Dmy initiates masculinity by altering Gsdf/Sox9a2/Rspo1 expression in medaka (Oryzias latipes)

Gsdf is not indispensable for male differentiation in the medaka species Oryzias hubbsi

Sex determination mechanisms differ widely among vertebrates, particularly in fish species, where diverse sex chromosomes and sex-determining genes have evolved. However, the sex-differentiation pathways activated by these sex-determining genes appear to be conserved. Gonadal soma-derived growth factor (Gsdf) is one of the genes conserved across teleost fish, especially in medaka fishes of the genus Oryzias, and is implicated in testis differentiation and germ cell proliferation. However, its role in sex differentiation remains unclear. In this study, we investigated Gsdf function in Oryzias hubbsi, a species with a ZW sex-determination system. We confirmed its male-dominant expression, as in other species. However, histological analyses revealed no male-to-female sex reversal in Gsdf-knockout fish, contrary to findings in other medaka species. Genetic sex determination remained intact without Gsdf function, indicating a Gsdf-independent sex-differentiation pathway in O. hubbsi. Instead, Gsdf loss led to germ cell overproliferation in both sexes and accelerated onset of meiosis in testes, suggesting a role in germ cell proliferation. Notably, the feminizing effect of germ cells observed in O. latipes was absent, suggesting diverse germ cell-somatic cell relationships in Oryzias gonad development. Our study highlights species-specific variations in the molecular pathways governing sex determination and differentiation, emphasizing the need for further exploration to elucidate the complexities of sexual development.

Exposure effects of benzalkonium chloride (BAC) on gonadal physiology and fertility suppression in medaka (Oryzias latipes)

Benzalkonium chloride (BAC), a commonly used quaternary ammonium compound in various products like antiseptics, cosmetics, and disinfectants, has raised concerns due to its potential to contaminate aquatic environments and subsequently affect the reproductive performance of the organisms within those ecosystems. The article underscores a critical concern regarding the impact of BAC on aquatic ecosystems, particularly its effect on fish reproductive quality, using medaka (Oryzias latipes) as a model organism. Firstly, while measuring lethal dose of BAC in adult medaka, we observed a dose dependent mortality in BAC treated fish (100 and 200 ppm: 100%; 60 ppm: 51.7%; 30 ppm or less: no mortality at 24 h post treatment (hpt)) and calculated the LD50 at 96 hpt as 39.291 ppm (95% confidence interval: 28.817-53.570 ppm). Further, we assessed the molecular, cellular and histological changes through long-term exposure. Enlarged sperm pockets and reduced spermatocyte were seen in BAC exposed testis while no significant structural changes were observed in the ovaries. Following BAC exposure, drastic alterations in the gene expression and cellular localization related to sex, estrogen signaling, and autophagy were also noted from gonads and liver. Subsequently, using a short-term exposure analysis, we confirmed the sex and time responsive transcriptional kinetics and found that BAC sequentially affected the gonadal somatic cells followed by germ cell differentiation. Finally, using reproductively competent male and female medaka, we conducted progeny production and performance analysis and depicted a drastic reduction in fecundity, and fertilization and hatching rate, indicating adverse effects of BAC on reproductive success. Cumulatively, these findings emphasize the consequences of widespread use of BAC on reproductive security of aquatic animals and highlights the need for further research to comprehend the potential harm posed by such compounds to aquatic animal health and ecosystem integrity.

Molecular biological, physiological, cytological, and epigenetic mechanisms of environmental sex differentiation in teleosts: A systematic review

Human activities have been exerting widespread stress and environmental risks in aquatic ecosystems. Environmental stress, including temperature rise, acidification, hypoxia, light pollution, and crowding, had a considerable negative impact on the life histology of aquatic animals, especially on sex differentiation (SDi) and the resulting sex ratios. Understanding how the sex of fish responds to stressful environments is of great importance for understanding the origin and maintenance of sex, the dynamics of the natural population in the changing world, and the precise application of sex control in aquaculture. This review conducted an exhaustive search of the available literature on the influence of environmental stress (ES) on SDi. Evidence has shown that all types of ES can affect SDi and universally result in an increase in males or masculinization, which has been reported in 100 fish species and 121 cases. Then, this comprehensive review aimed to summarize the molecular biology, physiology, cytology, and epigenetic mechanisms through which ES contributes to male development or masculinization. The relationship between ES and fish SDi from multiple aspects was analyzed, and it was found that environmental sex differentiation (ESDi) is the result of the combined effects of genetic and epigenetic factors, self-physiological regulation, and response to environmental signals, which involves a sophisticated network of various hormones and numerous genes at multiple levels and multiple gradations in bipotential gonads. In both normal male differentiation and ES-induced masculinization, the stress pathway and epigenetic regulation play important roles; however, how they co-regulate SDi is unclear. Evidence suggests that the universal emergence or increase in males in aquatic animals is an adaptation to moderate ES. ES-induced sex reversal should be fully investigated in more fish species and extensively in the wild. The potential aquaculture applications and difficulties associated with ESDi have also been addressed. Finally, the knowledge gaps in the ESDi are presented, which will guide the priorities of future research.

Insights into Early Ontogenesis of Salmo salar: RNA Extraction, Housekeeping Gene Validation and Transcriptional Expression of Important Primordial Germ Cell and Sex-Determination Genes

The challenge in extracting high-quality RNA impedes the investigation of the transcriptome of developing salmonid embryos. Furthermore, the mRNA expression pattern of important PGC and SD genes during the initial embryonic development of Salmo salar is yet to be studied. So, in the present study, we aimed to isolate high-quality RNA from eggs and developing embryos to check vasa, dnd1, nanos3a, sdf1, gsdf, amh, cyp19a, dmrt1 and foxl2 expression by qPCR. Additionally, four HKGs (GAPDH, UB2L3, eEf1a and β-actin) were validated to select the best internal control for qPCR. High-quality RNA was extracted, which was confirmed by spectrophotometer, agarose gel electrophoresis and Agilent TapeStation analysis. UB2L3 was chosen as a reference gene because it exhibited lower intra- and inter-sample variation. vasa transcripts were expressed in all the developmental stages, while dnd1 was expressed only up to 40 d°C. Nanos3a was expressed in later stages and remained at its peak for a shorter period, while sdf1 showed an irregular pattern of mRNA expression. The mRNA expression levels of SD genes were observed to be upregulated during the later stages of development, prior to hatching. This study presents a straightforward methodology for isolating high-quality RNA from salmon eggs, and the resulting transcript profiles of significant PGC and SD genes in S. salar could aid in improving our comprehension of reproductive development in this commercially important species.

Identification and functional analysis of Dmrt1 gene and the SoxE gene in the sexual development of sea cucumber, Apostichopus japonicus

Members of the Doublesex and Mab-3-related transcription factor (Dmrt) gene family handle various vital functions in several biological processes, including sex determination/differentiation and gonad development. Dmrt1 and Sox9 (SoxE in invertebrates) exhibit a very conserved interaction function during testis formation in vertebrates. However, the dynamic expression pattern and functional roles of the Dmrt gene family and SoxE have not yet been identified in any echinoderm species. Herein, five members of the Dmrt gene family (Dmrt1, 2, 3a, 3b and 5) and the ancestor SoxE gene were identified from the genome of Apostichopus japonicus. Expression studies of Dmrt family genes and SoxE in different tissues of adult males and females revealed different expression patterns of each gene. Transcription of Dmrt2, Dmrt3a and Dmrt3b was higher expressed in the tube feet and coelomocytes instead of in gonadal tissues. The expression of Dmrt1 was found to be sustained throughout spermatogenesis. Knocking-down of Dmrt1 by means of RNA interference (RNAi) led to the downregulation of SoxE and upregulation of the ovarian regulator foxl2 in the testes. This indicates that Dmrt1 may be a positive regulator of SoxE and may play a role in the development of the testes in the sea cucumber. The expression level of SoxE was higher in the ovaries than in the testes, and knocking down of SoxE by RNAi reduced SoxE and Dmrt1 expression but conversely increased the expression of foxl2 in the testes. In summary, this study indicates that Dmrt1 and SoxE are indispensable for testicular differentiation, and SoxE might play a functional role during ovary differentiation in the sea cucumber.

Sex Lethal Gene Manipulates Gonadal Development of Medaka, Oryzias latipes, through Estrogenic Interventions

Germ cells are pivotal for gonadal sexuality maintenance and reproduction. Sex lethal (sxl), the somatic sex determining gene of Drosophila, is the known regulator and initiator of germ cell femininity in invertebrates. However, the role of the Sxl homologue has rarely been investigated in vertebrates. So, we used medaka to clarify the role of sxl in vertebrate gonadogenesis and sexuality and identified two Sxl homologues, i.e., Sxl1a and Sxl1b. We found that sxl1a specifically expresses in the primordial germ cells (PGC), ovary, (early gonia and oocytes), while sxl1b distributions are ubiquitous. An mRNA overexpression of sxl1a accelerated germ cell numbers in 10 DAH XY fish, and sxl1a knockdown (KD), on the other hand, induced PGC mis-migration, aberrant PGC structuring and ultimately caused significant germ cell reduction in XX fish. Using an in vitro promoter analysis and in vivo steroid treatment, we found a strong link between sxl1a and estrogenic germ cell-population maintenance. Further, using sxl1a-KD and erβ2-knockout fish, we determined that sxl1 acts through erβ2 and controls PGC sexuality. Cumulatively, our study highlights the novel role of sxl1a in germ cell maintenance and sexual identity assignment and thus might become a steppingstone to understanding the commonalities of animal sexual development.

Knock-down of amh transcription by antisense RNA reduces FSH and increases follicular atresia in female Oreochromis niloticus

Anti-Müllerian hormone (Amh) plays an important role in regulating gonad development in teleosts. However, little is known about the effects of Amh on follicle development. In this study, we transfected the vector containing antisense RNA fragments of the amh gene to produce Nile tilapia, Oreochromis niloticus, with knocked-down Amh function in vivo. The results confirmed that the antisense RNA effectively inhibited amh transcription and Amh protein expression in female tilapia ovarian tissue. At 180 days of age, compared with control fish, female tilapia with knocked-down Amh function showed significantly increased growth and significantly decreased ovary weight and gonadosomatic index (P < 0.05). Female fish in the control group had ruddy-colored external genitalia, eggs extruded from the abdomen when gently squeezed, and most oocytes were developmental stage V. In contrast, the external genitalia of female fish with knocked-down Amh function did not have the ruddy color, no eggs extruded from the abdomen when squeezed, most oocytes were at developmental stages II and III, and considerable follicular atresia was apparent. At 180 days of age, the transcript levels of amhrII, cyp19a1a, foxl2 and sox9b in ovarian tissue, and the titers of luteinizing hormone, follicle stimulating hormone, and estradiol in the serum, were significantly lower in fish with knocked-down Amh function than in control fish (P < 0.05). We concluded that decreased serum hormone levels and an abnormal AMH signal delayed development and caused follicular degeneration in Nile tilapia with knocked-down Amh function. These findings show that antisense RNA is a feasible approach for gene silencing in fish, and represents an accurate and effective strategy to study gene function.

ceRNA crosstalk mediated by ncRNAs is a novel regulatory mechanism in fish sex determination and differentiation

Competing endogenous RNAs (ceRNAs) are vital regulators of gene networks in mammals. The involvement of noncoding RNAs (ncRNAs) as ceRNA in genotypic sex determination (GSD) and environmental sex determination (ESD) in fish is unknown. The Chinese tongue sole, which has both GSD and ESD mechanisms, was used to map the dynamic expression pattern of ncRNAs and mRNA in gonads during sex determination and differentiation. Transcript expression patterns shift during the sex differentiation phase, and ceRNA modulation occurs through crosstalk of differentially expressed long ncRNAs (lncRNAs), circular RNAs (circRNAs), microRNAs (miRNAs), and sex-related genes in fish. Of note was the significant up-regulation of a circRNA from the sex-determining gene dmrt1 (circular RNA dmrt1) and a lncRNA, called AMSDT (which stands for associated with male sex differentiation of tongue sole) in Chinese tongue sole testis. These two ncRNAs both share the same miRNA response elements with gsdf, which has an up-regulated expression when they bind to miRNA cse-miR-196 and concurrent down-regulated female sex-related genes to facilitate testis differentiation. This is the first demonstration in fish that ceRNA crosstalk mediated by ncRNAs modulates sexual development and unveils a novel regulatory mechanism for sex determination and differentiation.

Sex determination mechanisms and sex control approaches in aquaculture animals

Aquaculture is one of the most efficient modes of animal protein production and plays an important role in global food security. Aquaculture animals exhibit extraordinarily diverse sexual phenotypes and underlying mechanisms, providing an ideal system to perform sex determination research, one of the important areas in life science. Moreover, sex is also one of the most valuable traits because sexual dimorphism in growth, size, and other economic characteristics commonly exist in aquaculture animals. Here, we synthesize current knowledge of sex determination mechanisms, sex chromosome evolution, reproduction strategies, and sexual dimorphism, and also review several approaches for sex control in aquaculture animals, including artificial gynogenesis, application of sex-specific or sex chromosome-linked markers, artificial sex reversal, as well as gene editing. We anticipate that better understanding of sex determination mechanisms and innovation of sex control approaches will facilitate sustainable development of aquaculture.

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

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

Sexual development dysgenesis in interspecific hybrids of Medaka fish

Fish are amongst vertebrates the group with the highest diversity of known sex-determining genes. Particularly, the genus Oryzias is a suitable taxon to understand how different sex determination genetic networks evolved in closely related species. Two closely related species, O. latipes and O. curvinotus, do not only share the same XX/XY sex chromosome system, but also the same male sex-determining gene, dmrt1bY. We performed whole mRNA transcriptomes and morphology analyses of the gonads of hybrids resulting from reciprocal crosses between O. latipes and O. curvinotus. XY male hybrids, presenting meiotic arrest and no production of sperm were sterile, and about 30% of the XY hybrids underwent male-to-female sex reversal. Both XX and XY hybrid females exhibited reduced fertility and developed ovotestis while aging. Transcriptome data showed that male-related genes are upregulated in the XX and XY female hybrids. The transcriptomes of both types of female and of the male gonads are characterized by upregulation of meiosis and germ cell differentiation genes. Differences in the parental species in the downstream pathways of sexual development could explain sex reversal, sterility, and the development of intersex gonads in the hybrids. We hypothesize that male-to-female sex reversal may be connected to a different development time between species at which dmrt1bY expression starts. Our results provide molecular clues for the proximate mechanisms of hybrid incompatibility and Haldane’s rule.

Roles of anti-Müllerian hormone and its duplicates in sex determination and germ cell proliferation of Nile tilapia

Duplicates of amh are crucial for fish sex determination and differentiation. In Nile tilapia, unlike in other teleosts, amh is located on X chromosome. The Y chromosome amh (amhΔ-y) is mutated with 5 bp insertion and 233 bp deletion in the coding sequence, and tandem duplicate of amh on Y chromosome (amhy) has been identified as the sex determiner. However, the expression of amh, amhΔ-y, and amhy, their roles in germ cell proliferation and the molecular mechanism of how amhy determines sex is still unclear. In this study, expression and functions of each duplicate were analyzed. Sex reversal occurred only when amhy was mutated as revealed by single, double, and triple mutation of the 3 duplicates in XY fish. Homozygous mutation of amhy in YY fish also resulted in sex reversal. Earlier and higher expression of amhy/Amhy was observed in XY gonads compared with amh/Amh during sex determination. Amhy could inhibit the transcription of cyp19a1a through Amhr2/Smads signaling. Loss of cyp19a1a rescued the sex reversal phenotype in XY fish with amhy mutation. Interestingly, mutation of both amh and amhy in XY fish or homozygous mutation of amhy in YY fish resulted in infertile females with significantly increased germ cell proliferation. Taken together, these results indicated that up-regulation of amhy during the critical period of sex determination makes it the sex-determining gene, and it functions through repressing cyp19a1a expression via Amhr2/Smads signaling pathway. Amh retained its function in controlling germ cell proliferation as reported in other teleosts, while amhΔ-y was nonfunctionalized.

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

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

Sex-reversal and Histopathological Assessment of Potential Endocrine-Disrupting Effects of Graphene Oxide on Japanese medaka (Oryzias latipes) Larvae

Sex-ratio is considered as an end point during endocrine disrupting chemicals (EDCs) evaluation. Many fish species including Japanese medaka have XX/XY sex determination mechanism, however, sex reversal (SR) can be induced by external and genetic factors. SR imposed an imbalance in natural sex ratio of a population living in any ecosystem. Considering SR as an end point, we aimed to investigate the potential EDC effects of graphene oxide (GO), a nanocarbon, using Japanese medaka as a model. One-day post-hatch (dph) medaka fries were exposed to GO (2.5, 5.0, 10.0 and 20 mg/L) for 96 h without food, followed by 6 weeks depuration in a GO-free environment with feeding. Phenotypic sex was determined by gonad histology; genotypic sex by genotyping Y-chromosome-specific male sex determining gene, dmy. Our data indicated testes in both XY and XX genotypes, while ovaries were only in XX females. Histopathology of XY and XX testis showed isogenic spermatocysts with active spermatogenesis. Distribution of spermatocytes (SPTs), not the spermatogonium (SPGs), showed enhancement in XY than XX testis. Female phenotypes had single ovary, either in stage 0 or 1. Ovo-testis/testis-ova were absent in XX or XY gonads. GO (2.5-20 mg/L) had inconsistent concentration-dependent effect in both SPGs and SPTs; however, no effect on ovarian follicles. Despite genotypic differences (XY/XX), in the histopathology/histochemistry of liver and kidneys GO effects was found to be minimum. Taken together, present study showed spontaneous induction of SR in some XX genotypes; however, exposure of fasting fries to GO had no apparent EDC effects.

Testis-specific expression pattern of dmrt1 and its putative regulatory region in the sea urchin (Mesocentrotus nudus)

Sea urchin (Mseocentrotus nudus) is an economically important mariculture species in several Asian countries. The growth rate and immunocompetence differ by sex in this species. However, the mechanisms of sex determination in M. nudus have remain unclear. In the present study, we focus on the dmrt1 gene of M. nudus (Mndmrt1) to investigate its dynamic expression pattern during different developmental stages. Real-time quantitative PCR (RT-qPCR) revealed that Mndmrt1 exhibits testis-specific expression and undetectable during the whole embryogenesis. With the development of ontogenetic, Mndmrt1 transcripts are first detected at 9 months post-fertilization (mpf). In addition, both the transcripts and protein of Mndmrt1 gene were specifically expressed in spermatogonia and spermatocytes, indicating that it might be a male germ cells marker in sea urchin. Significantly, the 1441 bp promoter sequence of Mndmrt1 gene was obtained by DNA walking, and one positive regulatory region at -1197/ -968 in the promoter, as well as one negative regulatory region at -1441/ -1198 have been identified by promoter activity analysis. Moreover, two regulatory regions contain multiple putative binding sites for transcription factors, including Sp1, Egr1, Sox5, CEBP, GATA and SRY. These findings suggest that Mndmrt1 may be related to testis differentiation and spermatogenesis in sea urchin and will provide an insight into understanding the regulatory mechanism of the dmrt1 gene.

Evolution, Expression, and Function of Gonadal Somatic Cell-Derived Factor

Fish gonads develop in very diverse ways different from mammalian gonads. This diversity is contributed by species-specific factors. Gonadal somatic cell-derived factor (Gsdf) is one such factor. The gsdf gene exists mostly in teleosts and is absent in many tetrapods, probably as a result of two gene losses during evolution. The gsdf transcript is expressed mainly in gonadal somatic cells, including Sertoli cell in testis and granulosa cells in ovary; however, these gonadal somatic cells can surround many types of germ cells at different developmental stages depending on the fish species. The function of gsdf is also variable. It is involved in germ cell proliferation, testicular formation, ovarian development and even male sex determination. Here, we summarize the common and diverse expression, regulation and functions of gsdf among different fish species with aspect of evolution.

Allelic diversification after transposable element exaptation promoted gsdf as the master sex determining gene of sablefish

Concepts of evolutionary biology suggest that morphological change may occur by rare punctual but rather large changes, or by more steady and gradual transformations. It can therefore be asked whether genetic changes underlying morphological, physiological, and/or behavioral innovations during evolution occur in a punctual manner, whereby a single mutational event has prominent phenotypic consequences, or if many consecutive alterations in the DNA over longer time periods lead to phenotypic divergence. In the marine teleost, sablefish (Anoplopoma fimbria), complementary genomic and genetic studies led to the identification of a sex locus on the Y Chromosome. Further characterization of this locus resulted in identification of the transforming growth factor, beta receptor 1a (tgfbr1a) gene, gonadal somatic cell derived factor (gsdf), as the main candidate for fulfilling the master sex determining (MSD) function. The presence of different X and Y Chromosome copies of this gene indicated that the male heterogametic (XY) system of sex determination in sablefish arose by allelic diversification. The gsdfY gene has a spatio-temporal expression profile characteristic of a male MSD gene. We provide experimental evidence demonstrating a pivotal role of a transposable element (TE) for the divergent function of gsdfY. By insertion within the gsdfY promoter region, this TE generated allelic diversification by bringing cis-regulatory modules that led to transcriptional rewiring and thus creation of a new MSD gene. This points out, for the first time in the scenario of MSD gene evolution by allelic diversification, a single, punctual molecular event in the appearance of a new trigger for male development.

Diverse Regulation but Conserved Function: SOX9 in Vertebrate Sex Determination

Sex determination occurs early during embryogenesis among vertebrates. It involves the differentiation of the bipotential gonad to ovaries or testes by a fascinating diversity of molecular switches. In most mammals, the switch is SRY (sex determining region Y); in other vertebrates it could be one of a variety of genes including Dmrt1 or dmy. Downstream of the switch gene, SOX9 upregulation is a central event in testes development, controlled by gonad-specific enhancers across the 2 Mb SOX9 locus. SOX9 is a ‘hub’ gene of gonadal development, regulated positively in males and negatively in females. Despite this diversity, SOX9 protein sequence and function among vertebrates remains highly conserved. This article explores the cellular, morphological, and genetic mechanisms initiated by SOX9 for male gonad differentiation.

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

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

Fish reproductive biology - Reflecting on five decades of fundamental and translational research

Driven by the broad diversity of species and physiologies and by reproduction-related bottlenecks in aquaculture, the field of fish reproductive biology has rapidly grown over the last five decades. This review provides my perspective on the field during this period, integrating fundamental and applied developments and milestones. Our basic understanding of the brain-pituitary-gonadal axis led to overcoming the failure of farmed fish to ovulate and spawn in captivity, allowing us to close the fish life cycle and establish a predictable, year-round production of eggs. Dissecting the molecular and hormonal mechanisms associated with sex determination and differentiation drove technologies for producing better performing mono-sex and reproductively-sterile fish. The growing contingent of passionate fish biologists, together with the availability of innovative platforms such as transgenesis and gene editing, as well as new models such as the zebrafish and medaka, have generated many discoveries, also leading to new insights of reproductive biology in higher vertebrates including humans. Consequently, fish have now been widely accepted as vertebrate reproductive models. Perhaps the best testament of the progress in our discipline is demonstrated at the International Symposia on Reproductive Physiology of Fish (ISRPF), at which our scientific family has convened every four years since the grandfather of the field, the late Ronald Billard, organized the inaugural 1977 meeting in Paimpont, France. As the one person who has been fortunate enough to attend all of these meetings since their inception, I have witnessed first-hand the astounding evolution of our field as we capitalized on the molecular and biotechnological revolutions in the life sciences, which enabled us to provide a higher resolution of fish reproductive and endocrine processes, answer more questions, and dive into deeper comprehension. Undoubtedly, the next (five) decades will be similarly exciting as we continue to integrate physiology with genomics, basic and translational research, and the small fish models with the aquacultured species.

High temperature stress response is not sexually dimorphic at the whole-body level and is dependent on androgens to induce sex reversal

The understanding of the molecular and endocrine mechanisms behind environmentally-induced sex reversal in fish is of great importance in the context of predicting the potential effects of climate change, especially increasing temperature. Here, we demonstrate the global effects of high temperature on genome-wide transcription in medaka (Oryzias latipes) during early development. Interestingly, data analysis did not show sexual dimorphic changes, demonstrating that thermal stress is not dependent on genotypic sex. Additionally, our results revealed significant changes in several pathways under high temperature, such as stress response from brain, steroid biosynthesis, epigenetic mechanisms, and thyroid hormone biosynthesis, among others. These microarray data raised the question of what the exact molecular and hormonal mechanisms of action are for female-to-male sex reversal under high temperatures in fish. Complementary gene expression analysis revealed that androgen-related genes increase in females (XX) experiencing high water temperature. To test the involvement of androgens in thermal-induced sex reversal, an androgen antagonist was used to treat XX medaka under a high-temperature setup. Data clearly demonstrated failure of female-to-male sex reversal when androgen action is inhibited, corroborating the importance of androgens in environmentally-induced sex reversal.

Sex determination, gonadal sex differentiation, and plasticity in vertebrate species

A diverse array of sex determination (SD) mechanisms, encompassing environmental to genetic, have been found to exist among vertebrates, covering a spectrum from fixed SD mechanisms (mammals) to functional sex change in fishes (sequential hermaphroditic fishes). A major landmark in vertebrate SD was the discovery of the SRY gene in 1990. Since that time, many attempts to clone an SRY ortholog from nonmammalian vertebrates remained unsuccessful, until 2002, when DMY/dmrt1by was discovered as the SD gene of a small fish, medaka. Surprisingly, however, DMY/dmrt1by was found in only 2 species among more than 20 species of medaka, suggesting a large diversity of SD genes among vertebrates. Considerable progress has been made over the last 3 decades, such that it is now possible to formulate reasonable paradigms of how SD and gonadal sex differentiation may work in some model vertebrate species. This review outlines our current understanding of vertebrate SD and gonadal sex differentiation, with a focus on the molecular and cellular mechanisms involved. An impressive number of genes and factors have been discovered that play important roles in testicular and ovarian differentiation. An antagonism between the male and female pathway genes exists in gonads during both sex differentiation and, surprisingly, even as adults, suggesting that, in addition to sex-changing fishes, gonochoristic vertebrates including mice maintain some degree of gonadal sexual plasticity into adulthood. Importantly, a review of various SD mechanisms among vertebrates suggests that this is the ideal biological event that can make us understand the evolutionary conundrums underlying speciation and species diversity.

Molecular and morphological sex differentiation in sablefish (Anoplopoma fimbria), a marine teleost with XX/XY sex determination

Phenotypic sex of an organism is determined by molecular changes in the gonads, so-called molecular sex differentiation, which should precede the rise of cellular or anatomical sex-distinguishing features. This study characterized molecular and morphological sex differentiation in sablefish (Anoplopoma fimbria), a marine teleost with established XX/XY genotypic sex determination. Next generation sequencing was conducted on sablefish ovarian and testicular mRNAs to obtain sequences for transcripts associated with vertebrate sex determination and differentiation and early reproductive development. Gene-specific PCRs were developed to determine the distribution and ontogenetic gonadal expression of transcription, growth, steroidogenic and germline factors, as well as gonadotropin and steroid receptors. Molecular changes associated with sex differentiation were first apparent in both XY- and XX-genotype sablefish at ~ 60 mm in body length and prior to histological signs of sex differentiation. The earliest and most robust markers of testicular differentiation were gsdf, amh, dmrt1, cyp11b, star, sox9a, and fshr. Markedly elevated mRNA levels of several steroidogenesis-related genes and ar2 in differentiating testes suggested that androgens play a role in sablefish testicular differentiation. The earliest markers of ovarian differentiation were cyp19a1a, lhcgr, foxl2, nr0b1, and igf3. Other transcripts such as figla, zp3, and pou5f3 were expressed predominantly in XX-genotype fish and significantly increased with the first appearance and subsequent development of primary oocytes. This study provides valuable insight to the developmental sequence of events associated with gonadal sex differentiation in marine teleosts with XX/XY sex determination. It also implicates particular genes in processes of male and female development and establishes robust molecular markers for phenotypic sex in sablefish, useful for ongoing work related to sex control and reproductive sterilization.

Estrogen and estrogen receptors chauffeur the sex-biased autophagic action in liver

Autophagy, or cellular self-digestion, is an essential cellular process imperative for energy homeostasis, development, differentiation, and survival. However, the intrinsic factors that bring about the sex-biased differences in liver autophagy are still unknown. In this work, we found that autophagic genes variably expresses in the steroidogenic tissues, mostly abundant in liver, and is influenced by the individual's sexuality. Starvation-induced autophagy in a time-dependent female-dominated manner, and upon starvation, a strong gender responsive circulating steroid-HK2 relation was observed, which highlighted the importance of estrogen in autophagy regulation. This was further confirmed by the enhanced or suppressed autophagy upon estrogen addition (male) or blockage (female), respectively. In addition, we found that estrogen proved to be the common denominator between stress management, glucose metabolism, and autophagic action in female fish. To understand further, we used estrogen receptor (ER)α- and ER-β2-knockout (KO) medaka and found ER-specific differences in sex-biased autophagy. Interestingly, starvation resulted in significantly elevated mTOR transcription (compared with control) in male ERα-KO fish while HK2 and ULK activation was greatly decreased in both KO fish in a female oriented fashion. Later, ChIP analysis confirmed that, NRF2, an upstream regulator of mTOR, only binds to ERα, while both ERα and ERβ2 are effectively pulled down the HK2 and LC3. FIHC data show that, in both ER-KO fish, LC3 nuclear-cytoplasmic transport and its associated pathways involving SIRT1 and DOR were greatly affected. Cumulatively, our data suggest that, ERα-KO strongly affected the early autophagic initiation and altered the LC3 nuclear-cytoplasmic translocation, thereby influencing the sex-biased final autophagosome formation in medaka. Thus, existence of steroid responsive autophagy regulatory-switches and sex-biased steroid/steroid receptor availability influences the gender-skewed autophagy. Expectedly, this study may furnish newer appreciation for gender-specific medicine research and therapeutics.

Estrogen Receptor β2 Oversees Germ Cell Maintenance and Gonadal Sex Differentiation in Medaka, Oryzias latipes

In vertebrates, estrogen receptors are essential for estrogen-associated early gonadal sex development. Our previous studies revealed sexual dimorphic expression of estrogen receptor β2 (ERβ2) during embryogenesis of medaka, and here we investigated the functional importance of ERβ2 in female gonad development and maintenance using a transgenerational ERβ2-knockdown (ERβ2-KD) line and ERβ2-null mutants. We found that ERβ2 reduction favored male-biased gene transcription, suppressed female-responsive gene expression, and affected SDF1a and CXCR4b co-assisted chemotactic primordial germ cell (PGC) migration. Co-overexpression of SDF1a and CXXR4b restored the ERβ2-KD/KO associated PGC mismigration. Further analysis confirmed that curtailment of ERβ2 increased intracellular Ca²⁺ concentration, disrupted intra- and extracellular calcium homeostasis, and instigated autophagic germ cell degradation and germ cell loss, which in some cases ultimately affected the XX female sexual development. This study is expected improve our understanding of germ cell maintenance and sex spectrum, and hence open new avenues for reproductive disorder management.

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ERβ2 has a multifaceted role in early gonadal sex differentiation

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ERβ2 directly influences SDF1a/CXCR4b PGC chemotaxis and germ cell migration

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ERβ2-KD impairs intra- and extracellular calcium homeostasis and triggers cell death

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In some cases, ERβ2-KD and KO alters sexual development in female gonad

Transcriptome of tambaqui Colossoma macropomum during gonad differentiation: Different molecular signals leading to sex identity

Tambaqui (Colossoma macropomum) is the major native species in Brazilian aquaculture, and we have shown that females exhibit a higher growth compared to males, opening up the possibility for the production of all-female population. To date, there is no information on the sex determination and differentiation molecular mechanisms of tambaqui. In the present study, transcriptome sequencing of juvenile trunks was performed to understand the molecular network involved in the gonadal sex differentiation. The results showed that before differentiation, components of the Wnt/β-catenin pathway, fox and fst genes imprint female sex development, whereas antagonistic pathways (gsk3b, wt1 and fgfr2), sox9 and genes for androgen synthesis indicate male differentiation. Hence, in undifferentiated tambaqui, the Wnt/β-catenin exerts a role on sex differentiation, either upregulated in female-like individuals, or antagonized in male-like individuals.

Roles of estrogens in fish sexual plasticity and sex differentiation

Fish sex could be reversed at the undifferentiated stage of gonad by administration of exogenous estrogen (E2) or blockade of endogenous estrogen synthesis with aromatase inhibitors, which is designated as primary sex reversal (PSR). Recent studies have well demonstrated that gonochoristic fish maintain their sexual plasticity after sex determination/differentiation. The differentiated ovary could be transdifferentiated into functional testis, and vice versa, the differentiated testis could be transdifferentiated into ovary. By analyzing these two secondary sex reversal (SSR) models, it was found that induction of male-to-female sex reversal initiates from dorsal (near the blood vessel) to the ventral, while induction of female-to-male sex reversal initiates from the ventral to dorsal. Down regulation of endogenous estrogen is the prerequisite for the ovarian transdifferentiation. However, exogenous estrogen alone is not sufficient for inducing differentiated testis to ovary. Administration of E2 and simultaneous blockage of androgen synthesis could induce testicular transdifferentiation. Therefore, endogenous estrogen is critical for the ovarian differentiation/maintenance and androgen is critical for testicular maintenance. Recently, genetic studies with genome editing technologies also showed that disruption of Cyp19a1a induced testicular development, indicating that cyp19a1a is the key gene essential for estrogen synthesis and ovary differentiation/maintenance. Knockout of male pathway genes or overexpression of female pathway genes could up-regulate cyp19a1a expression and increase estrogen level so as to promote ovary. Conversely, knockout of female pathway genes or overexpression of male pathway genes could down-regulate cyp19a1a expression and decrease estrogen level so as to promote testis (transgenic or knockout sex reversal, TSR). Epigenetic regulation of cyp19a1a play a critical role in natural sex reversal (NSR), but its relation with PSR, SSR and TSR needs further detailed investigations. In all, these studies further highlighted the important roles of endogenous estrogens in fish sex differentiation/maintenance.

Expression and transcriptional regulation of gsdf in spotted scat (Scatophagus argus)

Gonadal soma-derived factor (Gsdf) is critical for testicular differentiation and early germ cell development in teleosts. The spotted scat (Scatophagus argus), with a stable XX-XY sex-determination system and the candidate sex determination gene dmrt1, provides a good model for understanding the mechanism of sex determination and differentiation in teleosts. In this study, we analyzed spotted scat gsdf tissue distribution and gene expression patterns in gonads, as well as further analysis of transcriptional regulation. Tissue distribution analysis showed that gsdf was only expressed in testis and ovary. Real-time PCR showed that both gsdf and dmrt1 were expressed significantly higher in testes at different phases (phase III, IV and V) compared to ovaries at phase II, III and IV, while gsdf was expressed significantly higher in phase II ovaries than those of phase III and IV. Western blot analysis also showed that Gsdf was more highly expressed in the testis than ovary. Immunohistochemistry analysis showed that Gsdf was expressed in Sertoli cells surrounding spermatogonia in the testis, while it was expressed in the somatic cells surrounding the oogonia of the ovary. Approximately 2.7 kb of the 5' upstream region of gsdf was cloned from the spotted scat genomic DNA and in silico promoter analysis revealed the putative transcription factor binding sites of Dmrt1 and Sf1. The luciferase reporter assay, using the human embryonic kidney cells, demonstrated that Dmrt1 activated gsdf expression in a dose-dependent manner in the presence of Sf1 in spotted scat. These results suggest that Gsdf could play a role in regulating the development of spermatogonia and oogonia, and also participate in male sex differentiation by acting as a downstream gene of Dmrt1 in spotted scat.

The central nervous system acts as a transducer of stress-induced masculinization through corticotropin-releasing hormone B

Exposure to environmental stressors, like high temperature (HT), during early development of fish induces sex reversal of genotypic females. Nevertheless, the involvement of the brain in this process is not well clarified. In the present work, we investigated the mRNA levels of corticotropin-releasing hormone b (crhb) and its receptors (crhr1 and crhr2), and found out that they were up-regulated at HT during the critical period of gonadal sex determination in medaka. In order to clarify their roles in sex reversal, biallelic mutants for crhr1 and crhr2 were produced by CRISPR/Cas9 technology. Remarkably, biallelic mutant of both loci (crhr1 and crhr2) did not undergo female-to-male sex reversal upon HT exposition. Inhibition of this process in double crhrs mutants could be successfully rescued through the administration of the downstream effector of the hypothalamic-pituitary interrenal axis, the cortisol. Taken together, these results revealed for the first time the participation of the CNS acting as a transducer of masculinization induced by thermal stress.

The autosomal Gsdf gene plays a role in male gonad development in Chinese tongue sole (Cynoglossus semilaevis)

Gsdf is a key gene for testicular differentiation in teleost. However, little is known about the function of Gsdf in Chinese tongue sole (Cynoglossus semilaevis). In this study, we obtained the full-length Gsdf gene (CS-Gsdf), and functional characterization revealed its potential participation during germ cell differentiation in testes. CS-Gsdf transcription was predominantly detected in gonads, while the levels in testes were significantly higher than those in ovaries. During the different developmental stages in male gonads, the mRNA level was significantly upregulated at 86 dph, and a peak appeared at 120 dph; then, the level decreased at 1 and 2 yph. In situ hybridization revealed that CS-Gsdf mRNA was mainly localized in the Sertoli cells, spermatogonia, and spermatids in mature testes. After CS-Gsdf knockdown in the male testes cell line by RNA interference, a series of sex-related genes was influenced, including several sex differentiation genes, CS-Wnt4a, CS-Cyp19a1a and CS-Star. Based on these data, we speculated that CS-Gsdf may play a positive role in germ differentiation and proliferation via influencing genes related to sex differentiation.

Screening and characterisation of sex differentiation-related long non-coding RNAs in Chinese soft-shell turtle (Pelodiscus sinensis)

Long non-coding RNAs (lncRNAs) perform distinct functions in various biological processes in mammals, including sex differentiation. However, the roles of lncRNAs in other vertebrates, especially in the Chinese soft-shell turtle (Pelodiscus sinensis), remain to be clarified. In this study, we performed genome-wide analysis of the lncRNA expression profiles in gonad tissues and screened numerous sex-specific lncRNAs in the Chinese soft-shell turtle. Of the 363,310,650 clean reads obtained, 5,994 sequences were typed as lncRNAs, of which 4,463 were novel. A selection of sex-specific lncRNAs (♀ 932, ♂ 449) from female ovaries and male testis were shown to act on target genes in cis and in trans, and most were involved in gonad differentiation based on Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis. Furthermore, interactions among the differentially expressed lncRNA-mRNAs and protein coding genes were identified by construction of correlation networks. Overall, our systematic analysis of lncRNA expression profiles in gonad tissues revealed numerous sex-specific lncRNAs in P. sinensis. Thereby, these findings provide new insights into the function of lncRNAs in sex differentiation and highlight a group of candidate lncRNAs for future studies.

Brain Sexual Differentiation and Requirement of SRY: Why or Why Not?

Brain sexual differentiation is orchestrated by precise coordination of sex steroid hormones. In some species, programming of select male brain regions is dependent upon aromatization of testosterone to estrogen. In mammals, these hormones surge during the organizational and activational periods that occur during perinatal development and adulthood, respectively. In various fish and reptiles, incubation temperature during a critical embryonic period results in male or female sexual differentiation, but this can be overridden in males by early exposure to estrogenic chemicals. Testes development in mammals requires a Y chromosome and testis determining gene SRY (in humans)/Sry (all other therian mammals), although there are notable exceptions. Two species of spiny rats: Amami spiny rat (Tokudaia osimensis) and Tokunoshima spiny rat (Tokudaia tokunoshimensis) and two species of mole voles (Ellobius lutescens and Ellobius tancrei), lack a Y chromosome/Sry and possess an XO chromosome system in both sexes. Such rodent species, prototherians (monotremes, who also lack Sry), and fish and reptile species that demonstrate temperature sex determination (TSD) seemingly call into question the requirement of Sry for brain sexual differentiation. This review will consider brain regions expressing SRY/Sry in humans and rodents, respectively, and potential roles of SRY/Sry in the brain will be discussed. The evidence from various taxa disputing the requirement of Sry for brain sexual differentiation in mammals (therians and prototherians) and certain fish and reptilian species will be examined. A comparative approach to address this question may elucidate other genes, pathways, and epigenetic modifications stimulating brain sexual differentiation in vertebrate species, including humans.

Gonadal soma controls ovarian follicle proliferation through Gsdf in zebrafish

BACKGROUND

Aberrant signaling between germ cells and somatic cells can lead to reproductive disease and depends on diffusible signals, including transforming growth factor-beta (TGFB) -family proteins. The TGFB-family protein Gsdf (gonadal soma derived factor) controls sex determination in some fish and is a candidate for mediating germ cell/soma signaling.

RESULTS

Zebrafish expressed gsdf in somatic cells of bipotential gonads and expression continued in ovarian granulosa cells and testicular Sertoli cells. Homozygous gsdf knockout mutants delayed leaving the bipotential gonad state, but then became a male or a female. Mutant females ovulated a few oocytes, then became sterile, accumulating immature follicles. Female mutants stored excess lipid and down-regulated aromatase, gata4, insulin receptor, estrogen receptor, and genes for lipid metabolism, vitellogenin, and steroid biosynthesis. Mutant females contained less estrogen and more androgen than wild-types. Mutant males were fertile. Genomic analysis suggests that Gsdf, Bmp15, and Gdf9, originated as paralogs in vertebrate genome duplication events.

CONCLUSIONS

In zebrafish, gsdf regulates ovarian follicle maturation and expression of genes for steroid biosynthesis, obesity, diabetes, and female fertility, leading to ovarian and extra-ovarian phenotypes that mimic human polycystic ovarian syndrome (PCOS), suggesting a role for a related TGFB signaling molecule in the etiology of PCOS. Developmental Dynamics 246:925-945, 2017. © 2017 Wiley Periodicals, Inc.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

Dmrt1 is required for primary male sexual differentiation in Chinese soft-shelled turtle Pelodiscus sinensis

In vertebrates, the primary sex-determining signals that initiate sexual development are remarkably diverse, ranging from complete genetic to environmental cues. However, no sex determination-related genes have been functionally identified in reptiles. Here, we characterized a conserved DM domain gene, Dmrt1, in Chinese soft-shelled turtle Pelodiscus sinensis (P. sinensis), which exhibits ZZ/ZW sex chromosomes. Dmrt1 exhibited early male-specific embryonic expression, preceding the onset of gonadal sex differentiation. The expression of Dmrt1 was induced in ZW embryonic gonads that were masculinized by aromatase inhibitor treatment. Dmrt1 knockdown in ZZ embryos by RNA interference resulted in male to female sex reversal, characterized by obvious feminization of gonads, significant down-regulation of testicular markers Amh and Sox9, and remarkable up-regulation of ovarian regulators, Cyp19a1 and Foxl2. Conversely, ectopic expression of Dmrt1 led to largely masculinized genetic females, production of Amh and Sox9, and a decline in Cyp19a1 and Foxl2. These findings demonstrate that Dmrt1 is both necessary and sufficient to initiate testicular development, thereby acting as an upstream regulator of the male pathway in P. sinensis.

Hatching enzymes disrupt aberrant gonadal degeneration by the autophagy/apoptosis cell fate decision

Environmental stressors, gonadal degenerative diseases and tumour development can significantly alter the oocyte physiology, and species fertility and fitness. To expand the molecular understanding about oocyte degradation, we isolated several spliced variants of Japanese anchovy hatching enzymes (AcHEs; ovastacin homologue) 1 and 2, and analysed their potential in oocyte sustenance. Particularly, AcHE1b, an ovary-specific, steroid-regulated, methylation-dependent, stress-responsive isoform, was neofunctionalized to regulate autophagic oocyte degeneration. AcHE1a and 2 triggered apoptotic degeneration in vitellogenic and mature oocytes, respectively. Progesterone, starvation, and high temperature elevated the total degenerating oocyte population and AcHE1b transcription by hyper-demethylation. Overexpression, knockdown and intracellular zinc ion chelation study confirmed the functional significance of AcHE1b in autophagy induction, possibly to mitigate the stress effects in fish, via ion-homeostasis. Our finding chronicles the importance of AcHEs in stress-influenced apoptosis/autophagy cell fate decision and may prove significant in reproductive failure assessments, gonadal health maintenance and ovarian degenerative disease therapy.

CRISPR/Cas9-induced disruption of wt1a and wt1b reveals their different roles in kidney and gonad development in Nile tilapia

Wilms tumor 1 (Wt1) is an essential factor for urogenital system development. Teleosts have two wt1s, named as wt1a and wt1b. In this study, the expression pattern of wt1a and wt1b and their functions on the urogenital system were analyzed by in situ hybridization and CRISPR/Cas9. wt1a was found to be expressed in the glomerulus at 3 dah (days after hatching), earlier than wt1b. wt1a and wt1b were simultaneously expressed in the somatic cells of gonads at 3 dah, while their cell locations were similar, but not identical in adult fish gonads. The wt1a^-/- fish displayed pericardial edema and yolk sac edema at 3 dah and subsequently expanded as general body edema at 6 dah, failed to develop glomerulus and died during 6-10 dah, whereas the wt1b^-/- fish were phenotypically normal. Immunohistochemical analyses revealed that the germ cell marker Vasa was expressed, while somatic cell genes Cyp19a1a, Amh, Gsdf and Dmrt1 were not expressed in the wt1a^-/- gonads at 6 dah. The sex phenotypes of XX and XY in the wt1b^-/- fish were not affected. Real-time PCR revealed that the ovarian cyp19a1a expression was up-regulated in XX wt1b^-/- fish, compared with XX control at 90 dah. Serum estradiol-17β level was also up-regulated in XX wt1b^-/- fish at 90 and 180 dah. The XY wt1b^-/- fish had normal serum estradiol-17β and 11-ketotestosterone levels and remained fertile. These results suggest that Wt1a and Wt1b have different functions in the kidneys and gonads of tilapia.

The Reversible Sex of Gonochoristic Fish: Insights and Consequences

Fish sex reversal is a means to understand sex determination and differentiation, but it is also used to control sex in aquaculture. This review discusses sex reversal in gonochoristic fish, with the coexistence of genetic and environmental influences. The different periods of fish sensitivity to sex reversal treatments are presented with the mechanisms implicated. The old players of sex differentiation are revisited with transcriptome data and loss of function studies following hormone- or temperature-induced sex reversal. We also discuss whether cortisol is the universal mediator of sex reversal in fish due to its implication in ovarian meiosis and 11KT increase. The large plasticity in fish for sex reversal is also evident in the brain, with a reversibility existing even in adulthood. Studies on epigenetics are presented, since it links the environment, gene expression, and sex reversal, notably the association of DNA methylation in sex reversal. Manipulations with exogenous factors reverse the primary sex in many fish species under controlled conditions, but several questions arise on whether this can occur under wild conditions and what is the ecological significance. Cases of sex reversal in wild fish populations are shown and their fitness and future perspectives are discussed.