Ontogenesis of female-to-male sex-reversal in XX polled goats

Insights into the role of FoxL2 in tebuconazole-induced male- biased sex differentiation of zebrafish

Tebuconazole (TEB) is a commonly used fungicide that inhibits the aromatase Cyp19A and downregulates the transcription factor forkhead box L2 (FoxL2), leading to male-biased sex differentiation in zebrafish larvae. However, the specific mechanism by which FoxL2 functions following TEB exposure remains unclear. In this study, the phosphorylation sites and kinase-specific residues in zebrafish FoxL2 protein (zFoxL2) were predicted. Subsequently, recombinant zFoxL2 was prepared via prokaryotic expression, and a polyclonal rabbit-anti-zFoxL2 antibody was generated. Zebrafish fibroblast (ZF4) cells were exposed to 100-μM TEB alone for 8 h, after which changes in the expression of genes involved in the foxl2 regulatory pathway (akt1, pi3k, cyp19a1b, c/ebpb and sox9a) were detected. When co-exposed to 1-μM estradiol and 100-μM TEB, the expression of these key genes tended to be restored. Interestingly, TEB did not affect the expression of the foxl2 gene or protein but it significantly suppressed the phosphorylation of FoxL2 (pFoxL2) at serine 238 (decreased by 43.64 %, p = 0.009). Co-immunoprecipitation assays showed that, following exposure to 100-μM TEB, the total precipitated proteins in ZF4 cells decreased by 17.02 % (p = 0.029) and 31.39 % (p = 0.027) in the anti-zFoxL2 antibody group and anti-pFoxL2 (ser238) antibody group, respectively, indicating that TEB suppressed the capacity of the FoxL2 protein to bind to other proteins via repression of its own phosphorylation. The pull-down assay confirmed this conclusion. This study preliminarily elucidated that the foxl2 gene functions via post-translational regulation through hypophosphorylation of its encoded protein during TEB-induced male-biased sex differentiation.

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.

Avian Sex Determination: A Chicken and Egg Conundrum

BACKGROUND

Primary sex determination is the developmental process that results in the sexual differentiation of the gonads. Vertebrate sex determination is generally considered to follow the model based on the mammalian system, where a sex-specific master regulatory gene activates one of the two different gene networks that underlie testis and ovary differentiation.

SUMMARY

It is now known that, while many of the molecular components of these pathways are conserved across different vertebrates, a wide variety of different trigger factors are utilized to initiate primary sex determination. In birds, the male is the homogametic sex (ZZ), and significant differences exist between the avian system of sex determination and that of mammals. For example, DMRT1, FOXL2, and estrogen are key factors in gonadogenesis in birds, but none are essential for primary sex determination in mammals.

KEY MESSAGE

Gonadal sex determination in birds is thought to depend on a dosage-based mechanism involving expression of the Z-linked DMRT1 gene, and it may be that this "mechanism" is simply an extension of the cell autonomous sex identity associated with avian tissues, with no sex-specific trigger required.

Early development of the human embryonic testis

Human gonadal development culminating in testicular differentiation is described through analysis of histologic sections derived from 33-day to 20-week human embryos/fetuses, focusing on early development (4-8 weeks of gestation). Our study updates the comprehensive studies of Felix (1912), van Wagenen and Simpson (1965), and Juric-Lekic et al. (2013), which were published in books and thus are unsearchable via PubMed. Human gonads develop from the germinal ridge, a thickening of coelomic epithelium on the medial side of the urogenital ridge. The bilateral urogenital ridges contain elements of the mesonephric kidney, namely the mesonephric duct, mesonephric tubules, and mesonephric glomeruli. The germinal ridge, into which primordial germ cells migrate, is initially recognized as a thickening of coelomic epithelium on the urogenital ridge late in the 4th week of gestation. Subsequently, in the 5th week of gestation, a dense mesenchyme develops sub-adjacent to the epithelium of the germinal ridge, and together these elements bulge into the coelomic cavity forming bilateral longitudinal ridges attached to the urogenital ridges. During development, primordial cells migrate into the germinal ridge and subsequently into testicular cords that form within the featureless dense mesenchyme of the germinal ridge at 6-8 weeks of gestation. The initial low density of testicular cords seen at 8 weeks remodels into a dense array of testicular cords surrounded by α-actin-positive myoid cells during the second trimester. Human testicular development shares many features with that of mice being derived from 4 elements: coelomic epithelium, sub-adjacent mesenchyme, primordial germ cells, and the mesonephros.

Becoming female: Ovarian differentiation from an evolutionary perspective

Differentiation of the bipotential gonadal primordium into ovaries and testes is a common process among vertebrate species. While vertebrate ovaries eventually share the same functions of producing oocytes and estrogens, ovarian differentiation relies on different morphogenetic, cellular, and molecular cues depending on species. The aim of this review is to highlight the conserved and divergent features of ovarian differentiation through an evolutionary perspective. From teleosts to mammals, each clade or species has a different story to tell. For this purpose, this review focuses on three specific aspects of ovarian differentiation: ovarian morphogenesis, the evolution of the role of estrogens on ovarian differentiation and the molecular pathways involved in granulosa cell determination and maintenance.

Whole genome sequencing identifies a missense polymorphism in PADI6 associated with testicular/ovotesticular XX disorder of sex development in dogs

Disorders of sex development (DSDs) are congenital malformations defined as discrepancies between sex chromosomes and phenotypical sex. Testicular or ovotesticular XX DSDs are frequently observed in female dogs, while monogenic XY DSDs are less frequent. Here, we applied whole genome sequencing (WGS) to search for causative mutations in XX DSD females in French Bulldogs (FB) and American Staffordshire Terries (AST) and in XY DSD Yorkshire Terries (YT). The WGS results were validated by Sanger sequencing and ddPCR. It was shown that a missense SNP of the PADI6 gene, is significantly associated with the XX DSD (SRY-negative) phenotype in AST (P = 0.0051) and FB (P = 0.0306). On the contrary, we did not find any associated variant with XY DSD in YTs. Our study suggests that the genetic background of the XX DSD may be more complex and breed-specific.

Gene expression profiles of bovine genital ridges during sex determination and early differentiation of the gonads†

Most current knowledge of sex determination in mammals has emerged from mouse and human studies. To investigate the molecular regulation of the sex determination process in cattle, we used an RNA sequencing strategy to analyze the transcriptome landscape of male and female bovine fetal gonads collected in vivo at key developmental stages: before, during, and after SRY gene activation on fetal days D35 (bipotential gonad formation), D39 (peak SRY expression), and D43 (early gonad differentiation). Differentially expressed genes (DEGs) were identified in male vs. female germinal ridges and among group genes showing similar expression profiles during the three periods. There were 143, 96, and 658 DEG between males and female fetuses at D35, D39, and D43, respectively. On D35, genes upregulated in females were enriched in translation, nuclear export, RNA localization, and mRNA splicing events, whereas those upregulated in males were enriched in cell proliferation regulation and male sex determination terms. In time-course experiments, 767 DEGs in males and 545 DEGs in females were identified between D35 vs. D39, and 3157 DEGs in males and 2008 in females were identified between D39 vs. D43. Results highlight unique aspects of sex determination in cattle, such as the expression of several Y chromosome genes (absent in mice and humans) before SRY expression and an abrupt increase in the nuclear expression of SOX10 (instead of SOX9 expression in the Sertoli cell cytoplasm as observed in mice) during male determination and early differentiation.

Interactive role of Wnt signaling and Zn in regulating testicular function of the common carp, Cyprinus carpio

Wnt signaling is conserved among all species and plays a significant role in various cellular processes including reproduction. The present study identified significant involvement of wnt4a, wnt5b, and wnt8a signaling in the testicular growth of common carp,Cyprinus carpio. Predominant expression of wnt4a, wnt5b, and wnt8a was found in the gonads and Wnt4a was localized in spermatocytes and interstitial cells. Ontogeny and testicular phase-wise analysis signified the importance of wnt isofoms analyzed in this study. Specific pathway activation of Wnt signaling revealed that Wnt4a and Wnt5b act through non-canonical while Wnt8a prefers the canonical pathway. The Wnt signaling regulates several steroidogenic enzyme and testis-related genes which was confirmed by the Wnt blockade experiments. Incidentally, zinc (Zn) is an essential trace element involved in the progression of spermatogenesis in teleosts. In adult male carp, a single administration of Zn at different doses elevated the expression of Wnt and Zn transporter genes and a single-dose (30 μg/g body weight [BW]) of Zn treatment elevated steroidogenic enzyme and testis-related genes which coincided with elevated androgens. Conversely, single-dose administration of Zn chelator to the Zn administered (30 μg/g BW) fish reversed the effects emphasizing a prominent role of Zn in the testicular function perhaps through Wnt signaling. Similar effects were observed in the in vitro experiments using the Zn chelator. Bioaccumulation of Zn and histological analysis revealed the importance of Zn in progression of spermatogenesis and sperm motility. Various assays related to cell viability and proliferation exhibited the role of Zn in promoting spermatogenic cell progression. Flow cytometric analysis confirmed Zn-induced elevation of Wnt and Zn transporter genes in germ and supporting cells. Furthermore, the effects of Zn are dose-related in carp. Taken together, it seems wnt4a, wnt5b, and wnt8a play an important role in testis and exposure of Wnt inhibitor, canonical as well as non-canonical activators, and Zn confirmed that Zn regulates Wnt signaling vis-à-vis promoting spermatogenesis in the common carp.

Cloning and characterization of wnt4a gene in a natural triploid teleost, Qi river crucian carp (Carassius auratus)

WNT4 (wingless-type MMTV integration site family, member 4) plays a key role in the ovarian differentiation and development in mammals. However, the possible roles of Wnt4 during gonadal differentiation and development need further clarification in teleosts. In this study, we cloned and characterized the full-length cDNA of Qi river crucian carp (Carassius auratus) wnt4a gene (CA-wnt4a). The cDNA of CA-wnt4a is 2337 bp, including the ORF of 1059 bp, encoding a putative protein with a transmembrane domain and a WNT family domain. Sequence and phylogenetic analyses revealed that the CA-Wnt4a identified is a genuine Wnt4a. Tissue distribution analysis showed that CA-wnt4a is expressed in all the tissues examined, including ovary. CA-wnt4a undergoes a stepwise increase in the embryonic stages, suggesting that CA-wnt4a might be involved in the early developmental stage. Ontogenic analysis demonstrated that CA-wnt4a expression is upregulated in the ovaries at 30-50 days after hatching (dah), the critical period of sex determination/differentiation in Qi river crucian carp. From 90 dah, the expression of CA-wnt4a was gradually downregulated in the developing ovaries. Immunohistochemistry demonstrated that CA-Wnt4a was expressed in the somatic and germ cells of the ovary by 30 dah, thereafter, positive signals of Wnt4a were detected in the somatic cells, oogonia and primary growth oocytes from 60 dah. In the sex-reversed testis induced by letrozole treatment, the expression level of CA-wnt4a was significantly downregulated. When CA-wnt4a expression was inhibited by injection of FH535 (an inhibitor of canonical Wnt/β-catenin signal pathway) in the ovaries, levels of cyp19a1a, foxl2 mRNA were significantly downregulated, while sox9b and cyp11c1 were upregulated, which suggested that together with Foxl2-leading estrogen pathway, CA-wnt4a signaling pathway might be involved in ovarian differentiation and repression of the male pathway gene expression in Qi river crucian carp.

Morphometric analyses and gene expression related to germ cells, gonadal ridge epithelial-like cells and granulosa cells during development of the bovine fetal ovary

Cells on the surface of the mesonephros give rise to replicating Gonadal Ridge Epithelial-Like (GREL) cells, the first somatic cells of the gonadal ridge. Later germ cells associate with the GREL cells in the ovigerous cords, and the GREL cells subsequently give rise to the granulosa cells in follicles. To examine these events further, 27 bovine fetal ovaries of different gestational ages were collected and prepared for immunohistochemical localisation of collagen type I and Ki67 to identify regions of the ovary and cell proliferation, respectively. The non-stromal cortical areas (collagen-negative) containing GREL cells and germ cells and later in development, the follicles with oocytes and granulosa cells, were analysed morphometrically. Another set of ovaries (n = 17) were collected and the expression of genes associated with germ cell lineages and GREL/granulosa cells were quantitated by RT-PCR. The total volume of non-stromal areas in the cortex increased significantly and progressively with ovarian development, plateauing at the time the surface epithelium developed. However, the proportion of non-stromal areas in the cortex declined significantly and progressively throughout gestation, largely due to a cessation in growth of the non-stroma cells and the continued growth of stroma. The proliferation index in the non-stromal area was very high initially and then declined substantially at the time follicles formed. Thereafter, it remained low. The numerical density of the non-stromal cells was relatively constant throughout ovarian development. The expression levels of a number of genes across gestation either increased (AMH, FSHR, ESR1, INHBA), declined (CYP19A1, ESR2, ALDH1A1, DSG2, OCT4, LGR5) or showed no particular pattern (CCND2, CTNNB1, DAZL, FOXL2, GATA4, IGFBP3, KRT19, NR5A1, RARRES1, VASA, WNT2B). Many of the genes whose expression changed across gestation, were positively or negatively correlated with each other. The relationships between these genes may reflect their roles in the important events such as the transition of ovigerous cords to follicles, oogonia to oocytes or GREL cells to granulosa cells.

Genome-wide analysis of Chongqing native intersexual goats using next-generation sequencing

Sex reversal has been studied extensively in vertebrate species, particularly in domestic goats, because polled intersex syndrome (PIS) has seriously affected their production efficiency. In the present study, we used histopathologically diagnosed cases of PIS to identify correlated genomic regions and variants using representative selection signatures and performed GWAS using Restriction-Site Associated Resequencing DNA. We identified 171 single-nucleotide polymorphisms (SNPs) that may have contributed to this phenotype, and 53 SNPs were determined to be located in coding regions using a general linear model. The transcriptome data sets of differentially expressed genes (DEGs) in the pituitary tissues of intersexual and nonintersexual goats were examined using high-throughput technology. A total of 10,063 DEGs and 337 long noncoding RNAs were identified. The DEGs were clustered into 56 GO categories and determined to be significantly enriched in 53 signaling pathways by KEGG analysis. In addition, according to qPCR results, PSPO2 and FSH were significantly more highly expressed in sexually mature pituitary tissues of intersexual goats compared to healthy controls (nonintersexual). These results demonstrate that certain novel potential genomic regions may be responsible for intersexual goats, and the transcriptome data indicate that the regulation of various physiological systems is involved in intersexual goat development. Therefore, these results provide helpful data for understanding the molecular mechanisms of intersex syndrome in goats.

Gametogenesis: A journey from inception to conception

Gametogenesis, the process of forming mature germ cells, is an integral part of both an individual's and a species' health and well-being. This chapter focuses on critical male and female genetic and epigenetic processes underlying normal gamete formation through their differentiation to fertilization. Finally, we explore how knowledge gained from this field has contributed to progress in areas with great clinical promise, such as in vitro gametogenesis.

At the Crossroads of Fate-Somatic Cell Lineage Specification in the Fetal Gonad

The reproductive endocrine systems are vastly different between males and females. This sexual dimorphism of the endocrine milieu originates from sex-specific differentiation of the somatic cells in the gonads during fetal life. Most gonadal somatic cells arise from the adrenogonadal primordium. After separation of the adrenal and gonadal primordia, the gonadal somatic cells initiate sex-specific differentiation during gonadal sex determination with the specification of the supporting cell lineages: Sertoli cells in the testis vs granulosa cells in the ovary. The supporting cell lineages then facilitate the differentiation of the steroidogenic cell lineages, Leydig cells in the testis and theca cells in the ovary. Proper differentiation of these cell types defines the somatic cell environment that is essential for germ cell development, hormone production, and establishment of the reproductive tracts. Impairment of lineage specification and function of gonadal somatic cells can lead to disorders of sexual development (DSDs) in humans. Human DSDs and processes for gonadal development have been successfully modeled using genetically modified mouse models. In this review, we focus on the fate decision processes from the initial stage of formation of the adrenogonadal primordium in the embryo to the maintenance of the somatic cell identities in the gonads when they become fully differentiated in adulthood.

A brief history of sex determination

A fundamental biological question that has puzzled, but also fascinated mankind since antiquity is the one pertaining to the differences between sexes. Ancient cultures and mythologies poetically intended to explain the origin of the two sexes; philosophy offered insightful albeit occasionally paradoxical perceptions about men and women; and society as a whole put forward numerous intuitive observations about the traits that distinguish the two sexes. However, it was only through meticulous scientific research that began in the 16th century, and gradual technical improvements that followed over the next centuries, that the study of sex determination bore fruit. Here, we present a brief history of sex determination studies from ancient times until today, by selectively interviewing some of the milestones in the field. We complete our review by outlining some yet unanswered questions and proposing future experimental directions.

Development of urogenital system in the Spix cavy: A model for studies on sexual differentiation

This study documented, for the first time, the morphological patterns of differentiation of male and female genital organs of Spix cavy (Galea spixii) using histological and ultrastructural analyses, with immuno-localization of steroidogenic enzymes, cytochromes P450 aromatase (P450arom) and 17α-hydroxylase/17, 20-lyase (P450c17), involved in the synthesis of estrogens and androgens respectively throughout fetal sexual development. Undifferentiated gonads of Spix cavy develop into ovaries in females after 25 days of gestation (DG), exhibiting P450arom immunoreactivity. After 25 DG, paramesonephric ducts develop and form oviducts, uterine horns and cranial portion of the vagina. The caudal portion of the vagina originates from the urogenital sinus, and a vaginal closure membrane is present at the end of gestation. Partial channeling of the urethra into the clitoris occurs after 40 DG, but complete channeling never occurs. A preputial meatus emerges near the tip of organ. In males, undifferentiated gonads develop into testes at 25 DG and develop immunoreactivity for P450c17, which is required for androgens synthesis and likely maintenance of mesonephric ducts. Mesonephric ducts develop subsequently, forming the epididymis and ductus deferens. The pelvic urethra develops after 25 DG with channeling into the penis occurring around 30 DG. This is the first morphological study describing the process of sexual differentiation during gestation in a hystricomorph rodent and one of the most comprehensive analyses conducted in any mammal. Male genital organ development follows the general pattern described in other domestic mammals, but does not include formation of the baculum as occurs in mice and rats. In females, clitoral development includes partial canalization by the urethra and development of a preputial meatus. Further studies are required to clarify the mechanisms involved in the differentiative processes described.

Uterine Foxl2 regulates the adherence of the Trophectoderm cells to the endometrial epithelium

BACKGROUND

Forkhead Transcription Factor L2 (FOXL2) is a member of the forkhead family with important roles in reproduction. Recent studies showed that FOXL2 is expressed in human and bovine endometrium and that its levels fluctuate during pregnancy. In this study, we aimed at evaluating the expression and function of FOXL2 in embryo implantation.

METHODS

Mouse uteri at different days of pregnancy were isolated and analyzed for the expression and localization of FOXL2. A lentiviral strategy was further employed to either knockdown or overexpress FOXL2 in non-receptive human endometrial AN3-CA cells and in receptive Ishikawa cells, respectively. These genetically modified cells were compared to cells infected with a control lentivirus to determine the function of FOXL2 in trophectoderm cells adherence to Endometrial Epithelium was associated with the expression of genes known to be involved in acquisition of uterine receptivity.

RESULTS

We report that FOXL2 is expressed in both, the luminal epithelium and the myometrium of the mouse uterus and that its expression declines prior to implantation. We found that endometrial cells expressing low FOXL2 levels, either endogenous or genetically manipulated, were associated with a higher attachment rate of mouse blastocysts or human Jeg3 spheroids and mouse blastocysts. In accordance, low-FOXL2 levels were associated with changes in the expression level of components of the Wnt/Fzd and apoptotic pathways, both of which are involved in uterine receptivity. Furthermore, FOXL2 expression was inversely correlated with G-protein signaling protein 2 (Rgs2) and cytokine expression.

CONCLUSIONS

These results suggest that FOXL2 interferes with embryo attachment. Better understanding of the function of FOXL2 in the uterus would possibly suggest novel strategies for treatment of infertility attributed to repeated implantation failure.

Expression of wnt4/5 during reproductive cycle of catfish and wnt5 promoter analysis

Signaling molecules, Wnt4 and Wnt5, are essential for ovarian growth during developmental stages in mammals. Although these molecules were identified in several teleosts, their precise expression and role in reproductive processes have not yet been explored in any lower vertebrates. In view of this, using catfish, Clarias batrachus as an animal model, cloning and expression analysis of wnt4 and wnt5 were analyzed in different tissues, at various developmental stages, during ovarian reproductive cycle and after gonadotropin induction. These studies indicate a plausible influence of Wnts in ovarian development and recrudescence. Transcript and protein localization revealed their presence in peri-nucleolar, pre-vitellogenic, vitellogenic and follicular layer of post-vitellogenic oocytes. Synchronous expression of pax2 and wnt5 during the ovarian development and recrudescence of catfish led us to analyze the importance of putative binding element of Pax2 in the 5'-promoter motif of wnt5 Promoter activity of wnt5 was analyzed by luciferase assays after transfecting progressive deletion constructs in pGL3 basic vector into the mammalian cell lines (HEK 293 and CHO). The constructs having putative Pax2 motif showed high promoter activity compared with controls. Likewise, the constructs with site-directed mutagenesis showed increased activity after supplementing recombinant Pax2 indicating the prominence of this motif in wnt5 promoter, in vitro Electrophoretic gel mobility shift, supershift and chromatin immunoprecipitation assays confirmed the binding of Pax2 to its corresponding cis-acting element in the upstream of wnt5 This study is the first of its kind to report the critical transcriptional interaction of Pax2 on wnt5 vis-à-vis ovarian development in teleosts.

Involvement of FOXL2 and RSPO1 in Ovarian Determination, Development, and Maintenance in Mammals

In mammals, sex determination is a process through which the gonad is committed to differentiate into a testis or an ovary. This process relies on a delicate balance between genetic pathways that promote one fate and inhibit the other. Once the gonad is committed to the female pathway, ovarian differentiation begins and, depending on the species, is completed during gestation or shortly after birth. During this step, granulosa cell precursors, steroidogenic cells, and primordial germ cells start to express female-specific markers in a sex-dimorphic manner. The germ cells then arrest at prophase I of meiosis and, together with somatic cells, assemble into functional structures. This organization gives the ovary its definitive morphology and functionality during folliculogenesis. Until now, 2 main genetic cascades have been shown to be involved in female sex differentiation. The first is driven by FOXL2, a transcription factor that also plays a crucial role in folliculogenesis and ovarian fate maintenance in adults. The other operates through the WNT/CTNNB1 canonical pathway and is regulated primarily by R-spondin1. Here, we discuss the roles of FOXL2 and RSPO1/WNT/ CTNNB1 during ovarian development and homeostasis in different models, such as humans, goats, and rodents.

Molecular cloning and sexually dimorphic expression of wnt4 in olive flounder (Paralichthys olivaceus)

WNT4 (wingless-type MMTV integration site family, member 4) is regarded as a key regulator of gonad differentiation in mammalians. However, the potential role of wnt4 in teleosts during gonad differentiation and development is still unclear. The full-length cDNA sequence of wnt4 in olive flounder (Paralichthys olivaceus) was obtained using RACE (rapid amplification of cDNA ends) technique. The wnt4 ORF contains 1059 nucleotides, encoding a protein with a signal peptide domain and a wnt family domain. Expression in tissues of adult flounders was analyzed by real-time RT-PCR. The results showed that wnt4 was widely expressed in multiple tissues of flounders, and the expression level was significantly higher in ovary than in testis. Then wnt4 expression pattern was investigated during gonadal differentiation period and at gonadal development stages (I-V). The results showed the expression levels were significantly higher in testis than in ovary during gonadal differentiation. Notably, wnt4 expression had a very significant increase before testis differentiation. At gonad different developmental stages, there was no expression signal at stage I or stage II, and the expression of wnt4 was much stronger in ovary than in testis at stage III and stage IV, followed by a faint expression in stage V in both sexes. Our results imply that cloned wnt4 could be wnt4a. It is a sex-related gene and its expression pattern in gonadal differentiation period of flounder is different from that in mammalians or other teleosts. Flounder wnt4 might play more important role in testis than in ovary during gonadal differentiation.

A specific role for PRND in goat foetal Leydig cells is suggested by prion family gene expression during gonad development in goats and mice

Three genes of the prion protein gene family are expressed in gonads. Comparative analyses of their expression patterns in mice and goats revealed constant expression of PRNP and SPRN in both species and in both male and female gonads, but with a weaker expression of SPRN. By contrast, expression of PRND was found to be sex‐dimorphic, in agreement with its role in spermatogenesis. More importantly, our study revealed that PRND seems to be a key marker of foetal Leydig cells specifically in goats, suggesting a yet unknown role for its encoded protein Doppel during gonadal differentiation in nonrodent mammals.

How Australian mammals contributed to our understanding of sex determination and sex chromosomes

Marsupials and monotremes can be thought of as independent experiments in mammalian evolution. The discovery of the human male-determining gene, SRY, how it works, how it evolved and defined our sex chromosomes, well illustrates the value of comparing distantly related animals and the folly of relying on humans and mice for an understanding of the most fundamental aspects of mammalian biology. The 25th anniversary of the discovery of SRY seems a good time to review the contributions of Australian mammals to these discoveries. The discovery of the mammalian sex determining gene, SRY, was a milestone in the history of human genetics. SRY opened up investigations into the pathway by which the genital ridge (bipotential gonad) becomes a testis. Studies of Australian mammals were important in the story of the discovery of SRY, not only in refuting the qualifications of the first candidate sex-determining gene, but also in confirming the ubiquity of SRY and raising questions as to how it works. Studies in marsupials also led to understanding of how SRY evolved from a gene on an autosome with functions in the brain and germ cells, and to identifying the ancestors of other genes on the human Y. The discovery that platypus have sex chromosomes homologous, not to the human XY, but to the bird ZW, dated the origin of the therian SRY and the XY chromosomes it defined. This led to important new models of how our sex chromosomes function, how they evolved, and what might befall this gene and the Y chromosome it defines.

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

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

Gonadal soma-derived factor (gsdf), a TGF-beta superfamily gene, induces testis differentiation in the teleost fish Oreochromis niloticus

The Nile tilapia, Oreochromis niloticus, is a gonochoristic teleost fish with an XX/XY genetic system and is an excellent model for gonadal sex differentiation. In the present study, we screened novel genes that were expressed predominantly in either XY or XX undifferentiated gonads during the critical period for differentiation of gonads into ovaries or testes using microarray screening. We focused on one of the isolated 12 candidate genes, #9475, which was an ortholog of gsdf (gonadal soma-derived factor), a member of the transforming growth factor-beta superfamily. #9475/gsdf showed sexual dimorphism in expression in XY gonads before any other testis differentiation-related genes identified in this species thus far. We also overexpressed the #9475/gsdf gene in XX tilapia, and XX tilapia bearing the #9475/gsdf gene showed normal testis development, which suggests that #9475/gsdf plays an important role in male determination and/or differentiation in tilapia.

Cloning and characterization of wnt4a gene and evidence for positive selection in half-smooth tongue sole (Cynoglossus semilaevis)

Wnt4 gene plays a role in developmental processes in mammals. However, little is known regarding its function in teleosts. We cloned and characterized the full-length half-smooth tongue sole (Cynoglossus semilaevis) wnt4a gene (CS-wnt4a). CS-wnt4a cDNA was 1746 bp in length encoding 353aa. CS-wnt4a expression level was highest in the testis, and gradually increased in the developing gonads until 1 year of age. In situ hybridization revealed that CS-wnt4a expression level was highest in stage II oocytes and sperm in the adult ovary and testis, respectively. CS-wnt4a expression level was significantly up-regulated in the gonads after exposure to high temperature. The level of methylation of the CS-wnt4a first exon was negatively correlated with the expression of CS-wnt4a. The branch-site model suggested that vertebrate wnt4a differed significantly from that of wnt4b, and that the selective pressures differed between ancestral aquatic and terrestrial organisms. Two positively selected sites were found in the ancestral lineages of teleost fish, but none in the ancestral lineages of mammals. One positively selected site was located on the α-helices of the 3D structure, the other on the random coil. Our results are of value for further study of the function of wnt4 and the mechanism of selection.

High-throughput sequencing analyses of XX genital ridges lacking FOXL2 reveal DMRT1 up-regulation before SOX9 expression during the sex-reversal process in goats

FOXL2 loss of function in goats leads to the early transdifferentiation of ovaries into testes, then to the full sex reversal of XX homozygous mutants. By contrast, Foxl2 loss of function in mice induces an arrest of follicle formation after birth, followed by complete female sterility. In order to understand the molecular role of FOXL2 during ovarian differentiation in the goat species, putative FOXL2 target genes were determined at the earliest stage of gonadal sex-specific differentiation by comparing the mRNA profiles of XX gonads expressing the FOXL2 protein or not. Of these 163 deregulated genes, around two-thirds corresponded to testicular genes that were up-regulated when FOXL2 was absent, and only 19 represented female-associated genes, down-regulated in the absence of FOXL2. FOXL2 should therefore be viewed as an antitestis gene rather than as a female-promoting gene. In particular, the key testis-determining gene DMRT1 was found to be up-regulated ahead of SOX9, thus suggesting in goats that SOX9 primary up-regulation may require DMRT1. Overall, our results equated to FOXL2 being an antitestis gene, allowing us to propose an alternative model for the sex-determination process in goats that differs slightly from that demonstrated in mice.

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

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

Organogenesis of the ovary: a comparative review on vertebrate ovary formation

The general perspective of ovary organogenesis is that the ovary is the default organ which develops in the absence of testis-promoting factors. Testis formation, on the other hand, is a male-specific event promoted by active components that override the default ovarian process. However, when comparing the sex determination mechanism among different vertebrate species, it is apparent that this default view of ovary formation can only be applied to mammals. In species such as reptiles and birds, ovary formation is an active process stimulated by estrogen. Remnants of this estrogen-dominant pathway are still present in marsupials, a close relative of eutherian mammals, like humans and mice. Although initial formation of the mammalian ovary has become strictly regulated by genetic components and is therefore independent of estrogen, the feminizing effect of estrogen regains its command in adult ovaries. When estrogen production, or its signaling, is inhibited, transdifferentiation of ovarian tissues to testis structures occur in adult females. Taken together, these observations prompt us to reconsider the process of ovary organogenesis as the default organ and question if testis development is actually the default pathway.

Mammalian ovary differentiation - a focus on female meiosis

Over the past 50 years, the ovary development has been subject of fewer studies as compare to the male pathway. Nevertheless due to the advancement of genetics, mouse ES cells and the development of genetic models, studies of ovarian differentiation was boosted. This review emphasizes some of new progresses in the research field of the mammalian ovary differentiation that have occurred in recent years with focuses of the period around prophase I of meiosis and of recent roles of small non-RNAs in the ovarian gene expression.

The transcription factor FOXL2: at the crossroads of ovarian physiology and pathology

FOXL2 is a gene encoding a forkhead transcription factor. Its mutations or misregulation have been shown to cause the blepharophimosis-ptosis-epicanthus inversus (BPES) syndrome and more recently have been associated with the development of Ovarian Granulosa Cell Tumors (OGCT). BPES is a genetic disorder involving mild craniofacial abnormalities often associated with premature ovarian failure. OGCTs are endocrine malignancies, accounting for 2-5% of ovarian cancers, the treatment of which is still challenging. In this review we summarize recent data concerning FOXL2 transcriptional targets and molecular partners, its post-translational modifications, its mutations and its involvement in newly discovered pathophysiological processes. In the ovary, FOXL2 is involved in the regulation of cholesterol and steroid metabolism, apoptosis, reactive oxygen species detoxification and cell proliferation. Interestingly, one of the main roles of FOXL2 is also to preserve the identity of ovarian granulosa cells even at the adult stage and to prevent their transdifferentiation into Sertoli-like cells. All these recent advances indicate that FOXL2 is central to ovarian development and maintenance. The elucidation of the impact of FOXL2 germinal and somatic mutations will allow a better understanding of the pathogenesis of BPES and of OGCTs.

Natural exceptions to normal gonad development in mammals

Gonads are the only organs with 2 possible developmental pathways, testis or ovary. A consequence of this unique feature is that mutations in genes controlling gonad development give rise not only to gonadal malformation or dysfunction but also to frequent cases of sex reversal, including XY females, XX males and intersexes. Most of our current knowledge on mammalian sex determination, the genetic process by which the gonadal primordia are committed to differentiate as either testes or ovaries, has derived mainly from the study of sex-reversed mice obtained by direct genetic manipulation. However, there are also numerous cases of natural exceptions to normal gonad development which have been described in a variety of mammals, including both domestic and wild species. Here, we review the most relevant cases of: (1) natural, non-induced sex reversal and intersexuality described in laboratory rodents, including Sxr and B6-Y(DOM) mice; (2) sex reversal in domestic animals, including freemartinism in bovids and pigs, XX sex reversal in pigs, goats and dogs, XY sex reversal in the horse, and sex chromosome chimerism and sex reversal in the cat, and (3) sex reversal in wild mammals, including the generalised true hermaphroditism described in talpid moles, XY sex reversal in Akodon, Microtus and Dicrostonyx species, males lacking a Y chromosome and SRY in Ellobius lutescens, the X* chromosome of Myopus schisticolor, and sex chromosome mosaicism and X0 females in Microtus oregoni. These studies are necessary to elucidate particular aspects of mammalian gonad development in some instances and to understand how the genetic mechanisms controlling gonad development have evolved.

Loss of R-spondin1 and Foxl2 amplifies female-to-male sex reversal in XX mice

In vertebrates, 2 main genetic pathways have been shown to regulate ovarian development. Indeed, a loss of function mutations in Rspo1 and Foxl2 promote partial female-to-male sex reversal. In mice, it has been shown that the secreted protein RSPO1 is involved in ovarian differentiation and the transcription factor FOXL2 is required for follicular formation. Here, we analysed the potential interactions between these 2 genetic pathways and have shown that while Rspo1 expression seems to be independent of Foxl2 up-regulation, Foxl2 expression partly depends of Rspo1 signalisation. This suggests that different Foxl2-positive somatic cell lineages exist within the ovaries. In addition, a combination of both mutated genes in XX Foxl2(-/-)/Rspo1(-/-) gonads promotes sex reversal, detectable at earlier stages than in XX Rspo1(-/-) mutants. Ectopic development of the steroidogenic lineage is more pronounced in XX Foxl2(-/-)/Rspo1(-/-) gonads than in XX Rspo1(-/-) embryos, suggesting that Foxl2 is involved in preventing ectopic steroidogenesis in foetal ovaries.

Telling the story of XX sex reversal in the goat: highlighting the sex-crossroad in domestic mammals

The conditions for sex reversal in vertebrate species have been studied extensively and have highlighted numerous key factors involved in sex differentiation. We review here the history of the development of knowledge, referring to one example of complete female-to-male XX sex reversal associated with a polled phenotype in the goat. The results and hypotheses concerning this polled intersex syndrome (PIS) are then presented, firstly with respect to the transcriptional regulatory effects of the PIS mutation, and secondly regarding the role of the main ovarian-differentiating factor in this PIS locus, the FOXL2 gene.

Polled Intersex Syndrome with urethral atresia in a goat

A 5-day-old hornless goat was referred with dysuria since birth. The scrotum was absent, and a small penis-like structure was seen below the perineal raphe. On the laparotomy, the testicles were found near the inguinal ring- and attached to a uterus-like structure. On histological analysis, the uterus-like structure was blind-end. Germ cells were absent in the testis. The karyotype of this goat was 60, XX and the SRY gene was absent. The goat was homozygous for a DNA deletion responsible for the Polled Intersex Syndrome (PIS). To the authors' knowledge, this is the first report as the clinical case of the PIS-/- goat with urethral atresia.

Physical, behavioral, endocrinologic, and cytogenetic evaluation of two Standardbred racehorses competing as mares with an intersex condition and high postrace serum testosterone concentrations

CASE DESCRIPTION

2 Standardbred racehorses that had been winning races while competing as mares underwent postrace drug testing and had serum testosterone concentrations above the acceptable limit for female racehorses.

CLINICAL FINDINGS

Initial physical examinations by the referring veterinarian revealed ambiguous external genitalia and suspected intra-abdominally located testes leading to a preliminary diagnosis of male pseudohermaphroditism. Horses were referred for further evaluation of sex. Physical examination of the external genitalia confirmed the findings of the referring veterinarian. Transrectal palpation and ultrasonography revealed gonads with an ultrasonographic appearance of testes. On cytogenetic analysis, both horses were determined to have a 64,XY karyotype and 8 intact Y chromosome markers and 5 SRY gene markers, which were indicative of a genetic male and confirmed an intersex condition. Additionally, both horses had some male-type behavior and endocrinologic findings consistent with those of sexually intact males.

TREATMENT AND OUTCOME

Taken together, these findings confirmed that both horses were male pseudohermaphrodites. Both horses returned to racing competition as males.

CLINICAL RELEVANCE

As of October 1, 2008, the Pennsylvania Horse and Harness Racing Commissions implemented a postrace drug testing policy that included analysis of blood samples for anabolic and androgenic steroids and set maximum allowable concentrations of testosterone for racing geldings and females. Within 8 months of initiation of this drug testing policy, the 2 horses of this report were identified as having an intersex condition. This raises the possibility that intersex conditions may be more common in racing Standardbreds than was previously suspected.

Building pathways for ovary organogenesis in the mouse embryo

Despite its significant role in oocyte generation and hormone production in adulthood, the ovary, with regard to its formation, has received little attention compared to its male counterpart, the testis. With the exception of germ cells, which undergo a female-specific pattern of meiosis, morphological changes in the fetal ovary are subtle. Over the past 40 years, a number of hypotheses have been proposed for the organogenesis of the mammalian ovary. It was not until the turn of the millennium, thanks to the advancement of genetic and genomic approaches, that pathways for ovary organogenesis that consist of positive and negative regulators have started to emerge. Through the action of secreted factors (R-spondin1, WNT4, and follistatin) and transcription regulators (beta-catenin and FOXL2), the developmental fate of the somatic cells is directed toward ovarian, while testicular components are suppressed. In this chapter, we review the history of studying ovary organogenesis in mammals and present the most recent discoveries using the mouse as the model organism.

Steroid signaling and temperature-dependent sex determination-Reviewing the evidence for early action of estrogen during ovarian determination in turtles

The developmental processes underlying gonadal differentiation are conserved across vertebrates, but the triggers initiating these trajectories are extremely variable. The red-eared slider turtle (Trachemys scripta elegans) exhibits temperature-dependent sex determination (TSD), a system where incubation temperature during a temperature-sensitive period of development determines offspring sex. However, gonadal sex is sensitive to both temperature and hormones during this period-particularly estrogen. We present a model for temperature-based differences in aromatase expression as a critical step in ovarian determination. Localized estrogen production facilitates ovarian development while inhibiting male-specific gene expression. At male-producing temperatures aromatase is not upregulated, thereby allowing testis development.

FOXL2: at the crossroads of female sex determination and ovarian function

The gene FOXL2 encodes a forkhead transcription factor whose mutations are responsible for the blepharophimosis ptosis epicanthus-inversus syndrome. This genetic disorder is characterized by eyelid and mild craniofacial abnormalities often in association with premature ovarian failure. FOXL2 orthologs are found throughout the animal phylum and its sequence is highly conserved in vertebrates. FOXL2 is one of the earliest ovarian markers and it offers, alongwith its targets, a model to study ovarian development and function. In this chapter, we review recent data concemingits mutations, targets, regulation and functions. Studies of the cellular consequences of FOXL2 mutations seem to indicate that aggregation is a common pathogenic mechanism. However, no reliable genotype/phenotype correlation has been established to predict the exact impact of point mutations in the coding region of FOXL2. FOXL2 has been suggested to be involved in the regulation of cholesterol homeostasis, steroid metabolism, apoptosis, reactive oxygen species detoxification and inflammation processes. Interestingly, all these processes are not equally affected by FOXL2 mutations. The elucidation of the impact of the FOXL2 function in the ovary will allow a better understanding of normal ovarian development and function as well as the pathogenic mechanisms underlying BPES.

Sex-specific roles of beta-catenin in mouse gonadal development

Sexually dimorphic development of the gonads is controlled by positive and negative regulators produced by somatic cells. Many Wnt ligands, including ones that signal via the canonical beta-catenin pathway, are expressed in fetal gonads. beta-catenin, a key transcriptional regulator of the canonical Wnt pathway and an element of the cell adhesion complex, is essential for various aspects of embryogenesis. To study the involvement of beta-catenin in sex determination, we ablated beta-catenin specifically in the SF1-positive population of somatic cells. Although beta-catenin was present in gonads of both sexes, it was necessary only for ovarian differentiation but dispensable for testis development. Loss of beta-catenin in fetal testes did not affect Sertoli cell differentiation, testis morphogenesis or masculinization of the embryos. However, we observed molecular and morphological defects in ovaries lacking beta-catenin, including formation of testis-specific coelomic vessel, appearance of androgen-producing adrenal-like cells and loss of female germ cells. These phenotypes were strikingly similar to those found in the R-spondin1 (Rspo1) and Wnt4 knockout ovaries. In the absence of beta-catenin, expression of Wnt4 was down-regulated while that of Rspo1 was not affected, placing beta-catenin as a component in between Rspo1 and Wnt4. Our results demonstrate that beta-catenin is responsible for transducing sex-specific signals in the SF1-positive somatic cell population during mouse gonadal development.

Molecular cloning and gene expression of Foxl2 in the frog Rana rugosa

Foxl2 is a transcription factor that plays a crucial role in the regulation of the early development of the female gonad in mammals and fish. However, little is known regarding its role in ovarian differentiation in amphibians. In this study, we isolated a Foxl2 cDNA from the ovary of the frog Rana rugosa and Xenopuslaevis and examined its expression during gonadal sex differentiation in R. rugosa. Alignment of known Foxl2 sequences from vertebrates showed high identity of the Foxl2 open reading frame and protein sequences, in particular the forkhead domain and C-terminal region, with other vertebrate sequences. Among different adult tissues, Foxl2 was expressed at its highest level in the ovary. Real-time RT-PCR analysis showed that Foxl2 expression was sexually dimorphic during gonadal sex differentiation in R. rugosa. In addition, Foxl2, which was detected immunochemically in somatic cells surrounding oocytes in the ovary, promoted R. rugosaCYP19 transcription in luciferase promoter assays conducted in A6 cells. We also found by FISH analysis that Foxl2 was an autosomal gene. Altogether, these results suggest that Foxl2 probably plays a very important role in ovarian differentiation of R. rugosa by possibly regulating CYP19 expression. The factor that up-regulates Foxl2 expression in female gonads still remains to be identified.