The role of germ cell loss during primordial follicle assembly: a review of current advances

Loss of Calponin 2 causes premature ovarian insufficiency in mice

BACKGROUND

Premature ovarian insufficiency (POI) is a condition defined as women developing menopause before 40 years old. These patients display low ovarian reserve at young age and difficulties to conceive even with assisted reproductive technology. The pathogenesis of ovarian insufficiency is not fully understood. Genetic factors may underlie most of the cases. Actin cytoskeleton plays a pivotal role in ovarian folliculogenesis. Calponin 2 encoded by the Cnn2 gene is an actin associated protein that regulates motility and mechanical signaling related cellular functions.

RESULTS

The present study compared breeding of age-matched calponin 2 knockout (Cnn2-KO) and wild type (WT) mice and found that Cnn2-KO mothers had significantly smaller litter sizes. Ovaries from 4 weeks old Cnn2-KO mice showed significantly lower numbers of total ovarian follicles than WT control with the presence of multi-oocyte follicles. Cnn2-KO mice also showed age-progressive earlier depletion of ovarian follicles. Cnn2 expression is detected in the cumulus cells of the ovarian follicles of WT mice and colocalizes with actin stress fiber, tropomyosin and myosin II in primary cultures of cumulus cells.

CONCLUSIONS

The findings demonstrate that the loss of calponin 2 impairs ovarian folliculogenesis with premature depletion of ovarian follicles. The role of calponin 2 in ovarian granulosa cells suggests a molecular target for further investigations on the pathogenesis of POI and for therapeutic development.

The influence of environmental factors on premature ovarian insufficiency and ovarian aging

Premature ovarian insufficiency and ovarian aging are complex conditions that affect women's reproductive health and overall well-being. They are both characterized by hypergonadotropic hypogonadism and infertility, and together affect about 1 in 100 women by the age of 40. This review explores the influence of environmental factors on the development and progression of premature ovarian insufficiency and ovarian aging. When referring to environmental factors, we include a wide range of external agents and conditions, including chemicals, socioeconomic factors and lifestyle choices. Through a review of the literature, we attempt to highlight the link between environmental factors and ovarian health. We examine the impact of endocrine-disrupting chemicals, such as bisphenol A and phthalates, on ovarian function and investigate the mechanisms by which these chemicals can disrupt hormone signaling pathways, leading to alterations in ovarian reserve, oocyte quality, and folliculogenesis. Moreover, we explore lifestyle factors like obesity, stress, smoking and alcohol in relation to their effects on ovarian aging. Epigenetic changes may play a crucial role in the prevalence of premature ovarian insufficiency. Understanding the impact of environmental factors on premature ovarian insufficiency and ovarian aging is very important in public and clinical health contexts. By identifying risk factors, healthcare providers can develop targeted and strategic prevention and intervention plans. Furthermore, this knowledge can promote reproductive health and minimize exposure to harmful environmental agents.

Epigenetic regulation in premature ovarian failure: A literature review

Premature ovarian failure (POF), or premature ovarian insufficiency (POI), is a multifactorial and heterogeneous disease characterized by amenorrhea, decreased estrogen levels and increased female gonadotropin levels. The incidence of POF is increasing annually, and POF has become one of the main causes of infertility in women of childbearing age. The etiology and pathogenesis of POF are complex and have not yet been clearly elucidated. In addition to genetic factors, an increasing number of studies have revealed that epigenetic changes play an important role in the occurrence and development of POF. However, we found that very few papers have summarized epigenetic variations in POF, and a systematic analysis of this topic is therefore necessary. In this article, by reviewing and analyzing the most relevant literature in this research field, we expound on the relationship between DNA methylation, histone modification and non-coding RNA expression and the development of POF. We also analyzed how environmental factors affect POF through epigenetic modulation. Additionally, we discuss potential epigenetic biomarkers and epigenetic treatment targets for POF. We anticipate that our paper may provide new therapeutic clues for improving ovarian function and maintaining fertility in POF patients.

Dynamic Autophagy Map in Mouse Female Germ Cells Throughout the Fetal to Postnatal Life

Autophagy plays vital roles in mouse female germ cells, but the potential mechanism is largely unknown. In this study, by interrogating single-cell RNA-seq dataset, we investigated the dynamic expression of autophagy-related genes in seven types of germ cells (mitosis, pre-leptotene, leptotene, zygotene, pachytene, diplotene, and dictyate) and discovered stage-specific autophagy-related genes. Using immunofluorescence (IF) and transmission electron microscopy (TEM), autophagy activity and autophagosome numbers were revealed from mitosis to follicular assembly (E12.5 (embryonic day 12.5) to P5 (postnatal day 5)). Furthermore, single-sample gene set enrichment analysis (ssGSEA) was performed to validate the autophagy kinetics from E12.5 to P5. Our study proved that the mitosis, diplotene, and dictyate female germ cells had relatively higher autophagy activity among the seven subtypes. In summary, our work provided an autophagy map, suggesting that autophagy was complicated in mouse female germ cell development from the fetal to postnatal life, which paved a new insight for deciphering the autophagy regulatory networks for cell-fate transition and female infertility issues like primary ovarian insufficiency (POI).

The Therapeutic Potential of Human Umbilical Cord Derived Mesenchymal Stem Cells for the Treatment of Premature Ovarian Failure

Premature ovarian failure (POF) affects 1% of women under 40, leading to infertility. The clinical symptoms of the POF include hypoestrogenism, lack of mature follicles, hypergonadotropinism, and amenorrhea. POF can be caused due to genetic defects, autoimmune illnesses, and environmental factors. The conventional treatment of POF remains a limited success rate. Therefore, an innovative treatment strategy like the regeneration of premature ovaries by using human umbilical cord mesenchymal stem cells (hUC-MSCs) can be a choice. To summarize all the theoretical frameworks for additional research and clinical trials, this review article highlights all the results, pros, and cons of the hUC-MSCs used to treat POF. So far, the data shows promising results regarding the treatment of POF using hUC-MSCs. Several properties like relatively low immunogenicity, multipotency, multiple origins, affordability, convenience in production, high efficacy, and donor/recipient friendliness make hUC-MSCs a good choice for treating basic POF. It has been reported that hUC-MSCs impact and enhance all stages of injured tissue regeneration by concurrently stimulating numerous pathways in a paracrine manner, which are involved in the control of ovarian fibrosis, angiogenesis, immune system modulation, and apoptosis. Furthermore, some studies demonstrated that stem cell treatment could lead to hormone-level restoration, follicular activation, and functional restoration of the ovaries. Therefore, all the results in hand regarding the use of hUC-MSCs for the treatment of POF encourage researchers for further clinical trials, which will overcome the ongoing challenges and make this treatment strategy applicable to the clinic in the near future.

Graphical Abstract

Tracking the dynamics of female germ cell development during peri-hatch periods using a gene-edited chicken model

In hens, egg production depends on the development of germ cells in the ovary. Germ cells are established before birth, and their number gradually decreases during their lifespan. Therefore, it is essential to determine the time points of massive germ cell loss and the underlying mechanism. In this study, a gene-edited chicken with mCherry fluorescence specifically expressed in the germline was generated by the integration of the mCherry gene into the 3'-end of the DAZL locus, which facilitated the isolation of germ cells from the gonads of DAZL-mCherry embryos or chicks and quantification using flow cytometry based on the observation of red fluorescence. The results demonstrated the dynamics of germ cell development from embryos at 17 d of hatching (dh) to chickens at 7 d post-hatch (dph) and revealed a substantial loss of germ cells in the late embryonic stage (18 -19 dh) and post-hatch period (2 -3 dph). Additionally, the number of germ cells in DAZL × Guangxi Ma chicken was significantly higher than that in DAZL × Lohmann Pink chicken at 19 dh and 3 dph (P < 0.05). Furthermore, the numbers of germ cells positively correlated with the body weight in DAZL × Lohmann Pink chicken. In conclusion, our results showed the dynamics of germ cell development in chicken ovaries during peri-hatch periods and indicated the time point of substantial germ cell loss. The results provide evidence for further exploration of the underlying mechanism and serve as a reference for chicken breeding and management.

VASA protein and gene expression analysis of human non-obstructive azoospermia and normal by immunohistochemistry, immunocytochemistry, and bioinformatics analysis

VASA, also known as DDX4, is a member of the DEAD-box proteins and an RNA binding protein with an ATP-dependent RNA helicase. The VASA gene expression, which is required for human germ cell development, may lead to infertility. Immunocytochemistry and immunohistochemistry were used to examine the expression of VASA protein in the human testis sections of azoospermic patients, in-vitro and in-silico models. Some studies of fertile humans showed VASA expression in the basal and adluminal compartments of seminiferous tubules. Our Immunocytochemistry and immunohistochemistry in infertile humans showed expression of VASA in the luminal compartments of the seminiferous tubule. The immunohistochemical analysis of three human cases with different levels of non-obstructive azoospermia revealed a higher expression of VASA-positive cells. For this purpose, Enrichr and Shiny Gene Ontology databases were used for pathway enrichment analysis and gene ontology. STRING and Cytoscape online evaluation were applied to predict proteins' functional and molecular interactions and performed to recognize the master genes, respectively. According to the obtained results, the main molecular functions of the up-regulated and downregulated genes include the meiotic cell cycle, RNA binding, and differentiation. STRING and Cytoscape analyses presented seven genes, i.e., DDX5, TNP2, DDX3Y, TDRD6, SOHL2, DDX31, and SYCP3, as the hub genes involved in infertility with VASA co-function and protein-protein interaction. Our findings suggest that VASA and its interacting hub proteins could help determine the pathophysiology of germ cell abnormalities and infertility.

Autophagy participates in germline cyst breakdown and follicular formation by modulating glycolysis switch via Akt signaling in newly-hatched chicken ovaries

In females, the establishment of the primordial follicle pool is accompanied by a remarkable programmed oocyte loss for unclear reasons. In this study, the role of autophagy was investigated to serve as a protective mechanism for oocyte survival during chicken folliculogenesis. Inhibition of autophagy by 3-methyladenine (3-MA) led to a remarkable delay in germ cell cyst breakdown that resulted in fewer primordial follicles and retarded sequent follicular development either in vivo or in the ovarian organ culture. Furthermore, the glycolysis level was downregulated in ovaries treated with 3-MA, while Recilisib (a specific activator of Akt) reversed this inhibiting effect of 3-MA on primordial folliculogenesis. Collectively, these data indicate that autophagy functions to maintain germ cell cyst breakdown and primordial follicle assembly by regulating ovarian glycolysis involving Akt signaling in the ovaries of newly-hatched chickens.

Impaired primordial follicle assembly in offspring ovaries from zearalenone-exposed mothers involves reduced mitochondrial activity and altered epigenetics in oocytes

Previous works have shown that zearalenone (ZEA), as an estrogenic pollutant, has adverse effects on mammalian folliculogenesis. In the present study, we found that prolonged exposure of female mice to ZEA around the end of pregnancy caused severe impairment of primordial follicle formation in the ovaries of newborn mice and altered the expression of many genes in oocytes as revealed by single-cell RNA sequencing (scRNA-seq). These changes were associated with morphological and molecular alterations of mitochondria, increased autophagic markers in oocytes, and epigenetic changes in the ovaries of newborn mice from ZEA-exposed mothers. The latter increased expression of HDAC2 deacetylases was leading to decreased levels of H3K9ac and H4K12ac. Most of these modifications were relieved when the expression of  Hdac2 in newborn ovaries was reduced by RNA interference during in vitro culture in the presence of ZEA. Such changes were also alleviated in offspring ovaries from mothers treated with both ZEA and the coenzyme Q10 (CoQ10), which is known to be able to restore mitochondrial activities. We concluded that impaired mitochondrial activities in oocytes caused by ZEA are at the origin of metabolic alterations that modify the expression of genes controlling autophagy and primordial follicle assembly through changes in epigenetic histones.

KDM1A/LSD1 as a promising target in various diseases treatment by regulating autophagy network

Epigenetics refers to alterations in gene expressions that are reversible and stable, but do not involve changes in DNA sequences. In recent years, an increasing number of studies have shown that epigenetics plays a critical role in autophagy, which can be schematized as a biological process comprising of the following steps: autophagy signal activation, autophagic vesicle elongation, autophagosome maturation and autophagosome-lysosome fusion. As previously reported, autophagy can maintain intracellular homeostasis and autophagy dysfunction will lead to various diseases. For instance, the abnormal expression of genes involved in autophagy can result in the occurrence of many cancers and atherosclerosis. It is also well known that epigenetic modifications can affect autophagy related genes expressions and modulate other signaling molecular involved in autophagy. As an important epigenetic enzyme, LSD1 (lysine specific demethylase 1) plays an essential role in modulating autophagy. On one hand, LSD1 directly regulates autophagy-related genes expressions, including ATGs, Beclin-1, LC3 and SQSTM1/p62. On the other hand, inhibition of LSD1 can activate autophagy through regulating the activities of some other proteins such as p53, SESN2, mTORC1 and PTEN. Since autophagy activation is tightly related to the occurrence of various diseases and can be induced by LSD1 inhibition, development of LSD1 inhibitors will provide a new direction to treat such diseases. In this review, we described the mechanisms by which LSD1 regulates autophagy in different manners and how autophagic dysfunction leads to diseases occurrence. In addition, some LSD1 inhibitors used to treat diseases through modulating autophagy are also summarized in our review.

Effects of endocrine disrupting chemicals on gonad development: Mechanistic insights from fish and mammals

Over the past century, evidence has emerged that endocrine disrupting chemicals (EDCs) have an impact on reproductive health. An increased frequency of reproductive disorders has been observed worldwide in both wildlife and humans that is correlated with accidental exposures to EDCs and their increased production. Epidemiological and experimental studies have highlighted the consequences of early exposures and the existence of key windows of sensitivity during development. Such early in life exposures can have an immediate impact on gonadal and reproductive tract development, as well as on long-term reproductive health in both males and females. Traditionally, EDCs were thought to exert their effects by modifying the endocrine pathways controlling reproduction. Advances in knowledge of the mechanisms regulating sex determination, differentiation and gonadal development in fish and rodents have led to a better understanding of the molecular mechanisms underlying the effects of early exposure to EDCs on reproduction. In this manuscript, we review the key developmental stages sensitive to EDCs and the state of knowledge on the mechanisms by which model EDCs affect these processes, based on the roadmap of gonad development specific to fish and mammals.

Aging conundrum: A perspective for ovarian aging

Progressive loss of physiological integrity and accumulation of degenerative changes leading to functional impairment and increased susceptibility to diseases are the main features of aging. The ovary, the key organ that maintains female reproductive and endocrine function, enters aging earlier and faster than other organs and has attracted extensive attention from society. Ovarian aging is mainly characterized by the progressive decline in the number and quality of oocytes, the regulatory mechanisms of which have yet to be systematically elucidated. This review discusses the hallmarks of aging to further highlight the main characteristics of ovarian aging and attempt to explore its clinical symptoms and underlying mechanisms. Finally, the intervention strategies related to aging are elaborated, especially the potential role of stem cells and cryopreservation of embryos, oocytes, or ovarian tissue in the delay of ovarian aging.

Genetics of ovarian insufficiency and defects of folliculogenesis

Primary ovarian insufficiency (POI) is determined by exhaustion of follicles in the ovaries, which leads to infertility before the age of 40 years. It is characterized by a strong familial and heterogeneous genetic background. Therefore, we will mainly discuss the genetic basis of POI in this review. We identified 107 genes related to POI etiology in mammals described by several independent groups. Thirty-four of these genes (AARS2, AIRE, ANTXR1, ATM, BMPR1B, CLPP, CYP17A1, CYP19A1, DCAF17, EIF2B, ERAL1, FANCA, FANCC, FMR1, FOXL2, GALT, GNAS, HARS2, HSD17B4, LARS2, LMNA, MGME1, NBN, PMM2, POLG, PREPL, RCBTB1, RECQL2/3/4, STAR, TWNK, and XRCC4/9) have been linked to syndromic POI and are mainly implicated in metabolism function and meiosis/DNA repair. In addition, the majority of genes associated with nonsyndromic POI, widely expanded by high-throughput techniques over the last decade, have been implicated in ovarian development and meiosis/DNA repair pathways (ATG7, ATG9, ANKRD31, BMP8B, BMP15, BMPR1A, BMPR1B, BMPR2, BNC1, BRCA2, CPEB1, C14ORF39, DAZL, DIAPH2, DMC1, ERCC6, FANCL, FANCM, FIGLA, FSHR, GATA4, GDF9, GJA4, HELQ, HSF2BP, HFM1, INSL3, LHCGR, LHX8, MCM8, MCM9, MEIOB, MSH4, MSH5, NANOS3, NOBOX, NOTCH2, NR5A1, NUP107, PGRMC1, POLR3H, PRDM1, PRDM9, PSMC3IP, SOHLH1, SOHLH2, SPIDR, STAG3, SYCE1, TP63, UBR2, WDR62, and XRCC2), whereas a few are related to metabolic functions (EIF4ENIF1, KHDRBS1, MRPS22, POLR2C). Some genes, such as STRA8, FOXO3A, KIT, KITL, WNT4, and FANCE, have been shown to cause ovarian insufficiency in rodents, but mutations in these genes have yet to be elucidated in women affected by POI. Lastly, some genes have been rarely implicated in its etiology (AMH, AMHR2, ERRC2, ESR1, INHA, LMN4, POF1B, POU5F1, REC8, SMC1B). Considering the heterogeneous genetic and familial background of this disorder, we hope that an overview of literature data would reinforce that genetic screening of those patients is worthwhile and helpful for better genetic counseling and patient management.

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.

Maternal aerobic running during mid or late gestation improves the quality of oogenesis and folliculogenesis in the ovary of neonatal rats: An experimental study

Background

Regular maternal exercise in pregnancy enhances the physiological, metabolic, and psychological health of mother and fetus.

Objective

To determine the effect of maternal aerobic running during mid or late gestation on plasma levels of estrogen and progesterone and the histological alterations in the ovary of neonatal rats.

Materials and Methods

Twenty-one female Wistar rats were randomly divided into experimental groups to exercises during the 2 nd or 3 rd wk of pregnancy (n = 14) and a control group (n = 7). After birth, the neonate's blood was obtained and the estrogen and progesterone levels were evaluated. The ovaries were then removed and used for histological investigations and apoptic assessment.

Results

Higher concentrations of estrogen and progesterone were found in the neonates of the experimental groups (p = 0.001) compared to the control group. The experimental groups had a large ovarian diameter (2 nd wk: p = 0.044; 3 rd wk: p = 0.005) and angiogenesis (2 nd wk: p = 0.003; 3 rd wk: p = 0.001). In addition, significant enhancements were seen in the the experimental groups in terms of the number (2 nd wk: p = 0.017; p = 0.035) and diameter (2 nd wk: p = 0.046; 3 rd wk: p = 0.004) of primordial follicles, as well as in the diameter of primary oocytes (2 nd wk: p = 0.073; 3 rd wk: p = 0.019) compared to the control group. Moreover, rats that exercised had a lower number of apoptotic primordial follicles than the control group (2 nd wk: p = 0.001; 3 rd wk: p = 0.001).

Conclusion

It was shown that maternal aerobic running can lead to increased plasma levels of estrogen and progesterone, also improved histological characteristics of the ovary in neonatal rats.

Exploring rare cellular activity in more than one million cells by a transscale scope

In many phenomena of biological systems, not a majority, but a minority of cells act on the entire multicellular system causing drastic changes in the system properties. To understand the mechanisms underlying such phenomena, it is essential to observe the spatiotemporal dynamics of a huge population of cells at sub-cellular resolution, which is difficult with conventional tools such as microscopy and flow cytometry. Here, we describe an imaging system named AMATERAS that enables optical imaging with an over-one-centimeter field-of-view and a-few-micrometer spatial resolution. This trans-scale-scope has a simple configuration, composed of a low-power lens for machine vision and a hundred-megapixel image sensor. We demonstrated its high cell-throughput, capable of simultaneously observing more than one million cells. We applied it to dynamic imaging of calcium ions in HeLa cells and cyclic-adenosine-monophosphate in Dictyostelium discoideum, and successfully detected less than 0.01% of rare cells and observed multicellular events induced by these cells.

Single-cell RNA-Seq reveals a highly coordinated transcriptional program in mouse germ cells during primordial follicle formation

The assembly of primordial follicles in mammals represents one of the most critical processes in ovarian biology. It directly affects the number of oocytes available to a female throughout her reproductive life. Premature depletion of primordial follicles contributes to the ovarian pathology primary ovarian insufficiency (POI). To delineate the developmental trajectory and regulatory mechanisms of oocytes during the process, we performed RNA‐seq on single germ cells from newborn (P0.5) ovaries. Three cell clusters were classified which corresponded to three cell states (germ cell cyst, cyst breakdown, and follicle) in the newborn ovary. By Monocle analysis, a uniform trajectory of oocyte development was built with a series of genes showed dynamic changes along the pseudo‐timeline. Gene Ontology term enrichment revealed a significant decrease in meiosis‐related genes and a dramatic increase in oocyte‐specific genes which marked the transition from a germ cell to a functional oocyte. We then established a network of regulons by using single‐cell regulatory network inference and clustering (SCENIC) algorithm and identified possible candidate transcription factors that may maintain transcription programs during follicle formation. Following functional studies further revealed the differential regulation of the identified regulon Id2 and its family member Id1, on the establishment of primordial follicle pool by using siRNA knockdown and genetic modified mouse models. In summary, our study systematically reconstructed molecular cascades in oocytes and identified a series of genes and molecular pathways in follicle formation and development.

Long non-coding RNA Xist regulates oocyte loss via suppressing miR-23b-3p/miR-29a-3p maturation and upregulating STX17 in perinatal mouse ovaries

The fecundity of female mammals is resolved by the limited size of the primordial follicle (PF) pool formed perinatally. The establishment of PF pool is accompanied by a significant programmed oocyte death. Long non-coding RNAs (lncRNA) are central modulators in regulating cell apoptosis or autophagy in multiple diseases, however, the significance of lncRNAs governing perinatal oocyte loss remains unknown. Here we find that Yin-Yang 1 (YY1) directly binds to the lncRNA X-inactive-specific transcript (Xist) promoter and facilitates Xist expression in the perinatal mouse ovaries. Xist is highly expressed in fetal ovaries and sharply downregulated along with the establishment of PF pool after birth. Gain or loss of function analysis reveals that Xist accelerates oocyte autophagy, mainly through binding to pre-miR-23b or pre-miR-29a in the nucleus and preventing the export of pre-miR-23b/pre-miR-29a to the cytoplasm, thus resulting in decreased mature of miR-23b-3p/miR-29a-3p expression and upregulation miR-23b-3p/miR-29a-3p co-target, STX17, which is essential for timely control of the degree of oocyte death in prenatal mouse ovaries. Overall, these findings identify Xist as a key non-protein factor that can control the biogenesis of miR-23b-3p/miR-29a-3p, and this YY1-Xist-miR-23b-3p/miR-29a-3p-STX17 regulatory axis is responsible for perinatal oocyte loss through autophagy.

Demographic and evolutionary trends in ovarian function and aging

BACKGROUND

The human female reproductive lifespan is regulated by the dynamics of ovarian function, which in turn is influenced by several factors: from the basic molecular biological mechanisms governing folliculogenesis, to environmental and lifestyle factors affecting the ovarian reserve between conception and menopause. From a broader point of view, global and regional demographic trends play an additional important role in shaping the female reproductive lifespan, and finally, influences on an evolutionary scale have led to the reproductive senescence that precedes somatic senescence in humans.

OBJECTIVE AND RATIONALE

The narrative review covers reproductive medicine, by integrating the molecular mechanisms of ovarian function and aging with short-term demographic and long-term evolutionary trends.

SEARCH METHODS

PubMed and Google Scholar searches were performed with relevant keywords (menopause, folliculogenesis, reproductive aging, reproductive lifespan and life history theory). The reviewed articles and their references were restricted to those written in English.

OUTCOMES

We discuss and summarize the rapidly accumulating information from large-scale population-based and single-reproductive-cell genomic studies, their constraints and advantages in the context of female reproductive aging as well as their possible evolutionary significance on the life history trajectory from foetal-stage folliculogenesis until cessation of ovarian function in menopause. The relevant environmental and lifestyle factors and demographic trends are also discussed in the framework of predominant evolutionary hypotheses explaining the origin and maintenance of menopause.

WIDER IMPLICATIONS

The high speed at which new data are generated has so far raised more questions than it has provided solid answers and has been paralleled by a lack of satisfactory interpretations of the findings in the context of human life history theory. Therefore, the recent flood of data could offer an unprecedented tool for future research to possibly confirm or rewrite human evolutionary reproductive history, at the same time providing novel grounds for patient counselling and family planning strategies.

LSD1 contributes to programmed oocyte death by regulating the transcription of autophagy adaptor SQSTM1/p62

In female mammals, the size of the initially established primordial follicle (PF) pool within the ovaries determines the reproductive lifespan of females. Interestingly, the establishment of the PF pool is accompanied by a remarkable programmed oocyte loss for unclear reasons. Although apoptosis and autophagy are involved in the process of oocyte loss, the underlying mechanisms require substantial study. Here, we identify a new role of lysine-specific demethylase 1 (LSD1) in controlling the fate of oocytes in perinatal mice through regulating the level of autophagy. Our results show that the relatively higher level of LSD1 in fetal ovaries sharply reduces from 18.5 postcoitus (dpc). Meanwhile, the level of autophagy increases while oocytes are initiating programmed death. Specific disruption of LSD1 resulted in significantly increased autophagy and obviously decreased oocyte number compared with the control. Conversely, the oocyte number is remarkably increased by the overexpression of Lsd1 in ovaries. We further demonstrated that LSD1 exerts its role by regulating the transcription of p62 and affecting autophagy level through its H3K4me2 demethylase activity. Finally, in physiological conditions, a decrease in LSD1 level leads to an increased level of autophagy in the oocyte when a large number of oocytes are being lost. Collectively, LSD1 may be one of indispensible epigenetic molecules who protects oocytes against preterm death through repressing the autophagy level in a time-specific manner. And epigenetic modulation contributes to programmed oocyte death by regulating autophagy in mice.

Intrafollicular barriers and cellular interactions during ovarian follicle development

Follicles are composed of different interdependent cell types including oocytes, cumulus, granulosa, and theca cells. Follicular cells and oocytes exchange signaling molecules from the beginning of the development of the primordial follicles until the moment of ovulation. The follicular structure transforms during folliculogenesis; barriers form between the germ and the somatic follicular cells, and between the somatic follicular cells. As such, communication systems need to adapt to maintain the exchange of signaling molecules. Two critical barriers are established at different stages of development: the zona pellucida, separating the oocyte and the cumulus cells limiting the communication through specific connections, and the antrum, separating subpopulations of follicular cells. In both situations, communication is maintained either by the development of specialized connections as transzonal projections or by paracrine signaling and trafficking of extracellular vesicles through the follicular fluid. The bidirectional communication between the oocytes and the follicle cells is vital for driving folliculogenesis and oogenesis. These communication systems are associated with essential functions related to follicular development, oocyte competence, and embryonic quality. Here, we discuss the formation of the zona pellucida and antrum during folliculogenesis, and their importance in follicle and oocyte development. Moreover, this review discusses the current knowledge on the cellular mechanisms such as the movement of molecules via transzonal projections, and the exchange of extracellular vesicles by follicular cells to overcome these barriers to support female gamete development. Finally, we highlight the undiscovered aspects related to intrafollicular communication among the germ and somatic cells, and between the somatic follicular cells and give our perspective on manipulating the above-mentioned cellular communication to improve reproductive technologies.

Rare mutations in the complement regulatory gene CSMD1 are associated with male and female infertility

Infertility in men and women is a complex genetic trait with shared biological bases between the sexes. Here, we perform a series of rare variant analyses across 73,185 women and men to identify genes that contribute to primary gonadal dysfunction. We report CSMD1, a complement regulatory protein on chromosome 8p23, as a strong candidate locus in both sexes. We show that CSMD1 is enriched at the germ-cell/somatic-cell interface in both male and female gonads. Csmd1-knockout males show increased rates of infertility with significantly increased complement C3 protein deposition in the testes, accompanied by severe histological degeneration. Knockout females show significant reduction in ovarian quality and breeding success, as well as mammary branching impairment. Double knockout of Csmd1 and C3 causes non-additive reduction in breeding success, suggesting that CSMD1 and the complement pathway play an important role in the normal postnatal development of the gonads in both sexes.

The role of autophagy during murine primordial follicle assembly

It is generally accepted that significant germ cell loss occurs during the establishment of the primordial follicle pool in most mammalian ovaries around the time of birth. However, the underlying mechanisms responsible for these processes remain largely unknown. In this investigation, we explored the role of autophagy during the establishment of the primordial follicle pool and found that autophagy was active in this process. Our data suggested that 17.5 dpc ovaries treated with rapamycin displayed a delay in germ cell cyst breakdown resulting in more oocytes at day 5 of treatment, while, ovaries that treated with 3-MA showed the opposite effect. We found that rapamycin treatment promoted autophagy and depressed cell apoptosis increasing the number of NOBOX positive oocytes. Furthermore, our results also revealed that epigenetic regulator, Sirt1, plays a role in germ cell loss. An epigenetic inhibitor or RNAi treatment of Sirt1, showed an increased level of H4K16ac and a decreased level of autophagy. Thus, these data indicate that autophagy prevents germ cell over loss during the establishment of primordial follicle pool, and this process may be influenced by Sirt1-invovled epigenetic regulation.

Apoptosis, Autophagy, and Necrosis in Murine Embryonic Gonadal Ridges and Neonatal Ovaries: An Animal Model

BACKGROUND

In mammalian ovaries, loss of over two-thirds of germ cells happens due to cell death. Nonetheless, the exact mechanism of cell death has yet to be determined. The present basic practical study was designed to detect 3 types of programmed cell death, namely apoptosis, autophagy, and necrosis, in murine embryonic gonadal ridges and neonatal ovaries.

METHODS

Twenty gonadal ridges and ovaries from female mouse embryos 13.5 days post coitum and newborn mice 1 day postnatal were collected. The TUNEL assay was performed to evaluate apoptosis. The interplay of autophagy was evaluated by immunohistochemistry for beclin-1. Necrotic cell death was analyzed by propidium iodide (PI) staining. The count and percentage of the labeled oocytes in the gonadal ridges and ovaries were evaluated and compared using the independent t test and one-way ANOVA. A P value less than 0.05 was considered statistically significant.

RESULTS

We detected TUNEL-positive reaction in the embryonic germ cells and in the small and large oocytes of the neonatal ovaries. The germ cells and small oocytes reacted to beclin-1. PI absorption was detected in the embryonic germ cells and the large oocytes of the neonatal ovaries, but not in the small oocytes. The percentage of the TUNEL-positive and PI-labeled oocytes in the gonadal ridges was significantly higher than that in the neonatal ovaries (P<0.01 and P=0.01). In the neonatal ovaries, the percentage of the beclin-1-labeled oocytes was significantly higher than that in the embryonic phase (P<0.01).

CONCLUSION

We showed that all 3 types of programmed cell death, namely apoptosis, autophagy, and necrosis, accounted for embryonic and neonatal germ-cell loss. Our observations demonstrated a potential role for necrosis, particularly in the embryonic gonadal ridge in comparison to the neonatal ovary, in mice.

Necrosis and necroptosis in germ cell depletion from mammalian ovary

The maximum number of germ cells is present during the fetal life in mammals. Follicular atresia results in rapid depletion of germ cells from the cohort of the ovary. At the time of puberty, only a few hundred (<1%) germ cells are either culminated into oocytes or further get eliminated during the reproductive life. Although apoptosis plays a major role, necrosis as well as necroptosis, might also be involved in germ cell elimination from the mammalian ovary. Both necrosis and necroptosis show similar morphological features and are characterized by an increase in cell volume, cell membrane permeabilization, and rupture that lead to cellular demise. Necroptosis is initiated by tumor necrosis factor and operated through receptor interacting protein kinase as well as mixed lineage kinase domain-like protein. The acetylcholinesterase, cytokines, starvation, and oxidative stress play important roles in necroptosis-mediated granulosa cell death. The granulosa cell necroptosis directly or indirectly induces susceptibility toward necroptotic or apoptotic cell death in oocytes. Indeed, prevention of necrosis and necroptosis pathways using their specific inhibitors could enhance growth/differentiation factor-9 expression, improve survivability as well as the meiotic competency of oocytes, and prevent decline of reproductive potential in several mammalian species and early onset of menopause in women. This study updates the information and focuses on the possible involvement of necrosis and necroptosis in germ cell depletion from the mammalian ovary.

AMH prevents primordial ovarian follicle loss and fertility alteration in cyclophosphamide-treated mice

The follicular ovarian reserve, constituted by primordial follicles (PMFs), is established early in life, then keeps declining regularly along reproductive life. The maintenance of a normal female reproductive function implies the presence of a vast amount of dormant PMFs. This process involves a continuous repression of PMF activation into early growing follicle through the balance between factors activating the initiation of follicular growth, mainly actors of the PI3K signaling pathway, and inhibiting factors such as anti-Müllerian hormone (AMH). Any disruption of this balance may induce follicle depletion and subsequent infertility. It has been recently proposed that cyclophosphamide (Cy), an alkylating agent commonly used for treating breast cancer, triggers PMF activation, further leading to premature ovarian insufficiency. Preventing chemotherapy-induced ovarian dysfunction might represent an interesting option for preserving optimal chances of natural or medically assisted conceptions after healing. The aim of the present study was to evaluate, in a model of Cy-treated pubertal mice, whether AMH administration might restrain PMF depletion. The counting of the total PMF number within mouse ovaries showed that recombinant AMH prevented Cy-induced PMF loss. Western blot analysis revealed activation of PI3K signaling pathway after Cy administration. After AMH injection, FOXO3A phosphorylation, a main actor of PMF activation, was significantly decreased. Taken together, these results support a protective role of AMH against Cy-induced follicular loss. We also provide evidence for a possible role of autophagy in the preservation of follicular pool reserve. Therefore, concomitant recombinant AMH administration during chemotherapy might offer a new option for preserving young patients' fertility.-Sonigo, C., Beau, I., Grynberg, M., Binart, N. AMH prevents primordial ovarian follicle loss and fertility alteration in cyclophosphamide-treated mice.

Activating the Anaphase Promoting Complex to Enhance Genomic Stability and Prolong Lifespan

In aging cells, genomic instability is now recognized as a hallmark event. Throughout life, cells encounter multiple endogenous and exogenous DNA damaging events that are mostly repaired, but inevitably DNA mutations, chromosome rearrangements, and epigenetic deregulation begins to mount. Now that people are living longer, more and more late life time is spent suffering from age-related disease, in which genomic instability plays a critical role. However, several major questions remain heavily debated, such as the following: When does aging start? How long can we live? In order to minimize the impact of genomic instability on longevity, it is important to understand when aging starts, and to ensure repair mechanisms remain optimal from the very start to the very end. In this review, the interplay between the stress and nutrient response networks, and the regulation of homeostasis and genomic stability, is discussed. Mechanisms that link these two networks are predicted to be key lifespan determinants. The Anaphase Promoting Complex (APC), a large evolutionarily conserved ubiquitin ligase, can potentially serve this need. Recent work demonstrates that the APC maintains genomic stability, mounts a stress response, and increases longevity in yeast. Furthermore, inhibition of APC activity by glucose and nutrient response factors indicates a tight link between the APC and the stress/nutrient response networks.

Temperature- vs. estrogen-induced sex determination in Caiman latirostris embryos: Both females, but with different expression patterns of key molecules involved in ovarian development

Caiman latirostris is a species with temperature dependent sex determination (TSD), which implies that the incubation temperature of the eggs is the main factor that determines the sex during a thermo-sensitive period (TSP). However, estrogens play a critical role in this process. The administration of 17β-estradiol (E₂) previous to TSP overrides the effects of male incubation temperature, producing phenotypic females. This effect has been defined as sex reversal or estrogen-induced sex determination (E₂SD). The aim of the present study is to describe similarities and differences in the effects of TSD and E₂SD treatment conditions on ovary development. Our results show that the two treatment conditions studied are able to produce different ovaries. Treatment with E₂ modified the expression pattern of estrogen receptor alpha and progesterone receptor, and expression of the enzyme aromatase. Moreover, in E₂SD females, the proliferation/apoptosis dynamic was also altered and high expression of TAp63 was observed suggesting the presence of greater DNA damage in germ cells. To the best of our knowledge, this is the first report that describes the morphology of the female gonad of C. latirostris in three stages of embryonic development and shows the expression of TAp63 during the gonad development of a reptile. It is important to emphasize that the changes demonstrated in E₂SD female gonads of embryos show that environmental compounds with proven estrogenic activity alter the follicular dynamics of C. latirostris in neonatal as much as in juvenile animals, endangering their reproductive health and possibly bringing consequences to ecology and evolution.

Different cell death types determination in juvenile mice ovarian follicles

Follicular atresia is a phenomenon that leads to evacuation of the ovary from the oocytes and the occurrence of menopause. The contribution of various types of cell death in atresia at different follicular developmental stages requires extensive investigation. In this study, we evaluated 3 types of programmed cell death (PCD), apoptosis, autophagy, and necrosis, in juvenile mouse ovary when we can observe all follicular stages as well as atresia. Ovaries from juvenile mice on the 21st post-natal (PN) day were prepared histologically for terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) to evaluate apoptosis and immunohistochemistry for beclin-1 to evaluate the autophagy marker. Necrotic cell death was also assessed by penetration of propidium iodide (PI). The count and percentage of the labeled follicles at different stages in the ovaries were evaluated and compared using the Kruskal-Wallis and Mann-Whitney tests. We detected TUNEL-positive granulosa cells in pre-antral and antral follicles but not in the primordial and primary follicles. Somatic cells and oocytes of primordial, primary, pre-antral and antral follicles reacted to beclin-1. The percentage of the PI-labeled primordial and primary follicles were significantly higher than the beclin-1 positive (P=0.01 and P=0.01). In conclusion, we showed that apoptosis, autophagy, and necrosis play a role in follicular atresia and the contributions of each one depends on the follicular stages. It was also demonstrated that necrosis happens particularly in the small follicles while in the large one, all three cell death types occurred with an equal ratio.