Sexual cell-fate reprogramming in the ovary by DMRT1

Natural sex change in fish

Sexual fate can no longer be considered an irreversible deterministic process that once established during early embryonic development, plays out unchanged across an organism's life. Rather, it appears to be a dynamic process, with sexual phenotype determined through an ongoing battle for supremacy between antagonistic male and female developmental pathways. That sexual fate is not final and is actively regulated via the suppression or activation of opposing genetic networks creates the potential for flexibility in sexual phenotype in adulthood. Such flexibility is seen in many fish, where sex change is a usual and adaptive part of the life cycle. Many fish are sequential hermaphrodites, beginning life as one sex and changing sometime later to the other. Sequential hermaphrodites include species capable of female-to-male (protogynous), male-to-female (protandrous), or bidirectional (serial) sex change. These natural forms of sex change involve coordinated transformations across multiple biological systems, including behavioral, anatomical, neuroendocrine and molecular axes. Here we review the biological processes underlying this amazing transformation, focusing particularly on the molecular aspects, where new genomic technologies are beginning to help us understand how sex change is initiated and regulated at the molecular level.

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.

Genetic predisposition to uterine leiomyoma is determined by loci for genitourinary development and genome stability

Uterine leiomyomas (ULs) are benign tumors that are a major burden to women’s health. A genome-wide association study on 15,453 UL cases and 392,628 controls was performed, followed by replication of the genomic risk in six cohorts. Effects of the risk alleles were evaluated in view of molecular and clinical characteristics. 22 loci displayed a genome-wide significant association. The likely predisposition genes could be grouped to two biological processes. Genes involved in genome stability were represented by TERT, TERC, OBFC1 - highlighting the role of telomere maintenance - TP53 and ATM. Genes involved in genitourinary development, WNT4, WT1, SALL1, MED12, ESR1, GREB1, FOXO1, DMRT1 and uterine stem cell marker antigen CD44, formed another strong subgroup. The combined risk contributed by the 22 loci was associated with MED12 mutation-positive tumors. The findings link genes for uterine development and genetic stability to leiomyomagenesis, and in part explain the more frequent occurrence of UL in women of African origin.

Fibroids – also known as uterine leiomyomas, or myomas – are a very common form of benign tumor that grows in the muscle wall of the uterus. As many as 70% of women develop fibroids in their lifetime. About a fifth of women report symptoms including severe pain, heavy bleeding during periods and complications in pregnancy. In the United States, the cost of treating fibroids is estimated to be $34 billion each year.

Despite the prevalence of fibroids in women, there are few treatments available. Drugs to target them have limited effect and often an invasive procedure such as surgery is needed to remove the tumors. However, a better understanding of the genetics of fibroids could lead to a way to develop better treatment options.

Välimäki, Kuisma et al. used a genome-wide association study to seek out DNA variations that are more common in people with fibroids. Using data from the UK Biobank, the genomes of over 15,000 women with fibroids were analyzed against a control population of over 392,000 individuals. The analysis revealed 22 regions of the genome that were associated with fibroids. These regions included genes that may well contribute to fibroid development, such as the gene TP53, which influences the stability of the genome, and ESR1, which codes for a receptor for estrogen – a hormone known to play a role in the growth of fibroids. Variation in a set of genes known to control development of the female reproductive organs was also identified in women with fibroids.

The findings are the result of the largest genome-wide association study on fibroids, revealing a set of genes that could influence the development of fibroids. Studying these genes could lead to more effective drug development to treat fibroids. Revealing this group of genes could also help to identify women at high risk of developing fibroids and help to prevent or manage the condition.

Sex determination and maintenance: the role of DMRT1 and FOXL2

In many species, including mammals, sex determination is genetically based. The sex chromosomes that individuals carry determine sex identity. Although the genetic base of phenotypic sex is determined at the moment of fertilization, the development of testes or ovaries in the bipotential early gonads takes place during embryogenesis. During development, sex determination depends upon very few critical genes. When one of these key genes functions inappropriately, sex reversal may happen. Consequently, an individual's sex phenotype may not necessarily be consistent with the sex chromosomes that are present. For some time, it has been assumed that once the fetal choice is made between male and female in mammals, the gonadal sex identity of an individual remains stable. However, recent studies in mice have provided evidence that it is possible for the gonadal sex phenotype to be switched even in adulthood. These studies have shown that two key genes, doublesex and mad-3 related transcription factor 1 (Dmrt1) and forkhead box L2 (Foxl2), function in a Yin and Yang relationship to maintain the fates of testes or ovaries in adult mammals, and that mutations in either gene might have a dramatic effect on gonadal phenotype. Thus, adult gonad maintenance in addition to fetal sex determination may both be important for the fertility.

Yes-associated protein and WW-containing transcription regulator 1 regulate the expression of sex-determining genes in Sertoli cells, but their inactivation does not cause sex reversal

Yes-associated protein (YAP) and WW-containing transcription regulator 1 (WWTR1) are two functionally redundant transcriptional regulators that are downstream effectors of the Hippo signaling pathway, and that act as major regulators of cell growth and differentiation. To elucidate their role in Sertoli cells, primary Sertoli cell culture from Yapflox/flox; Wwtr1flox/flox animals were infected with a Cre recombinase-expressing adenovirus. Concomitant inactivation of Yap and Wwtr1 resulted in a decrease in the mRNA levels of the male sex differentiation genes Dhh, Dmrt1, Sox9, and Wt1, whereas those of genes involved in female differentiation (Wnt4, Rspo1, and Foxl2) were induced. SOX9, FOXL2, and WNT4 proteins were regulated in the same manner as their mRNAs in response to loss of YAP and WWTR1. To further characterize the role of YAP and WWTR1 in Sertoli cells, we generated a mouse model (Yapflox/flox; Wwtr1flox/flox; Amhcre/+) in which Yap and Wwtr1 were conditionally deleted in Sertoli cells. An increase in the number of apoptotic cells was observed in the seminiferous tubules of 4 dpp mutant mice, leading to a reduction in testis weights and a decrease in the number of Sertoli cells in adult animals. Gene expression analyses of testes from 4 dpp Yapflox/flox; Wwtr1flox/flox; Amhcre/+ mice showed that Sertoli cell differentiation is initially altered, as Dhh, Dmrt1, and Sox9 mRNA levels were downregulated, whereas Wnt4 mRNA levels were increased. However, expression of these genes was not changed in older animals. Together, these results suggest a novel role of the Hippo signaling pathway in the mechanisms of sex differentiation.

Loss of DMRT1 gene in a Mos 45,XY,-9[8]/46,XY,r(9)[29]/47,XY,+idic r(9)× 2[1]/46,XY,idic r(9)[1]/46,XY[1] female presenting with short stature

Background

A 46,XY sex reversal syndrome is characterized by discordant genetic and phenotypic sex, leading to normal external female genitalia, undeveloped gonads and presence of Müllerian structures in an otherwise 46,XY individual. Chromosome 9pter aberrations, such as ring chromosome have been reported to cause 46,XY disorders of sex development (DSD), due to involvement of DMRT1 gene located at the 9p24.3 region.

Case presentation

This study presents a unique case of a 12-year-old female with mos 46,XY, (r)9[31]/45,XY,-9[9] karyotype, presenting with intellectual disability and short stature, mimicking Turner syndrome. Re-karyotyping was performed using standard GTL-banding technique. Further cytogenetic study using standard metaphase fluorescent in situ hybridization (FISH) technique was applied to cultured lymphocytes from peripheral blood, hybridized using green control probe specific to 9q21 loci, and red DMRT1 probe specific to 9p24.3 loci. Cytogenetics and FISH analysis revealed mos 45,XY,-9[8]/46,XY,r(9)[29]/47,XY,+idic r(9)× 2[1]/46,XY,idic r(9)[1]/46,XY[1] and haploinsufficiency of DMRT1 gene in most cells. CGH array revealed a deletion around 1.25 Mb at 9p24.3 loci [arr 9p24.3(204,193-1,457,665)× 1] and three duplications around 13 Mb [9p24.3p22.3(1,477,660-14,506,754)× 3] near the breakage point that formed the ring chromosome 9.

Conclusions

The clinical presentation of the subject that mimics Turner syndrome highlights the importance of cytogenetic analysis to detect the possibility of ring chromosome 9. Sex reversal due to haploinsufficiency of DMRT1 gene in ring chromosome 9 structures is exceedingly rare with only a handful of cases ever reported. This finding further highlights the importance of DMRT1 gene in sex determination and differentiation in males. More research is required to pinpoint the exact mechanism that underlies sex reversal caused by DMRT1 haploinsufficiency.

Sox5 is involved in germ-cell regulation and sex determination in medaka following co-option of nested transposable elements

Background

Sex determination relies on a hierarchically structured network of genes, and is one of the most plastic processes in evolution. The evolution of sex-determining genes within a network, by neo- or sub-functionalization, also requires the regulatory landscape to be rewired to accommodate these novel gene functions. We previously showed that in medaka fish, the regulatory landscape of the master male-determining gene dmrt1bY underwent a profound rearrangement, concomitantly with acquiring a dominant position within the sex-determining network. This rewiring was brought about by the exaptation of a transposable element (TE) called Izanagi, which is co-opted to act as a silencer to turn off the dmrt1bY gene after it performed its function in sex determination.

Results

We now show that a second TE, Rex1, has been incorporated into Izanagi. The insertion of Rex1 brought in a preformed regulatory element for the transcription factor Sox5, which here functions in establishing the temporal and cell-type-specific expression pattern of dmrt1bY. Mutant analysis demonstrates the importance of Sox5 in the gonadal development of medaka, and possibly in mice, in a dmrt1bY-independent manner. Moreover, Sox5 medaka mutants have complete female-to-male sex reversal.

Conclusions

Our work reveals an unexpected complexity in TE-mediated transcriptional rewiring, with the exaptation of a second TE into a network already rewired by a TE. We also show a dual role for Sox5 during sex determination: first, as an evolutionarily conserved regulator of germ-cell number in medaka, and second, by de novo regulation of dmrt1 transcriptional activity during primary sex determination due to exaptation of the Rex1 transposable element.

Electronic supplementary material

The online version of this article (10.1186/s12915-018-0485-8) contains supplementary material, which is available to authorized users.

Expression and cellular localization of double sex and mab-3 related transcription factor 1 in testes of postnatal Small-Tail Han sheep at different developmental stages

Double sex and mab-3 related transcription factor 1 (Dmrt1), an evolutionarily conserved gene, is a sex-related gene expressed in male gonads, that is involved in the regulation of sex differentiation, testicular development and reproductive function maintenance. Until now, functional studies on the Dmrt1 gene in sheep (Ovis aries) have been lacking. In this study, testis, heart, liver, spleen, lung, kidney and longissimus dorsi muscle tissues were collected from Small-Tail Han sheep at 0, 2, 5, 12 and 24months after birth (mab). Dmrt1 expression and cellular localization were detected in various testicular tissues by quantitative real time PCR (qRT-PCR), western blot and immunohistochemistry methods. The morphological structures of testicular tissues at different developmental stages were observed by hematoxylin & eosin (HE) staining. The Dmrt1 mRNA expression levels in 12 and 24 mab sheep were significantly higher than those in 0 and 2 mab sheep (P<0.05), and Dmrt1 protein expression showed a similar trend. The qRT-PCR results in various tissues at 12 mab showed that Dmrt1 mRNA was predominantly expressed in testes. Immunohistochemical staining in testes at different developmental stages showed that Dmrt1 protein immunoreactive responses were mainly localized in Sertoli cells and gonocytes at 0, 2 and 5 mab, while they were localized in spermatocytes, sperm cells and some spermatogonia and Sertoli cells at 12 and 24 mab. We speculate that the Dmrt1 gene plays a vital role in postnatal sheep spermatogenesis, perhaps by regulating the maturation and functional maintenance of Sertoli cells, the proliferation and differentiation of gonocytes in prepubertal sheep testes, and the mitosis and meiosis of germ cells in adult sheep, but the specific mechanisms underlying these phenomena must be further studied and verified.

ABBREVIATIONS

In mammalian foetal testes, SOX9 regulates expression of its target genes by binding to genomic regions with conserved signatures

In mammalian embryonic gonads, SOX9 is required for the determination of Sertoli cells that orchestrate testis morphogenesis. To identify genetic networks directly regulated by SOX9, we combined analysis of SOX9-bound chromatin regions from murine and bovine foetal testes with sequencing of RNA samples from mouse testes lacking Sox9. We found that SOX9 controls a conserved genetic programme that involves most of the sex-determining genes. In foetal testes, SOX9 modulates both transcription and directly or indirectly sex-specific differential splicing of its target genes through binding to genomic regions with sequence motifs that are conserved among mammals and that we called ‘Sertoli Cell Signature’ (SCS). The SCS is characterized by a precise organization of binding motifs for the Sertoli cell reprogramming factors SOX9, GATA4 and DMRT1. As SOX9 biological role in mammalian gonads is to determine Sertoli cells, we correlated this genomic signature with the presence of SOX9 on chromatin in foetal testes, therefore equating this signature to a genomic bar code of the fate of foetal Sertoli cells. Starting from the hypothesis that nuclear factors that bind to genomic regions with SCS could functionally interact with SOX9, we identified TRIM28 as a new SOX9 partner in foetal testes.

Regulation of mitosis-meiosis transition by the ubiquitin ligase β-TrCP in male germ cells

The mitosis-meiosis transition is essential for spermatogenesis. Specific and timely downregulation of the transcription factor DMRT1, and consequent induction of Stra8 expression, is required for this process in mammals, but the molecular mechanism has remained unclear. Here, we show that β-TrCP, the substrate recognition component of an E3 ubiquitin ligase complex, targets DMRT1 for degradation and thereby controls the mitosis-meiosis transition in mouse male germ cells. Conditional inactivation of β-TrCP2 in male germ cells of β-TrCP1 knockout mice resulted in sterility due to a lack of mature sperm. The β-TrCP-deficient male germ cells did not enter meiosis, but instead underwent apoptosis. The induction of Stra8 expression was also attenuated in association with the accumulation of DMRT1 at the Stra8 promoter in β-TrCP-deficient testes. DMRT1 contains a consensus β-TrCP degron sequence that was found to bind β-TrCP. Overexpression of β-TrCP induced the ubiquitylation and degradation of DMRT1. Heterozygous deletion of Dmrt1 in β-TrCP-deficient spermatogonia increased meiotic cells with a concomitant reduction of apoptosis. Collectively, our data indicate that β-TrCP regulates the transition from mitosis to meiosis in male germ cells by targeting DMRT1 for degradation.

DMRT proteins and coordination of mammalian spermatogenesis

DMRT genes encode a deeply conserved family of transcription factors that share a unique DNA binding motif, the DM domain. DMRTs regulate development in a broad variety of metazoans and they appear to have controlled sexual differentiation for hundreds of millions of years. In mice, starting during embryonic development, three Dmrt genes act sequentially to help establish and maintain spermatogenesis. Dmrt1 has notably diverse functions that include repressing pluripotency genes and promoting mitotic arrest in embryonic germ cells, reactivating prospermatogonia perinatally, establishing and maintaining spermatogonial stem cells (SSCs), promoting spermatogonial differentiation, and controlling the mitosis/meiosis switch. Dmrt6 acts in differentiating spermatogonia to coordinate an orderly exit from the mitotic/spermatogonial program and allow proper timing of entry to the meiotic/spermatocyte program. Finally, Dmrt7 takes over during the first meiotic prophase to help choreograph a transition in histone modifications that maintains transcriptional silencing of the sex chromosomes. The combined action of these three Dmrt genes helps ensure robust and sustainable spermatogenesis.

Environmental influences on ovarian dysgenesis - developmental windows sensitive to chemical exposures

A woman's reproductive health and ability to have children directly affect numerous aspects of her life, from personal well-being and socioeconomic standing, to morbidity and lifespan. In turn, reproductive health depends on the development of correctly functioning ovaries, a process that starts early during fetal life. Early disruption to ovarian programming can have long-lasting consequences, potentially manifesting as disease much later in adulthood. A growing body of evidence suggests that exposure to chemicals early in life, including endocrine-disrupting chemicals, can cause a range of disorders later in life, such as those described in the ovarian dysgenesis syndrome hypothesis. In this Review, we discuss four specific time windows during which the ovary is particularly sensitive to disruption by exogenous insults: gonadal sex determination, meiotic division, follicle assembly and the first wave of follicle recruitment. To date, most evidence points towards the germ cell lineage being the most vulnerable to chemical exposure, particularly meiotic division and follicle assembly. Environmental chemicals and pharmaceuticals, such as bisphenols or mild analgesics (including paracetamol), can also affect the somatic cell lineages. This Review summarizes our current knowledge pertaining to environmental chemicals and pharmaceuticals, and their potential contributions to the development of ovarian dysgenesis syndrome. We also highlight knowledge gaps that need addressing to safeguard female reproductive health.

Retinoic acid signaling is dispensable for somatic development and function in the mammalian ovary

Retinoic acid (RA) is a potent inducer of cell differentiation and plays an essential role in sex-specific germ cell development in the mammalian gonad. RA is essential for male gametogenesis and hence fertility. However, RA can also disrupt sexual cell fate in somatic cells of the testis, promoting transdifferentiation of male Sertoli cells to female granulosa-like cells when the male sexual regulator Dmrt1 is absent. The feminizing ability of RA in the Dmrt1 mutant somatic testis suggests that RA might normally play a role in somatic cell differentiation or cell fate maintenance in the ovary. To test for this possibility we disrupted RA signaling in somatic cells of the early fetal ovary using three genetic strategies and one pharmaceutical approach. We found that deleting all three RA receptors (RARs) in the XX somatic gonad at the time of sex determination did not significantly affect ovarian differentiation, follicle development, or female fertility. Transcriptome analysis of adult triple mutant ovaries revealed remarkably little effect on gene expression in the absence of somatic RAR function. Likewise, deletion of three RA synthesis enzymes (Aldh1a1-3) at the time of sex determination did not masculinize the ovary. A dominant-negative RAR transgene altered granulosa cell proliferation, likely due to interference with a non-RA signaling pathway, but did not prevent granulosa cell specification and oogenesis or abolish fertility. Finally, culture of fetal XX gonads with an RAR antagonist blocked germ cell meiotic initiation but did not disrupt sex-biased gene expression. We conclude that RA signaling, although crucial in the ovary for meiotic initiation, is not required for granulosa cell specification, differentiation, or reproductive function.

Leveraging Online Resources to Prioritize Candidate Genes for Functional Analyses: Using the Fetal Testis as a Test Case

With each new microarray or RNA-seq experiment, massive quantities of transcriptomic information are generated with the purpose to produce a list of candidate genes for functional analyses. Yet an effective strategy remains elusive to prioritize the genes on these candidate lists. In this review, we outline a prioritizing strategy by taking a step back from the bench and leveraging the rich range of public databases. This in silico approach provides an economical, less biased, and more effective solution. We discuss the publicly available online resources that can be used to answer a range of questions about a gene. Is the gene of interest expressed in the system of interest (using expression databases)? Where else is this gene expressed (using added-value transcriptomic resources)? What pathways and processes is the gene involved in (using enriched gene pathway analysis and mouse knockout databases)? Is this gene correlated with human diseases (using human disease variant databases)? Using mouse fetal testis as an example, our strategies identified 298 genes annotated as expressed in the fetal testis. We cross-referenced these genes to existing microarray data and narrowed the list down to cell-type-specific candidates (35 for Sertoli cells, 11 for Leydig cells, and 25 for germ cells). Our strategies can be customized so that they allow researchers to effectively and confidently prioritize genes for functional analysis.

Dmrt1 is necessary for male sexual development in zebrafish

The dmrt1 (doublesex and mab-3 related transcription factor 1) gene is a key regulator of sex determination and/or gonadal sex differentiation across metazoan animals. This is unusual given that sex determination genes are typically not well conserved. The mechanisms by which zebrafish sex is determined have remained elusive due to the lack of sex chromosomes and the complex polygenic nature of sex determination in domesticated strains. To investigate the role of dmrt1 in zebrafish sex determination and gonad development, we isolated mutations disrupting this gene. We found that the majority of dmrt1 mutant fish develop as fertile females suggesting a complete male-to-female sex reversal in mutant animals that would have otherwise developed as males. A small percentage of mutant animals became males, but were sterile and displayed testicular dysgenesis. Therefore zebrafish dmrt1 functions in male sex determination and testis development. Mutant males had aberrant gonadal development at the onset of gonadal sex-differentiation, displaying reduced oocyte apoptosis followed by development of intersex gonads and failed testis morphogenesis and spermatogenesis. By contrast, female ovaries developed normally. We found that Dmrt1 is necessary for normal transcriptional regulation of the amh (anti-Müllerian hormone) and foxl2 (forkhead box L2) genes, which are thought to be important for male or female sexual development respectively. Interestingly, we identified one dmrt1 mutant allele that co-operates with a linked segregation distorter locus to generate an apparent XY sex determination mechanism. We conclude that dmrt1 is dispensable for ovary development but necessary for testis development in zebrafish, and that dmrt1 promotes male development by transcriptionally regulating male and female genes as has been described in other animals. Furthermore, the strong sex-ratio bias caused by dmrt1 reduction-of-function points to potential mechanisms through which sex chromosomes may evolve.

CRISPR/Cas9-mediated simultaneous knockout of Dmrt1 and Dmrt3 does not recapitulate the 46,XY gonadal dysgenesis observed in 9p24.3 deletion patients

DM domain transcription factors play important roles in sexual development in a wide variety of species from invertebrate to humans. Among seven mammalian family members of DM domain transcription factors, DMRT1 has been studied in mouse and human for its conserved role in male gonadal identity. Chromosomal deletion of 9p24.3, the region in which DMRT1 is located, is associated with 46,XY gonadal dysgenesis. Dmrt1 knockout (KO) mice also showed male-to-female gonadal reprogramming. However, the phenotype of Dmrt1 KO mouse appears only after birth while 46,XY gonadal dysgenesis occurs during the developmental phase, and the cause behind this difference remained unknown. We hypothesized that in human the function of other DMRT genes clustered with DMRT1, namely DMRT3, might also be impaired by the chromosomal deletion, which leads to the gonadal dysgenesis phenotype. Thus, simultaneous loss of multiple DM domain genes in mice could have a more severe impact on gonadal development. To address this issue, we generated double KO mice for Dmrt1 and Dmrt3 via the CRISPR/Cas9 system. Comparing adult and neonatal testes of single and double KO mice, we found that loss of Dmrt1 or Dmrt3, or both, does not have apparent effect on male gonadal formation during embryonic development. Our study demonstrated that the discrepancy between human with 9p24.3 deletion and Dmrt1 KO mouse could not be explained by the simultaneous loss of Dmrt3 gene. CRISPR/Cas9 is a versatile and straightforward approach to elucidate the questions that were otherwise difficult to address with conventional methods.

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We have generated Dmrt1 KO, Dmrt3 KO and Dmrt1/3 DKO mice via the CRISPR/Cas9 system.

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.CRISPR/Cas9-mediated gene KO could generate 3 KO lines via single microinjection.

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Double KO of Dmrt1 and Dmrt3 could not recapitulate human 9p24.3 deletion symptom.

Normal Levels of Sox9 Expression in the Developing Mouse Testis Depend on the TES/TESCO Enhancer, but This Does Not Act Alone

During mouse sex determination, transient expression of the Y-linked gene Sry up-regulates its direct target gene Sox9, via a 3.2 kb testis specific enhancer of Sox9 (TES), which includes a core 1.4 kb element, TESCO. SOX9 activity leads to differentiation of Sertoli cells, rather than granulosa cells from the bipotential supporting cell precursor lineage. Here, we present functional analysis of TES/TESCO, using CRISPR/Cas9 genome editing in mice. Deletion of TESCO or TES reduced Sox9 expression levels in XY fetal gonads to 60 or 45% respectively relative to wild type gonads, and reduced expression of the SOX9 target Amh. Although human patients heterozygous for null mutations in SOX9, which are assumed to have 50% of normal expression, often show XY female sex reversal, mice deleted for one copy of Sox9 do not. Consistent with this, we did not observe sex reversal in either TESCO-/- or TES-/- XY embryos or adult mice. However, embryos carrying both a conditional Sox9 null allele and the TES deletion developed ovotestes. Quantitative analysis of these revealed levels of 23% expression of Sox9 compared to wild type, and a significant increase in the expression of the granulosa cell marker Foxl2. This indicates that the threshold in mice where sex reversal begins to be seen is about half that of the ~50% levels predicted in humans. Our results demonstrate that TES/TESCO is a crucial enhancer regulating Sox9 expression in the gonad, but point to the existence of additional enhancers that act redundantly.

Bending Genders: The Biology of Natural Sex Change in Fish

Sexual fate is no longer seen as an irreversible deterministic switch set during early embryonic development but as an ongoing battle for primacy between male and female developmental trajectories. That sexual fate is not final and must be actively maintained via continuous suppression of the opposing sexual network creates the potential for flexibility into adulthood. In many fishes, sexuality is not only extremely plastic, but sex change is a usual and adaptive part of the life cycle. Sequential hermaphrodites begin life as one sex, changing sometime later to the other, and include species capable of protandrous (male-to-female), protogynous (female-to-male), or serial (bidirectional) sex change. Natural sex change involves coordinated transformations across multiple biological systems, including behavioural, anatomical, neuroendocrine, and molecular axes. We here review the biological processes underlying this amazing transformation, focussing particularly on its molecular basis, which remains poorly understood, but where new genomic technologies are significantly advancing our understanding of how sex change is initiated and progressed at the molecular level. Knowledge of how a usually committed developmental process remains plastic in sequentially hermaphroditic fishes is relevant to understanding the evolution and functioning of sexual developmental systems in vertebrates generally, as well as pathologies of sexual development in humans.

Sex Change in Clownfish: Molecular Insights from Transcriptome Analysis

Sequential hermaphroditism is a unique reproductive strategy among teleosts that is displayed mainly in fish species living in the coral reef environment. The reproductive biology of hermaphrodites has long been intriguing; however, very little is known about the molecular pathways underlying their sex change. Here, we provide the first de novo transcriptome analyses of a hermaphrodite teleost´s undergoing sex change in its natural environment. Our study has examined relative gene expression across multiple groups-rather than just two contrasting conditions- and has allowed us to explore the differential expression patterns throughout the whole process. Our analysis has highlighted the rapid and complex genomic response of the brain associated with sex change, which is subsequently transmitted to the gonads, identifying a large number of candidate genes, some well-known and some novel, involved in the process. The present study provides strong evidence of the importance of the sex steroidogenic machinery during sex change in clownfish, with the aromatase gene playing a central role, both in the brain and the gonad. This work constitutes the first genome-wide study in a social sex-changing species and provides insights into the genetic mechanism governing social sex change and gonadal restructuring in protandrous hermaphrodites.

Mechanistic study of chlordecone-induced endocrine disruption: Based on an adverse outcome pathway network

The adverse outcome pathway (AOP) framework could be helpful for chemical risk assessment and mechanistic research. The aim of the present study was to unravel the mechanism of chlordecone-induced endocrine disruption by illustrating the main molecular initiating event (MIE)/perturbations responsible for the observed effects. In silico simulations were performed to predict the MIE(s), and the results pointed to agonistic interaction with estrogen receptors (ERα, ERβ), androgen receptor (AR), cytochrome P450 (CYP19A) by chlordecone. In vivo endocrine disruptions were evaluated in rare minnow (Gobiocypris rarus) exposed to 0.01, 0.1, 1 and 10 μg L(-1) chlordecone from 2 h post-fertilization until sexually mature. In the females, increases of vitellogenin (vtg) mRNA levels in liver and gonad, plasma estradiol (E2), testosterone (T) and E2/T, and renalsomatic index confirmed the role of agonism of ER and CYP19A as MIEs, but the decreased gonadosomatic index, degenerated ovaries as well as the feed-forward response pointed to other potential but important MIEs and corresponding AOPs. In the males, increased E2/T ratio, increased testis vtg mRNA levels and occurrence of intersex confirmed the roles of agonism of ERα and CYP19A as main MIEs in chlordecone-induced endocrine disruptions. Our results also fetches out the limit of AOPs in predicting the adverse outcomes and explaining the mechanism of chemicals at present, thus reflected a critical need for expanding AOPs and AOP network before using it in chemical risk assessment.

Sexual plasticity: A fishy tale

Teleost fish exhibit remarkably diverse and plastic patterns of sexual development. One of the most fascinating modes of plasticity is functional sex change, which is widespread in marine fish including species of commercial importance; however, the regulatory mechanisms remain elusive. In this review, we explore such sexual plasticity in fish, using the bluehead wrasse (Thalassoma bifasciatum) as the primary model. Synthesizing current knowledge, we propose that cortisol and key neurochemicals modulate gonadotropin releasing hormone and luteinizing hormone signaling to promote socially controlled sex change in protogynous fish. Future large-scale genomic analyses and systematic comparisons among species, combined with manipulation studies, will likely uncover the common and unique pathways governing this astonishing transformation. Revealing the molecular and neuroendocrine mechanisms underlying sex change in fish will greatly enhance our understanding of vertebrate sex determination and differentiation as well as phenotypic plasticity in response to environmental influences. Mol. Reprod. Dev. 84: 171-194, 2017. © 2016 Wiley Periodicals, Inc.

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

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

Sox9 and Sox8 protect the adult testis from male-to-female genetic reprogramming and complete degeneration

The new concept of mammalian sex maintenance establishes that particular key genes must remain active in the differentiated gonads to avoid genetic sex reprogramming, as described in adult ovaries after Foxl2 ablation. Dmrt1 plays a similar role in postnatal testes, but the mechanism of adult testis maintenance remains mostly unknown. Sox9 and Sox8 are required for postnatal male fertility, but their role in the adult testis has not been investigated. Here we show that after ablation of Sox9 in Sertoli cells of adult, fertile Sox8(-/-) mice, testis-to-ovary genetic reprogramming occurs and Sertoli cells transdifferentiate into granulosa-like cells. The process of testis regression culminates in complete degeneration of the seminiferous tubules, which become acellular, empty spaces among the extant Leydig cells. DMRT1 protein only remains in non-mutant cells, showing that SOX9/8 maintain Dmrt1 expression in the adult testis. Also, Sox9/8 warrant testis integrity by controlling the expression of structural proteins and protecting Sertoli cells from early apoptosis. Concluding, this study shows that, in addition to its crucial role in testis development, Sox9, together with Sox8 and coordinately with Dmrt1, also controls adult testis maintenance.

Primary sex determination of placental mammals: a modelling study uncovers dynamical developmental constraints in the formation of Sertoli and granulosa cells

BACKGROUND

Primary sex determination in placental mammals is a very well studied developmental process. Here, we aim to investigate the currently established scenario and to assess its adequacy to fully recover the observed phenotypes, in the wild type and perturbed situations. Computational modelling allows clarifying network dynamics, elucidating crucial temporal constrains as well as interplay between core regulatory modules.

RESULTS

Relying on a comprehensive revision of the literature, we define a logical model that integrates the current knowledge of the regulatory network controlling this developmental process. Our analysis indicates the necessity for some genes to operate at distinct functional thresholds and for specific developmental conditions to ensure the reproducibility of the sexual pathways followed by bi-potential gonads developing into either testes or ovaries. Our model thus allows studying the dynamics of wild type and mutant XX and XY gonads. Furthermore, the model analysis reveals that the gonad sexual fate results from the operation of two sub-networks associated respectively with an initiation and a maintenance phases. At the core of the process is the resolution of two connected feedback loops: the mutual inhibition of Sox9 and ß-catenin at the initiation phase, which in turn affects the mutual inhibition between Dmrt1 and Foxl2, at the maintenance phase. Three developmental signals related to the temporal activity of those sub-networks are required: a signal that determines Sry activation, marking the beginning of the initiation phase, and two further signals that define the transition from the initiation to the maintenance phases, by inhibiting the Wnt4 signalling pathway on the one hand, and by activating Foxl2 on the other hand.

CONCLUSIONS

Our model reproduces a wide range of experimental data reported for the development of wild type and mutant gonads. It also provides a formal support to crucial aspects of the gonad sexual development and predicts gonadal phenotypes for mutations not tested yet.

Identification and characterization of novel and conserved microRNAs in several tissues of the Chinese rare minnow (Gobiocypris rarus) based on illumina deep sequencing technology

BACKGROUND

MicroRNAs (miRNAs), which comprise a large family of endogenous small non-coding RNA molecules, play important roles in the regulation of gene expression in various biological processes. The Chinese rare minnow (Gobiocypris rarus) is a Chinese native fish species and is used extensively as an experimental fish in China; however, relevant biological data, especially miRNA transcriptome data, have not been well documented. To discover conserved and potential novel miRNAs in Chinese rare minnows, a pool of equal amounts of RNA obtained from 6 different adult rare minnow tissues (brain, eye, gill, liver, muscle and heart) was sequenced using illumina deep sequencing technology.

RESULTS

In the present study, 26,930,553 raw reads, representing 2,118,439 unique high-quality reads, were obtained from the pooled small RNA library. Using bioinformatics analysis, 352 conserved and 112 novel Chinese rare minnow miRNAs were first discovered and characterized in this study. Moreover, we found extensive sequence variations (isomiRs) in rare minnow miRNAs, including internal miRNA isomiRs and terminal isomiRs at both the 5' and 3' ends and nucleotide variants. Six conserved and 4 novel miRNAs were selected and validated in 6 different adult rare minnow tissues using quantitative real-time PCR (qPCR). The results showed that miR-30a, miR-30b, and Novel-37 are ubiquitously expressed in a variety of tissues. miR-16a, miR-9, miR-125b, miR-34a, and Novel-69 were predominantly expressed in the brain. Novel-115 and Novel-7 were highly expressed in gills, but were relatively weakly expressed in other tissues. These results provided the expression patterns of miRNA genes in Chinese rare minnow. Finally, based on bioinformatics predictions, we mainly found that Novel-94 and Novel-1b-5p were simultaneously targeted to the 3'UTR of Dmrt1, which controls sex determination and/or sexual differentiation in a variety of metazoans at different sites. Novel-29b targeted the 3'UTR of Foxl2, which is involved in the maintenance of ovarian function and the transcriptional regulation of gonadal differentiation-related genes. Novel-62 and Novel-53 targeted the 3'UTR of ERbeta1 and ERbeta2 (which regulate the transcription of target genes), respectively.

CONCLUSIONS

Rare minnow is a widely used model for assessing the risk of environmental pollution in China. Identifying and characterizing rare minnow miRNA genes is necessary to discover the biological function of miRNAs and to screen for new molecule biomarkers to assess the risk of environmental pollution in the future.

The Modulatable Stem Cell Niche: Tissue Interactions during Hair and Feather Follicle Regeneration

Hair and feathers are unique because (1) their stem cells are contained within a follicle structure, (2) they undergo cyclic regeneration repetitively throughout life, (3) regeneration occurs physiologically in healthy individuals and (4) regeneration is also induced in response to injury. Precise control of this cyclic regeneration process is essential for maintaining the homeostasis of living organisms. While stem cells are regulated by the intra-follicle-adjacent micro-environmental niche, this niche is also modulated dynamically by extra-follicular macro-environmental signals, allowing stem cells to adapt to a larger changing environment and physiological needs. Here we review several examples of macro-environments that communicate with the follicles: intradermal adipose tissue, innate immune system, sex hormones, aging, circadian rhythm and seasonal rhythms. Related diseases are also discussed. Unveiling the mechanisms of how stem cell niches are modulated provides clues for regenerative medicine. Given that stem cells are hard to manipulate, focusing translational therapeutic applications at the environments appears to be a more practical approach.

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

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

Molecular mechanisms associated with 46,XX disorders of sex development

In the female gonad, distinct signalling pathways activate ovarian differentiation while repressing the formation of testes. Human disorders of sex development (DSDs), such as 46,XX DSDs, can arise when this signalling is aberrant. Here we review the current understanding of the genetic mechanisms that control gonadal development, with particular emphasis on those that drive or inhibit ovarian differentiation. We discuss how disruption to these molecular pathways can lead to 46,XX disorders of ovarian development. Finally, we look at recently characterized novel genes and pathways that contribute and speculate how advances in technology will aid in further characterization of normal and disrupted human ovarian development.

Chinmo is sufficient to induce male fate in somatic cells of the adult Drosophila ovary

Sexual identity is continuously maintained in specific differentiated cell types long after sex determination occurs during development. In the adult Drosophila testis, the putative transcription factor Chronologically inappropriate morphogenesis (Chinmo) acts with the canonical male sex determinant DoublesexM (Dsx(M)) to maintain the male identity of somatic cyst stem cells and their progeny. Here we find that ectopic expression of chinmo is sufficient to induce a male identity in adult ovarian somatic cells, but it acts through a Dsx(M)-independent mechanism. Conversely, the feminization of the testis somatic stem cell lineage caused by loss of chinmo is enhanced by expression of the canonical female sex determinant Dsx(F), indicating that chinmo acts in parallel with the canonical sex determination pathway to maintain the male identity of testis somatic cells. Consistent with this finding, ectopic expression of female sex determinants in the adult testis disrupts tissue morphology. The miRNA let-7 downregulates chinmo in many contexts, and ectopic expression of let-7 in the adult testis is sufficient to recapitulate the chinmo loss-of-function phenotype, but we find no apparent phenotypes upon removal of let-7 in the adult ovary or testis. Our finding that chinmo is necessary and sufficient to promote a male identity in adult gonadal somatic cells suggests that the sexual identity of somatic cells can be reprogrammed in the adult Drosophila ovary as well as in the testis.

The Gonadal Supporting Cell Lineage and Mammalian Sex Determination: The Differentiation of Sertoli and Granulosa Cells

The supporting cell lineage plays a crucial role in nurturing the development of germ cells in the adult gonad. Sertoli cells in the testis support the progression of spermatogonial stem cells through meiosis to the production of motile spermatozoa. Granulosa cells, meanwhile, are a critical component of the ovarian follicle that produces the mature oocyte. It is a distinctive feature of the embryonic gonad that at least some of the supporting cells are derived from a single sexually bipotential precursor lineage. It is the commitment of this somatic lineage to either the Sertoli or granulosa cell fate that defines sex determination. In this chapter we review what is known about the key molecules responsible for this lineage decision in the developing mammalian gonads, relying primarily on data from studies of mice and humans. We focus on recent advances in our understanding of the mutually antagonistic interactions of testis- and ovary-determining pathways and their complexity as revealed by genetic analyses. For the sake of simplicity, we will deal with supporting cells in testis and ovary development in separate sections, but numerous points of contact exist between these accounts of gonadogenesis in male and female embryos, primarily due to the aforementioned mutual antagonisms. The final section will offer a brief synthesis of these organ-specific overviews and a summary of the key themes that emerge in this review of supporting cell differentiation in mammalian sex determination.

Zebrafish Germ Cell Tumors

Germ cell tumors (GCTs) are malignant cancers that arise from embryonic precursors known as Primordial Germ Cells. GCTs occur in neonates, children, adolescents and young adults and can occur in the testis, the ovary or extragonadal sites. Because GCTs arise from pluripotent cells, the tumors can exhibit a wide range of different histologies. Current cisplatin-based combination therapies cures most patients, however at the cost of significant toxicity to normal tissues. While GWAS studies and genomic analysis of human GCTs have uncovered somatic mutations and loci that might confer tumor susceptibility, little is still known about the exact mechanisms that drive tumor development, and animal models that faithfully recapitulate all the different GCT subtypes are lacking. Here, we summarize current understanding of germline development in humans and zebrafish, describe the biology of human germ cell tumors, and discuss progress and prospects for zebrafish GCT models that may contribute to better understanding of human GCTs.

Differentiation of Fetal Male Germline and Gonadal Progenitor Cells Is Disrupted in Organ Cultures Containing Knockout Serum Replacement

Germ cells occupy a unique place in development through their requirement to maintain underlying totipotency while producing highly differentiated gametes. This is reflected in the expression of key regulators of pluripotency in the fetal germline and the ability of these cells to form pluripotent stem cells and germ cell tumors. Culture of whole fetal testes, including germ cells, provides a key model for studying gonad and germline development, but it is critical that such models mimic physiological development as closely as possible. We aimed to determine the effects of differing culture conditions, including serum-free and serum-containing conditions, on fetal germ cell and testis development. We tested a commonly used model that employs knockout serum replacement (KSR) to provide more defined culture conditions than media containing fetal bovine serum (FBS). In FBS conditions, cell cycle parameters in germ and Sertoli cells closely resembled normal development. In contrast, KSR significantly inhibited male germ cell entry into mitotic arrest, a key milestone in male germline development. Moreover, KSR disrupted molecular control of cell cycle and inhibited the transcription of a range of male germ cell differentiation markers. In the somatic compartment, KSR stimulated proliferation and inhibited differentiation in Sertoli cells. These data demonstrate that KSR substantially alters germ and somatic cell differentiation in fetal testis culture and should not be used to replicate normal gonadal development. In contrast, basal media with or without serum support germ and supporting cell differentiation and cell cycle dynamics that are in line with in vivo characteristics.

Plasticity of gene-regulatory networks controlling sex determination: of masters, slaves, usual suspects, newcomers, and usurpators

Sexual dimorphism is one of the most pervasive and diverse features of animal morphology, physiology, and behavior. Despite the generality of the phenomenon itself, the mechanisms controlling how sex is determined differ considerably among various organismic groups, have evolved repeatedly and independently, and the underlying molecular pathways can change quickly during evolution. Even within closely related groups of organisms for which the development of gonads on the morphological, histological, and cell biological level is undistinguishable, the molecular control and the regulation of the factors involved in sex determination and gonad differentiation can be substantially different. The biological meaning of the high molecular plasticity of an otherwise common developmental program is unknown. While comparative studies suggest that the downstream effectors of sex-determining pathways tend to be more stable than the triggering mechanisms at the top, it is still unclear how conserved the downstream networks are and how all components work together. After many years of stasis, when the molecular basis of sex determination was amenable only in the few classical model organisms (fly, worm, mouse), recently, sex-determining genes from several animal species have been identified and new studies have elucidated some novel regulatory interactions and biological functions of the downstream network, particularly in vertebrates. These data have considerably changed our classical perception of a simple linear developmental cascade that makes the decision for the embryo to develop as male or female, and how it evolves.

An ancient protein-DNA interaction underlying metazoan sex determination

DMRT transcription factors are deeply conserved regulators of metazoan sexual development. They share the DM DNA-binding domain, a unique intertwined double zinc-binding module followed by a C-terminal recognition helix, which binds a pseudopalindromic target DNA. Here we show that DMRT proteins use a unique binding interaction, inserting two adjacent antiparallel recognition helices into a widened DNA major groove to make base-specific contacts. Versatility in how specific base contacts are made allows human DMRT1 to use multiple DNA binding modes (tetramer, trimer and dimer). Chromatin immunoprecipitation with exonuclease treatment (ChIP-exo) indicates that multiple DNA binding modes also are used in vivo. We show that mutations affecting residues crucial for DNA recognition are associated with an intersex phenotype in flies and with male-to-female sex reversal in humans. Our results illuminate an ancient molecular interaction underlying much of metazoan sexual development.