Inducers and Inhibitors of Pyroptotic Death of Granulosa Cells in Models of Premature Ovarian Insufficiency and Polycystic Ovary Syndrome

Granulosa cells (GCs), the largest cell population and primary source of steroid hormones in the ovary, are the important somatic ovarian components. They have critical roles in folliculogenesis by supporting oocyte, facilitating its growth, and providing a microenvironment suitable for follicular development and oocyte maturation, thus having essential functions in maintaining female fertility and in reproductive health in general. Pyroptotic death of GCs and associated inflammation have been implicated in the pathogenesis of several reproductive disorders in females including Premature Ovarian Insufficiency (POI) and Polycystic Ovary Syndrome (PCOS). Here, I reviewed factors, either intrinsic or extrinsic, that induce or inhibit pyroptosis in GCs in various models of these disorders, both in vitro and in vivo, and also covered associated molecular mechanisms. Most of these studied factors influence NLRP3 inflammasome- and GSDMD (Gasdermin D)-mediated pyroptosis in GCs, compared to other inflammasomes and gasdermins (GSDMs). I conclude that a more complete mechanistic understanding of these factors in terms of GC pyroptosis is required to be able to develop novel strategies targeting inflammatory cell death in the ovary.

Tissue clearing and imaging approaches for in toto analysis of the reproductive system†

New microscopy techniques in combination with tissue clearing protocols and emerging analytical approaches have presented researchers with the tools to understand dynamic biological processes in a three-dimensional context. This paves the road for the exploration of new research questions in reproductive biology, for which previous techniques have provided only approximate resolution. These new methodologies now allow for contextualized analysis of far-larger volumes than was previously possible. Tissue optical clearing and three-dimensional imaging techniques posit the bridging of molecular mechanisms, macroscopic morphogenic development, and maintenance of reproductive function into one cohesive and comprehensive understanding of the biology of the reproductive system. In this review, we present a survey of the various tissue clearing techniques and imaging systems, as they have been applied to the developing and adult reproductive system. We provide an overview of tools available for analysis of experimental data, giving particular attention to the emergence of artificial intelligence-assisted methods and their applicability to image analysis. We conclude with an evaluation of how novel image analysis approaches that have been applied to other organ systems could be incorporated into future experimental evaluation of reproductive biology.

Nonlinear compartmental modeling to monitor ovarian follicle population dynamics on the whole lifespan

In this work, we introduce a compartmental model of ovarian follicle development all along lifespan, based on ordinary differential equations. The model predicts the changes in the follicle numbers in different maturation stages with aging. Ovarian follicles may either move forward to the next compartment (unidirectional migration) or degenerate and disappear (death). The migration from the first follicle compartment corresponds to the activation of quiescent follicles, which is responsible for the progressive exhaustion of the follicle reserve (ovarian aging) until cessation of reproductive activity. The model consists of a data-driven layer embedded into a more comprehensive, knowledge-driven layer encompassing the earliest events in follicle development. The data-driven layer is designed according to the most densely sampled experimental dataset available on follicle numbers in the mouse. Its salient feature is the nonlinear formulation of the activation rate, whose formulation includes a feedback term from growing follicles. The knowledge-based, coating layer accounts for cutting-edge studies on the initiation of follicle development around birth. Its salient feature is the co-existence of two follicle subpopulations of different embryonic origins. We then setup a complete estimation strategy, including the study of structural identifiability, the elaboration of a relevant optimization criterion combining different sources of data (the initial dataset on follicle numbers, together with data in conditions of perturbed activation, and data discriminating the subpopulations) with appropriate error models, and a model selection step. We finally illustrate the model potential for experimental design (suggestion of targeted new data acquisition) and in silico experiments.

PARP1-catalyzed PARylation of YY1 mediates endoplasmic reticulum stress in granulosa cells to determine primordial follicle activation

Although only a small number of primordial follicles are known to be selectively activated during female reproductive cycles, the mechanisms that trigger this recruitment remain largely uncharacterized. Misregulated activation of primordial follicles may lead to the exhaustion of the non-renewable pool of primordial follicles, resulting in premature ovarian insufficiency. Here, we found that poly(ADP-ribose) polymerase 1 (PARP1) enzymatic activity in the surrounding granulosa cells (GCs) in follicles determines the subpopulation of the dormant primordial follicles to be awakened. Conversely, specifically inhibiting PARP1 in oocytes in an in vitro mouse follicle reconstitution model does not affect primordial follicle activation. Further analysis revealed that PARP1-catalyzed transcription factor YY1 PARylation at Y185 residue facilitates YY1 occupancy at Grp78 promoter, a key molecular chaperone of endoplasmic reticulum stress (ERS), and promotes Grp78 transcription in GCs, which is required for GCs maintaining proper ERS during primordial follicle activation. Inhibiting PARP1 prevents the loss of primordial follicle pool by attenuating the excessive ERS in GCs under fetal bisphenol A exposure. Together, we demonstrate that PARP1 in GCs acts as a pivotal modulator to determine the fate of the primordial follicles and may represent a novel therapeutic target for the retention of primordial follicle pool in females.

Biased precursor ingression underlies the center-to-pole pattern of male sex determination in mouse

During mammalian development, gonadal sex determination results from the commitment of bipotential supporting cells to Sertoli or granulosa cell fates. Typically, this decision is coordinated across the gonad to ensure commitment to a single organ fate. When unified commitment fails in an XY mouse, an ovotestis forms in which supporting cells in the center of the gonad typically develop as Sertoli cells, while supporting cells in the poles develop as granulosa cells. This central bias for Sertoli cell fate was thought to result from the initial expression of the drivers of Sertoli cell fate, SRY and/or SOX9, in the central domain, followed by paracrine expansion to the poles. However, we show here that the earliest cells expressing SRY and SOX9 are widely distributed across the gonad. In addition, Sertoli cell fate does not spread among supporting cells through paracrine relay. Instead, we uncover a center-biased pattern of supporting cell precursor ingression that occurs in both sexes and results in increased supporting cell density in the central domain. Our findings prompt a new model of gonad patterning in which a density-dependent organizing principle dominates Sertoli cell fate stabilization.

Pivotal role of High-Mobility Group Box 2 in ovarian folliculogenesis and fertility

BACKGROUND

High-Mobility Group Box 1 (HMGB1) and HMGB2 are chromatin-associated proteins that belong to the HMG protein family, and are involved in the regulation of DNA transcription during cell differentiation, proliferation and regeneration in various tissues. However, the role of HMGB2 in ovarian folliculogenesis is largely unknown.

METHODS

We investigated the functional role of HMGB1 and HMGB2 in ovarian folliculogenesis and fertilization using C57BL/6 wild type (WT) and HMGB2-knockout (KO) mice. Ovarian tissues were obtained from WT and HMGB2-KO mice at postnatal days 0, 3, 7, and 2, 6 months of age, then performed immunohistochemistry, qPCR and Western blotting analyses. Oocyte fertilization capability was examined by natural breeding and in vitro fertilization experiments.

RESULTS

In HMGB2-KO mice, ovary weight was decreased due to reduced numbers of oocytes and follicles. Natural breeding and in vitro fertilization results indicated that HMGB2-KO mice are subfertile, but not sterile. Immunohistochemistry showed that oocytes expressed HMGB2, but not HMGB1, in neonatal and adult WT ovaries. Interestingly, in HMGB2-KO ovaries, a compensatory increase in HMGB1 was found in oocyte nuclei of neonatal and 2-month-old mice; however, this was lost at 6 months of age.

CONCLUSIONS

The depletion of HMGB2 led to alterations in ovarian morphology and function, suggesting that HMGB2 plays an essential role in ovarian development, folliculogenesis and fertilization.

Reconstitution of reproductive organ system that produces functional oocytes

Reproductive organs have unique developmental and functional properties that enable them to manage both germ cell development and the endocrine system in a sex-dependent manner. Proper reconstitution of the reproductive organs, therefore, will contribute to a deeper understanding of the mechanisms underlying germ cell development and sex-determination. However, reproductive organs have not yet been systematically reconstituted from pluripotent stem cells. This is largely due to technical problems in the reconstitution of the germ cell and somatic cell lineages, which have very different developmental trajectories. Accordingly, faithful construction of reproductive organoids requires that the reconstitution and evaluation of these two different cell lineages be performed separately. Here, we update the state-of-the-art in the reconstitution of reproductive organoids that produce functional oocytes.

Gonadal Sex Differentiation and Ovarian Organogenesis along the Cortical-Medullary Axis in Mammals

In most mammals, the sex of the gonads is based on the fate of the supporting cell lineages, which arises from the proliferation of coelomic epithelium (CE) that surfaces on the bipotential genital ridge in both XY and XX embryos. Recent genetic studies and single-cell transcriptome analyses in mice have revealed the cellular and molecular events in the two-wave proliferation of the CE that produce the supporting cells. This proliferation contributes to the formation of the primary sex cords in the medullary region of both the testis and the ovary at the early phase of gonadal sex differentiation, as well as to that of the secondary sex cords in the cortical region of the ovary at the perinatal stage. To support gametogenesis, the testis forms seminiferous tubules in the medullary region, whereas the ovary forms follicles mainly in the cortical region. The medullary region in the ovary exhibits morphological and functional diversity among mammalian species that ranges from ovary-like to testis-like characteristics. This review focuses on the mechanism of gonadal sex differentiation along the cortical-medullary axis and compares the features of the cortical and medullary regions of the ovary in mammalian species.

Integration of mouse ovary morphogenesis with developmental dynamics of the oviduct, ovarian ligaments, and rete ovarii

Morphogenetic events during the development of the fetal ovary are crucial to the establishment of female fertility. However, the effects of structural rearrangements of the ovary and surrounding reproductive tissues on ovary morphogenesis remain largely uncharacterized. Using tissue clearing and lightsheet microscopy, we found that ovary folding correlated with regionalization into cortex and medulla. Relocation of the oviduct to the ventral aspect of the ovary led to ovary encapsulation, and mutual attachment of the ovary and oviduct to the cranial suspensory ligament likely triggered ovary folding. During this process, the rete ovarii (RO) elaborated into a convoluted tubular structure extending from the ovary into the ovarian capsule. Using genetic mouse models in which the oviduct and RO are perturbed, we found the oviduct is required for ovary encapsulation. This study reveals novel relationships among the ovary and surrounding tissues and paves the way for functional investigation of the relationship between architecture and differentiation of the mammalian ovary.

A New Understanding, Guided by Single-Cell Sequencing, of the Establishment and Maintenance of the Ovarian Reserve in Mammals

BACKGROUND

Oocytes are a finite and non-renewable resource that are maintained in primordial follicle structures. The ovarian reserve is the totality of primordial follicles, present from birth, within the ovary and its establishment, size, and maintenance dictates the duration of the female reproductive lifespan. Understanding the cellular and molecular dynamics relevant to the establishment and maintenance of the reserve provides the first steps necessary for modulating both individual human and animal reproductive health as well as population dynamics.

SUMMARY

This review details the key stages of establishment and maintenance of the ovarian reserve, encompassing germ cell nest formation, germ cell nest breakdown, and primordial follicle formation and activation. Furthermore, we spotlight several formative single-cell sequencing studies that have significantly advanced our knowledge of novel molecular regulators of the ovarian reserve, which may improve our ability to modulate female reproductive lifespans.

KEY MESSAGES

The application of single-cell sequencing to studies of ovarian development in mammals, especially when leveraging genetic and environmental models, offers significant insights into fertility and its regulation. Moreover, comparative studies looking at key stages in the development of the ovarian reserve across species has the potential to impact not just human fertility, but also conservation biology, invasive species management, and agriculture.

SOX Genes and Their Role in Disorders of Sex Development

SOX genesare master regulatory genes controlling development and are fundamental to the establishment of sex determination in a multitude of organisms. The discovery of the master sex-determining gene SRY in 1990 was pivotal for the understanding of how testis development is initiated in mammals. With this discovery, an entire family of SOX factors were uncovered that play crucial roles in cell fate decisions during development. The importance of SOX genes in human reproductive development is evident from the various disorders of sex development (DSD) upon loss or overexpression of SOX gene function. Here, we review the roles that SOX genes play in gonad development and their involvement in DSD. We start with an overview of sex determination and differentiation, DSDs, and the SOX gene family and function. We then provide detailed information and discussion on SOX genes that have been implicated in DSDs, both at the gene and regulatory level. These include SRY, SOX9, SOX3, SOX8, and SOX10. This review provides insights on the crucial balance of SOX gene expression levels needed for gonad development and maintenance and how changes in these levels can lead to DSDs.

Using Experimental Models to Decipher the Effects of Acetaminophen and NSAIDs on Reproductive Development and Health

Nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin (acetylsalicylic acid), diclofenac and ibuprofen (IBU), and analgesic drugs, such as acetaminophen (APAP, or paracetamol), are widely used to treat inflammation and pain. APAP and IBU are over-the-counter drugs and are among the most commonly taken drugs in the first trimester of pregnancy, even in combination. Furthermore, these drugs and their metabolites are released in the environment, and can be frequently detected in wastewater, surface water, and importantly in drinking water. Although their environmental concentrations are much lower than the therapeutics doses, this suggests an uncontrolled low-dose exposure of the general population, including pregnant women and young children, two particularly at risk populations. Epidemiological studies show that exposure to these molecules in the first and second trimester of gestation can favor genital malformations in new-born boys. To investigate the cellular, molecular and mechanistic effects of exposure to these molecules, ex vivo studies with human or rodent gonadal explants and in vivo experiments in rodents have been performed in the past years. This review recapitulates recent data obtained in rodent models after in utero or postnatal exposure to these drugs. The first part of this review discusses the mechanisms by which NSAIDs and analgesics may impair gonadal development and maturation, puberty development, sex hormone production, maturation and function of adult organs, and ultimately fertility in the exposed animals and their offspring. Like other endocrine disruptors, NSAIDs and APAP interfere with endocrine gland function and may have inter/transgenerational adverse effects. Particularly, they may target germ cells, resulting in reduced quality of male and female gametes, and decreased fertility of exposed individuals and their descendants. Then, this review discusses the effects of exposure to a single drug (APAP, aspirin, or IBU) or to combinations of drugs during early embryogenesis, and the consequences on postnatal gonadal development and adult reproductive health. Altogether, these data may increase medical and public awareness about these reproductive health concerns, particularly in women of childbearing age, pregnant women, and parents of young children.

Metabolic Control of Germline Formation and Differentiation in Mammals

BACKGROUND

The germ cell lineage involves dynamic epigenetic changes during its formation and differentiation that are completely different from those of the somatic cell lineage. Metabolites and metabolic pathways have been reported as key factors related to the regulation of epigenetics as cofactors and substrates. However, our knowledge about the metabolic characteristics of germ cells, especially during the fetal stage, and their transition during differentiation is quite limited due to the rarity of the cells. Nevertheless, recent developments in omics technologies have made it possible to extract comprehensive metabolomic features of germ cells.

SUMMARY

In this review, we present the latest researches on the metabolic properties of germ cells in 4 stages: primordial germ cell specification, fetal germ cell differentiation, spermatogenesis, and oogenesis. At every stage, extensive published data has been accumulated on energy metabolism, and it is possible to describe its changes during germ cell differentiation in detail. As pluripotent stem cells differentiate into germ cells, energy metabolism shifts from glycolysis to oxidative phosphorylation; however, in spermatogenesis, glycolytic pathways are also temporarily dominant in spermatogonial stem cells. Although the significance of metabolic pathways other than energy metabolism in germ cell differentiation is largely unknown, the relation of the pentose phosphate pathway and Ser-Gly-one-carbon metabolism with germ cell properties has been suggested at various stages. We further discuss the relationship between these characteristic metabolic pathways and epigenetic regulation during germ cell specification and differentiation. Finally, the relevance of dietary and supplemental interventions on germ cell function and epigenomic regulation is also discussed. Key Messages: Comprehensive elucidation of metabolic features and metabolism-epigenome crosstalk in germ cells is important to reveal how the characteristic metabolic pathways are involved in the germ cell regulation. The accumulation of such insights would lead to suggestions for optimal diets and supplements to maintain reproductive health through modulating metabolic and epigenetic status of germ cells.

The impact of oocyte death on mouse primordial follicle formation and ovarian reserve

Background

Ovaries, the source of oocytes, maintain the numbers of primordial follicles, develop oocytes for fertilization and embryonic development. Although it is well known that about two‐thirds of oocytes are lost during the formation of primordial follicles through cyst fragmentation and the aggregation of oocytes within the cyst, the mechanism responsible for this remains unclear.

Methods

We provide an overview of cell death that is associated with the oocyte cyst breakdown and primordial follicle assembly along with our recent findings for mice that had been treated with a TNFα ligand inhibitor.

Main Findings

It is generally accepted that apoptosis is the major mechanism responsible for the depletion of germ cells. In fact, a gene deficiency or the overexpression of apoptosis regulators can have a great effect on follicle numbers and/or fertility. Apoptosis, however, may not be the only cause of the large‐scale oocyte attrition during oocyte cyst breakdown, and other mechanisms, such as aggregation, may also be involved in this process.

Conclusion

The continued study of oocyte death during primordial follicle formation could lead to the development of novel strategies for manipulating the primordial follicle pool, leading to improved fertility by enhancing the ovarian reserve.

LIF and bFGF enhanced chicken primordial follicle activation by Wnt/β-catenin pathway

The cytokines leukemia inhibitory factor (LIF) and basic fibroblast growth factor (bFGF) are closely related to the development of primordial follicles. In this study, the functions and correlation of LIF and bFGF in the development of chicken primordial follicles were examined, along with the signaling pathways including protein kinase B (AKT), extracellular regulated protein kinase (ERK) and Wnt/β-catenin signaling pathways. Ovarian tissues were collected from four-day-old chicks and incubated with LIF and bFGF alone or in combination for three days to observe the changes in follicular development. Results showed that there was a time-dependent correlation between the changes in expression of LIF/its receptor (LIFR) and the developmental process of primordial follicles. LIF and bFGF exerted a synergistic effect on the activation of primordial follicles. However, SC144 (an antagonist of LIFR) inhibited this stimulating action. The effect by LIF and bFGF were shown to operate at AKT and ERK signaling pathways to suppress cell apoptosis and promote proliferation (P < 0.05) via the Wnt/β-catenin signaling (P < 0.05). In conclusion, local cytokines LIF and bFGF functioned to enhance the activation of chicken primordial follicles by increasing cell proliferation and decreasing apoptosis in the ovary involving AKT, ERK and Wnt/β-catenin signaling.

Effect of BMP-Wnt-Nodal signal on stem cell differentiation

The generation of germ cells from embryonic stem cells in vitro has current historical significance. Western blot, qPCR, immunofluorescence and flow cytometry assays were used to investigate the differences in expression levels of totipotency and specific markers for Wnt regulation and the related signalling pathways during primordial germ cell-like cell (PGCLC) induction and differentiation. During PGCLC induction, activation of WNT3a increased the expression of NANOG, SOX2 and OCT4, but Mvh, DAZL, Blimp1, TFAP2C, Gata4, SOX17, EOMES, Brachyury and PRDM1 expression levels were significantly reduced. Inhibition of the WNT signal demonstrated the opposite effect. Similarly, inhibitors of BMP and the Nodal/Activin signal were used to determine the effect of signal pathways on differentiation. CER1 affected the Wnt signal and differentiation, but the inhibitor SB only regulated differentiation. BMP-WNT-NODAL were mainly responsible for regulating differentiation. Our results provide a reliable theoretical basis and feasibility for further clinical medical research.

Establishing and maintaining fertility: the importance of cell cycle arrest

In this review, Frost et al. summarize the current knowledge on the Cip/Kip family of cyclin-dependent kinase inhibitors in mouse gonad development and highlight new roles for cell cycle inhibitors in controlling and maintaining female fertility.

Development of the ovary or testis is required to establish reproductive competence. Gonad development relies on key cell fate decisions that occur early in embryonic development and are actively maintained. During gonad development, both germ cells and somatic cells proliferate extensively, a process facilitated by cell cycle regulation. This review focuses on the Cip/Kip family of cyclin-dependent kinase inhibitors (CKIs) in mouse gonad development. We particularly highlight recent single-cell RNA sequencing studies that show the heterogeneity of cyclin-dependent kinase inhibitors. This diversity highlights new roles for cell cycle inhibitors in controlling and maintaining female fertility.

A study on steroidogenic elaborations of stroma and their regulation in response to ovarian hormones in goats

Stromal tissue is an essential componenlt of the ovary not only for providing structural support but also for contributing to the early follicular growth with their bi-directional paracrine signaling. Estradiol is a major female hormone mainly secreted by the follicular cells in the ovary. To examine the relationship between 17β-estradiol and the factors involved in androgen production in stromal cells, ovarian stromal cells were cultured in the graded concentrations (50 and 100 ng/mL) of 17β-estradiol for varying time periods (24 and 48 h). The cells were processed for transmission electron microscopy to study the changes in steroidogenic functions of the cells. The effect of estradiol treatment was also evaluated on the quantity of androgen production and abundance of steroidogenic enzymes and proteins. The results indicated 17β-estradiol increased androgen production in ovarian stromal cells. In addition to enhanced androstenedione and testosterone production, estradiol stimulation was also based on the marked increase in abundance of mRNA transcript of steroidogenic enzymes [Star (Steroidogenic Acute Regulatory Protein), Cyp11a1, Cyp17a1, and hsd3b1 (3β-hydroxysteroid dehydrogenase)], as well as abundances of StAR and CYP11A1 protein. Thus, 17β-estradiol enhanced steroidogenesis in ovarian stromal cells. This study provided a basis for further exploration of regulation of steroidogenesis in ovarian stromal cells and the feedback mechanisms in association with estradiol.

The conditional deletion of steroidogenic factor 1 (Nr5a1) in Sox9-Cre mice compromises testis differentiation

Steroidogenic factor 1 (NR5A1) is essential for gonadal development. To study the importance of NR5A1 during early gonadal sex differentiation, we generated Sox9-Cre-Nr5a1 conditional knockout (cKO) mice: Sox9-Cre;Nr5a1^flox/flox and Sox9-Cre;Nr5a1^flox/− mice. Double-immunostaining for NR5A1 and AMH revealed silenced NR5A1 in Sertoli cells and reduced AMH⁺ cells in the gonads of XY Sox9-Cre-Nr5a1 cKO mice between embryonic days 12.5 (E12.5) and E14.5. Double-immunostaining for SOX9 and FOXL2 further indicated an early block in Sertoli cells and ectopic granulosa cell differentiation. The number of cells expressing the Leydig cell marker 3βHSD obviously reduced in the gonads of XY Sox9-Cre;Nr5a1^flox/− but not Sox9-Cre;Nr5a1^flox/flox mice at E15.5. The presence of STRA8⁺ cells indicated that germ cells entered meiosis in the gonads of XY Sox9-Cre-Nr5a1 cKO mice. The results of qRT-PCR revealed remarkably reduced and elevated levels of testis and ovary markers, respectively, in the gonads of XY Sox9-Cre-Nr5a1 cKO mice at E12.5‒E13.5. These data suggested that the loss of Nr5a1 abrogates the testicular pathway and induces the ectopic ovarian pathway, resulting in postnatal partial/complete male-to-female gonadal sex reversal. Our findings provide evidence for the critical role of NR5A1 in murine gonadal sex determination in vivo.

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

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

Proteomic and metabolomic analyses uncover sex-specific regulatory pathways in mouse fetal germline differentiation†

Regulatory mechanisms of germline differentiation have generally been explained via the function of signaling pathways, transcription factors, and epigenetic regulation; however, little is known regarding proteomic and metabolomic regulation and their contribution to germ cell development. Here, we conducted integrated proteomic and metabolomic analyses of fetal germ cells in mice on embryonic day (E)13.5 and E18.5 and demonstrate sex- and developmental stage-dependent changes in these processes. In male germ cells, RNA processing, translation, oxidative phosphorylation, and nucleotide synthesis are dominant in E13.5 and then decline until E18.5, which corresponds to the prolonged cell division and more enhanced hyper-transcription/translation in male primordial germ cells and their subsequent repression. Tricarboxylic acid cycle and one-carbon pathway are consistently upregulated in fetal male germ cells, suggesting their involvement in epigenetic changes preceding in males. Increased protein stability and oxidative phosphorylation during female germ cell differentiation suggests an upregulation of aerobic energy metabolism, which likely contributes to the proteostasis required for oocyte maturation in subsequent stages. The features elucidated in this study shed light on the unrevealed mechanisms of germ cell development.

Transcriptome analyses of ovarian stroma: tunica albuginea, interstitium and theca interna

The ovary has specialised stromal compartments, including the tunica albuginea, interstitial stroma and theca interna, which develops concurrently with the follicular antrum. To characterise the molecular determinants of these compartments, stroma adjacent to preantral follicles (pre-theca), interstitium and tunica albuginea were laser microdissected (n = 4 per group) and theca interna was dissected from bovine antral follicles (n = 6). RNA microarray analysis showed minimal differences between interstitial stroma and pre-theca, and these were combined for some analyses and referred to as stroma. Genes significantly upregulated in theca interna compared to stroma included INSL3, LHCGR, HSD3B1, CYP17A1, ALDH1A1, OGN, POSTN and ASPN. Quantitative RT-PCR showed significantly greater expression of OGN and LGALS1 in interstitial stroma and theca interna versus tunica and greater expression of ACD in tunica compared to theca interna. PLN was significantly higher in interstitial stroma compared to tunica and theca. Ingenuity pathway, network and upstream regulator analyses were undertaken. Cell survival was also upregulated in theca interna. The tunica albuginea was associated with GPCR and cAMP signalling, suggesting tunica contractility. It was also associated with TGF-β signalling and increased fibrous matrix. Western immunoblotting was positive for OGN, LGALS1, ALDH1A1, ACD and PLN with PLN and OGN highly expressed in tunica and interstitial stroma (each n = 6), but not in theca interna from antral follicles (n = 24). Immunohistochemistry localised LGALS1 and POSTN to extracellular matrix and PLN to smooth muscle cells. These results have identified novel differences between the ovarian stromal compartments.

Molecular Characterization of XX Maleness

Androgens and anti-Müllerian hormone (AMH), secreted by the foetal testis, are responsible for the development of male reproductive organs and the regression of female anlagen. Virilization of the reproductive tract in association with the absence of Müllerian derivatives in the XX foetus implies the existence of testicular tissue, which can occur in the presence or absence of SRY. Recent advancement in the knowledge of the opposing gene cascades driving to the differentiation of the gonadal ridge into testes or ovaries during early foetal development has provided insight into the molecular explanation of XX maleness.

In utero exposure to acetaminophen and ibuprofen leads to intergenerational accelerated reproductive aging in female mice

Nonsteroidal anti-inflammatory drugs (NSAIDs) and analgesic drugs, such as acetaminophen (APAP), are frequently taken during pregnancy, even in combination. However, they can favour genital malformations in newborn boys and reproductive disorders in adults. Conversely, the consequences on postnatal ovarian development and female reproductive health after in utero exposure are unknown. Here, we found that in mice, in utero exposure to therapeutic doses of the APAP-ibuprofen combination during sex determination led to delayed meiosis entry and progression in female F1 embryonic germ cells. Consequently, follicular activation was reduced in postnatal ovaries through the AKT/FOXO3 pathway, leading in F2 animals to subfertility, accelerated ovarian aging with abnormal corpus luteum persistence, due to decreased apoptosis and increased AKT-mediated luteal cell survival. Our study suggests that administration of these drugs during the critical period of sex determination could lead in humans to adverse effects that might be passed to the offspring.

CAV1 regulates primordial follicle formation via the Notch2 signalling pathway and is associated with premature ovarian insufficiency in humans

STUDY QUESTION

What is the function of CAV1 in folliculogenesis and female reproduction?

SUMMARY ANSWER

CAV1 regulates germline cyst breakdown and primordial follicle (PF) formation in mice, and CAV1 mutation may be related to premature ovarian insufficiency (POI).

WHAT IS KNOWN ALREADY

Pre-granulosa cells are essential for the establishment of the PF pool, which determines female fertility and reproductive lifespan. Cav1 participates in vascularization in fetal mouse ovaries. However, the role of CAV1 in early folliculogenesis and POI pathogenesis remains unclear.

STUDY DESIGN, SIZE, DURATION

Cav1 function was investigated in mice and Human Embryonic Kidney 293 cells. Ovaries (six per group) were randomly assigned to Cav1-vivo-morpholino, control and control-morpholino groups, and all experiments were repeated at least three times. To investigate CAV1 mutations in women, 200 Chinese women with POI and 200 control individuals with regular menstrual cycles and normal endocrine profiles were recruited from the Center for Reproductive Medicine of Shandong University between September 2012 and December 2013.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Wild-type CD1 mice, Lgr5-EGFP-ires-CreERT2 (Lgr5-KI) reporter mice and Human Embryonic Kidney 293 cells were used for these experiments. Protein expression was detected by Western blot, and quantitative RT-PCR was used to detect gene expression. The expression pattern of CAV1 in mouse ovaries and the phenotype of Cav1 deficiency in mice were detected by immunofluorescence. Pre-granulosa cell proliferation in ovaries was detected by bromodeoxyuridine (BrdU) assay and immunofluorescence. The coding region of the CAV1 gene was sequenced in 200 women with POI and 200 controls. The functional effect of the novel mutation c.142 G > C (p.Glu48Gln) was investigated by Cell Counting Kit-8 (CCK8) assays and Western blot.

MAIN RESULTS AND THE ROLE OF CHANCE

We confirmed that Cav1 deficiency in mouse ovary induced by CAV1-vivo-morpholino resulted in more multi-oocyte follicles than in the control and control-morpholino groups (P < 0.01). Suppression of Cav1 decreased Leucine rich repeat containing G protein coupled receptor 5 (Lgr5)-positive cell proliferation (P < 0.01) and reduced the number of Lgr5 and Forkhead box L2 (Foxl2) double-positive cells (P < 0.01). Furthermore, suppression of Cav1 inhibited ovarian epithelial Lgr5-positive cell proliferation and differentiation through the Notch2 signalling pathway. Two of the POI women carried novel CAV1 mutations (c.45 C > G synonymous and c.142 G > C [Glu48Gln]). The deleterious effect of p.Glu48Gln was corroborated by showing that it adversely affected the function of CAV1 in cell proliferation and NOTCH2 expression in HEK293FT cells.

LARGE-SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

The novel Glu48Gln mutation was only detected in one of 200 POI patients and we were unable to investigate its effects in the ovary.

WIDER IMPLICATIONS OF THE FINDINGS

The identification of CAV1 as a potentially causative gene for POI provides a theoretical basis to devise treatments for POI in women.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Basic Research Program of China (973 Programs: 2012CB944700; 2013CB945501; 2013CB911400; 2014CB943202), the National Key Research and Development Program of China (2016YFC1000604, 2017YFC1001301), the State Key Program of National Natural Science Foundation of China (81430029), and the National Natural Science Foundation of China (31571540, 81522018, 81471509, 81601245, 81701406, 81571406). The authors declare no competing financial interests.

Nr5a1 suppression during the murine fetal period optimizes ovarian development by fine-tuning Notch signaling

The nuclear receptor NR5A1 is equally expressed and required for development of the gonadal primordia of both sexes, but, after sex determination, it is upregulated in XY testes and downregulated in XX ovaries. We have recently demonstrated, in mice, that this downregulation is mediated by forkhead box L2 (FOXL2) and hypothesized that adequate suppression of Nr5a1 is essential for normal ovarian development. Further, analysis of human patients with disorders/differences of sex development suggests that overexpression of NR5A1 can result in XX (ovo)testicular development. Here, we tested the role of Nr5a1 by overexpression in fetal gonads using a Wt1-BAC (bacterial artificial chromosome) transgene system. Enforced Nr5a1 expression compromised ovarian development in 46,XX mice, resulting in late-onset infertility, but did not induce (ovo)testis differentiation. The phenotype was similar to that of XX mice lacking Notch signaling. The expression level of Notch2 was significantly reduced in Nr5a1 transgenic mice, and the ovarian phenotype was almost completely rescued by in utero treatment with a NOTCH2 agonist. We conclude that suppression of Nr5a1 during the fetal period optimizes ovarian development by fine-tuning Notch signaling.

Molecular and genetic characterization of partial masculinization in embryonic ovaries grafted into male nude mice

In most of mammalian embryos, gonadal sex differentiation occurs inside the maternal uterus before birth. In several fetal ovarian grafting experiments using male host mice, an experimental switch from the maternal intrauterine to male-host environment gradually induces partial masculinization of the grafted ovaries even under the wild-type genotype. However, either host-derived factors causing or molecular basis underlying this masculinization of the fetal ovaries are not clear. Here, we demonstrate that ectopic appearance of SOX9-positive Sertoli cell-like cells in grafted ovaries was mediated by the testosterone derived from the male host. Neither Sox8 nor Amh activity in the ovarian tissues is essential for such ectopic appearance of SOX9-positive cells. The transcriptome analyses of the grafted ovaries during this masculinization process showed early downregulation of pro-ovarian genes such as Irx3, Nr0b1/Dax1, Emx2, and Fez1/Lzts1 by days 7-10 post-transplantation, and subsequent upregulation of several pro-testis genes, such as Bhlhe40, Egr1/2, Nr4a2, and Zc3h12c by day 20, leading to a partial sex reversal with altered expression profiles in one-third of the total numbers of the sex-dimorphic pre-granulosa and Sertoli cell-specific genes at 12.5 dpc. Our data imply that the paternal testosterone exposure is partially responsible for the sex-reversal expression profiles of certain pro-ovarian and pro-testis genes in the fetal ovaries in a temporally dependent manner.

Lineage Tracing Reveals the Bipotency of SOX9+ Hepatocytes during Liver Regeneration

Elucidation of the role of different cell lineages in the liver could offer avenues to drive liver regeneration. Previous studies showed that SOX9⁺ hepatocytes can differentiate into ductal cells after liver injuries. It is unclear whether SOX9⁺ hepatocytes are uni- or bipotent progenitors at a single-cell level during liver injury. Here, we developed a genetic tracing system to delineate the lineage potential of SOX9⁺ hepatocytes during liver homeostasis and regeneration. Fate-mapping data showed that these SOX9⁺ hepatocytes respond specifically to different liver injuries, with some contributing to a substantial number of ductal cells. Clonal analysis demonstrated that a single SOX9⁺ hepatocyte gives rise to both hepatocytes and ductal cells after liver injury. This study provides direct evidence that SOX9⁺ hepatocytes can serve as bipotent progenitors after liver injury, producing both hepatocytes and ductal cells for liver repair and regeneration.

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SOX9⁺ hepatocytes respond distinctly to different liver injuries

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Generation of a Confetti reporter responsive to dual recombinases

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SOX9⁺ hepatocytes can serve as bipotent progenitors after liver injury

The molecular complexity of primary ovarian insufficiency aetiology and the use of massively parallel sequencing

Primary ovarian insufficiency (POI) is a frequently occurring pathology, leading to infertility. Genetic anomalies have been described in POI and mutations in numerous genes have been definitively related to the pathogenesis of the disease. Some studies based on next generation sequencing (NGS) have been successfully undertaken as they have led to identify new mutations associated with POI aetiology. The purpose of this review is to present the most relevant molecules involved in diverse complex pathways, which may contribute towards POI. The main genes participating in bipotential gonad formation, sex determination, meiosis, folliculogenesis and ovulation are described to enable understanding how they may be considered putative candidates involved in POI. Considerations regarding NGS technical aspects such as design and data interpretation are mentioned. Successful NGS initiatives used for POI studying and future challenges are also discussed.

Morphogenesis-related gene-expression profile in porcine oocytes before and after in vitro maturation

Mammalian oocyte maturation is achieved when oocytes reach metaphase II (MII) stage, and accumulate mRNA and proteins in the cytoplasm following fertilization. It has been shown that oocytes investigated before and after in vitro maturation (IVM) differ significantly in transcriptomic and proteomic profiles. Additionally, folliculogenesis and oogenesis is accompanied by morphogenetic changes, which significantly influence further zygote formation and embryo growth. This study aimed to determine new transcriptomic markers of porcine oocyte morphogenesis that are associated with cell maturation competence. An Affymetrix microarray assay was performed on an RNA template isolated from porcine oocytes before (n = 150) and after (n = 150) IVM. The brilliant cresyl blue (BCB) staining test was used for identification of cells with the highest developmental capacity. DAVID (Database for Annotation, Visualization, and Integrated Discovery) software was used for the extraction of the genes belonging to a cell morphogenesis Gene Ontology group. The control group consisted of freshly isolated oocytes. In total, 12,000 different transcripts were analysed, from which 379 genes were downregulated and 40 were upregulated in oocytes following IVM. We found five genes, SOX9, MAP1B, DAB2, FN1, and CXCL12, that were significantly upregulated in oocytes after IVM (in vitro group) compared with oocytes analysed before IVM (in vivo group). In conclusion, we found new transcriptomic markers of oocyte morphogenesis, which may be also recognized as significant mediators of cellular maturation capacity in pigs. Genes SOX9, MAP1B, DAB2, FN1, and CXCL12 may be involved in the regulation of the MII stage oocyte formation and several other processes that are crucial for porcine reproductive competence.

Mechanisms controlling germline cyst breakdown and primordial follicle formation

In fetal females, oogonia proliferate immediately after sex determination. The progress of mitosis in oogonia proceeds so rapidly that the incompletely divided cytoplasm of the sister cells forms cysts. The oogonia will then initiate meiosis and arrest at the diplotene stage of meiosis I, becoming oocytes. Within each germline cyst, oocytes with Balbiani bodies will survive after cyst breakdown (CBD). After CBD, each oocyte is enclosed by pre-granulosa cells to form a primordial follicle (PF). Notably, the PF pool formed perinatally will be the sole lifelong oocyte source of a female. Thus, elucidating the mechanisms of CBD and PF formation is not only meaningful for solving mysteries related to ovarian development but also contributes to the preservation of reproduction. However, the mechanisms that regulate these phenomena are largely unknown. This review summarizes the progress of cellular and molecular research on these processes in mice and humans.

Defects in the first wave of folliculogenesis in mouse XO ovaries

In mouse ovaries, the first wave of folliculogenesis perinatally starts near the medullary region, which directs the initial round of follicular growth soon after birth. At the same time, cortical primordial follicles start forming in the ovarian surface region, and then some are cyclically recruited for the second and subsequent rounds of follicular growth. Recent studies suggest different dynamics between the first and subsequent waves of follicular growth in postnatal ovaries. However, the phenotypic differences between these phases remain unclear. Here, we show direct evidence that XO female mice, a murine model for Turner Syndrome, lack the first wave of folliculogenesis. Our histopathological analyses of XX and XO littermates revealed a lack of anti-Müllerian hormone (AMH)-positive primary follicles in the XO ovaries by 4 days post partum (dpp). This loss of first follicles was also confirmed by histological bioassay for SRY-dependent SOX9 inducibility, a specific marker for the first follicular granulosa cells. In contrast, cortical primordial follicles formed properly in XO ovaries, and some of them formed primary and secondary follicles in the subcortical region by 7 dpp. They rapidly developed into late antral follicles, showing similarities to XX littermate ovaries by 21 dpp. These results suggest distinct X-monosomy effects between the first and subsequent waves of follicular growth, highlighting the high susceptibility to elimination of XO oocytes in the first wave of mammalian folliculogenesis.

Does MAX open up a new avenue for meiotic research?

Meiosis is a central event of sexual reproduction. Like somatic cells, germ cells conduct mitosis to increase their cell number, but unlike somatic cells, germ cells switch their cell division mode from mitosis to meiosis at a certain point in gametogenesis. However, the molecular basis of this switch remains elusive. In this review article, we give an overview of the onset of mammalian meiosis, including our recent finding that MYC Associated Factor X (MAX) prevents ectopic and precocious meiosis in embryonic stem cells (ESCs) and germ cells, respectively. We present a hypothetical model of a MAX-centered molecular network that regulates meiotic entry in mammals and propose that inducible Max knockout ESCs provide an excellent platform for exploring the molecular mechanisms of meiosis initiation, while excluding other aspects of gametogenesis.

ADAM10-Notch signaling governs the recruitment of ovarian pregranulosa cells and controls folliculogenesis in mice

Ovarian follicles are the basic functional units of female reproduction in the mammalian ovary. We show here that the protein a disintegrin and metalloproteinase domain 10 (ADAM10), a cell surface sheddase, plays an indispensable role in controlling primordial follicle formation by regulating the recruitment of follicle supporting cells in mice. We demonstrate that suppressing ADAM10 in vitro or deletion of Adam10 in vivo disrupts germline cyst breakdown and primordial follicle formation. Using a cell lineage tracing approach, we show that ADAM10 governs the recruitment of ovarian follicle cells by regulating the differentiation and proliferation of LGR5-positive follicle supporting progenitor cells. By detecting the development of FOXL2-positive pregranulosa cells, we found that inhibiting ADAM10 reduced the number of FOXL2-positive cells in perinatal ovaries. Furthermore, inhibiting ADAM10 suppressed the activation of Notch signaling, and blocking Notch signaling also disrupted the recruitment of follicle progenitor cells. Taken together, these results show that ADAM10-Notch signaling in ovarian somatic cells governs the primordial follicle formation by controlling the development of ovarian pregranulosa cells. The proper recruitment of ovarian follicle supporting cells is essential for establishment of the ovarian reserve in mice.

Disorders of Sex Development with Testicular Differentiation in SRY-Negative 46,XX Individuals: Clinical and Genetic Aspects

Virilisation of the XX foetus is the result of androgen excess, resulting most frequently from congenital adrenal hyperplasia in individuals with typical ovarian differentiation. In rare cases, 46,XX gonads may differentiate into testes, a condition known as 46,XX testicular disorders of sex development (DSD), or give rise to the coexistence of ovarian and testicular tissue, a condition known as 46,XX ovotesticular DSD. Testicular tissue differentiation may be due to the translocation of SRY to the X chromosome or an autosome. In the absence of SRY, overexpression of other pro-testis genes, e.g. SOX family genes, or failure of pro-ovarian/anti-testis genes, such as WNT4 and RSPO1, may underlie the development of testicular tissue. Recent experimental and clinical evidence giving insight into SRY-negative 46,XX testicular or ovotesticular DSD is discussed.