Follicular growth: the basic event in the mouse and human ovary

Single-Cell Transcriptomic Analysis of the Potential Mechanisms of Follicular Development in Stra8-Deficient Mice

Follicle development is a critical process in mammalian reproduction, with significant implications for ovarian reserve and fertility. Stra8 is a known key factor regulating the initiation of meiosis; however, oocyte-like cells still appear in Stra8-deficient mice. Nevertheless, the underlying mechanism remains unclear and requires further investigation. Therefore, we used single-cell RNA sequencing to construct a comprehensive transcriptional atlas of ovarian cells from both wild-type and Stra8-deficient mice at embryonic stages E14.5 and E16.5. With stringent quality control, we obtained a total of 14,755 single cells of six major cell types. A further fine-scale analysis of the germ cell clusters revealed notable heterogeneity between wild-type and Stra8-deficient mice. Compared to the wild-type mice, the deficiency in Stra8 led to the downregulation of meiosis-related genes (e.g., Pigp, Tex12, and Sycp3), and the upregulation of apoptosis-related genes (e.g., Fos, Jun, and Actb), thereby hindering the meiotic process. Notably, we observed that, following Stra8 deficiency, the expression levels of Sub1 and Stk31 remained elevated at this stage. Furthermore, an RNA interference analysis confirmed the potential role of these genes as regulatory factors in the formation of primordial follicle-like cells. Additionally, Stra8 deficiency disrupted the signaling between germ cells and pregranulosa cells that is mediated by Mdk-Sdc1, leading to the abnormal expression of the PI3K/AKT signaling pathway. Together, these results shed light on the molecular processes governing germ cell differentiation and folliculogenesis, emphasizing the complex role of Stra8 in ovarian function.

Lymphangiogenesis in mouse embryonic and early postnatal ovaries

BACKGROUND

The critical importance and remodeling capacity of the blood vasculature within the ovary have been extensively analyzed, while the lymphatic vasculature has received limited attention, and its characteristics were reported by only a few studies.

OBJECTIVES

To investigate the morphological patterns of lymphatic vessel formation in mouse embryonic and early postnatal ovary.

MATERIAL AND METHODS

Immunostaining was performed on ovarian tissues from Prox1-EGFP transgenic mice and wild-type mice to investigate the lymphangiogenesis, and the CD31 was employed to label vascular endothelium and LYVE1 and Prox1 as co-markers for lymphatic endothelium.

RESULT

Prox1+ cells, LYVE1+ cells, and Prox1-EGFP+/LYVE1+ vessels were absent in the medulla near the ovarian hilum until P7, and YAP1 was expressed in the nucleus and cytoplasm of granulosa cells, alongside the observation of scattered primary follicles within the ovary. By P10, these markers were abundantly expressed in the ovarian medulla, while YAP1 was localized primarily in the cytoplasm of granulosa cells, alongside the occurrence of secondary follicles. By P14, Prox1+ cells, LYVE1+ cells, and Prox1-EGFP+/LYVE1+ vessels extended to the cortex, and YAP1 shifted to the nuclei of granulosa cells, alongside the reaching of follicles to the antral stage. From P14 to P28, these markers exhibited a further increasing trend, while YAP1 localized in the nucleus of granulosa cells, alongside the progress of follicles to the preovulatory stage.

CONCLUSION

Ovarian lymphangiogenesis in the mouse began on postnatal day 7 and subsequently developed from the medulla to the cortex. Additionally, ovarian lymphangiogenesis occurred in synchrony with follicular maturation, during which YAP1 exhibited an ectopic expression pattern.

Graduate Student Literature Review: A review of mathematical modeling methods for bovine hormone dynamics

This article explores various approaches to modeling the bovine estrus cycle, focusing on improving estrus detection to enhance reproductive management in dairy cattle. The review examines a range of mathematical models, including hormonal models based on ordinary differential equations that simulate hormone dynamics, as well as follicular competition models that track the maturation of individual follicles. In addition to these, precision dairy monitoring technologies (PDMT) are discussed, which utilize real-time physiological and behavioral data to provide predictive insights into estrus. The article assesses the effectiveness of both traditional modeling approaches and PDMT in improving breeding efficiency, minimizing labor, and optimizing herd management practices.

Accuracy and errors about the human ovary; the good, bad and the ugly

This collection is dedicated to the memory of Professor Ken McNatty and Professor Rex Scaramuzzi, both of whom made outstanding contributions to the understanding of reproductive, and particularly ovarian, biology. In fact, the impetus for this commentary began when the authors questioned why some textbooks continued to print an earlier theory of ovarian development by Haward Sawyer and Ken McNatty (Sawyer et al . 2002 ), when important additional findings were published in 2013 (Hummitzsch et al . 2013 ). The authors question why textbooks, websites and YouTube videos continue to present misinformation about the ovary with statements and illustrations that are patently inaccurate or incorrect. We are aware that medical and science textbook publishers may take no responsibility for the accuracy of content by printing a disclaimer to this effect. Webpages and YouTube videos, in the main, exist with no such caveat. Do authors of textbooks accept responsibility to publish up-to-date factual material and avoid demonstrably incorrect information? In some cases, apparently not. Here we will show examples from the ovarian biology that we encounter regularly, that authors often do not check nor update content for the multiple book editions published over decades. If original sources are not consulted by authors, where are they getting their information? Erroneous statements and dogma continue to be represented in scientific literature as established facts. Textbooks, in particular, are supposed to be reliable sources of information. Unfortunately, too many mislead students and scholars and promulgate misinformation. If the contributions of Professor Ken McNatty, Professor Rex Scaramuzzi and others are to be truly valuable, then knowledge amplified by textbooks and the web must at least be accurate.

Oocyte-specific EXOC5 expression is required for mouse oogenesis and folliculogenesis

EXOC5 is a crucial component of a large multi-subunit tethering complex, the exocyst complex, that is required for fusion of secretory vesicles with the plasma membrane. Exoc5 deleted mice die as early embryos. Therefore, to determine the role of EXOC5 in follicular and oocyte development, it was necessary to produce a conditional knockout (cKO), Zp3-Exoc5-cKO, in which Exoc5 was deleted only in oocytes. The first wave of folliculogenesis appeared histologically normal and progressed to the antral stage. However, after IVF with normal sperm, oocytes collected from the first wave (superovulated 21-day-old cKO mice) were shown to be developmentally incompetent. Adult follicular waves did not progress beyond the secondary follicle stage where they underwent apoptosis. Female cKO mice were infertile. Overall, these data suggest that the first wave of folliculogenesis is less sensitive to oocyte-specific loss of Exoc5, but the resulting gametes have reduced developmental competence. In contrast, subsequent waves of folliculogenesis require oocyte-specific Exoc5 for development past the preantral follicle stage. The Zp3-Exoc5-cKO mouse provides a model for disrupting folliculogenesis that also enables the separation between the first and subsequent waves of folliculogenesis.

The origin of betaine in mouse oocytes and preimplantation embryos†

Betaine has important roles in preimplantation mouse embryos, including as an organic osmolyte that functions in cell volume regulation in the early preimplantation stages and as a donor to the methyl pool in blastocysts. The origin of betaine in oocytes and embryos was largely unknown. Here, we found that betaine was present from the earliest stage of growing oocytes. Neither growing oocytes nor early preantral follicles could take up betaine, but antral follicles were able to transport betaine and supply the enclosed oocyte. Betaine is synthesized by choline dehydrogenase, and female mice lacking Chdh did not have detectable betaine in their oocytes or early embryos. Supplementing betaine in their drinking water restored betaine in the oocyte only when supplied during the final stages of antral follicle development but not earlier in folliculogenesis. Together with the transport results, this implies that betaine can only be exogenously supplied during the final stages of oocyte growth. Previous work showed that the amount of betaine in the oocyte increases sharply during meiotic maturation due to upregulated activity of choline dehydrogenase within the oocyte. This betaine present in mature eggs was retained after fertilization until the morula stage. There was no apparent role for betaine uptake via the SIT1 (SLC6A20) betaine transporter that is active at the 1- and 2-cell stages. Instead, betaine was apparently retained because its major route of efflux, the volume-sensitive organic osmolyte - anion channel, remained inactive, even though it is expressed and capable of being activated by a cell volume increase.

Hypoxia Leads to Diminished Ovarian Reserve in an Age-Dependent Manner

OBJECTIVES

Perinatal hypoxia causes premature activation and initiation of growth in dormant follicles, leading to diminished ovarian reserve. An indirect mechanism such as the release of stress-related hormones may influence ovarian follicle recruitment under hypoxic conditions. We wanted to determine whether hypoxic ovarian damage results from increased follicle growth and "burnout" or from increased apoptosis and whether this damage is age-dependent.

DESIGN

Animal study was conducted.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Using adult 6-week-old (n = 8) and one-day-old newborn (n = 20) ICR (CD-1) female mice, ovarian follicular counts were conducted on H&E-stained sections.

METHODS

Immunohistochemistry was performed on sections stained with Ki-67, anti-Caspase 3, and anti-FOXO3A.

RESULTS

Exposure to hypoxia resulted in significantly reduced proportion of primordial follicles versus normoxia in both adult dams and newborn pups (3.17 ± 2.75 vs. 17.89 ± 4.4%; p = 0.004; 40.59 ± 14.88 vs. 81.92 ± 31.56%, p = 0.001, respectively), concomitant with increased growing-primary and secondary follicles, and more pronounced in adult dams versus newborn pups (6-fold vs. 2-fold, respectively). Ki67 staining revealed higher scores of cell proliferation in follicular granulosa cells after exposure to hypoxia than normoxia. However, Caspase 3 and Foxo3A staining did not show any differences in these markers of apoptosis in oocytes, granulosa cells, theca cells, or stromal cells when exposed to hypoxia versus normoxia.

LIMITATIONS

The current study has several limitations; first, the sample size for each group is relatively small, which could limit the generalizability of the findings. Second, the study used an ex vivo culture system, which may not fully capture the complex interactions that occur in the whole animal. Third, the exposure to hypoxia only lasted for 3 h, which may not be long enough to observe all the potential effects. In addition, the study only analyzed specific markers of apoptosis in a few cell types, and other cell types or apoptotic pathways might be involved. Lastly, the study provides evidence for accelerated follicular activation and decreased ovarian reserve, but the underlying mechanisms are not fully explored.

CONCLUSIONS

Direct tissue hypoxia led to premature activation and initiation of growth in dormant follicles leading to diminished ovarian reserve. Hypoxic damage is age-dependent, with adult ovaries more susceptible than newborn ovaries. These findings support the possibility of follicular "burn out" as a potential mechanism responsible for hypoxia-induced loss of ovarian reserve.

Impact of prepubertal bovine ovarian tissue pre-freeze holding duration on follicle quality

Ovarian tissue cryopreservation prior to gonadotoxic treatment is the only recommended option for fertility preservation in prepubertal girls. Due to the technical complexity of this technique, limited number of centres across the world are equipped to offer the facility. Hence, the retrieved ovarian tissue needs to be maintained at hypothermic temperature (4 °C) for long time during shipment. The time taken between tissue retrieval and cryopreservation could influence the functionality of cells during fertility restoration. This study explored the tissue integrity and follicle quality of ovarian cortical slices subjected to pre-freeze holding for various time durations in vitro. Prepubertal bovine ovarian tissue from < 12 months old animals were handled at hypothermic holding (4 °C) for 0, 24, 48 and 72 h. The tissues were assessed for follicle viability through confocal analysis of live-dead labelled samples, and follicle quality and tissue integrity through histology. Results have shown that follicle viability, and overall follicle quality were not significantly affected at the end of 72 h hypothermic holding. Though, the observation reassures extended hypothermic holding prior to freezing, findings need to be validated in human tissue prior to use in clinical fertility preservation programs.

Beyond apoptosis: evidence of other regulated cell death pathways in the ovary throughout development and life

BACKGROUND

Regulated cell death is a fundamental component of numerous physiological processes; spanning from organogenesis in utero, to normal cell turnover during adulthood, as well as the elimination of infected or damaged cells throughout life. Quality control through regulation of cell death pathways is particularly important in the germline, which is responsible for the generation of offspring. Women are born with their entire supply of germ cells, housed in functional units known as follicles. Follicles contain an oocyte, as well as specialized somatic granulosa cells essential for oocyte survival. Follicle loss-via regulated cell death-occurs throughout follicle development and life, and can be accelerated following exposure to various environmental and lifestyle factors. It is thought that the elimination of damaged follicles is necessary to ensure that only the best quality oocytes are available for reproduction.

OBJECTIVE AND RATIONALE

Understanding the precise factors involved in triggering and executing follicle death is crucial to uncovering how follicle endowment is initially determined, as well as how follicle number is maintained throughout puberty, reproductive life, and ovarian ageing in women. Apoptosis is established as essential for ovarian homeostasis at all stages of development and life. However, involvement of other cell death pathways in the ovary is less established. This review aims to summarize the most recent literature on cell death regulators in the ovary, with a particular focus on non-apoptotic pathways and their functions throughout the discrete stages of ovarian development and reproductive life.

SEARCH METHODS

Comprehensive literature searches were carried out using PubMed and Google Scholar for human, animal, and cellular studies published until August 2022 using the following search terms: oogenesis, follicle formation, follicle atresia, oocyte loss, oocyte apoptosis, regulated cell death in the ovary, non-apoptotic cell death in the ovary, premature ovarian insufficiency, primordial follicles, oocyte quality control, granulosa cell death, autophagy in the ovary, autophagy in oocytes, necroptosis in the ovary, necroptosis in oocytes, pyroptosis in the ovary, pyroptosis in oocytes, parthanatos in the ovary, and parthanatos in oocytes.

OUTCOMES

Numerous regulated cell death pathways operate in mammalian cells, including apoptosis, autophagic cell death, necroptosis, and pyroptosis. However, our understanding of the distinct cell death mediators in each ovarian cell type and follicle class across the different stages of life remains the source of ongoing investigation. Here, we highlight recent evidence for the contribution of non-apoptotic pathways to ovarian development and function. In particular, we discuss the involvement of autophagy during follicle formation and the role of autophagic cell death, necroptosis, pyroptosis, and parthanatos during follicle atresia, particularly in response to physiological stressors (e.g. oxidative stress).

WIDER IMPLICATIONS

Improved knowledge of the roles of each regulated cell death pathway in the ovary is vital for understanding ovarian development, as well as maintenance of ovarian function throughout the lifespan. This information is pertinent not only to our understanding of endocrine health, reproductive health, and fertility in women but also to enable identification of novel fertility preservation targets.

Mapping Human Reproduction with Single-Cell Genomics

The trillions of cells in the human body develop as a result of the fusion of two extremely specialized cells: an oocyte and a sperm. This process is essential for the continuation of our species, as it ensures that parental genetic information is mixed and passed on from generation to generation. In addition to producing oocytes, the female reproductive system must provide the environment for the appropriate development of the fetus until birth. New genomic and computational tools offer unique opportunities to study the tight spatiotemporal regulatory mechanisms that are required for the cycle of human reproduction. This review explores how single-cell technologies have been used to build cellular atlases of the human reproductive system across the life span and how these maps have proven useful to better understand reproductive pathologies and dissect the heterogeneity of in vitro model systems. Expected final online publication date for the Annual Review of Genomics and Human Genetics, Volume 23 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The Crazy Ovary

From fetal life until senescence, the ovary is an extremely active tissue undergoing continuous structural and functional changes. These ever-changing events are best summarized by a quotation attributed to Plato when describing motion in space and time-'nothing ever is but is always becoming…'. With respect to the ovary, these changes include, at the beginning, the processes of follicular formation and thereafter those of follicular growth and atresia, steroidogenesis, oocyte maturation, and decisions relating to the number of mature oocytes that are ovulated for fertilization and the role of the corpus luteum. The aims of this review are to offer some examples of these complex and hitherto unknown processes. The ones herein have been elucidated from studies undertaken in vitro or from normal in vivo events, natural genetic mutations or after experimental inactivation of gene function. Specifically, this review offers insights concerning the initiation of follicular growth, pathologies relating to poly-ovular follicles, the consequences of premature loss of germ cells or oocytes loss, the roles of AMH (anti-Müllerian hormone) and BMP (bone morphogenetic protein) genes in regulating follicular growth and ovulation rate together with species differences in maintaining luteal function during pregnancy. Collectively, the evidence suggests that the oocyte is a key organizer of normal ovarian function. It has been shown to influence the phenotype of the adjacent somatic cells, the growth and maturation of the follicle, and to determine the ovulation rate. When germ cells or oocytes are lost prematurely, the ovary becomes disorganized and a wide range of pathologies may arise.

Figla promotes secondary follicle growth in mature mice

The in vitro growth (IVG) of human follicles is a potential fertility option for women for whom cryopreserved ovarian tissues cannot be transplanted due to the risk of cancer cell reintroduction; however, there is currently no established method. Furthermore, optimal IVG conditions may differ between the follicles of adult and pre-pubertal females due to molecular differences suggested by basic research. To systematically identify differences between the secondary follicles of adult and pre-pubertal females, a comparative transcriptomic study using mice was conducted herein. Among differentially expressed genes (DEGs), Figla was up-regulated in mature mice. We successfully down-regulated Figla expression in secondary follicle oocytes by a Figla siRNA microinjection, and the subsequent IVG of follicles showed that the diameter of these follicles was smaller than those of controls in mature mice, whereas no significant difference was observed in premature mice. The canonical pathways of DEGs between control and Figla-reduced secondary follicles suggest that Figla up-regulates VDR/RXR activation and down-regulates stem cell pluripotency as well as estrogen signaling. We demonstrated for the first time that folliculogenesis of the secondary follicles of premature and mature mice may be regulated by different factors, such as Figla with its possible target genes, providing insights into optimal IVG conditions for adult and pre-pubertal females, respectively.

Genome diversity and instability in human germ cells and preimplantation embryos

Genome diversity is essential for evolution and is of fundamental importance to human health. Generating genome diversity requires phases of DNA damage and repair that can cause genome instability. Humans have a high incidence of de novo congenital disorders compared to other organisms. Recent access to eggs, sperm and preimplantation embryos is revealing unprecedented rates of genome instability that may result in infertility and de novo mutations that cause genomic imbalance in at least 70% of conceptions. The error type and incidence of de novo mutations differ during developmental stages and are influenced by differences in male and female meiosis. In females, DNA repair is a critical factor that determines fertility and reproductive lifespan. In males, aberrant meiotic recombination causes infertility, embryonic failure and pregnancy loss. Evidence suggest germ cells are remarkably diverse in the type of genome instability that they display and the DNA damage responses they deploy. Additionally, the initial embryonic cell cycles are characterized by a high degree of genome instability that cause congenital disorders and may limit the use of CRISPR-Cas9 for heritable genome editing.

New Anti-Müllerian Hormone Target Genes Involved in Granulosa Cell Survival in Women With Polycystic Ovary Syndrome

PURPOSE

A protective effect of anti-Müllerian hormone (AMH) on follicle atresia was recently demonstrated using long-term treatments, but this effect has never been supported by mechanistic studies. This work aimed to gain an insight into the mechanism of action of AMH on follicle atresia and on how this could account for the increased follicle pool observed in women with polycystic ovary syndrome (PCOS).

METHODS

In vivo and in vitro experiments were performed to study the effects of AMH on follicle atresia and on the proliferation and apoptosis of granulosa cells (GCs). RNA-sequencing was carried out to identify new AMH target genes in GCs. The expression of some of these genes in GCs from control and PCOS women was compared using microfluidic real time quantitative RT-PCR.

RESULTS

A short-term AMH treatment prevented follicle atresia in prepubertal mice. Consistent with this result, AMH inhibited apoptosis and promoted proliferation of different models of GCs. Moreover, integrative biology analyses of 965 AMH target genes identified in 1 of these GC models, confirmed that AMH had initiated a gene expression program favoring cell survival and proliferation. Finally, on 43 genes selected among the most up- and down-regulated AMH targets, 8 were up-regulated in GCs isolated from PCOS women, of which 5 are involved in cell survival.

MAIN CONCLUSIONS

Our results provide for the first time cellular and molecular evidence that AMH protects follicles from atresia by controlling GC survival and suggest that AMH could participate in the increased follicle pool of PCOS patients.

Postpartum ovulation and early pregnancy in the menstruating spiny mouse, Acomys cahirinus

Egyptian spiny mice are the only known species to have human-like menstruation and a postpartum ovulation. Unfortunately, no endocrine or morphological evidence has been provided for a postpartum ovulation in spiny mice, and while later stages of pregnancy have been well studied, early events including embryo implantation and spiral artery remodelling have not been reported. This study compared the sex steroid endocrinology and reproductive tract morphology of dams at eight timepoints (n = 40) postpartum to determine the timing of ovulation and the timing and invasiveness of embryo implantation in A. cahirinus. Reproductive tracts were fixed and stained for histology and immunohistochemistry, and plasma was prepared for enzyme-linked immunosorbent assay. Ovarian histology and estradiol-17B concentrations indicate ovulation within 48 h of parturition and then immediate resumption of follicular growth. Uterine histology and immunohistochemistry revealed progressive epithelial repair, endometrial growth and spiral artery assembly and remodelling in dams postpartum. Blastocysts were seen in the uterine lumen at day 4-5 postpartum and embryos had implanted superficially with minimal stromal invasion by day 5-6. This study provides further evidence for the unique, humanesque reproductive biology of spiny mice and for a postpartum ovulation using endocrine and morphological changes observed during early pregnancy. Taken together, our data suggest that spiny mice may act as appropriate models of human pregnancy disorders such as implantation failure or pre-eclampsia.

Comparison of serum antimüllerian hormone levels after robotic-assisted vs. laparoscopic approach for ovarian cystectomy in endometrioma

OBJECTIVE

Serum antimüllerian hormone (sAMH) is regarded as a useful marker in predicting for ovarian functional reserve. To evaluate whether postoperative change in ovarian reserve differs between robotic-assisted and laparoscopic single-site ovarian cystectomy in patients with ovarian endometrioma by comparing sAMH levels.

STUDY DESIGN

The perioperative outcomes in 94 patients with ovarian endometrioma who underwent robotic assisted (n = 40) or laparoscopic (n = 54) cystectomy were compared retrospectively. The sAMH levels were measured by enzyme immunoassay preoperatively and at 3 months and 6 months after surgery. The difference and ratio of sAMH levels between preoperative and 3 months, 6 months after cystectomy were compared between robotic-assisted and laparoscopic approach for predicting which method is better for preservation of ovarian function.

RESULT(S)

The sAMH levels were obviously decreased after the surgery (ratio of sAMH levels between preoperative and 3 months, 0.49 ± 0.46 versus 0.52 ± 0.28 ng/mL, mean ± standard deviation) in both groups. There was no difference of the recovery sAMH level at 6 months (ratio of 6 months sAMH to preoperative sAMH level) after cystectomy in unilateral ovarian cystectomy. However, in patients with bilateral endometrioma, the recovery of sAMH level was higher in robotic assisted approach than those of laparoscopic surgery (0.40 ± 0.24 versus 0.21 ± 0.23, p = 0.009). In multivariate linear regression analysis, the coefficient of robot surgery was 0.442 (p = 0.028).

CONCLUSION(S)

In our study, robotic-assisted cystectomy had higher preservation of ovarian function than the laparoscopic approach for bilateral ovarian endometrioma, but not for unilateral endometrioma. The robotic-assisted approach could be considered for preserving ovarian function in patients with bilateral ovarian endometrioma.

Accelerated Ovarian Failure as a Unique Model to Study Peri-Menopause Influence on Alzheimer's Disease

Despite decades of extensive research efforts, efficacious therapies for Alzheimer's disease (AD) are lacking. The multi-factorial nature of AD neuropathology and symptomatology has taught us that a single therapeutic approach will most likely not fit all. Women constitute ~70% of the affected AD population, and pathology and rate of symptoms progression are 2-3 times higher in women than men. Epidemiological data suggest that menopausal estrogen loss may be causative of the more severe symptoms observed in AD women, however, results from clinical trials employing estrogen replacement therapy are inconsistent. AD pathological hallmarks-amyloid β (Aβ), neurofibrillary tangles (NFTs), and chronic gliosis-are laid down during a 20-year prodromal period before clinical symptoms appear, which coincides with the menopause transition (peri-menopause) in women (~45-54-years-old). Peri-menopause is marked by widely fluctuating estrogen levels resulting in periods of irregular hormone-receptor interactions. Recent studies showed that peri-menopausal women have increased indicators of AD phenotype (brain Aβ deposition and hypometabolism), and peri-menopausal women who used hormone replacement therapy (HRT) had a reduced AD risk. This suggests that neuroendocrine changes during peri-menopause may be a trigger that increases risk of AD in women. Studies on sex differences have been performed in several AD rodent models over the years. However, it has been challenging to study the menopause influence on AD due to lack of optimal models that mimic the human process. Recently, the rodent model of accelerated ovarian failure (AOF) was developed, which uniquely recapitulates human menopause, including a transitional peri-AOF period with irregular estrogen fluctuations and a post-AOF stage with low estrogen levels. This model has proven useful in hypertension and cognition studies with wild type animals. This review article will highlight the molecular mechanisms by which peri-menopause may influence the female brain vulnerability to AD and AD risk factors, such as hypertension and apolipoprotein E (APOE) genotype. Studies on these biological mechanisms together with the use of the AOF model have the potential to shed light on key molecular pathways underlying AD pathogenesis for the development of precision medicine approaches that take sex and hormonal status into account.

Low glucose availability stimulates progesterone production by mouse ovaries in vitro

Steroid production by the ovary is primarily stimulated by gonadotropins but can also be affected by biological cues that provide information about energy status and environmental stress. To further understand which metabolic cues the ovary can respond to, we exposed gonadotropin-stimulated mouse ovaries in vitro to glucose metabolism inhibitors and measured steroid accumulation in media. Gonadotropin-stimulated ovaries exposed to 2-deoxy-d-glucose increased progesterone production and steroidogenic acute regulatory protein mRNA levels. However, oocytes and granulosa cells in antral follicles do not independently mediate this response because targeted treatment of these cell types with a different inhibitor of glucose metabolism (bromopyruvic acid) did not affect progesterone production. Elevated progesterone production is consistent with the homeostatic role of progesterone in glucose regulation in mammals. It also may regulate follicle growth and/or atresia within the ovary. These results suggest that ovaries can regulate glucose homeostasis in addition to their primary role in reproductive activity.

Detrimental effect of maternal and post-weaning high-fat diet on the reproductive function in the adult female offspring rat: roles of insulin-like growth factor 2 and the ovarian circadian clock

PURPOSE

We evaluate the impact of maternal and post-weaning high-fat (HF) diet on ovarian follicular population, steroidogenesis, and gene expression with a focus on the circadian clock system and insulin-like growth factor 2 (Igf2) in adult offspring ovaries, and to elucidate whether a maternal and post-weaning diet confers similar risks.

METHODS

Virgin Sprague-Dawley rats were fed with normal chow (C) diet or HF diet for 5 weeks before mating, during gestation, and lactation. Female offspring were fed with the C or HF diet from weaning to 6 months of age, resulting in four study groups (n = 6 per group): C/C, C/HF, HF/C, and HF/HF.

RESULTS

Ovaries from offspring exposed to post-weaning HF diet (i.e., the C/HF and HF/HF groups) had a decrease in small follicle numbers, but with similar numbers of antral follicles and corpora lutea. Offspring from HF-fed dams (i.e., the HF/C and HF/HF groups) had increased plasma estradiol concentrations and decreased luteinizing hormone levels at 6 months of age. In addition, Igf2 and each of the circadian rhythm core genes Clock, Per1, Per2, and Per3 were increased in the ovaries of offspring exposed to maternal HF diet (both HF/C and HF/HF groups).

CONCLUSIONS

Maternal and post-weaning HF diet programs the reproductive profile of the female offspring in adult life through different manners. Post-weaning HF intake resulted in the reduction of small follicles in adulthood, whereas maternal HF diet had long-term deleterious consequences on female offspring steroidogenesis and coincided with alteration of the upregulation of the imprinted gene Igf2 and changes in ovarian circadian rhythms.

A novel action of follicle-stimulating hormone in the ovary promotes estradiol production without inducing excessive follicular growth before puberty

In cyclic females, FSH stimulates ovarian estradiol (E2) production and follicular growth up to the terminal stage. A transient elevation in circulating FSH and E2 levels occurs shortly after birth. But what could be the action of FSH on the ovary during this period, and in particular how it stimulates ovarian steroidogenesis without supporting terminal follicular maturation is intriguing. By experimentally manipulating FSH levels, we demonstrate in mice that the mid-infantile elevation in FSH is mandatory for E2 production by the immature ovary, but that it does not stimulate follicle growth. Importantly, FSH increases aromatase expression to stimulate E2 synthesis, however it becomes unable to induce cyclin D2, a major driver of granulosa cell proliferation. Besides, although FSH prematurely induces luteinizing hormone (LH) receptor expression in granulosa cells, LH pathway is not functional in these cells to induce their terminal differentiation. In line with these results, supplying infantile mice with a superovulation regimen exacerbates E2 production, but it does not stimulate the growth of follicles and it does not induce ovulation. Overall, our findings unveil a regulation whereby high postnatal FSH concentrations ensure the supply of E2 required for programming adult reproductive function without inducing follicular maturation before puberty.

Potential Use of Antiapoptotic Proteins and Noncoding RNAs for Efficient In Vitro Follicular Maturation and Ovarian Bioengineering

In vitro culture of ovarian follicles is a promising bioengineering technique for preserving fecundity in reproductive-aged female by providing fertilizable oocytes. Successful clinical application should be preceded by developing the protocols that can efficiently overcome follicular cell apoptosis since the apoptosis is a critical phenomenon in in vivo folliculogenesis and in in vitro follicular maturation. Numerous prosurvival and antiapoptotic molecules, including follicular developmental regulators, have been reported to be involved in the intraovarian apoptosis. The authors searched literature and analyzed the current knowledge of these proteins and noncoding RNAs, and their antiapoptotic roles in the dynamics of follicular development in vivo and in vitro. Two-dimensional (2D) culture method has widely been used, however, with recent emergence of various biomaterials, three-dimensional (3D) culture is also considered a proper environment for maintenance of solid structure of ovarian follicles. The identification of candidate paracrine and endocrine intracellular effectors that are responsible for the coordination occurring between oocyte, granulosa, and theca cells during follicular development was explored in this review, to assess the possibility of their use as antiapoptotic factors in establishing more efficacious 2D or 3D in vitro follicular microenvironment. The retrieved information will provide an inventory and the insight for defining more sophisticated culture conditions that are essential for functional artificial ovarian bioengineering.

Rac1 modulates the formation of primordial follicles by facilitating STAT3-directed Jagged1, GDF9 and BMP15 transcription in mice

The size of the primordial follicle pool determines the reproductive potential of mammalian females, and establishment of the pool is highly dependent on specific genes expression. However, the molecular mechanisms by which the essential genes are regulated coordinately to ensure primordial follicle assembly remain a mystery. Here, we show that the small GTPase Rac1 plays an indispensable role in controlling the formation of primordial follicles in mouse ovary. Employing fetal mouse ovary organ culture system, we demonstrate that disruption of Rac1 retarded the breakdown of germline cell cysts while Rac1 overexpression accelerated the formation of primordial follicles. In addition, in vivo inhibitor injection resulted in the formation of multi-oocyte follicles. Subsequent investigation showed that Rac1 induced nuclear import of STAT3 by physical binding. In turn, nuclear STAT3 directly activated the transcription of essential oocyte-specific genes, including Jagged1, GDF9, BMP15 and Nobox. Further, GDF9 and BMP15 regulated the translation of Notch2 via mTORC1 activation in pregranulosa cells. Overexression or addition of Jagged1, GDF9 and BMP15 not only reversed the effect of Rac1 disruption, but also accelerated primordial follicle formation via Notch2 signaling activation. Collectively, these results indicate that Rac1 plays important roles as a key regulator in follicular assembly.

Inhibitors of c-Jun phosphorylation impede ovine primordial follicle activation

STUDY HYPOTHESIS

Is the c-Jun-N-terminal kinase (JNK) pathway implicated in primordial follicle activation?

STUDY FINDING

Culture of ovine ovarian cortex in the presence of two different c-Jun phosphorylation inhibitors impeded pre-antral follicle activation.

WHAT IS KNOWN ALREADY

Despite its importance for fertility preservation therapies, the mechanisms of primordial follicle activation are poorly understood. Amongst different signalling pathways potentially involved, the JNK pathway has been previously shown to be essential for cell cycle progression and pre-antral follicle development in mice.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

Ovine ovarian cortex pieces were cultured with varying concentrations of SP600125, JNK inhibitor VIII or anti-Mullerian hormone (AMH) in the presence of FSH for 9 days. Follicular morphometry and immunohistochemistry for proliferating cell nuclear antigen (PCNA), apoptosis and follicle activation (Foxo3a) were assessed.

MAIN RESULTS AND THE ROLE OF CHANCE

Inhibition of primordial follicle activation occurred in the presence of SP600125, JNK inhibitor VIII and AMH when compared with controls (all P < 0.05) after 2 days of culture. However, only in the highest concentrations used was the inhibition of activation associated with induction of follicular apoptosis (P < 0.05). In growing follicles, PCNA antigen expression was reduced when the JNK inhibitors or AMH were used (P < 0.05 versus control), indicating reduced proliferation of the somatic compartment.

LIMITATIONS, REASONS FOR CAUTION

Although we evaluated the effects of inhibition of c-Jun phosphorylation on primordial follicle development, we did not determine the cellular targets and mechanism of action of the inhibitors.

WIDER IMPLICATIONS OF THE FINDINGS

These results are the first to implicate the JNK pathway in primordial follicle activation and could have significant consequences for the successful development of fertility preservation strategies and our understanding of primordial follicle activation.

LARGE SCALE DATA

n/a.

STUDY FUNDING AND COMPETING INTERESTS

Dr Michael J. Bertoldo and the laboratories involved in the present study were supported by a grant from 'Région Centre' (CRYOVAIRE, Grant number #320000268). There are no conflicts of interest to declare.

Morphometric and Ultrastructure studies of Primordial Follicles and Expression of Estrogen-dependent Genes in the Ovaries of Domestic Cats

The aim of this study was to compare and estimate the population of the primordial follicle morphometrically and ultrastructurally in the left and right side ovaries of 10 ovariohysterectomied healthy domestic shorthair cats. The ovaries were processed for light microscopy, electron microscopy, and estrogen-dependent gene expression for assessments. A total of 15,092 primordial follicles with and without a nucleus were examined and counted. A total of 6842 primordial follicles with a nucleus were examined and counted. The light-microscopy numerical data were collected from two histological sections per ovary for a total of 20 sections from the left ovary and 20 sections from the right ovary. The average surface area of the histological sections was 645.99 mm². The number of tertiary follicles was found to be higher in the left ovaries than in the right ovaries. The primordial follicles are under the tunica albuginea at various levels. Some are crowded or scattered in one or two rows, although at times, there were areas without any primordial follicles. The primordial follicles varied in size, and were surrounded by 4–10 squamous granulosa cells. Some primordial follicles shared their ooplasm with one or two neighboring primordial follicles, forming a giant primordial follicle with two or three nuclei. The ultrastructure of the primordial follicles showed rounded nuclei with distinct nucleoli, rounded and elongated mitochondria, and a considerably thick basement membrane under the granulosa cells. The squamous granulosa cells showed well-developed microvilli intermingled with the microvilli of the oocyte oolemma. Elongated mitochondria, coated pits, multicytoplasmic vesicles, ribosomes, and Golgi apparatuses were obvious in the oocyte ooplasm. Large vesicles contain small multivesicles and some scattered lipid globules in the ooplasm. There were estrogen-dependent gene-expression differences between the right and left ovaries. Further gene research is in the plan, using a larger pool of cats, with a focus on age differences.

Regulation of FOXO3 subcellular localization by Kit ligand in the neonatal mouse ovary

PURPOSE

Foxo3 protein is required in the oocyte nucleus for the maintenance of primordial follicles in a dormant state. PI3K/AKT-dependent phosphorylation of Foxo3 leads to its relocalization to the cytoplasm and subsequent follicular activation. However, the nature of the upstream signals controlling Foxo3 activity and subcellular localization remains unknown. We aimed to study the in vitro effects of Kit ligand (stem cell factor) on the subcellular localization of Foxo3 in primordial follicles within the postnatal mouse ovary.

METHODS

This was an in vitro study using explants of intact neonatal mouse ovaries. The study was performed in laboratory animal facility and basic science research laboratory at a University Hospital. The animals used for this study were FVB mice. Neonatal FVB mice ovaries at postnatal day 7 (PD7) were harvested and incubated in culture medium (DMEM) at 37 °C and 5 % CO(2) for 60-90 min with (n = 3) or without (n = 3) Kit ligand at 150 ng/mL (8 nM). Similar experimental conditions were used to establish a dose-response curve for the effects of Kit ligand and assess the effects of imatinib (small molecule inhibitor of the Kit receptor). Immunofluorescence was used to identify the subcellular location of Foxo3 in oocytes. Proportions of cytoplasmic versus nuclear Foxo3 in primordial follicles were determined.

RESULTS

Kit ligand treatment increased the cytoplasmic localization of Foxo3 from 40 % in the untreated ovaries to 74 % in the treated group (p = 0.007 in paired samples and p = 0.03 in unpaired samples). Furthermore, this effect was reversible with imatinib (p = 0.005). A dose-response curve for Kit ligand treatment showed that maximum effect was seen at 150 ng/mL.

CONCLUSION

Kit ligand treatment in vitro increases the proportion of cytoplasmic Foxo3 in primordial follicles at PD7, lending support to the idea that Kit receptor/ligand controls Foxo3 activity in the context of primordial follicle activation.

Heat Stress Alters Ovarian Insulin-Mediated Phosphatidylinositol-3 Kinase and Steroidogenic Signaling in Gilt Ovaries

Heat stress (HS) compromises a variety of reproductive functions in several mammalian species. Inexplicably, HS animals are frequently hyperinsulinemic despite marked hyperthermia-induced hypophagia. Our objectives were to determine the effects of HS on insulin signaling and components essential to steroid biosynthesis in the pig ovary. Female pigs (35 ± 4 kg) were exposed to constant thermoneutral (20°C; 35%-50% humidity; n = 6) or HS conditions (35°C; 20%-35% humidity; n = 6) for either 7 (n = 10) or 35 days (n = 12). After 7 days, HS increased (P < 0.05) ovarian mRNA abundance of the insulin receptor (INSR), insulin receptor substrate 1 (IRS1), protein kinase B subunit 1 (AKT1), low-density lipoprotein receptor (LDLR), luteinizing hormone receptor (LHCGR), and aromatase (CYP19a). After 35 days, HS increased INSR, IRS1, AKT1, LDLR, LHCGR, CYP19a, and steroidogenic acute regulatory protein (STAR) ovarian mRNA abundance. In addition, after 35 days, HS increased ovarian phosphorylated IRS1 (pIRS1), phosphorylated AKT (pAKT), STAR, and CYP19a protein abundance. Immunostaining analysis revealed similar localization of INSR and pAKT1 in the cytoplasmic membrane and oocyte cytoplasm, respectively, of all stage follicles, and in theca and granulosa cells. Collectively, these results demonstrate that HS alters ovarian insulin-mediated PI3K signaling pathway members, which likely impacts follicle activation and viability. In summary, environmentally induced HS is an endocrine-disrupting exposure that modifies ovarian physiology and potentially compromises production of ovarian hormones essential for fertility and pregnancy maintenance.

Exploratory study of pre-surgical medications with dienogest or leuprorelin in laparoscopic cystectomy of endometrial cysts

AIM

The aim of this study was to compare the effects of pre-surgical medication with dienogest or leuprorelin on post-surgical ovarian function.

MATERIAL AND METHODS

We conducted an exploratory study in two centers in Japan that comprised 30 patients with ovarian endometrial cysts for whom surgical excision was planned. Patients were enrolled and divided into pre-surgical medication groups with dienogest or leuprorelin for 12 weeks. Thereafter, patients were treated by laparoscopic cystectomy. The primary outcome was ovarian function post-surgery, as assessed by serum anti-Müllerian hormone (AMH) level, antral follicle count (AFC) and resumption of menses. Secondary outcome was the effect of pre-surgical medication, as assessed by the size of endometrial cysts and visual analog scale (VAS) score. Serum AMH, AFC, size of endometrial cysts, and VAS scores were measured at baseline (before medication), after medication (1 day before surgery), and at 4 and 12 weeks post-surgery.

RESULTS

Serum AMH levels did not change after pre-surgical medication with either dienogest or leuprorelin. Although AMH decreased after surgery, it recovered by 12 weeks post-surgery in both groups with no statistically significant difference. Mean AFC did not change after surgery in either group. Menses returned by 12 weeks post-surgery in all patients except for those who were pregnant. The rate of reduction of endometrial cyst volume did not differ between the groups. Both dienogest and leuprorelin were associated with substantial reductions in VAS scores.

CONCLUSION

There were no statistically significant differences between pre-surgical medication with dienogest and leuprorelin in post-surgical ovarian function. Both medications were effective in reducing endometrial cyst volume and VAS score.

PI3K/PTEN/Akt and TSC/mTOR signaling pathways, ovarian dysfunction, and infertility: an update

Abnormalities in ovarian function, including defective oogenesis and folliculogenesis, represent a key female reproductive deficiency. Accumulating evidence in the literature has shown that the PI3K/PTEN/Akt and TSC/mTOR signaling pathways are critical regulators of ovarian function including quiescence, activation, and survival of primordial follicles, granulosa cell proliferation and differentiation, and meiotic maturation of oocytes. Dysregulation of these signaling pathways may contribute to infertility caused by impaired follicular development, intrafollicular oocyte development, and ovulation. This article reviews the current state of knowledge of the functional role of the PI3K/PTEN/Akt and TSC/mTOR pathways during mammalian oogenesis and folliculogenesis and their association with female infertility.

Diet-induced maternal obesity alters ovarian morphology and gene expression in the adult mouse offspring

OBJECTIVE

To examine the effects of high-fat (HF) diet-induced maternal obesity on follicular population and gene expression in adult offspring ovaries.

DESIGN

Experimental mouse study.

SETTING

Laboratory.

ANIMAL(S)

Mice on HF diet.

INTERVENTION(S)

Female C57BL/6J mice were fed an HF or standard chow (C) diet 6 weeks before conception, through pregnancy and lactation. Offspring were fed the C or HF diet from weaning, creating the HF/HF, HF/C, C/HF, C/C offspring groups.

MAIN OUTCOME MEASURE(S)

Follicular counts and gene expression in adult offspring ovaries.

RESULT(S)

Prenatal exposure to maternal HF nutrition resulted in the reduction of primordial, antral, and Graafian follicle numbers in offspring ovaries (both HF/C and HF/HF). Expression levels of genes involved in apoptosis (FoXO3a), follicular growth and development (Gdf9), and circadian rhythms generation (Clock and Bmal1) were elevated in the ovaries of HF/C and HF/HF offspring, while expression of the circadian clock genes Cry1 and Per1 were lower in HF/HF ovaries.

CONCLUSION(S)

Maternal obesity during pregnancy has long-term deleterious consequences on follicular growth and development in the adult offspring ovaries, which may impact their reproductive potential.

Novel dynamic culture system to support initiation of primordial follicle growth in prepubertal mouse ovaries

OBJECTIVE

To evaluate the impact of dynamic in vitro culture on initiation of early follicular growth in prepubertal mouse ovaries.

DESIGN

Ovaries from 8-day-old BALB/c mice were cultured either in a dynamic system (n=28) or in a static system (n=20) for 4 days. Uncultured 8-day-old (n=9) or 12-day-old (n=17) ovaries served as baseline or in vivo controls, respectively.

SETTING

Academic research center.

ANIMAL(S)

Newborn female BALB/c mice (n=37).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Histologic follicle classification and counting and assessment of follicular viability via immunofluorescent staining.

RESULT(S)

The percentage of secondary follicles after dynamic culture was identical to the 12-day-old in vivo control. In contrast, after static culture ovaries showed a significantly higher percentage of secondary follicles. For immunofluorescent viability assessment 6.78 follicles per ovary could be isolated after dynamic culture, whereas only 3.8 follicles per ovary could be isolated after static culture.

CONCLUSION(S)

Dynamic in vitro culture supports physiologic follicular growth initiation, comparable to that observed in vivo. In contrast, accelerated follicular growth was observed after static culture. These findings add additional evidence to the idea that dynamic culture might be a beneficial first step to initiate follicle growth in vitro within the context of fertility preservation.

Impact of obesity on ovotoxicity induced by 7,12-dimethylbenz[a]anthracene in mice

Insulin, elevated during obesity, regulates xenobiotic biotransformation enzymes, potentially through phosphatidylinositol 3-kinase (PI3K) signaling, in extraovarian tissues. PI3K regulates oocyte viability, follicular activation, and ovarian chemical biotransformation. 7,12-Dimethylbenz[a]anthracene (DMBA), a carcinogen and ovotoxicant, destroys all stages of follicles, leading to premature ovarian failure. Obesity has been reported to promote DMBA-induced tumors, but it remains unknown whether obesity affects ovarian xenobiotic metabolism. Therefore, we investigated ovarian expression of xenobiotic metabolism genes-microsomal epoxide hydrolase (Ephx1), glutathione S-transferase (GST) class Pi (Gstp1) and class mu 1 (Gstm1), and PI3K-signaling members (protein kinase B [AKT] alpha [Akt1], beta [Akt2], and the forkhead transcription factor subfamily 3 [Foxo3])-in lean and obese female mice after DMBA exposure (1 mg/kg; intraperitoneal injection for 14 days). Relative to lean, obese mice had decreased (P < 0.05) healthy primordial and primary follicle numbers but increased (P < 0.05) secondary and preovulatory follicles numbers. Obesity increased (P < 0.05) Akt1, Akt2, Gstm1, and Ephx1 mRNA and pAKT(Ser473/Thr308), GSTM1, GSTP1, and EPHX1 protein levels. DMBA decreased (P < 0.05) ovarian weight in lean and obese mice, however, obese DMBA-treated females had a greater reduction (P < 0.05) in ovarian weight. In both lean and obese mice, DMBA decreased (P < 0.05) all stages of healthy follicle numbers, increased Gstp1 and Ephx1 mRNA as well as GSTM1, GSTP1, and EPHX1 protein levels, and decreased Akt1 and Akt2 mRNA as well as pAKT(Ser473) or pAKT(Thr308), FOXO3, and pFOXO3(Ser253) protein expression. There was an additive effect between obesity and DMBA exposure for increased Gstm1 and Ephx1 mRNA as well as GSTM1 and EPHX1 protein expression.

Roles of Gremlin 1 and Gremlin 2 in regulating ovarian primordial to primary follicle transition

A network of extracellular signaling factors has previously been shown to act in concert to control the ovarian primordial to primary follicle transition. The current study was designed to investigate the roles of the endogenous bone morphogenetic protein (BMP) inhibitors Gremlin 1 (GREM1) and GREM2 in primordial follicle transition in the rat ovary. GREM1 and GREM2 treatments were found to reverse the effects of anti-Müllerian hormone (AMH) to inhibit follicle transition in a whole-ovary culture system. GREM1 reversed the effect of BMP4 to stimulate primordial follicle transition. Immunohistochemical studies showed that GREM2, but not GREM1, was present in primordial follicles suggesting that GREM2 may regulate primordial follicle transition in vivo. Co-immunoprecipitation studies indicated that GREM2 directly binds to AMH, as well as to BMP4. Transcriptome analyses of ovaries treated with GREM2 or GREM1 yielded negligible numbers of differentially expressed genes, suggesting that the immediate effects of GREM2 or GREM1 appear to be at the level of protein-protein interactions, rather than direct actions on the cells. A number of other ovarian growth factors were found to influence the expression of Grem2. Observations suggest that Grem2 is a part of the signaling network of growth factors that regulate the primordial to primary follicle transition. Insights into the regulatory networks affecting the pool of primordial follicles are important to understand the molecular basis for reproductive diseases such as primary ovarian insufficiency.

The immature human ovary shows loss of abnormal follicles and increasing follicle developmental competence through childhood and adolescence

STUDY QUESTION

Do the ovarian follicles of children and adolescents differ in their morphology and in vitro growth potential from those of adults?

SUMMARY ANSWER

Pre-pubertal ovaries contained a high proportion of morphologically abnormal non-growing follicles, and follicles showed reduced capacity for in vitro growth.

WHAT IS KNOWN ALREADY

The pre-pubertal ovary is known to contain follicles at the early growing stages. How this changes over childhood and through puberty is unknown, and there are no previous data on the in vitro growth potential of follicles from pre-pubertal and pubertal girls.

STUDY DESIGN, SIZE, DURATION

Ovarian biopsies from five pre-pubertal and seven pubertal girls and 19 adult women were analysed histologically, cultured in vitro for 6 days, with growing follicles then isolated and cultured for a further 6 days.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Ovarian biopsies were obtained from girls undergoing ovarian tissue cryopreservation for fertility preservation, and compared with biopsies from adult women. Follicle stage and morphology were classified. After 6 days in culture, follicle growth initiation was assessed. The growth of isolated secondary follicles was assessed over a further 6 days, including analysis of oocyte growth.

MAIN RESULTS AND THE ROLE OF CHANCE

Pre-pubertal ovaries contained a high proportion of abnormal non-growing follicles (19.4 versus 4.85% in pubertal ovaries; 4004 follicles analysed; P = 0.02) characterized by indistinct germinal vesicle membrane and absent nucleolus. Follicles with this abnormal morphology were not seen in the adult ovary. During 6 days culture, follicle growth initiation was observed at all ages; in pre-pubertal samples there was very little development to secondary stages, while pubertal samples showed similar growth activation to that seen in adult tissue (pubertal group: P = 0.02 versus pre-pubertal, ns versus adult). Isolated secondary follicles were cultured for a further 6 days. Those from pre-pubertal ovary showed limited growth (P < 0.05 versus both pubertal and adult follicles) and no change in oocyte diameter over that period. Follicles from pubertal ovaries showed increased growth; this was still reduced compared with follicles from adult women (P < 0.05) but oocyte growth was proportionate to follicle size.

LIMITATIONS, REASONS FOR CAUTION

These data derive from only a small number of ovarian biopsies, although large numbers of follicles were analysed. It is unclear whether the differences between groups are related to puberty, or just age.

WIDER IMPLICATIONS OF THE FINDINGS

These findings show that follicles from girls of all ages can be induced to grow in vitro, which has important implications for some patients who are at high risk of malignant contamination of their ovarian tissue. The reduced growth of isolated follicles indicates that there are true intrafollicular differences in addition to potential differences in their local environment, and that there are maturational processes occurring in the ovary through childhood and adolescence, which involve the loss of abnormal follicles, and increasing follicle developmental competence.

STUDY FUNDING/COMPETING INTEREST(S)

Funded by MRC grants G0901839 and G1100357. No competing interests.

Polycystic ovary syndrome: current status and future perspective

Polycystic ovary syndrome (PCOS) is a widespread reproductive disorder that encompasses many associated health conditions and has an impact on various metabolic processes. PCOS is depicted by hyperandrogenism, polycystic ovaries, and anovulation. It increases the risk of insulin resistance (IR), type 2 diabetes, obesity, and cardiovascular disease. The etiology of the disease remains unclear, and the subjective phenotype makes a united diagnosis difficult among physicians. It seems to be a familial genetic syndrome caused by a combination of environmental and genetic factors. It can be linked with metabolic disorders in first-degree family members. PCOS is the cause of up to 30% of infertility in couples seeking treatment. Currently, there is no cure for PCOS. Despite the growing incidence of this syndrome, limited research has been done that encompasses the entirety of PCOS spectrum. In this review, the current status and possible future perspective will be discussed.

Involvement of androgens in ovarian health and disease

In women, ovary and adrenal gland produce androgens. Androgens are essential drivers of the primordial to antral follicle development, prior to serving as substrate for estrogen production in the later stages of folliculogenesis. Androgens play a crucial role in the follicular-stromal intertalk by fine tuning the extracellular matrix and vessel content of the ovarian stroma. Local auto-and paracrine factors regulate androgen synthesis in the pre-antral follicle. Androgen excess is a hallmark of polycystic ovary syndrome and is a key contributor in the exaggerated antral follicle formation, stromal hyperplasia and hypervascularity. Hyperandrogenaemia overrides the follicular-stromal dialog, resulting in follicular arrest and disturbed ovulation. On the other hand, androgen deficiency is likely to have a negative impact on fertility as well, and further research is needed to examine the benefits of androgen-replacement therapy in subfertility.

Two classes of ovarian primordial follicles exhibit distinct developmental dynamics and physiological functions

In the mammalian ovary, progressive activation of primordial follicles serves as the source of fertilizable ova, and disorders in the development of primordial follicles lead to various ovarian diseases. However, very little is known about the developmental dynamics of primordial follicles under physiological conditions, and the fates of distinct populations of primordial follicles also remain unclear. In this study, by generating the Foxl2-CreER(T2) and Sohlh1-CreER(T2) inducible mouse models, we have specifically labeled and traced the in vivo development of two classes of primordial follicles, the first wave of simultaneously activated follicles after birth and the primordial follicles that are gradually activated in adulthood. Our results show that the first wave of follicles exists in the ovaries for ∼3 months and contributes to the onset of puberty and to early fertility. The primordial follicles at the ovarian cortex gradually replace the first wave of follicles and dominate the ovary after 3 months of age, providing fertility until the end of reproductive life. Moreover, by tracing the time periods needed for primordial follicles to reach various advanced stages in vivo, we were able to determine the exact developmental dynamics of the two classes of primordial follicles. We have now revealed the lifelong developmental dynamics of ovarian primordial follicles under physiological conditions and have clearly shown that two classes of primordial follicles follow distinct, age-dependent developmental paths and play different roles in the mammalian reproductive lifespan.

High fat diet induced obesity alters ovarian phosphatidylinositol-3 kinase signaling gene expression

Insulin regulates ovarian phosphatidylinositol-3-kinase (PI3 K) signaling, important for primordial follicle viability and growth activation. This study investigated diet-induced obesity impacts on: (1) insulin receptor (Insr) and insulin receptor substrate 1 (Irs1); (2) PI3K components (Kit ligand (Kitlg), kit (c-Kit), protein kinase B alpha (Akt1) and forkhead transcription factor subfamily 3 (Foxo3a)); (3) xenobiotic biotransformation (microsomal epoxide hydrolase (Ephx1), Cytochrome P450 isoform 2E1 (Cyp2e1), Glutathione S-transferase (Gst) isoforms mu (Gstm) and pi (Gstp)) and (4) microRNA's 184, 205, 103 and 21 gene expression. INSR, GSTM and GSTP protein levels were also measured. Obese mouse ovaries had decreased Irs1, Foxo3a, Cyp2e1, MiR-103, and MiR-21 but increased Kitlg, Akt1, and miR-184 levels relative to lean littermates. These results support that diet-induced obesity potentially impairs ovarian function through aberrant gene expression.

MicroRNA-181a suppresses mouse granulosa cell proliferation by targeting activin receptor IIA

Activin, a member of the transforming growth factor-β superfamily, promotes the growth of preantral follicles and the proliferation of granulosa cells. However, little is known about the role of microRNAs in activin-mediated granulosa cell proliferation. Here, we reported a dose- and time-dependent suppression of microRNA-181a (miR-181a) expression by activin A in mouse granulosa cells (mGC). Overexpression of miR-181a in mGC suppressed activin receptor IIA (acvr2a) expression by binding to its 3'-untranslated region (3'-UTR), resulting in down-regulation of cyclin D2 and proliferating cell nuclear antigen expression, leading to inhibition of the cellular proliferation, while overexpression of acvr2a attenuated the suppressive effect of miR-181a on mGC proliferation. Consistent with the inhibition of acvr2a expression, miR-181a prevented the phosphorylation of the activin intracellular signal transducer, mothers against decapentaplegic homolog 2 (Smad2), leading to the inactivation of activin signaling pathway. Interestingly, we found that miR-181a expression decreased in ovaries of mice at age of 8, 12, and 21 days, as compared with that in ovaries of 3-day old mice, and its level was reduced in preantral and antral follicles of mice compared with that in primary ones. Moreover, the level of miR-181a in the blood of patients with premature ovarian failure was significantly increased compared with that in normal females. This study identifies an interplay between miR-181a and acvr2a, and reveals an important role of miR-181a in regulating granulosa cell proliferation and ovarian follicle development.

The infant and pubertal human ovary: Balbiani's body-associated VASA expression, immunohistochemical detection of apoptosis-related BCL2 and BAX proteins, and DNA fragmentation

STUDY QUESTION

How do apoptosis-related BCL2 and BAX genes, known to regulate death or survival of germ cells in fetal and adult life, and germ-cell-specific VASA protein behave from birth to puberty in the human ovary?

SUMMARY ANSWER

In resting primordial follicles in both infant and pubertal ovaries, BCL2 family members and germ-cell-specific VASA behave as in fetal life. After birth, once follicles leave the resting reserve to enter the growing follicular pool, detection of apoptosis-related genes moves from the germ cell to granulosa cells and VASA expression is lost.

WHAT IS KNOWN ALREADY

In the human ovary, around 85% of the 7 × 10⁶ potential oocytes produced at mid-gestation are lost before birth, an extra 10% before puberty, and loss continues throughout reproductive life until germinal exhaustion of the ovary. Oocyte loss is mainly driven through a balanced expression of BCL2 gene family members. Apoptosis-inducing BAX gene shows a sustained expression throughout fetal and adult life, whereas apoptosis-inhibiting BCL2 is detectable during the proliferative stage of primordial germ cells and oogonia in the fetal ovary and proliferation of granulosa cells in growing follicles in the adult ovary. The germ-cell marker VASA is detectable in the fetal ovary from early oogenesis and is conspicuously expressed in primordial follicles, where in late pregnancy it is associated with the Balbiani's vitelline space. VASA expression is not detectable in the adult ovary.

STUDY DESIGN, SIZE, DURATION

This is a qualitative analysis involving infant/pubertal paraffin-embedded human ovaries screened for apoptosis-related proteins, DNA fragmentation and germ-cell identity.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Ovaries from 13 patients ranging in age from 4 to 16 years, undergoing gynaecological surgical procedures due to benign pathology, were studied. Tissues were fixed in 10% formalin, paraffin-embedded and processed for immunohistochemistry to screen the temporal and cellular localization of germ-cell-specific VASA protein and BCL2 and BAX apoptosis-related proteins. In addition, a terminal deoxynucleotidyl transferase-mediated deoxiuridinetriphosphate nick-end labelling (TUNEL) assay was performed to detect DNA fragmentation. General histology and tissue integrity were assessed by haematoxylin-eosin staining.

MAIN RESULTS AND THE ROLE OF CHANCE

VASA showed a differential pattern of expression; in the resting primordial follicle reserve in infant and pubertal ovaries, it was associated with the Balbiani's body space in the germ cell. VASA remained detectable in primary follicles leaving the resting reserve, but once follicles entered the growing pool it became undetectable. This pattern of VASA expression is the same as in the fetal ovary. BAX was expressed both in the resting primordial reserve and in the pool of growing follicles, whereas BCL2 was detected only in granulosa cells in antral follicles in the growing pool. Apoptosis-related protein expression moved from the germ cell to the somatic stratum when primordial follicles left the resting reserve to enter the pool of growing follicles, irrespective of female age. Most TUNEL-positive cells were detected in the granulosa cells of antral follicles. No TUNEL-positive cells were found in resting primordial follicles.

LIMITATIONS, REASONS FOR CAUTION

The study was limited by the qualitative nature of the immuno-histochemical analysis and the TUNEL assay. The results neither quantify the levels of germ-cell death nor exclude other concurrent cell death mechanisms that could act in the regulation of female germ-cell number.

WIDER IMPLICATIONS OF THE FINDING

This study provides missing knowledge about apoptosis and germ-cell-specific VASA expression in the human ovary between birth and puberty and the participation of BCL2 and BAX genes in the balance between death and survival throughout female germ-line development. Intracellular localization of VASA in resting follicles emerges as a possible marker with prognostic value that needs further investigation, especially in infant patients entering ovarian cryo-preservation programmes. This knowledge will be valuable in optimizing the rescue and clinical use of germ cells to restore fertility in women.

STUDY FUNDING/COMPETING INTEREST(S)

No external funding was obtained for this study. The authors have no conflicts of interest to declare.

Multiple follicle culture supports primary follicle growth through paracrine-acting signals

In vitro follicle growth in alginate hydrogels is a unique and versatile method for studying ovarian and follicle biology that may also have implications for fertility preservation. Current culture systems support the development of isolated mouse follicles from the secondary stage onward. However, it has been a challenge to grow smaller follicles in vitro due to the dissociation of the oocyte from companion somatic cells. Recent work has demonstrated that coculturing primary follicles with mouse embryonic fibroblasts or ovarian stromal cells supports follicle survival and growth. In this study, we demonstrate that follicles themselves can exert a beneficial coculture effect. When primary follicles were cultured in groups of five or ten (multiple follicle culture), there was increased growth and survival. The multiple follicle culture approach maintained follicle integrity and resulted in the formation of antral stage follicles containing meiotically competent gametes. The growth and survival of primary follicles were highly number dependent, with the most significant enhancement observed when the largest number of follicles was grown together. Our data suggest that the follicle unit is necessary to produce the secreted factors responsible for the supportive effects of multiple follicle culture, as neither denuded oocytes, oocyte-secreted factors, nor granulosa cells alone were sufficient to support early follicle growth in vitro. Therefore, there may be signaling from both the oocyte and the follicle that enhances growth but requires both components in a feedback mechanism. This work is consistent with current in vivo models for follicle growth and thus advances the movement to recapitulate the ovarian environment in vitro.

Hormone-controlled culture of secondary follicles of domestic cats

Ovaries were obtained from domestic cats during ovariohysterectomy. Large, preantral follicles were freed by dissection and mechanical crushing, and were cultured in TCM 199 + 10% FCS medium in the presence or absence of hormones (FSH, hydrocortisone and Insulin-Transferrin-Selenite) as well as in hypoxanthine. A decline in growth potential along with increasing follicle size were observed after one week, with no FSH added. Hormone-supplemented medium was found to induce growth to 2 or 3 times the original volume in more than 80% of follicles of all sizes. Oocyte diameters were continuously increasing, depending on follicle size, and reached 90 mum (80 %) at the point of antrum formation. Nuclear configuration of oocytes from follicles which had been cultured without addition of hormones up to the antral stage indicated a high rate of degeneration which, however, could be reduced by gonadotrophic stimulation. Meiosis at the germinal vesicle stage was found to be inhibited by hypoxanthine. For some oocytes, evidence was provided to meiotic maturation up to extrusion of the first polar body.

Environmentally induced epigenetic transgenerational inheritance of ovarian disease

The actions of environmental toxicants and relevant mixtures in promoting the epigenetic transgenerational inheritance of ovarian disease was investigated with the use of a fungicide, a pesticide mixture, a plastic mixture, dioxin and a hydrocarbon mixture. After transient exposure of an F0 gestating female rat during embryonic gonadal sex determination, the F1 and F3 generation progeny adult onset ovarian disease was assessed. Transgenerational disease phenotypes observed included an increase in cysts resembling human polycystic ovarian disease (PCO) and a decrease in the ovarian primordial follicle pool size resembling primary ovarian insufficiency (POI). The F3 generation granulosa cells were isolated and found to have a transgenerational effect on the transcriptome and epigenome (differential DNA methylation). Epigenetic biomarkers for environmental exposure and associated gene networks were identified. Epigenetic transgenerational inheritance of ovarian disease states was induced by all the different classes of environmental compounds, suggesting a role of environmental epigenetics in ovarian disease etiology.

Total synthesis of the α-subunit of human glycoprotein hormones: toward fully synthetic homogeneous human follicle-stimulating hormone

Described herein is the first total chemical synthesis of the unique α-subunit of the human glycoprotein hormone (α-hGPH). Unlike the biologically derived glycoprotein hormones, which are isolated as highly complex mixtures of glycoforms, α-hGPH obtained by chemical synthesis contains discrete homogeneous glycoforms. Two such systems have been prepared. One contains the disaccharide chitobiose at the natural N-glycosylation sites. The other contains dodecamer oligosaccharides at these same sites. The dodecamer sugar is a consensus sequence incorporating the key features associated with human glycoproteins.

The ratio of growth differentiation factor 9: bone morphogenetic protein 15 mRNA expression is tightly co-regulated and differs between species over a wide range of ovulation rates

Recent evidence suggests that the species-specific ovulation-rate phenotypes may be influenced by differences in the expression levels of bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) mRNA and protein. The aim of this study was to compare GDF9 and BMP15 mRNA levels in individual denuded oocytes (DO) from a range of single (i.e. cow, red deer), single-to-triple (i.e. sheep) and high (i.e. pig, mouse, rat) ovulation-rate species. Compared to all other species studied, GDF9 mRNA levels were lower in DO of cows and deer, whilst BMP15 levels were highest in DO of pigs. There was no detectable expression of either GDF9 or BMP15 mRNA in CC from any species. The ratio of GDF9:BMP15 mRNA expression was highly correlated (R(2)>0.80) within each species but differed markedly between species (P<0.01). Thus, we conclude that the ratio of GDF9:BMP15 mRNA is species-specific across a wide range of ovulation-rate phenotypes.

Inhibitory actions of Anti-Müllerian Hormone (AMH) on ovarian primordial follicle assembly

The current study was designed to investigate the actions of Anti-Müllerian Hormone (AMH) on primordial follicle assembly. Ovarian primordial follicles develop from the breakdown of oocyte nests during fetal development for the human and immediately after birth in rodents. AMH was found to inhibit primordial follicle assembly and decrease the initial primordial follicle pool size in a rat ovarian organ culture. The AMH expression was found to be primarily in the stromal tissue of the ovaries at this period of development, suggesting a stromal-epithelial cell interaction for primordial follicle assembly. AMH was found to promote alterations in the ovarian transcriptome during primordial follicle assembly with over 200 genes with altered expression. A gene network was identified suggesting a potential central role for the Fgf2/Nudt6 antisense transcript in the follicle assembly process. A number of signal transduction pathways are regulated by AMH actions on the ovarian transcriptome, in particular the transforming growth factor – beta (TGFß) signaling process. AMH is the first hormone/protein shown to have an inhibitory action on primordial follicle assembly. Due to the critical role of the primordial follicle pool size for female reproduction, elucidation of factors, such as AMH, that regulate the assembly process will provide insights into potential therapeutics to manipulate the pool size and female reproduction.