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

Reconstituted ovaries self-assemble without an ovarian surface epithelium

Three-dimensional (3D) stem cell models of the ovary have the potential to benefit women's reproductive health research. One such model, the reconstituted ovary (rOvary) self-assembles with pluripotent stem cell-derived germ cells creating a 3D ovarian mimic competent to support the differentiation of functional oocytes inside follicles. In this study, we evaluated the cellular composition of the rOvary revealing the capacity to generate multiple follicles surrounded by NR2F2+ stroma cells. However, the rOvary does not develop a surface epithelium, the source of second-wave pre-granulosa cells, or steroidogenic theca. Therefore, the rOvary models represent the self-assembly of activated follicles in a pre-pubertal ovary poised but not yet competent for hormone production.

From Enrico Sertoli to freemartinism: the many phases of the master testis-determining cell†

Sertoli cells, first identified in the adult testis by Enrico Sertoli in the mid-nineteenth century, are known for their role in fostering male germ cell differentiation and production of mature sperm. It was not until the late twentieth century with the discovery of the testis-determining gene SRY that Sertoli cells' new function as the master regulator of testis formation and maleness was unveiled. Fetal Sertoli cells facilitate the establishment of seminiferous cords, induce appearance of androgen-producing Leydig cells, and cause regression of the female reproductive tracts. Originally thought be a terminally differentiated cell type, adult Sertoli cells, at least in the mouse, retain their plasticity and ability to transdifferentiate into the ovarian counterpart, granulosa cells. In this review, we capture the many phases of Sertoli cell differentiation from their fate specification in fetal life to fate maintenance in adulthood. We also introduce the discovery of a new phase of fetal Sertoli cell differentiation via autocrine/paracrine factors with the freemartin characteristics. There remains much to learn about this intriguing cell type that lay the foundation for the maleness.

Es-β-CATENIN affects the hemolymph-testes barrier in Eriocheir sinensis by disrupting cell junctions and cytoskeleton

β-CATENIN is an evolutionarily conserved multifunctional molecule that maintains cell adhesion as a cell junction protein to safeguard the integrity of the mammalian blood-testes barrier, and also regulates cell proliferation and apoptosis as a key signaling molecule in the WNT/β-CATENIN signaling pathway. In the crustacean Eriocheir sinensis, Es-β-CATENIN has been shown to be involved in spermatogenesis, but the testes of E. sinensis have large and well-defined structural differences from those of mammals, and the impact of Es-β-CATENIN in them is still unknown. In the present study, we found that Es-β-CATENIN, Es-α-CATENIN and Es-ZO-1 interact differently in the testes of the crab compared to mammals. In addition, defective Es-β-CATENIN resulted in increased Es-α-CATENIN protein expression levels, distorted and deformed F-ACTIN, and disturbed localization of Es-α-CATENIN and Es-ZO-1, leading to loss of hemolymph-testes barrier integrity and impaired sperm release. In addition to this, we also performed the first molecular cloning and bioinformatics analysis of Es-AXIN in the WNT/β-CATENIN pathway to exclude the effect of the WNT/β-CATENIN pathway on the cytoskeleton. In conclusion, Es-β-CATENIN participates in maintaining the hemolymph-testes barrier in the spermatogenesis of E. sinensis.

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.

Deciphering Sex-Specific Differentiation of Human Fetal Gonads: Insight From Experimental Models

Sex-specific gonadal differentiation is initiated by the expression of SRY in male foetuses. This promotes a signalling pathway directing testicular development, while in female foetuses the absence of SRY and expression of pro-ovarian factors promote ovarian development. Importantly, in addition to the initiation of a sex-specific signalling cascade the opposite pathway is simultaneously inhibited. The somatic cell populations within the gonads dictates this differentiation as well as the development of secondary sex characteristics via secretion of endocrine factors and steroid hormones. Opposing pathways SOX9/FGF9 (testis) and WNT4/RSPO1 (ovary) controls the development and differentiation of the bipotential mouse gonad and even though sex-specific gonadal differentiation is largely considered to be conserved between mice and humans, recent studies have identified several differences. Hence, the signalling pathways promoting early mouse gonad differentiation cannot be directly transferred to human development thus highlighting the importance of also examining this signalling in human fetal gonads. This review focus on the current understanding of regulatory mechanisms governing human gonadal sex differentiation by combining knowledge of these processes from studies in mice, information from patients with differences of sex development and insight from manipulation of selected signalling pathways in ex vivo culture models of human fetal gonads.

Transcriptome Profiling Reveals Genes Related to Sex Determination and Differentiation in Sugarcane Borer (Chilo sacchariphagus Bojer)

Simple Summary

Chilo sacchariphagus Bojer is an important sugarcane pest globally. The identification of key genes associated with sex determination and differentiation will provide important basic information for the sterile insect technique control strategy. In this study, the comparative transcriptomic analysis of female and male adults revealed sex-biased gene expression, indicating putative genetic elements of sex determination and differentiation in this species.

Abstract

Chilo sacchariphagus Bojer is an important sugarcane pest globally. Along with genetic modification strategies, the sterile insect technique (SIT) has gained more attention as an environment-friendly method for pest control. The identification of key genes associated with sex determination and differentiation will provide important basic information for this control strategy. As such, the transcriptome sequencing of female and male adults was conducted in order to understand the sex-biased gene expression and molecular basis of sex determination and differentiation in this species. A total of 60,429 unigenes were obtained; among them, 34,847 genes were annotated. Furthermore, 11,121 deferentially expressed genes (DEGs) were identified, of which 8986 were male-biased and 2135 were female-biased genes. The male-biased genes were enriched for carbon metabolism, peptidase activity and transmembrane transport, while the female-biased genes were enriched for the cell cycle, DNA replication, and the MAPK signaling pathway. In addition, 102 genes related to sex-determination and differentiation were identified, including the protein toll, ejaculatory bulb-specific protein, fruitless, transformer-2, sex-lethal, beta-Catenin, sox, gata4, beta-tubulin, cytosol aminopeptidase, seminal fluid, and wnt4. Furthermore, transcription factors such as myb, bhlh and homeobox were also found to be potentially related to sex determination and differentiation in this species. Our data provide new insights into the genetic elements associated with sex determination and differentiation in Chilo sacchariphagus, and identified potential candidate genes to develop pest-control strategies.

Jumonji Domain-containing Protein-3 (JMJD3/Kdm6b) Is Critical for Normal Ovarian Function and Female Fertility

In females, reproductive success is dependent on the expression of a number of genes regulated at different levels, one of which is through epigenetic modulation. How a specific epigenetic modification regulates gene expression and their downstream effect on ovarian function are important for understanding the female reproductive process. The trimethylation of histone3 at lysine27 (H3K27me3) is associated with gene repression. JMJD3 (or KDM6b), a jumonji domain-containing histone demethylase specifically catalyzes the demethylation of H3K27me3, that positively influences gene expression. This study reports that the expression of JMJD3 specifically in the ovarian granulosa cells (GCs) is critical for maintaining normal female fertility. Conditional deletion of Jmjd3 in the GCs results in a decreased number of total healthy follicles, disrupted estrous cycle, and increased follicular atresia culminating in subfertility and premature ovarian failure. At the molecular level, the depletion of Jmjd3 and RNA-seq analysis reveal that JMJD3 is essential for mitochondrial function. JMJD3-mediated reduction of H3K27me3 induces the expression of Lif (Leukemia inhibitory factor) and Ctnnb1 (β-catenin), that in turn regulate the expression of key mitochondrial genes critical for the electron transport chain. Moreover, mitochondrial DNA content is also significantly decreased in Jmjd3 null GCs. Additionally, we have uncovered that the expression of Jmjd3 in GCs decreases with age, both in mice and in humans. Thus, in summary, our studies highlight the critical role of JMJD3 in nuclear-mitochondrial genome coordination that is essential for maintaining normal ovarian function and female fertility and underscore a potential role of JMJD3 in female reproductive aging.

Developmental dynamics of sex reprogramming by high incubation temperatures in a dragon lizard

BACKGROUND

In some vertebrate species, gene-environment interactions can determine sex, driving bipotential gonads to differentiate into either ovaries or testes. In the central bearded dragon (Pogona vitticeps), the genetic influence of sex chromosomes (ZZ/ZW) can be overridden by high incubation temperatures, causing ZZ male to female sex reversal. Previous research showed ovotestes, a rare gonadal phenotype with traits of both sexes, develop during sex reversal, leading to the hypothesis that sex reversal relies on high temperature feminisation to outcompete the male genetic cue. To test this, we conducted temperature switching experiments at key developmental stages, and analysed the effect on gonadal phenotypes using histology and transcriptomics.

RESULTS

We found sexual fate is more strongly influenced by the ZZ genotype than temperature. Any exposure to low temperatures (28 °C) caused testes differentiation, whereas sex reversal required longer exposure to high temperatures. We revealed ovotestes exist along a spectrum of femaleness to male-ness at the transcriptional level. We found inter-individual variation in gene expression changes following temperature switches, suggesting both genetic sensitivity to, and the timing and duration of the temperature cue influences sex reversal.

CONCLUSIONS

These findings bring new insights to the mechanisms underlying sex reversal, improving our understanding of thermosensitive sex systems in vertebrates.

John JC, Anderson RA, Rodgers RJ. Analysis of Upstream Regulators, Networks, and Pathways Associated With the Expression Patterns of Polycystic Ovary Syndrome Candidate Genes During Fetal Ovary Development

Polycystic Ovary Syndrome (PCOS) is a multifactorial syndrome with reproductive, endocrine, and metabolic symptoms, affecting about 10% women of reproductive age. Pathogenesis of the syndrome is poorly understood with genetic and fetal origins being the focus of the conundrum. Genetic predisposition of PCOS has been confirmed by candidate gene studies and Genome-Wide Association Studies (GWAS). Recently, the expression of PCOS candidate genes across gestation has been studied in human and bovine fetal ovaries. The current study sought to identify potential upstream regulators and mechanisms associated with PCOS candidate genes. Using RNA sequencing data of bovine fetal ovaries (62-276 days, n = 19), expression of PCOS candidate genes across gestation was analysed using Partek Flow. A supervised heatmap of the expression data of all 24,889 genes across gestation was generated. Most of the PCOS genes fell into one of four clusters according to their expression patterns. Some genes correlated negatively (early genes; C8H9orf3, TOX3, FBN3, GATA4, HMGA2, and DENND1A) and others positively (late genes; FDFT1, LHCGR, AMH, FSHR, ZBTB16, and PLGRKT) with gestational age. Pathways associated with PCOS candidate genes and genes co-expressed with them were determined using Ingenuity pathway analysis (IPA) software as well as DAVID Bioinformatics Resources for KEGG pathway analysis and Gene Ontology databases. Genes expressed in the early cluster were mainly involved in mitochondrial function and oxidative phosphorylation and their upstream regulators included PTEN, ESRRG/A and MYC. Genes in the late cluster were involved in stromal expansion, cholesterol biosynthesis and steroidogenesis and their upstream regulators included TGFB1/2/3, TNF, ERBB2/3, VEGF, INSIG1, POR, and IL25. These findings provide insight into ovarian development of relevance to the origins of PCOS, and suggest that multiple aetiological pathways might exist for the development of PCOS.

Protein kinase A drives paracrine crisis and WNT4-dependent testis tumor in Carney complex

Large-cell calcifying Sertoli cell tumors (LCCSCTs) are among the most frequent lesions occurring in male Carney complex (CNC) patients. Although they constitute a key diagnostic criterion for this rare multiple neoplasia syndrome resulting from inactivating mutations of the tumor suppressor PRKAR1A, leading to unrepressed PKA activity, LCCSCT pathogenesis and origin remain elusive. Mouse models targeting Prkar1a inactivation in all somatic populations or separately in each cell type were generated to decipher the molecular and paracrine networks involved in the induction of CNC testis lesions. We demonstrate that the Prkar1a mutation was required in both stromal and Sertoli cells for the occurrence of LCCSCTs. Integrative analyses comparing transcriptomic, immunohistological data and phenotype of mutant mouse combinations led to the understanding of human LCCSCT pathogenesis and demonstrated PKA-induced paracrine molecular circuits in which the aberrant WNT4 signal production is a limiting step in shaping intratubular lesions and tumor expansion both in a mouse model and in human CNC testes.

Developmental mechanisms of sex differences: from cells to organisms

Male-female differences in many developmental mechanisms lead to the formation of two morphologically and physiologically distinct sexes. Although this is expected for traits with prominent differences between the sexes, such as the gonads, sex-specific processes also contribute to traits without obvious male-female differences, such as the intestine. Here, we review sex differences in developmental mechanisms that operate at several levels of biological complexity - molecular, cellular, organ and organismal - and discuss how these differences influence organ formation, function and whole-body physiology. Together, the examples we highlight show that one simple way to gain a more accurate and comprehensive understanding of animal development is to include both sexes.

Evolutionary Turnover in Wnt Gene Expression but Conservation of Wnt Signaling during Ovary Determination in a TSD Reptile

Temperature-dependent sex determination (TSD) is a well-known characteristic of many reptilian species. However, the molecular processes linking ambient temperature to determination of gonad fate remain hazy. Here, we test the hypothesis that Wnt expression and signaling differ between female- and male-producing temperatures in the snapping turtle Chelydra serpentina. Canonical Wnt signaling involves secretion of glycoproteins called WNTs, which bind to and activate membrane bound receptors that trigger β-catenin stabilization and translocation to the nucleus where β-catenin interacts with TCF/LEF transcription factors to regulate expression of Wnt targets. Non-canonical Wnt signaling occurs via 2 pathways that are independent of β-catenin: one involves intracellular calcium release (the Wnt/Ca2+ pathway), while the other involves activation of RAC1, JNK, and RHOA (the Wnt/planar cell polarity pathway). We screened 20 Wnt genes for differential expression between female- and male-producing temperatures during sex determination in the snapping turtle. Exposure of embryos to the female-producing temperature decreased expression of 7 Wnt genes but increased expression of 2 Wnt genes and Rspo1 relative to embryos at the male-producing temperature. Temperature also regulated expression of putative Wnt target genes in vivo and a canonical Wnt reporter (6x TCF/LEF sites drive H2B-GFP expression) in embryonic gonadal cells in vitro. Results indicate that Wnt signaling was higher at the female- than at the male-producing temperature. Evolutionary analyses of all 20 Wnt genes revealed that thermosensitive Wnts, as opposed to insensitive Wnts, were less likely to show evidence of positive selection and experienced stronger purifying selection within TSD species.

A novel approach to nonsurgical sterilization; application of menadione-modified gonocyte-targeting M13 bacteriophage for germ cell ablation in utero

There remains a compelling need for the development of nonsurgical sterilizing agents to expand the fertility management options for both domestic and feral animal species. We hypothesize that an efficacious sterilization approach would be to selectively ablate nonrenewable cell types that are essential for reproduction, such as the undifferentiated gonocytes within the embryonic gonad. Here, we report a novel strategy to achieve this goal centered on the use of a chemically modified M13 bacteriophage to effect the targeted delivery of menadione, a redox‐cycling naphthoquinone, to mouse gonocytes. Panning of the M13 random peptide ‘phage display library proved effective in the isolation of gonocyte‐specific targeting clones. One such clone was modified via N‐succinimidyl‐S‐acetylthioacetate (SATA) linkage to the N‐terminus of the major PVIII capsid protein. Subsequent deacetylation of the SATA was undertaken to expose a thiol group capable of reacting with menadione through Michael addition. This chemical modification was confirmed using UV spectrophotometry. In proof‐of‐concept experiments we applied the modified ‘phage to primary cultures of fetal germ cells and induced, an approximately, 60% reduction in the viability of the target cell population. These studies pave the way for in vivo application of chemically modified M13 bacteriophage in order to achieve the selective ablation of nonrenewable cell types in the reproductive system, thereby providing a novel nonsurgical approach the regulation of fertility in target species.

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.

Ocean acidification but not hypoxia alters the gonad performance in the thick shell mussel Mytilus coruscus

Ocean acidification and hypoxia have become increasingly severe in coastal areas, and their co-occurrence poses emerging threats to coastal ecosystems. Here, we investigated the combined effects of ocean acidification and hypoxia on the reproductive capacity of the thick-shelled mussel Mytilus coruscus. Our results demonstrated low pH but not low oxygen induced decreased gonadosomatic index (GSI) in mussels. Male mussels had a lower level of sex steroids (estradiol, testosterone, and progesterone) when kept at low pH. Expression of genes related to reproduction were also impacted by low pH with a downregulation of genes involved in gonad development in males (β-catenin and Wnt-7b involved in males) and an upregulation of testosterone synthesis inhibition-related gene (Wnt-4) in females. Overall, our results suggest that ocean acidification has an impact on the gonadal development through an alternation of gene expression and level of steroids while hypoxia had no significant effect.

Dynamics of the transcriptional landscape during human fetal testis and ovary development

STUDY QUESTION

Which transcriptional program triggers sex differentiation in bipotential gonads and downstream cellular events governing fetal testis and ovary development in humans?

SUMMARY ANSWER

The characterization of a dynamically regulated protein-coding and non-coding transcriptional landscape in developing human gonads of both sexes highlights a large number of potential key regulators that show an early sexually dimorphic expression pattern.

WHAT IS KNOWN ALREADY

Gonadal sex differentiation is orchestrated by a sexually dimorphic gene expression program in XX and XY developing fetal gonads. A comprehensive characterization of its non-coding counterpart offers promising perspectives for deciphering the molecular events underpinning gonad development and for a complete understanding of the etiology of disorders of sex development in humans.

STUDY DESIGN, SIZE, DURATION

To further investigate the protein-coding and non-coding transcriptional landscape during gonad differentiation, we used RNA-sequencing (RNA-seq) and characterized the RNA content of human fetal testis (N = 24) and ovaries (N = 24) from 6 to 17 postconceptional week (PCW), a key period in sex determination and gonad development.

PARTICIPANTS/MATERIALS, SETTING, METHODS

First trimester fetuses (6-12 PCW) and second trimester fetuses (13-14 and 17 PCW) were obtained from legally induced normally progressing terminations of pregnancy. Total RNA was extracted from whole human fetal gonads and sequenced as paired-end 2 × 50 base reads. Resulting sequences were mapped to the human genome, allowing for the assembly and quantification of corresponding transcripts.

MAIN RESULTS AND THE ROLE OF CHANCE

This RNA-seq analysis of human fetal testes and ovaries at seven key developmental stages led to the reconstruction of 22 080 transcripts differentially expressed during testicular and/or ovarian development. In addition to 8935 transcripts displaying sex-independent differential expression during gonad development, the comparison of testes and ovaries enabled the discrimination of 13 145 transcripts that show a sexually dimorphic expression profile. The latter include 1479 transcripts differentially expressed as early as 6 PCW, including 39 transcription factors, 40 long non-coding RNAs and 20 novel genes. Despite the use of stringent filtration criteria (expression cut-off of at least 1 fragment per kilobase of exon model per million reads mapped, fold change of at least 2 and false discovery rate adjusted P values of less than <1%), the possibility of assembly artifacts and of false-positive differentially expressed transcripts cannot be fully ruled out.

LARGE-SCALE DATA

Raw data files (fastq) and a searchable table (.xlss) containing information on genomic features and expression data for all refined transcripts have been submitted to the NCBI GEO under accession number GSE116278.

LIMITATIONS, REASONS FOR CAUTION

The intrinsic nature of this bulk analysis, i.e. the sequencing of transcripts from whole gonads, does not allow direct identification of the cellular origin(s) of the transcripts characterized. Potential cellular dilution effects (e.g. as a result of distinct proliferation rates in XX and XY gonads) may account for a few of the expression profiles identified as being sexually dimorphic. Finally, transcriptome alterations that would result from exposure to pre-abortive drugs cannot be completely excluded. Although we demonstrated the high quality of the sorted cell populations used for experimental validations using quantitative RT-PCR, it cannot be totally excluded that some germline expression may correspond to cell contamination by, for example, macrophages.

WIDER IMPLICATIONS OF THE FINDINGS

For the first time, this study has led to the identification of 1000 protein-coding and non-coding candidate genes showing an early, sexually dimorphic, expression pattern that have not previously been associated with sex differentiation. Collectively, these results increase our understanding of gonad development in humans, and contribute significantly to the identification of new candidate genes involved in fetal gonad differentiation. The results also provide a unique resource that may improve our understanding of the fetal origin of testicular and ovarian dysgenesis syndromes, including cryptorchidism and testicular cancers.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the French National Institute of Health and Medical Research (Inserm), the University of Rennes 1, the French School of Public Health (EHESP), the Swiss National Science Foundation [SNF n° CRS115_171007 to B.J.], the French National Research Agency [ANR n° 16-CE14-0017-02 and n° 18-CE14-0038-02 to F.C.], the Medical Research Council [MR/L010011/1 to P.A.F.] and the European Community's Seventh Framework Programme (FP7/2007-2013) [under grant agreement no 212885 to P.A.F.] and from the European Union's Horizon 2020 Research and Innovation Programme [under grant agreement no 825100 to P.A.F. and S.M.G.]. There are no competing interests related to this study.

Immune and vascular contributions to organogenesis of the testis and ovary

Gonad development is a highly regulated process that coordinates cell specification and morphogenesis to produce sex-specific organ structures that are required for fertility, such as testicular seminiferous tubules and ovarian follicles. While sex determination occurs within specialized gonadal supporting cells, sexual differentiation is evident throughout the entire organ, including within the interstitial compartment, which contains immune cells and vasculature. While immune and vascular cells have been traditionally appreciated for their supporting roles during tissue growth and homeostasis, an increasing body of evidence supports the idea that these cell types are critical drivers of sexually dimorphic morphogenesis of the gonad. Myeloid immune cells, such as macrophages, are essential for multiple aspects of gonadogenesis and fertility, including for forming and maintaining gonadal vasculature in both sexes at varying stages of life. While vasculature is long known for supporting organ growth and serving as an export mechanism for gonadal sex steroids in utero, it is also an important component of fetal testicular morphogenesis and differentiation; additionally, it is vital for ovarian corpus luteal function and maintenance of pregnancy. These findings point toward a new paradigm in which immune cells and blood vessels are integral components of sexual differentiation and organogenesis. In this review, we discuss the state of the field regarding the diverse roles of immune and vascular cells during organogenesis of the testis and ovary and highlight outstanding questions in the field that could stimulate new research into these previously underappreciated constituents of the gonad.

R-spondin1 in loach (Misgurnus anguillicaudatus): Identification, characterization, and analysis of its expression patterns and DNA methylation in response to high-temperature stress

With a well-understood function in mammals, R-spondin1 (Rspo1) is an important regulator of ovarian development via the Wnt/β-catenin pathway. Rspo1 deficiency causes retardation of ovarian development in XX fish, and increases Rspo1 function induces femininity and sex reversal in XY fish. In this study, Rspo1 was successfully cloned from loach (Misgurnus anguillicaudatus), and its expression profile was analyzed. The full-length cDNA of Misgurnus anguillicaudatus Rspo1 (MaRspo1) comprised 1322 bp and included an open reading frame (ORF) of 795 bp, which encoded a predicted polypeptide measuring 264 amino acids in length. Phylogenetic and gene structure analyses showed a highly conserved sequence of MaRspo1 (identical to the Rspo1 genes of other species), consisting of an N-terminal signal peptide (SP), two furin-like cysteine-rich domains (FU1 and FU2), a thrombospondin type 1 repeat (TSP1) and a C-terminal region. Real-time PCR revealed the female-biased expression profile of MaRspo1, with the highest expression level among tested tissues detected in ovary. Investigation of MaRspo1 expression levels throughout the early development stage (10-60 days post hatching) under three temperature treatments (25 °C, 28 °C, and 31 °C) revealed significantly differential expression of MaRspo1 among the three temperature groups, with decreased MaRspo1 expression in the high-temperature (31 °C) group. The results of DNA methylation analysis indicated that exposure to high temperature during early development can increase the average promoter methylation level of MaRspo1 in both females and males. Taken together, the results of this study provide the basis for the further investigation of the molecular mechanism of Rspo1 in response to temperature.

Estrogen suppresses SOX9 and activates markers of female development in a human testis-derived cell line

Background

The increasing incidence of reproductive disorders in humans has been attributed to in utero exposure to estrogenic endocrine disruptors. In particular, exposure of the developing testis to exogenous estrogen can negatively impact male reproductive health. To determine how estrogens impact human gonad function, we treated the human testis-derived cell line NT2/D1 with estrogen and examined its impact on SOX9 and the expression of key markers of granulosa (ovarian) and Sertoli (testicular) cell development.

Results

Estrogen successfully activated its cognate receptor (estrogen receptor alpha; ESR1) in NT2/D1 cells. We observed a significant increase in cytoplasmic SOX9 following estrogen treatment. After 48 h of estrogen exposure, mRNA levels of the key Sertoli cell genes SOX9, SRY, AMH, FGF9 and PTGDS were significantly reduced. This was followed by a significant increase in mRNA levels for the key granulosa cell genes FOXL2 and WNT4 after 96 h of estrogen exposure.

Conclusions

These results are consistent with estrogen's effects on marsupial gonads and show that estrogen has a highly conserved impact on gonadal cell fate decisions that has existed in mammals for over 160 million years. This effect of estrogen presents as a potential mechanism contributing to the significant decrease in male fertility and reproductive health reported over recent decades. Given our widespread exposure to estrogenic endocrine disruptors, their effects on SOX9 and Sertoli cell determination could have considerable impact on the adult testis.

Two distinct pathways of pregranulosa cell differentiation support follicle formation in the mouse ovary

This paper improves knowledge of the somatic and germ cells of the developing mouse ovary that assemble into ovarian follicles, by determining cellular gene expression, and tracing lineage relationships. The study covers the last week of fetal development through the first five days of postnatal development. During this time, many critically important processes take place, including sex determination, follicle assembly, and the initial events of meiosis. We report expression differences between pregranulosa cells of wave 1 follicles that function at puberty and wave 2 follicles that sustain fertility. These studies illuminate ovarian somatic cells and provide a resource to study the development, physiology, and evolutionary conservation of mammalian ovarian follicle formation.

We sequenced more than 52,500 single cells from embryonic day 11.5 (E11.5) postembryonic day 5 (P5) gonads and performed lineage tracing to analyze primordial follicles and wave 1 medullar follicles during mouse fetal and perinatal oogenesis. Germ cells clustered into six meiotic substages, as well as dying/nurse cells. Wnt-expressing bipotential precursors already present at E11.5 are followed at each developmental stage by two groups of ovarian pregranulosa (PG) cells. One PG group, bipotential pregranulosa (BPG) cells, derives directly from bipotential precursors, expresses Foxl2 early, and associates with cysts throughout the ovary by E12.5. A second PG group, epithelial pregranulosa (EPG) cells, arises in the ovarian surface epithelium, ingresses cortically by E12.5 or earlier, expresses Lgr5, but delays robust Foxl2 expression until after birth. By E19.5, EPG cells predominate in the cortex and differentiate into granulosa cells of quiescent primordial follicles. In contrast, medullar BPG cells differentiate along a distinct pathway to become wave 1 granulosa cells. Reflecting their separate somatic cellular lineages, second wave follicles were ablated by diptheria toxin treatment of Lgr5-DTR-EGFP mice at E16.5 while first wave follicles developed normally and supported fertility. These studies provide insights into ovarian somatic cells and a resource to study the development, physiology, and evolutionary conservation of mammalian ovarian follicles.

Mouse Gonad Development in the Absence of the Pro-Ovary Factor WNT4 and the Pro-Testis Factor SOX9

The transcription factors SRY and SOX9 and RSPO1/WNT4/β-Catenin signaling act as antagonistic pathways to drive testis and ovary development respectively, from a common gonadal primordium in mouse embryos. In this work, we took advantage of a double knockout mouse model to study gonadal development when Sox9 and Wnt4 are both mutated. We show that the XX gonad mutant for Wnt4 or for both Wnt4 and Sox9 develop as ovotestes, demonstrating that ectopic SOX9 function is not required for the partial female-to-male sex reversal caused by a Wnt4 mutation. Sox9 deletion in XY gonads leads to ovarian development accompanied by ectopic WNT/β-catenin signaling. In XY Sox9 mutant gonads, SRY-positive supporting precursors adopt a female-like identity and develop as pre-granulosa-like cells. This phenotype cannot be fully prevented by the deletion of Wnt4 or Rspo1, indicating that SOX9 is required for the early determination of the male supporting cell identity independently of repressing RSPO1/WNT4/β-Catenin signaling. However, in XY Sox9 Wnt4 double mutant gonads, pre-granulosa cells are not maintained, as they prematurely differentiate as mature granulosa cells and then trans-differentiate into Sertoli-like cells. Together, our results reveal the dynamics of the specific and independent actions of SOX9 and WNT4 during gonadal differentiation: SOX9 is essential in the testis for early specification of male-supporting cells whereas WNT4 functions in the ovary to maintain female-supporting cell identity and inhibit male-specific vascular and steroidogenic cell differentiation.

R-spondin2 signaling is required for oocyte-driven intercellular communication and follicular growth

R-spondin2 (RSPO2) is a member of the R-spondin family, which are secreted activators of the WNT/β-catenin (CTNNB1) signaling pathway. In the mouse postnatal ovary, WNT/CTNNB1 signaling is active in the oocyte and in the neighboring supporting cells, the granulosa cells. Although the role of Rspo2 has been previously studied using in vitro experiments, the results are conflicting and the in vivo ovarian function of Rspo2 remains unclear. In the present study, we found that RSPO2/Rspo2 expression is restricted to the oocyte of developing follicles in both human and mouse ovaries from the beginning of the follicular growth. In mice, genetic deletion of Rspo2 does not impair oocyte growth, but instead prevents cell cycle progression of neighboring granulosa cells, thus resulting in an arrest of follicular growth. We further show this cell cycle arrest to be independent of growth promoting GDF9 signaling, but rather associated with a downregulation of WNT/CTNNB1 signaling in granulosa cells. To confirm the contribution of WNT/CTNNB1 signaling in granulosa cell proliferation, we induced cell type specific deletion of Ctnnb1 postnatally. Strikingly, follicles lacking Ctnnb1 failed to develop beyond the primary stage. These results show that RSPO2 acts in a paracrine manner to sustain granulosa cell proliferation in early developing follicles. Taken together, our data demonstrate that the activation of WNT/CTNNB1 signaling by RSPO2 is essential for oocyte-granulosa cell interactions that drive maturation of the ovarian follicles and eventually female fertility.

Canonical Wnt/β-catenin activity and differential epigenetic marks direct sexually dimorphic regulation of Irx3 and Irx5 in developing mouse gonads

Members of the Iroquois B (IrxB) homeodomain cluster genes, specifically Irx3 and Irx5, are crucial for heart, limb and bone development. Recently, we reported their importance for oocyte and follicle survival within the developing ovary. Irx3 and Irx5 expression begins after sex determination in the ovary but remains absent in the fetal testis. Mutually antagonistic molecular signals ensure ovary versus testis differentiation with canonical Wnt/β-catenin signals paramount for promoting the ovary pathway. Notably, few direct downstream targets have been identified. We report that Wnt/β-catenin signaling directly stimulates Irx3 and Irx5 transcription in the developing ovary. Using in silico analysis of ATAC- and ChIP-Seq databases in conjunction with mouse gonad explant transfection assays, we identified TCF/LEF-binding sequences within two distal enhancers of the IrxB locus that promote β-catenin-responsive ovary expression. Meanwhile, Irx3 and Irx5 transcription is suppressed within the developing testis by the presence of H3K27me3 on these same sites. Thus, we resolved sexually dimorphic regulation of Irx3 and Irx5 via epigenetic and β-catenin transcriptional control where their ovarian presence promotes oocyte and follicle survival vital for future ovarian health.

Retinoic Acid Antagonizes Testis Development in Mice

Mammalian sex determination depends on a complex interplay of signals that promote the bipotential fetal gonad to develop as either a testis or an ovary, but the details are incompletely understood. Here, we investigated whether removal of the signaling molecule retinoic acid (RA) by the degradative enzyme CYP26B1 is necessary for proper development of somatic cells of the testes. Gonadal organ culture experiments suggested that RA promotes expression of some ovarian markers and suppresses expression of some testicular markers, acting downstream of Sox9. XY Cyp26b1-null embryos, in which endogenous RA is not degraded, develop mild ovotestes, but more important, steroidogenesis is impaired and the reproductive tract feminized. Experiments involving purified gonadal cells showed that these effects are independent of germ cells and suggest the direct involvement of the orphan nuclear receptor DAX1. Our results reveal that active removal of endogenous RA is required for normal testis development in the mouse.

Identification of Hc-β-catenin in freshwater mussel Hyriopsis cumingii and its involvement in innate immunity and sex determination

β-catenin is a multifunctional protein that participates in a variety of physiological activities, including immune regulation, sex determination, nervous system development and, cell differentiation. However, the function of β-catenin in freshwater mussel Hyriopsis cumingii remains unclear. Herein, the gene encoding β-catenin from H. cumingii (Hc-β-catenin) was cloned and characterised. The full-length 5544 bp gene includes an open reading frame (ORF) of 2463 bp encoding a putative protein of 820 amino acids residues containing 12 armadillo (ARM) repeats. After injecting H. cumingii with Aeromonas hydrophila or lipopolysaccharides, Hc-β-catenin transcription was induced in hemocytes and gills, and the greatest responses occurred at 24 h after bacterial challenge, confirming an important role in immune responses. Quantitative real-time PCR analysis showed that Hc-β-catenin mRNA was distributed in the gill, foot, liver, kidney, mantle, adductor muscle and gonad of male and female mussels. In gonad, Hc-β-catenin expression was markedly higher in females than males. During the embryonic period, Hc-β-catenin expression was highest at 3 day. In 1-, 2- and 3-year-old mature mussels, Hc-β-catenin expression in female gonad tissue was notably higher than in males. In situ hybridisation revealed a significant hybridisation signal in female gonads, indicating that Hc-β-catenin is a pro-ovarian, anti-testis gene. Our findings demonstrate that Hc-β-catenin is important in immune regulation and sex determination in freshwater mussel.

Genome-wide identification of FOXL2 binding and characterization of FOXL2 feminizing action in the fetal gonads

The identity of the gonads is determined by which fate, ovarian granulosa cell or testicular Sertoli cell, the bipotential somatic cell precursors choose to follow. In most vertebrates, the conserved transcription factor FOXL2 contributes to the fate of granulosa cells. To understand FOXL2 functions during gonad differentiation, we performed genome-wide analysis of FOXL2 chromatin occupancy in fetal ovaries and established a genetic mouse model that forces Foxl2 expression in the fetal testis. When FOXL2 was ectopically expressed in the somatic cell precursors in the fetal testis, FOXL2 was sufficient to repress Sertoli cell differentiation, ultimately resulting in partial testis-to-ovary sex-reversal. Combining genome-wide analysis of FOXL2 binding in the fetal ovary with transcriptomic analyses of our Foxl2 gain-of-function and previously published Foxl2 loss-of-function models, we identified potential pathways responsible for the feminizing action of FOXL2. Finally, comparison of FOXL2 genome-wide occupancy in the fetal ovary with testis-determining factor SOX9 genome-wide occupancy in the fetal testis revealed extensive overlaps, implying that antagonistic signals between FOXL2 and SOX9 occur at the chromatin level.

GSK-3β protects fetal oocytes from premature death via modulating TAp63 expression in mice

Background

Female mammals have a limited reproductive lifespan determined by the size of the primordial follicle pool established perinatally. Over two thirds of fetal oocytes are abolished via programmed cell death during early folliculogenesis. However, the underlying mechanisms governing fetal oocyte attrition remain largely elusive.

Results

Here, we demonstrate that glycogen synthase kinase-3 beta (GSK-3β) is indispensable for fetal oocyte maintenance during meiotic prophase I in mice. In vitro inhibition of GSK-3β activity or in vivo conditional deletion of Gsk-3β in the germline led to a dramatic loss of fetal oocytes via apoptosis, which subsequently resulted in a reduced capacity of the primordial follicle pool. Inhibition of GSK-3β also impeded meiotic progression in fetal oocytes and led to a deficiency in DNA double-strand break (DSB) repair associated with premature upregulation of Tap63, the major genome guardian of the female germline, following GSK-3β inhibition in fetal ovaries. Mechanistically, we demonstrated that aberrant nuclear translocation of β-catenin was responsible for the abnormal expression of TAp63 and global fetal oocyte attrition following GSK-3β inhibition.

Conclusions

In summary, GSK-3β was essential for sustaining fetal oocyte survival and folliculogenesis via fine-tuning the cytoplasmic-nuclear translocation of β-catenin, which in turn modulates timely TAp63 expression during meiotic prophase I in mice. Our study provides a perspective on the physiological regulatory role of DNA damage checkpoint signaling in fetal oocyte guardianship and female fertility.

Electronic supplementary material

The online version of this article (10.1186/s12915-019-0641-9) contains supplementary material, which is available to authorized users.

Oocyte-derived E-cadherin acts as a multiple functional factor maintaining the primordial follicle pool in mice

In mammals, female fecundity is determined by the size of the primordial follicle (PF) pool, which is established during the perinatal period. As a non-renewable resource, the preservation of dormant PFs is crucial for sustaining female reproduction throughout life. Although studies have revealed that several oocyte-derived functional genes and pathways, such as newborn ovary homeobox (NOBOX) and 3-phosphoinositide-dependent protein kinase-1, participate in maintaining the PF pool, our understanding of the underlying molecular mechanisms is still incomplete. Here, we demonstrate that E-cadherin (E-cad) plays a crucial role in the maintenance of PFs in mice. E-cad is specifically localized to the cytomembrane of oocytes in PFs. Knockdown of E-cad in neonatal ovaries resulted in significant PF loss owing to oocyte apoptosis. In addition, the expression pattern of NOBOX is similar to that of E-cad. Knockdown of E-cad resulted in a decreased NOBOX level, whereas overexpression of Nobox partially rescued the follicle loss induced by silencing E-cad. Furthermore, E-cad governed NOBOX expression by regulating the shuttle protein, β-catenin, which acts as a transcriptional co-activator. Notably, E-cad, which is a transmembrane protein expressed in the oocytes, was also responsible for maintaining the PF structure by facilitating cell–cell adhesive contacts with surrounding pregranulosa cells. In conclusion, E-cad in oocytes of PFs plays an indispensable role in the maintenance of the PF pool by facilitating follicular structural stability and regulating NOBOX expression. These findings shed light on the physiology of sustaining female reproduction.

Transcriptomic analysis of mRNA expression and alternative splicing during mouse sex determination

Mammalian sex determination hinges on sexually dimorphic transcriptional programs in developing fetal gonads. A comprehensive view of these programs is crucial for understanding the normal development of fetal testes and ovaries and the etiology of human disorders of sex development (DSDs), many of which remain unexplained. Using strand-specific RNA-sequencing, we characterized the mouse fetal gonadal transcriptome from 10.5 to 13.5 days post coitum, a key time window in sex determination and gonad development. Our dataset benefits from a greater sensitivity, accuracy and dynamic range compared to microarray studies, allows global dynamics and sex-specificity of gene expression to be assessed, and provides a window to non-transcriptional events such as alternative splicing. Spliceomic analysis uncovered female-specific regulation of Lef1 splicing, which may contribute to the enhanced WNT signaling activity in XX gonads. We provide a user-friendly visualization tool for the complete transcriptomic and spliceomic dataset as a resource for the field.

Thermal Response of Epigenetic Genes Informs Turtle Sex Determination with and without Sex Chromosomes

Vertebrate sexual fate can be established by environmental cues (e.g., temperature-dependent sex determination, TSD) or by genetic content (genotypic sex determination, GSD). While methylation is implicated in TSD, the influence of broader epigenetic processes in sexual development remains obscure. Here, we investigated for the first time the embryonic gonadal expression of the genome-wide epigenetic machinery in turtles, including genes and noncoding RNAs (ncRNAs) involved in DNA/histone acetylation, methylation, ubiquitination, phosphorylation, and RNAi. This machinery was active and differentially thermosensitive in TSD versus GSD (ZZ/ZW) turtles. Methylation and histone acetylation genes responded the strongest. The results suggest these working hypotheses: (i) TSD might be mediated by epigenetically controlled hormonal pathways (via acetylation, methylation, and ncRNAs), or by (ii) hormonally controlled epigenetic processes, and (iii) key epigenetic events prior to the canonical thermosensitive period may explain differences between TSD and GSD. Novel epigenetic candidate regulators other than methylation were identified, including previously unknown ncRNAs that could potentially mediate gonadogenesis. These findings illuminate the molecular ecology of reptilian sex determination and permitted hypothesis building to help guide future functional studies on the epigenetic transduction of external cues in TSD versus GSD systems.

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.

Stromal interaction molecule 1 is required for neonatal testicular development in mice

Stromal interaction molecule 1 (STIM1) is a transmembrane endoplasmic reticulum protein, and it serves as a Ca²⁺ sensor and activator of store-operated Ca²⁺ entry (SOCE). We have previously identified STIM1 in the proteome profile of mice neonatal testes, revealing STIM1 to be associated with neonatal testicular development. Here, to further explore the location and function of STIM1 in mice testes, we studied the effect of Stim1 gene knockdown on neonatal testicular development by testicular culture. Our results revealed that STIM1 was primarily located in Sertoli cells. Knockdown of Stim1 gene using morpholino in neonatal testis caused the mislocation of Sertoli cells and loss of germ cells, which were associated with the aberrant reactive oxygen species (ROS) activation, while inhibition of ROS could partly rescue the phenotypes caused by Stim1 gene knockdown. In conclusion, our study suggests that STIM1 can maintain neonatal testicular development by inhibiting ROS activation.

Cellular nucleic acid-binding protein is vital to testis development and spermatogenesis in mice

The cellular nucleic acid-binding protein (CNBP), also known as zinc finger protein 9, is a highly conserved zinc finger protein that is strikingly conserved among vertebrates. Data collected from lower vertebrates showed that CNBP is expressed at high levels and distributed in the testes during spermatogenesis. However, the location and function of CNBP in mammalian testes are not well known. Here, by neonatal mouse testis culture and spermatogonial stem cells (SSC) culture methods, we studied the effect of CNBP knockdown on neonatal testicular development. Our results revealed that CNBP was mainly located in the early germ cells and Sertoli cells. Knockdown of CNBP using morpholino in neonatal testis culture caused disruption of seminiferous tubules, mislocation of Sertoli cells and loss of germ cells, which were associated with the aberrant Wnt/β-catenin pathway activation. However, knockdown of CNBP in SSC culture did not affect the survival of germ cells. In conclusion, our study suggests that CNBP could maintain testicular development by inhibiting the Wnt/β-catenin pathway, particularly by influencing Sertoli cells.

Identification of General Patterns of Sex-Biased Expression in Daphnia, a Genus with Environmental Sex Determination

Daphnia reproduce by cyclic-parthenogenesis, where phases of asexual reproduction are intermitted by sexual production of diapause stages. This life cycle, together with environmental sex determination, allow the comparison of gene expression between genetically identical males and females. We investigated gene expression differences between males and females in four genotypes of Daphnia magna and compared the results with published data on sex-biased gene expression in two other Daphnia species, each representing one of the major phylogenetic clades within the genus. We found that 42% of all annotated genes showed sex-biased expression in D. magna This proportion is similar both to estimates from other Daphnia species as well as from species with genetic sex determination, suggesting that sex-biased expression is not reduced under environmental sex determination. Among 7453 single copy, one-to-one orthologs in the three Daphnia species, 707 consistently showed sex-biased expression and 675 were biased in the same direction in all three species. Hence these genes represent a core-set of genes with consistent sex-differential expression in the genus. A functional analysis identified that several of them are involved in known sex determination pathways. Moreover, 75% were overexpressed in females rather than males, a pattern that appears to be a general feature of sex-biased gene expression in Daphnia.

A transcriptomic comparison of theca and granulosa cells in chicken and cattle follicles reveals ESR2 as a potential regulator of CYP19A1 expression in the theca cells of chicken follicles

Previous studies have shown that theca and granulosa cell layers in follicles do not play the same roles in mammals and birds, especially regarding the synthesis of estrogen. The functions of these two cell types have been well characterized in cattle, but they remain unclear in chickens. To clarify this issue, a comparison of small yellow follicles (SYFs) in chickens and cattle at different follicular development stages was done by weighted gene co-expression network analysis (WGCNA). The modules obtained from WGCNA were used for further identification of the key genes associated with CYP19A1 expression. Module preservation analysis showed high similarity between cow_D (the follicular phase before the LH surge) and chicken_SYF (small yellow follicle between 6 and 8 mm in diameter) datasets, and 10 top hub genes highly associated with CYP19A1 expression in chicken SYFs were identified in each module. A comparison of the transcriptomes of theca and granulosa cells (TCs and GCs) between chicken SYFs and cattle follicles at the differentiation stage, as well as the aforementioned hub genes, revealed that ESR2 is a potential regulator of CYP19A1 expression in the theca cells of chicken SYFs. Furthermore, 197 cell-specific (179 in theca and 18 in granulosa) and 235 cell-biased expressed genes (196 in theca and 39 in granulosa) in chicken small yellow follicles were also identified by transcriptomic comparison of theca and granulosa cells.

Duplication and gene expression patterns of β-catenin in Nile tilapia

β-Catenin, a key transcriptional coactivator of the Wnt pathway, plays an important role in animal embryonic development and organogenesis. In our earlier study, we have reported that two types of β-catenin (β-catenin-1 and β-catenin-2) were ubiquitously expressed in almost all the tissues examined in tilapia. However, the immunolocalization of β-catenin in those tissues, especially in extra-gonadal tissues, remains unclear. In the present study, we further confirm that these two types of β-catenin gene exist only in teleosts and are derived from 3R (third round of genome duplication) by phylogenetic and syntenic analyses. Moreover, the transcriptome analysis conducted in this investigation reveals that two β-catenins exhibited similar expression patterns in seven adult tissues and four key developmental stages of XX and XY gonads. Finally, immunohistochemistry analysis was performed to detect the cell localization of β-catenin. A positive signal of β-catenin was observed in various tissues of tilapia, such as the intestine, liver, kidney, spleen, eye, brain, and gonads. The results of our study indicate that tilapia β-catenin might be involved in the organ development and play some specific functions in biological processes; all these data will provide basic reference for understanding the molecular mechanism of β-catenin in regulating of teleost organogenesis.

MicroRNA dynamics at the onset of primordial germ and somatic cell sex differentiation during mouse embryonic gonad development

In mammals, commitment and specification of germ cell lines involves complex programs that include sex differentiation, control of proliferation, and meiotic initiation. Regulation of these processes is genetically controlled by fine-tuned mechanisms of gene regulation in which microRNAs (miRNAs) are involved. We have characterized, by small-RNA-seq and bioinformatics analyses, the miRNA expression patterns of male and female mouse primordial germ cells (PGCs) and gonadal somatic cells at embryonic stages E11.5, E12.5, and E13.5. Differential expression analyses revealed differences in the regulation of key miRNA clusters such as miR-199-214, miR-182-183-96, and miR-34c-5p, whose targets have defined roles during gonadal sexual determination in both germ and somatic cells. Extensive analyses of miRNA sequences revealed an increase in noncanonical isoforms on PGCs at E12.5 and dramatic changes of 3' isomiR expression and 3' nontemplate nucleotide additions in female PGCs at E13.5. Additionally, RT-qPCR analyses of genes encoding proteins involved in miRNA biogenesis and 3' nucleotide addition uncovered sexually and developmentally specific expression, characterized by the decay of Drosha, Dgcr8, and Xpo5 expression along gonadal development. These results demonstrate that miRNAs, their isomiRs, and miRNA machinery are differentially regulated and participate actively in gonadal sexual differentiation in both PGCs and gonadal somatic cells.

Loss of p300 and CBP disrupts histone acetylation at the mouse Sry promoter and causes XY gonadal sex reversal

CREB-binding protein (CBP, CREBBP, KAT3A) and its closely related paralogue p300 (EP300, KAT3B), together termed p300/CBP, are histone/lysine acetyl-transferases that control gene expression by modifying chromatin-associated proteins. Here, we report roles for both of these chromatin-modifying enzymes in mouse sex determination, the process by which the embryonic gonad develops into a testis or an ovary. By targeting gene ablation to embryonic gonadal somatic cells using an inducible Cre line, we show that gonads lacking either gene exhibit major abnormalities of XY gonad development at 14.5 dpc, including partial sex reversal. Embryos lacking three out of four functional copies of p300/Cbp exhibit complete XY gonadal sex reversal and have greatly reduced expression of the key testis-determining genes Sry and Sox9. An analysis of histone acetylation at the Sry promoter in mutant gonads at 11.5 dpc shows a reduction in levels of the positive histone mark H3K27Ac. Our data suggest a role for CBP/p300 in testis determination mediated by control of histone acetylation at the Sry locus and reveal a novel element in the epigenetic control of Sry and mammalian sex determination. They also suggest possible novel causes of human disorders of sex development (DSD).

β-Catenin directs the transformation of testis Sertoli cells to ovarian granulosa-like cells by inducing Foxl2 expression

Sertoli and granulosa cells are two major types of somatic cells in male and female gonads, respectively. Previous studies have shown that Sertoli and granulosa cells are derived from common progenitor cells and that differentiation of these two cell types is regulated by sex differentiation genes. The signaling pathway including the adhesion and transcription factor Ctnnb1 (cadherin-associated protein, β1, also known as β-catenin) regulates differentiation of granulosa cells in the absence of the transcription factor Sry, and overactivation of β-catenin in the presence of Sry leads to granulosa prior to sex determination. Surprisingly, our previous study found that β-catenin overactivation in Sertoli cells after sex determination can also cause disruption of the testicular cord and aberrant testis development. However, the underlying molecular mechanism was unclear. In this study, we found that constitutive activation of Ctnnb1 in Sertoli cells led to ectopic expression of the granulosa cell-specific marker FOXL2 in testes. Co-staining experiments revealed that FOXL2-positive cells were derived from Sertoli cells, and Sertoli cells were transformed into granulosa-like cells after Ctnnb1 overactivation. Further studies demonstrated that CTNNB1 induced Foxl2 expression by directly binding to transcription factor Tcf/Lef-binding sites in the FOXL2 promoter region. We also found that direct overexpression of Foxl2 decreased the expression of Sertoli cell-specific genes in primary Sertoli cells. Taken together, these results demonstrate that repression of β-catenin (CTNNB1) signaling is required for lineage maintenance of Sertoli cells. Our study provides a new mechanism for Sertoli cell lineage maintenance during gonad development.

Identification and analysis of the β-catenin1 gene in half-smooth tongue sole (Cynoglossus semilaevis)

β-catenin is a key signalling molecule in the canonical Wnt pathway, which plays a role in cell adhesion, embryogenesis and sex determination. However, little is known about its function in teleosts. We cloned and characterized the full-length β-catenin1 gene from half-smooth tongue sole (Cynoglossus semilaevis), which was designated CS-β-catenin1. The CS-β-catenin1 cDNA consists of 2,346 nucleotides and encodes a protein with 782 amino acids. Although CS-β-catenin1 was transcribed in the gonads of both sexes, the level was significantly higher in ovaries compared to testes. Furthermore, the mRNA level of CS-β-catenin1 was significantly upregulated at 160 days and constantly increased until 2 years of age. In situ hybridization revealed that CS-β-catenin1 mRNA was mainly localized in oocyte cells, especially in stage I, II and III oocytes. When CS-β-catenin1 expression was inhibited by injection of quercetin in the ovaries, levels of CS-Figla and CS-foxl2 mRNA were significantly down-regulated, and CS-dmrt1 was up-regulated, which suggested that CS-β-catenin1 is a potential upstream gene of CS-Figla and is involved in the development of the ovaries, i.e., folliculogenesis.

Transcriptomic responses to environmental temperature by turtles with temperature-dependent and genotypic sex determination assessed by RNAseq inform the genetic architecture of embryonic gonadal development

Vertebrate sexual fate is decided primarily by the individual's genotype (GSD), by the environmental temperature during development (TSD), or both. Turtles exhibit TSD and GSD, making them ideal to study the evolution of sex determination. Here we analyze temperature-specific gonadal transcriptomes (RNA-sequencing validated by qPCR) of painted turtles (Chrysemys picta TSD) before and during the thermosensitive period, and at equivalent stages in soft-shell turtles (Apalone spinifera-GSD), to test whether TSD's and GSD's transcriptional circuitry is identical but deployed differently between mechanisms. Our data show that most elements of the mammalian urogenital network are active during turtle gonadogenesis, but their transcription is generally more thermoresponsive in TSD than GSD, and concordant with their sex-specific function in mammals [e.g., upregulation of Amh, Ar, Esr1, Fog2, Gata4, Igf1r, Insr, and Lhx9 at male-producing temperature, and of β-catenin, Foxl2, Aromatase (Cyp19a1), Fst, Nf-kb, Crabp2 at female-producing temperature in Chrysemys]. Notably, antagonistic elements in gonadogenesis (e.g., β-catenin and Insr) were thermosensitive only in TSD early-embryos. Cirbp showed warm-temperature upregulation in both turtles disputing its purported key TSD role. Genes that may convert thermal inputs into sex-specific development (e.g., signaling and hormonal pathways, RNA-binding and heat-shock) were differentially regulated. Jak-Stat, Nf-κB, retinoic-acid, Wnt, and Mapk-signaling (not Akt and Ras-signaling) potentially mediate TSD thermosensitivity. Numerous species-specific ncRNAs (including Xist) were differentially-expressed, mostly upregulated at colder temperatures, as were unannotated loci that constitute novel TSD candidates. Cirbp showed warm-temperature upregulation in both turtles. Consistent transcription between turtles and alligator revealed putatively-critical reptilian TSD elements for male (Sf1, Amh, Amhr2) and female (Crabp2 and Hspb1) gonadogenesis. In conclusion, while preliminary, our data helps illuminate the regulation and evolution of vertebrate sex determination, and contribute genomic resources to guide further research into this fundamental biological process.

Genome-wide identification of regulatory elements in Sertoli cells

A current goal of molecular biology is to identify transcriptional networks that regulate cell differentiation. However, identifying functional gene regulatory elements has been challenging in the context of developing tissues where material is limited and cell types are mixed. To identify regulatory sites during sex determination, we subjected Sertoli cells from mouse fetal testes to DNaseI-seq and ChIP-seq for H3K27ac. DNaseI-seq identified putative regulatory sites around genes enriched in Sertoli and pregranulosa cells; however, active enhancers marked by H3K27ac were enriched proximal to only Sertoli-enriched genes. Sequence analysis identified putative binding sites of known and novel transcription factors likely controlling Sertoli cell differentiation. As a validation of this approach, we identified a novel Sertoli cell enhancer upstream of Wt1, and used it to drive expression of a transgenic reporter in Sertoli cells. This work furthers our understanding of the complex genetic network that underlies sex determination and identifies regions that potentially harbor non-coding mutations underlying disorders of sexual development.

Urban fine particulate matter exposure causes male reproductive injury through destroying blood-testis barrier (BTB) integrity

Blood-testis barrier (BTB) provides a suitable microenvironment for germ cells that is required for spermatogenesis. Exposure to particulate matter (PM) is recognized to occasion male reproductive impairment, but the mechanism of which remains unclear. Male Sprague-Dawley (SD) rats were used to establish animal models with PM_2.5 exposure concentration of 0, 10, and 20mg/kg.b.w. once a day for four weeks. Success rate of mating, sperm quality, epididymal morphology, expressions of spermatogenesis markers, superoxide dismutases (SOD) activity and expression in testicular tissues, and expressions of BTB junction proteins were detected. In addition, in vitro experiments were also performed. After PM_2.5 treatment, reactive oxygen species (ROS) production and apoptosis of Sertoli cells were analyzed. Our results indicated that after PM_2.5 exposure male rats presented inferior uberty and sperm quality, with decreased expressions of spermatogenesis markers, escalated SOD activity and expression levels, and reduced expressions of tight junction, adherens junction, and gap junction proteins in testicular tissues. Meantime, PM_2.5-treated Sertoli cells displayed increased SOD production and apoptosis. PM_2.5 exposure engenders male reproductive function injury through breaking BTB integrity.

Sexual Fate Change of XX Germ Cells Caused by the Deletion of SMAD4 and STRA8 Independent of Somatic Sex Reprogramming

The differential programming of sperm and eggs in gonads is a fundamental topic in reproductive biology. Although the sexual fate of germ cells is believed to be determined by signaling factors from sexually differentiated somatic cells in fetal gonads, the molecular mechanism that determines germ cell fate is poorly understood. Herein, we show that mothers against decapentaplegic homolog 4 (SMAD4) in germ cells is required for female-type differentiation. Germ cells in Smad4-deficient ovaries respond to retinoic acid signaling but fail to undergo meiotic prophase I, which coincides with the weaker expression of genes required for follicular formation, indicating that SMAD4 signaling is essential for oocyte differentiation and meiotic progression. Intriguingly, germline-specific deletion of Smad4 in Stra8-null female germ cells resulted in the up-regulation of genes required for male gonocyte differentiation, including Nanos2 and PLZF, suggesting the initiation of male-type differentiation in ovaries. Moreover, our transcriptome analyses of mutant ovaries revealed that the sex change phenotype is achieved without global gene expression changes in somatic cells. Our results demonstrate that SMAD4 and STRA8 are essential factors that regulate the female fate of germ cells.

Double ablation of SMAD4 and STRA8 causes female-to-male switching of XX germ cells without affecting somatic cell fate. This suggests that SMAD4 and STRA8 are essential intrinsic factors that determine the female fate of germ cells, collaborating to suppress expression of male genes.

Mammalian sex depends on a male-specific gene, sex-determining region Y (SRY), which is located on the Y chromosome. Individuals lacking this gene will develop as female. Accordingly, germ cell fate also changes from male to female in the absence of SRY. Therefore, it is thought that somatic cells regulate germ cells to become sperm or oocytes. However, it is largely unknown what factor is responsible for sexual fate determination in germ cells. In fetal ovaries, retinoic acid (RA) initiates STRA8 expression in germ cells and induces meiosis. Female germ cells without STRA8 fail to enter meiosis but still progress to oogenesis and form oocyte-like cells, indicating that RA is not the regulator of oogenesis. Here, we found that female germ cells lacking both SMAD4 and STRA8 (but not a single knockout) develop as male gonocyte-like cells in ovaries, indicating that these two factors work as female germ cell determinants. To our surprise, the sexual fate switch observed in the double knockout ovary is not accompanied by gene expression changes in somatic cells, revealing the unexpected finding that somatic factors controlled by SRY are dispensable for the upregulation of male-specific genes in germ cells.

Sry and SoxE genes: How they participate in mammalian sex determination and gonadal development?

In mammals, sex determination defines the differentiation of the bipotential genital ridge into either testes or ovaries. Sry, the mammalian Y-chromosomal testis-determining gene, is a master regulator of male sex determination. It acts to switch the undifferentiated genital ridge towards testis development, triggering the adoption of a male fate. Sry initiates a cascade of gene networks through the direct regulation of Sox9 expression and promotes supporting cell differentiation, Leydig cell specification, vasculature formation and testis cord development. In the absence of Sry, alternative genetic cascades, including female sex-determining genes RSPO1, Wnt4/β-catenin and Foxl2, are involved in the formation of female genitalia and the maintenance of female ovarian development. The mutual antagonisms between male and female sex-determining pathways are crucial in not just the initiation but also the maintenance of the somatic sex of the gonad throughout the organism's lifetime. Any imbalances in above sex-determining genes can cause disorders of sex development in humans and mice. In this review, we provide a detailed summary of the expression profiles, biochemical properties and developmental functions of Sry and SoxE genes in embryonic testis development and adult gonadal development. We also briefly summarize the dedicate balances between male and female sex-determining genes in mammalian sex development, with particular highlights on the molecular actions of Sry and Sox9 transcription factors.

From primordial germ cells to primordial follicles: a review and visual representation of early ovarian development in mice

Background

Normal development of reproductive organs is crucial for successful reproduction. In mice the early ovarian developmental process occurs during the embryonic and postnatal period and is regulated through a series of molecular signaling events. Early ovarian development in mice is a seventeen-day process that begins with the rise of six primordial germ cells on embryonic day five (E5) and ends with the formation of primordial follicles on postnatal day two (P2).

Results

We reviewed the current literature and created a visual representation of early ovarian development that depicts the important molecular events and associated phenotypic outcomes based on primary data. The visual representation shows the timeline of key signaling interactions and regulation of protein expression in different cells involved in ovarian development. The major developmental events were divided into five phases: 1) origin of germ cells and maintenance of pluripotency; 2) primordial germ cell migration; 3) sex differentiation; 4) formation of germ cell nests; and 5) germ cell nest breakdown and primordial follicle formation.

Conclusions

This review and visual representation provide a summary of the current scientific understanding of the key regulation and signaling during ovarian development and highlights areas needing further study. The visual representation can be used as an educational resource to link molecular events with phenotypic outcomes; serves as a tool to generate new hypotheses and predictions of adverse reproductive outcomes due to perturbations at the molecular and cellular levels; and provides a comprehendible foundation for computational model development and hypothesis testing.