1b suppress the ability of zNoxa to regulate mitosis and apoptosis at different developmental stages. In addition, mammalian mouse Noxa (mNoxa) mRNA was demonstrated to rescue the arrest of mitosis when zNoxa was knocked down, suggesting that mouse and zebrafish Noxa might have similar dual functions. Therefore, the current findings indicate that Noxa is a novel regulator of early mitosis before 75% epiboly stage when it translates into a key mediator of apoptosis in subsequent embryogenesis.

Water homeostasis in the fish oocyte: new insights into the role and molecular regulation of a teleost-specific aquaporin

The discovery of the role of a teleost-specific aquaporin (Aqp1ab) during the process of oocyte hydration in marine fish producing pelagic (floating) eggs, recently confirmed by molecular approaches, has revealed that this mechanism is more sophisticated than initially thought. Recent phylogenetic and genomic studies suggest that Aqp1ab likely evolved by tandem duplication from a common ancestor and further neofunctionalized in oocytes for water transport. Investigations into the regulation of Aqp1ab during oogenesis indicate that the mRNA and protein product are highly accumulated during early oocyte growth, possibly through the transcriptional activation of the aqp1ab promoter by the classical nuclear progesterone receptor and perhaps by Sry-related high mobility group [HMG]-box (Sox) transcription factors. During oocyte growth and maturation, Aqp1ab intracellular trafficking may be regulated by phosphorylation and/or dephosphorylation of specific C-terminal residues in Aqp1ab, as well as by signal-mediated sorting processes. These mechanisms possibly regulate the temporal insertion of Aqp1ab into the oocyte plasma membrane during oocyte hydration, although the intracellular signaling pathways involved are yet unknown. Interestingly, in some freshwater species that spawn partially hydrated eggs, high accumulation of transcripts encoding functional Aqp1ab channels have also been found in the ovary. These findings suggest that the Aqp1ab-mediated mechanism for oocyte hydration is likely conserved in teleosts. The tight regulation of Aqp1ab during oogenesis, at both the transcriptional and posttranslational levels, highlights the essential physiological role of this water channel and opens new research avenues for understanding the molecular basis of egg formation in fish.

Mapping of DNA sex-specific markers and genes related to sex differentiation in turbot (Scophthalmus maximus)

Production of all-female populations in turbot can increase farmer's benefits since sexual dimorphism in growth in this species is among the highest within marine fish, turbot females reaching commercial size 3-6 months earlier than males. Puberty in males occurs earlier than in females, which additionally slows their growth. Thus, elucidating the mechanisms of sex determination and gonad differentiation is a relevant goal for turbot production. A ZZ/ZW sex determination mechanism has been suggested for this species, and four sex-related quantitative trait loci (QTL) were detected, the major one located in linkage group (LG) 5 and the three minor ones in LG6, LG8, and LG21. In the present work, we carried out a linkage analysis for several sex-related markers: (1) three anonymous sex-associated RAPD and (2) several candidate genes related to sex determination and gonad differentiation in other species (Sox3, Sox6, Sox8, Sox9, Sox17, Sox19, Amh, Dmrta2, Cyp19a, Cyp19b). We focused our attention on their co-localization with the major and minor sex-related QTL trying to approach to the master sex-determining gene of this species. Previously described growth-related QTL were also considered since the association observed between growth and sex determination in fish. Amh, Dmrta2, and one RAPD were located in LG5, while Sox9 and Sox17 (LG21), Cyp19b (LG6), and a second RAPD (LG8) co-mapped with suggestive sex-related QTL, thus supporting further analyses on these genes to elucidate the genetic basis of this relevant trait for turbot farming.

Dimorphic expression of various transcription factor and steroidogenic enzyme genes during gonadal ontogeny in the air-breathing catfish, Clarias gariepinus

In the present study the expression of 13 genes known to be involved in sex differentiation and steroidogenesis in catfish was analyzed during gonadal ontogeny by quantitative real-time RT-PCR. Dmrt1 and sox9a showed exclusive expression in male gonads while ovarian aromatase (cyp19a1) and foxl2 were abundant in differentiating female gonads. Most of the genes related to steroidogenesis were expressed only after gonadal differentiation. However, genes coding for 3β-hydroxysteroid dehydrogenase (3β-hsd), 17α-hydroxylase/C17-20 lyase type 1 (cyp17) and steroidogenic acute regulatory protein (star) were barely detectable during gonadal differentiation. Ovarian aromatase, cyp19a1, which is responsible for estradiol-17β biosynthesis in females, was expressed very early in the undifferentiated gonads of catfish, around 30-40 days post hatch (dph). The steroidogenic enzyme, 11β-hydroxylase (cyp11b1) required for the production of 11-ketotestosterone (11-KT) was expressed only after differentiation of testis. These results suggest that estradiol-17β has a critical role in ovarian differentiation, while the role of 11-KT in testicular differentiation is doubtful. In conclusion, dimorphic expression of dmrt1 and sox9a in gonads during early development is required for testicular differentiation, and sex-specific expression of cyp19a1 and foxl2 in females plays a critical role in ovarian development. Our study reveals that the critical period of gonadal differentiation in catfish starts around 30-40 dph when sex-specific genes showed differential expression.

Sox3 functions in a cell-autonomous manner to regulate spermatogonial differentiation in mice

The X-linked Sox3 gene encodes a member of the Sry high-mobility group box proteins, which play a role in many developmental processes including neurogenesis and testis development. This study further examined the role of Sox3 in spermatogenesis. Males without Sox3 expression exhibited a similar number of germ cell nuclear antigen-positive germ cells at 1, 5, and 10 d postpartum (dpp) compared to their wild-type littermates, but there was significant germ cell depletion by 20 dpp. However, spermatogenesis later resumed and postmeiotic germ cells were observed by 56 dpp. The VasaCre transgene was used to generate a germ cell-specific deletion of Sox3. The phenotype of the germ cell-specific Sox3 knockout was similar to the ubiquitous knockout, indicating an intrinsic role for Sox3 in germ cells. The residual germ cells in 20 dpp Sox3(-/Y) males were spermatogonia as indicated by their expression of neurogenin3 but not synaptonemal complex protein 3, which is expressed within cells undergoing meiosis. RNA expression analyses corroborated the histological analyses and revealed a gradual transition from relatively increased expression of spermatogonia genes at 20 dpp to near normal expression of genes characteristic of undifferentiated and meiotic germ cells by 84 dpp. Fluorescent-activated cell sorting of undifferentiated (ret tyrosine kinase receptor positive) and differentiated (kit receptor tyrosine kinase-positive) spermatogonia revealed depletion of differentiated spermatogonia in Sox3(-/Y) tubules. These results indicate that Sox3 functions in an intrinsic manner to promote differentiation of spermatogonia in prepubertal mice but it is not required for ongoing spermatogenesis in adults. The Sox3(-/Y) males provide a unique model for studying the mechanism of germ cell differentiation in prepubertal testes.

Antibacterial and antiviral roles of a fish β-defensin expressed both in pituitary and testis

Defensins are a group of cationic peptides that exhibit broad-spectrum antimicrobial activity. In this study, we cloned and characterized a β-defensin from pituitary cDNA library of a protogynous hermaphroditic orange-spotted grouper (Epinephelus coioides). Interestingly, the β-defensin was shown to be dominantly expressed in pituitary and testis by RT-PCR and Western blot analysis, and its transcript level is significantly upregulated in reproduction organs from intersexual gonad to testis during the natural and artificial sex reversal. Promoter sequence and the responsible activity region analyses revealed the pituitary-specific POU1F1a transcription binding site and testis-specific SRY responsible site, and demonstrated that the pituitary-specific POU1F1a transcription binding site that locates between −180 and −208 bp is the major responsible region of grouper β-defensin promoter activity. Immunofluorescence localization observed its pituicyte expression in pituitary and spermatogonic cell expression in testis. Moreover, both in vitro antibacterial activity assay of the recombinant β-defensin and in vivo embryo microinjection of the β-defensin mRNA were shown to be effective in killing Gram-negative bacteria. And, its antiviral role was also demonstrated in EPC cells transfected with the β-defensin construct. Additionally, the antibacterial activity was sensitive to concentrations of Na⁺, K⁺, Ca²⁺ and Mg²⁺. The above intriguing findings strongly suggest that the fish β-defensin might play significant roles in both innate immunity defense and reproduction endocrine regulation.

Molecular mechanisms underlying sex change in hermaphroditic groupers

Groupers are widely distributed throughout the tropical and subtropical waters of the world and are regarded as a favourite marine food fish. However, their large-scale aquaculture has been hindered by the rarity of natural males. Being protogynous hermaphrodites, groupers have been considered as study model for development and reproduction, especially for sex determination or sex differentiation, owing to the advantage that grouper gonad development undergoes transition from ovary to intersexual gonad and then to testis, and primordial germ cells and different stages of gametic cells during oogenesis and spermatogenesis are synchronously observed in the transitional gonads. Recently, a series of genes related to the reproduction regulation or sex differentiation have been identified in the groupers, mainly by researchers in China. One important finding was that the grouper gene, doublesex/male abnormal 3-related transcription factor 1 (DMRT1), is not only differentially expressed in gonads at different stages, but that it is also restricted to specific stages and specific cells of spermatogenesis. Grouper DMRT1 protein exists only in spermatogonia, primary spermatocytes and secondary spermatocytes, but not in the supporting Sertoli cells. Moreover, no introns were found in the grouper DMRT1, and no duplicated DMRT1 genes were detected. The finding implies that the intronless DMRT1 that is able to undergo rapid transcriptional turnover might be a significant gene for stimulating spermatogenesis in the protogynous hermaphroditic gonad. Additionally, we have found that grouper expression of sex-determining region Y-related high-mobility group-box gene 3 (SOX3) is a significant time point for enterable gametogenesis of primordial germ cells, because SOX3 is obviously expressed and localized in primordial germ cells. As SOX3 continues to express, the SOX3-positive primordial germ cells develop toward oogonia and then oocytes, whereas, when SOX3 expression is ceased, the SOX3-positive primordial germ cells develop toward spermatogonia. Therefore, we suggest that SOX3, as a transcription factor, might have more important roles in oogenesis than in spermatogenesis. Based on the findings, a hypothetic molecular mechanism underlying sex change is proposed in the hermaphroditic groupers, and some candidate genes related to the grouper sex change are also suggested for further research.

Expression pattern, cellular localization and promoter activity analysis of ovarian aromatase (Cyp19a1a) in protogynous hermaphrodite red-spotted grouper

Aromatase plays a key role in sex differentiation of gonads. In this study, we cloned the full-length cDNA of ovarian aromatase from protogynous hermaphrodite red-spotted grouper (Epinephelus akaara), and prepared the corresponding anti-EaCyp19a1a antiserum. Western blot and immunofluorescence studies revealed ovary-specific expression pattern of EaCyp19a1a in adults and its dynamic expression change during artificial sex reversal. EaCyp19a1a was expressed by follicular cells of follicular layer around oocytes because strong EaCyp19a1a immunofluorescence was observed in the cells of ovaries. During artificial sex reversal, EaCyp19a1a expression dropped significantly from female to male, and almost no any positive EaCyp19a1a signal was observed in testicular tissues. Then, we cloned and sequenced a total of 1967 bp 5'-flanking sequence of EaCyp19a1a promoter, and showed a number of potential binding sites for some transcriptional factors, such as SOX5, GATA gene family, CREB, AP1, FOXL1, C/EBP, ARE and SF-1. Moreover, we prepared a series of 5' deletion promoter constructs and performed in vitro luciferase assays of EaCyp19a1a promoter activities. The data indicated that the CREB regulation region from -1010 to -898 might be a major cis-acting element to EaCyp19a1a promoter, whereas the elements GATA and SOX5 in the region from -1216 to -1010 might be suppression elements. Significantly, we found a common conserved sequence region in the fish ovary-type aromatase promoters with identities from 93% to 34%. And, the motifs of TATA box, SF-1, SOX5, and CREB existed in the region and were conserved among the most of fish species.

Quantitative mRNA expression of sox3 and DMRT1 during sex reversal, and expression profiles after GnRHa administration in black porgy, Acanthopagrus schlegeli

We cloned full-length sox3 cDNA from testis of black porgy, Acanthopagrus schlegeli. Black porgy sox3 cDNA consists of 897 base pairs (bp) and encodes a protein of 298 amino acids. We have investigated the expression pattern of sox3 and DMRT1 mRNA during the sex-reverse process from male to female (immature testis, mature testis, testicular portion of mostly testis, ovarian portion of mostly testis, testicular portion of mostly ovary, ovarian portion of mostly ovary and ovary). The expression of sox3 and DMRT1 mRNA was high in mature testis of black porgy during sex-reverse process. In a histological analysis, testicular portion of gonad was degenerated and the ovary portion was increased during sex reversal from male to female, and then oocytes were increased in ovary. Also we examined the expression of sox3 and DMRT1 mRNA after gonadotropin-releasing hormone analogue (GnRHa) treatment in immature black porgy. The expression of sox3 and DMRT1 mRNA was increased after GnRHa treatment (in vivo and in vitro experiment) in immature black porgy. Therefore, we concluded that sox3 and DMRT1 were involved in the development of testis than ovary in black porgy.

Sox3: a transcription factor for Cyp19 expression in the frog Rana rugosa

Cyp19 is expressed at a high level in the gonad of the female tadpole of the frog Rana rugosa during sex determination. To identify sequence elements important for expression of Cyp19, we isolated a genomic clone (approximately 40 kbp) carrying R. rugosa Cyp19 and analyzed the nucleotide sequence of the 5'-flanking region to search for potential transcription factor binding sites. Sox (SRY-related HMG box) protein and Sf1 binding sites were found in the ovary-specific promoter region of Cyp19. Because Sox3 is located on the sex chromosome in R. rugosa, we conducted the luciferase reporter assay in Xenopus A6 cells using the promoter region. Sox3 drove the reporter gene in the cells, but Sf1 did not. When sequential deletion of the 2.7 kbp Cyp19-promoter region was undertaken, a fragment spanning nucleotides -191 to +48 was sufficient to drive the transcription of the reporter gene. In site-directed mutagenesis, the binding site at -57 in the region was critical for Sox3 responsiveness. Sox3 lacking the HMG box had no ability to promote Cyp19 transcription. In addition, a chromatin immunoprecipitation (ChIP) assay showed that DNA fragments were enriched 8-fold, as determined by real-time PCR, when chromatin was immunoprecipitated with the anti-His antibody against His-tagged Sox3. The results, taken together, suggest that Sox3 activates Cyp19 transcription by its direct binding to the binding site of the Cyp19 promoter region. Sox3 appears to be a factor that directs indifferent gonads to develop into an ovary in R. rugosa.

Antimicrobial activity-specific to Gram-negative bacteria and immune modulation-mediated NF-kappaB and Sp1 of a medaka beta-defensin

Defensins are a group of cationic antimicrobial peptides which play an important role in the innate immune system by exerting their antimicrobial activity against pathogens. In this study, we cloned a novel beta-defensin cDNA from medaka (Oryzias latipes) by rapid amplification of cDNA ends (RACE) technique. The full-length cDNA consists of 480 bp, and the open reading frame (ORF) of 189 bp encodes a polypeptide of 63 amino acids (aa) with a predicted molecular weight of 7.44 kDa. Its genomic organization was analyzed, and Southern blot detection confirmed that only one copy of beta-defensin exists in the medaka HNI strain. RT-PCR, Western blot and immunohistochemistry detections showed that the beta-defensin transcript and protein could be detected in eyes, liver, kidney, blood, spleen and gill, and obviously prevalent expression was found in eyes. Antimicrobial activity of the medaka beta-defensin was evaluated, and the antibacterial activity-specific to Gram-negative bacteria was revealed. Furthermore, the lipopolysaccharide (LPS), a major component of the outer membrane of Gram-negative bacteria, was demonstrated to be able to induce about 13-fold up-regulation of the beta-defensin within first 12h. In addition, promoter and promoter mutagenesis analysis were performed in the medaka beta-defensin. A proximal 100 base pair (bp) sequence (+26 to -73) and the next 1700 bp sequence (-73 to -1755) were demonstrated to be responsible for the basal promoter activity and for the transcription regulation. Three nuclear factor kappa B (NF-kappaB) cis-elements and a Sp1 cis-element were revealed by mutagenesis analysis to exist in the 5' flanking sequence, and they were confirmed to be responsible for the up-regulation of medaka beta-defensin stimulated by LPS. And, the Sp1 cis-element was further revealed to be related to the basal promoter activity, and transcriptional factor II D (TFIID) was found to be in charge of the gene transcription initiation. All the obtained data suggested that the novel medaka beta-defensin should have antimicrobial activity-specific to Gram-negative bacteria, and the antibacterial immune function should be modulated by NF-kappaB and Sp1.

Molecular cloning and expression characterization of ApoC-I in the orange-spotted grouper

Endogenous yolk nutrients are crucial for embryo and larval development in fish, but developmental behavior of the genes that control yolk utilization remains unknown. Apolipoproteins have been shown to play important roles in lipid transport and uptake through the circulation system. In this study, EcApoC-I, the first cloned ApoC-I in teleosts, has been screened from pituitary cDNA library of female orange-spotted grouper (Epinephelus coioides), and the deduced amino acid sequence shows 43.5% identity to one zebrafish (Danio rerio) hypothetical protein similar to ApoC-I, and 21.2%, 21.7%, 22.5%, 20%, and 22.5% identities to Apo C-I of human (Homo sapiens), house mouse (Mus musculus), common tree shrew (Tupaia glis), dog (Canis lupus familiaris) and hamadryas baboon (Papio hamadryas), respectively. Although the sequence identity is low, amphipathic alpha-helices with the potential to bind to lipid were predicted to exist in the EcApoC-I. RT-PCR analysis revealed that it was first transcribed in gastrula embryos and maintained a relatively stable expression level during the following embryogenesis. During embryonic and early larval development, a very high level of EcApoC-I expression was in the yolk syncytial layer, indicating that it plays a significant role in yolk degradation and transfers nutrition to the embryo and early larva. By the day 7 after hatching, EcApoC-I transcripts were observed in brain. In adult, EcApoC-I mRNA was detected abundantly in brain and gonad. In transitional gonads, the EcApoC-I expression is restricted to the germ cells. The data suggested that EcApoC-I might play an important role in brain and gonad morphogenesis and growth.

Identification and characterization of a MBP isoform specific to hypothalamus in orange-spotted grouper (Epinephelus coioides)

Myelin basic protein (MBP), as a major component of the myelin sheath, has been revealed to play an important role in forming and maintaining myelin structure in vertebrate nervous system. In teleost, hypothalamus is an instinctive brain center and plays significant roles in many physiological functions, such as energy metabolism, growth, reproduction, and stress response. In comparison with other MBP identified in vertebrates, a smallest MBP is cloned and identified from the orange-spotted grouper hypothalamic cDNA plasmid library in this study. RT-PCR analysis and Western blot detection indicate that the EcMBP is specific to hypothalamus, and expresses mainly in the tuberal hypothalamus in adult grouper. Immunofluorescence localization suggests that EcMBP should be expressed by oligodendrocytes, and the expressing cells should be concentrated in hypothalamus and the area surrounding hypothalamus, such as NPOpc, VC, DP, NLTm, and NDLI. The studies on EcMBP expression pattern and developmental behaviour in the brains of grouper embryos and larvae reveal that the EcMBP-expressing cells are only limited in a defined set of cells on the border of hypothalamus, and suggest that the EcMBP-expressing cells might be a subpopulation of oligodendrocyte progenitor cells. This study not only identifies a smallest MBP isoform specific to hypothalamus that can be used as a molecular marker of oligodendrocytes in fish, but also provides new insights for MBP evolution and cellular distribution.