Kit ligand and basic fibroblast growth factor interactions in the induction of ovarian primordial to primary follicle transition

Swine in vitro embryo production: Potential, challenges, and advances

Pig production, a vital sector of the meat industry, faces demands for improved quality, efficiency, and sustainability. Advancements in breeding, disease control, and artificial insemination have enhanced production, while biotechnologies such as in vitro embryo production (IVP) and genetic engineering offer further progress. In vitro embryo production could facilitate the global exchange of valuable genetic material, accelerate breeding programs, and improve productivity, and it is essential for generating genetically modified (GM) pigs. These GM pigs have two main applications: first, they allow for targeted modifications aimed at improving production traits relevant to pig production in agriculture, such as meat quality and disease resistance. Second, they serve as valuable biomedical models for human disease research, regenerative medicine, and organ transplantation. Yet, despite notable advancements in recent decades, the efficiency of the current IVP systems for porcine embryos remains a challenge. Compared to the in vivo environment, suboptimal culture conditions lead to issues such as elevated polyspermy, poor embryo development, and the production of low-quality blastocysts. This review provides an overview of the key steps and recent advancements in porcine IVP technology. We will emphasize the promising utilization of oocytes from live females of high genetic value through ovum pick-up and the incorporation of extracellular vesicles and cytokines into IVP media. These innovative strategies hold immense potential to significantly enhance embryo development and overall success rates in porcine IVP, and could open the door for significant progress in both agriculture and biomedicine applications.

Sleep Deprivation Triggers the Excessive Activation of Ovarian Primordial Follicles via β2 Adrenergic Receptor Signaling

Sleep deprivation (SD) is observed to adversely affect the reproductive health of women. However, its precise physiological mechanisms remain largely elusive. In this study, using a mouse model of SD, it is demonstrated that SD induces the depletion of ovarian primordial follicles, a phenomenon not attributed to immune-mediated attacks or sympathetic nervous system activation. Rather, the excessive secretion of stress hormones, namely norepinephrine (NE) and epinephrine (E), by overactive adrenal glands, has emerged as a key mediator. The communication pathway mediated by the KIT ligand (KITL)-KIT between granulosa cells and oocytes plays a pivotal role in primordial follicle activation. SD heightened the levels of NE/E that stimulates the activation of the KITL-KIT/PI3K and mTOR signaling cascade in an β2 adrenergic receptor (ADRB2)-dependent manner, thereby promoting primordial follicle activation and consequent primordial follicle loss in vivo. In vitro experiments further corroborate these observations, revealing that ADRB2 upregulates KITL expression in granulosa cells via the activation of the downstream cAMP/PKA pathway. Together, these results reveal the significant involvement of ADRB2 signaling in the depletion of ovarian primordial follicles under sleep-deprived conditions. Additionally, ADRB2 antagonists are proposed for the treatment or prevention of excessive activation of primordial follicles induced by SD.

In-depth analysis of transcriptomes in ovarian cortical follicles from children and adults reveals interfollicular heterogeneity

The ovarian cortical reserve of follicles is vital for fertility. Some medical treatments are toxic to follicles, leading to premature ovarian insufficiency. Ovarian tissue cryopreservation is an established method to preserve fertility in adults and even applied in prepuberty despite unproven efficacy. Here, we analyze transcriptomes of 120 cortical follicles from children and adults for detailed comparison. We discover heterogeneity with two main types of follicles in both age groups: one with expected oocyte-granulosa profiles and another with predicted role in signaling. Transcriptional changes during growth to the secondary stage are similar overall in children and adults, but variations related to extracellular matrix, theca cells, and miRNA profiles are found. Notably, cyclophosphamide dose correlates with interferon signaling in child follicles. Additionally, morphology alone is insufficient for follicle categorization suggesting a need for additional markers. Marker genes for early follicle activation are determined. These findings will help refine follicular classification and fertility preservation techniques across critical ages.

Hypoxia, NSAIDs, and autism: A biocultural analysis of stressors in gametogenesis

Cultural and generational trends have increasingly favored "anti-inflammatory" action, innovating a new class of analgesic, non-steroidal anti-inflammatory drugs (NSAIDs) in the 20th century. The modern human body has been molded over evolutionary time and while acknowledging inflammation can be pathologically entwined, it also serves an important role in healthy folliculogenesis and ovulation, shaping cues that drive needed vascular change. This review argues that because of anti-inflammatory action, the cultural invention of NSAIDs represents a particular stressor on female reproductive-age bodies, interacting with natural, underlying variation and placing limits on healthy growth and development in the follicles, creating potential autism risk through hypoxia and mutagenic or epigenetic effects. Since testes are analogs to ovaries, the biological grounding extends naturally to spermatogenesis. This review suggests the introduction of over-the-counter NSAIDs in the 1980s failed to recognize the unique functioning of reproductive-age bodies, challenging the cyclical inflammation needed for healthy gamete development. NSAIDs are framed as one (notable) stressor in an anti-inflammatory era focused on taming the risks of inflammation in modern human life.

The Roles of GDF-9, BMP-15, BMP-4 and EMMPRIN in Folliculogenesis and In Vitro Fertilization

Growth differentiation factor 9 (GDF-9) contributes to early ovarian development and oocyte survival. Higher concentrations of GDF-9 in follicular fluid (FF) are associated with oocyte nuclear maturation and optimal embryo development. In in vitro fertilization (IVF), GDF-9 affects the ability of the oocyte to fertilize and subsequent embryonic development. Bone morphogenetic protein 15 (BMP-15) is involved in the regulation of ovarian function and affects oocyte development. During IVF, BMP-15 contributes to the formation of competent blastocysts. BMP-15 may play a role in embryo implantation by affecting endometrial receptivity. Bone morphogenetic protein 4 (BMP-4) is involved in the regulation of follicle growth and development and affects granulosa cell (GC) differentiation. In relation to IVF, BMP-4 is important for embryonic development, influences cell fate and differentiation, and plays a role in facilitating embryo-endometrial interactions during the implantation process. Extracellular matrix metalloproteinase inducer (EMMPRIN) is associated with ovulation and follicle rupture, promotes the release of mature eggs, and affects the modification of the extracellular matrix of the follicular environment. In IVF, EMMPRIN is involved in embryo implantation by modulating the adhesive properties of endometrial cells and promotes trophoblastic invasion, which is essential for pregnancy to occur. The purpose of the current article is to review the studies and recent findings of GDF-9, BMP-15, BMP-4 and EMMPRIN as fundamental factors in normal follicular development and in vitro fertilization.

FGF2, LIF, and IGF-1 supplementation improves mouse oocyte in vitro maturation via increased glucose metabolism†

Chemically defined oocyte maturation media supplemented with FGF2, LIF, and IGF-1 (FLI medium) enabled significantly improved oocyte quality in multiple farm animals, yet the molecular mechanisms behind such benefits were poorly defined. Here, we first demonstrated that FLI medium enhanced mouse oocyte quality assessed by blastocyst formation after in vitro fertilization and implantation and fetal development after embryo transfer. We then analyzed the glucose concentrations in the spent media; reactive oxygen species concentrations; mitochondrial membrane potential; spindle morphology in oocytes; and the abundance of transcripts of endothelial growth factor-like factors, cumulus expansion factors, and glucose metabolism-related genes in cumulus cells. We found that FLI medium enabled increased glucose metabolism through glycolysis, pentose phosphate pathway, and hexosamine biosynthetic pathway, as well as more active endothelial growth factor-like factor expressions in cumulus cells, resulting in improved cumulus cell expansion, decreased spindle abnormality, and overall improvement in oocyte quality. In addition, the activities of MAPK1/3, PI3K/AKT, JAK/STAT3, and mTOR signaling pathways in cumulus cells were assessed by the phosphorylation of MAPK1/3, AKT, STAT3, and mTOR downstream target RPS6KB1. We demonstrated that FLI medium promoted activations of all these signaling pathways at multiple different time points during in vitro maturation.

Mechanisms of primordial follicle activation and new pregnancy opportunity for premature ovarian failure patients

Primordial follicles are the starting point of follicular development and the basic functional unit of female reproduction. Primordial follicles are formed around birth, and most of the primordial follicles then enter a dormant state. Since primordial follicles are limited in number and can't be renewed, dormant primordial follicles cannot be reversed once they enter the growing state. Thus, the orderly occurrence of primordial follicles selective activation directly affects the rate of follicle consumption and thus determines the length of female reproductive lifespan. Studies have found that appropriately inhibiting the activation rate of primordial follicles can effectively slow down the rate of follicle consumption, maintain fertility and delay ovarian aging. Based on the known mechanisms of primordial follicle activation, primordial follicle in vitro activation (IVA) technique has been clinically developed. IVA can help patients with premature ovarian failure, middle-aged infertile women, or infertile women due to gynecological surgery treatment to solve infertility problems. The study of the mechanism of selective activation of primordial follicles can contribute to the development of more efficient and safe IVA techniques. In this paper, recent mechanisms of primordial follicle activation and its clinical application are reviewed.

Intraovarian condensed platelet cytokines for infertility and menopause-Mirage or miracle?

On a therapeutic landscape unchanged since the 1980's, oocyte donation with IVF still stands as the solitary medical answer to diminished reserve and premature ovarian insufficiency. In 2016, intraovarian platelet-rich plasma (PRP) crossed the horizon as a hopeful reply to these intertwined problems. The once remote mirage of platelet cytokine effects on gene regulation or telomere stabilization has been brought into sharper focus, with current work clarifying how PRP corrects oxidative stress, rectifies tissue hypoxia, downregulates apoptosis, and enhances cellular metabolism. Not yet ready for routine use, this innovative treatment has already offered at least one point of early consensus: How intraovarian PRP results should be classified-Patients are either responders or non-responders. From this it is intriguing that no published PRP protocol has ever reported a supranormal ovarian rebound or hyperstimulation effect. This might be explained by baseline age-related ovarian conditions prevalent among poor responders, but since dysregulated or malignant transformations are also missing in other tissue contexts following autologous PRP treatment, the contribution of some platelet product which intrinsically delimits regenerative action cannot be discounted. Here we summarize results with recent experimental and clinical platelet research, framing those most likely to help advance reproductive endocrinology practice.

In vivo promotion of primordial follicle activation by stem cell factor treatment in mice with premature ovarian insufficiency and advanced age

Dormant primordial follicles (PFs) are the most abundant reproductive resource in mammalian ovaries. With advances in the mechanism of study of the regulation of PF activation, PFs have been used to improve fertility in clinical practice. As a central controlling element of follicle activation signaling, the pre-granulosa cell-secreted stem cell factor (SCF; also known as KIT ligand, KITL), which initiates the growth of dormant oocytes, is an ideal natural activator that stimulates follicle activation. However, no systematic study has been conducted to identify the activating effect of SCF in vivo and in vitro. In this study, by combining an in vitro whole ovary culture system and several mouse models, we provide a series of experimental evidence that SCF is an efficient activator for improving PF activation in mouse ovaries. Our in vitro study showed that SCF increased phosphatidylinositol 3-kinase (PI3K) signaling and PF activation ratio in neonatal ovaries. In vivo ovarian non-invasive topical administrations of SCF to the ovaries efficiently improved follicle activation and development, oocyte retrieval ratio and fertility in inducible premature ovarian insufficiency mouse models and aged mice. Our study suggests that SCF is an efficient growth factor that can be applied to improve PF activation.

Tamoxifen Activates Dormant Primordial Follicles in Mouse Ovaries

Our previous study found that 17β-estradiol (E2) suppresses primordial follicle activation and growth in cultured mouse ovaries. In this study, we administered tamoxifen, an estrogen receptor antagonist, into the abdominal cavity of mice to clarify the relationship between primordial follicle activation and the physiological concentration of E2 in mouse ovaries. The results showed that tamoxifen promoted primordial follicle activation. Administration of tamoxifen promoted degradation of the extracellular matrix surrounding primordial follicles in the ovaries. Furthermore, tamoxifen decreased the expression of stefin A, an inhibitor of cathepsins that digest some proteins and extracellular matrix, in the ovaries. Mechanical stress produced by the extracellular matrix reportedly suppresses the activation of primordial follicles. The collective results show that tamoxifen can promote primordial follicle activation through the degradation of the extracellular matrix surrounding primordial follicles. Our results indicate that E2 suppresses primordial follicle activation in vivo and that tamoxifen may be useful as a therapeutic agent against infertility.

Impact of obesity on medically assisted reproductive treatments

Increasing evidence has demonstrated that obesity impairs female fertility and negatively affects human reproductive outcome following medically assisted reproduction (MAR) treatment. In the United States, 36.5% of women of reproductive age are obese. Obesity results not only in metabolic disorders including type II diabetes and cardiovascular disease, but might also be responsible for chronic inflammation and oxidative stress. Several studies have demonstrated that inflammation and reactive oxygen species (ROS) in the ovary modify steroidogenesis and might induce anovulation, as well as affecting oocyte meiotic maturation, leading to impaired oocyte quality and embryo developmental competence. Although the adverse effect of female obesity on human reproduction has been an object of debate in the past, there is growing evidence showing a link between female obesity and increased risk of infertility. However, further studies need to clarify some gaps in knowledge. We reviewed the recent evidence on the association between female obesity and infertility. In particular, we highlight the association between fat distribution and reproductive outcome, and how the inflammation and oxidative stress mechanisms might reduce ovarian function and oocyte quality. Finally, we evaluate the connection between female obesity and endometrial receptivity.

Ovarian Stem Cells Differentiation into Primary Oocytes Using Follicle Stimulating Hormone, Basic Fibroblast Growth Factor, and Neurotrophin 3

Background:

In vitro obtaining oocytes can be an appropriate alternative for patients with gonadal insufficiency or cancer survivors. The purpose of the current research was isolating stem cells from ovarian cortical tissue as well as evaluating the effectiveness of follicle stimulating hormone (FSH), basic fibroblast growth factor (bFGF), and neurotrophin 3 (NT3) in differentiating to oocyte-like cells.

Methods:

A human ovary was dissected and cortical tissue pieces were cultured for cell isolation. Isolated cells were divided into 8 groups (3 cases in each group) of control, FSH, NT3, bFGF, FSH+NT3, FSH+bFGF, NT3+bFGF, and FSH+NT3+ bFGF. Pluripotency specific gene (OCT4-A and Nanog), initial germ cells (c-KIT and VASA) and PF growth initiators (GDF-9 and Lhx-8) were evaluated by qRTPCR. Experiments were performed in triplicate and there were 3 samples in each group. The results were analyzed using one-way ANOVA and p-value less than 0.05 was considered statistically significant.

Results:

Flow cytometry results showed that cells isolated from the ovarian cortex expressed markers of pluripotency. The results showed that the expression of Nanog, OCT4, GDF-9 and VASA was significantly increased in FSH+NT3 group, while treatment with bFGF caused significant expression of c-KIT and Lhx-8 (p<0.05). Also, according to the results, isolated cells treated with NT3 significantly increased c-KIT expression.

Conclusion:

According to our results, the ovarian cortex cells could be differentiated into primordial follicles if treated with the proper combination of FSH, bFGF, and NT3. These findings provided a new perspective for the future of in vitro gamete proudest.

Reduced retinoic acid synthesis accelerates prophase I and follicle activation

In female mammals, reproductive potential is determined during fetal life by the formation of a non-renewable pool of primordial follicles. Initiation of meiosis is one of the defining features of germ cell differentiation and is well established to commence in response to retinoic acid. WIN 18,446 inhibits the conversion of retinol to retinoic acid, and therefore it was used to explore the impact of reduced retinoic acid synthesis on meiotic progression and thus germ cell development and subsequent primordial follicle formation. e13.5 mouse fetal ovaries were cultured in vitro and treated with WIN 18,446 for the first 3 days of a total of up to 12 days. Doses as low as 0.01 µM reduced transcript levels of the retinoic acid response genes Stra8 and Rarβ without affecting germ cell number. Higher doses resulted in germ cell loss, rescued with the addition of retinoic acid. WIN 18,446 significantly accelerated the progression of prophase I; this was seen as early as 48 h post treatment using meiotic chromosome spreads and was still evident after 12 days of culture using Tra98/Msy2 immunostaining. Furthermore, ovaries treated with WIN 18,446 at e13.5 but not at P0 had a higher proportion of growing follicles compared to vehicle controls, thus showing evidence of increased follicle activation. These data therefore indicate that retinoic acid is not necessary for meiotic progression but may have a role in the regulation of its progression and germ cell survival at that time and provide evidence for a link between meiotic arrest and follicle growth initiation.

Ovarian tissue damage after grafting: systematic review of strategies to improve follicle outcomes

Frozen-thawed human ovarian tissue endures large-scale follicle loss in the early post-grafting period, characterized by hypoxia lasting around 7 days. Tissue revascularization occurs progressively through new vessel invasion from the host and neoangiogenesis from the graft. Such reoxygenation kinetics lead to further potential damage caused by oxidative stress. The aim of the present manuscript is to provide a systematic review of proangiogenic growth factors, hormones and various antioxidants administered in the event of ovarian tissue transplantation to protect the follicle pool from depletion by boosting revascularization or decreasing oxidative stress. Although almost all investigated studies revealed an advantage in terms of revascularization and reduction in oxidative stress, far fewer demonstrated a positive impact on follicle survival. As the cascade of events driven by ischaemia after transplantation is a complex process involving numerous players, it appears that acting on specific molecular mechanisms, such as concentrations of proangiogenic growth factors, is not enough to significantly mitigate tissue damage. Strategies exploiting the activated tissue response to ischaemia for tissue healing and remodelling purposes, such as the use of antiapoptotic drugs and adult stem cells, are also discussed in the present review, since they yielded promising results in terms of follicle pool protection.

In vitro differentiation of theca cells from ovarian cells isolated from postmenopausal women

STUDY QUESTION

Can human theca cells (TCs) be differentiated in vitro?

SUMMARY ANSWER

It is possible to differentiate human TCs in vitro using a medium supplemented with growth factors and hormones.

WHAT IS KNOWN ALREADY

There are very few studies on the origin of TCs in mammalian ovaries. Precursor TCs have been described in neonatal mice ovaries, which can differentiate into TCs under the influence of factors from oocytes and granulosa cells (GCs). On the other hand, studies in large animal models have reported that stromal cells (SCs) isolated from the cortical ovarian layer can also differentiate into TCs.

STUDY DESIGN, SIZE, DURATION

After obtaining informed consent, ovarian biopsies were taken from eight menopausal women (53-74 years of age) undergoing laparoscopic surgery for gynecologic disease not related to the ovaries. SCs were isolated from the ovarian cortex and in vitro cultured for 8 days in basic medium (BM) (G1), enriched with growth factors, FSH and LH in plastic (G2) or collagen substrate without (G3) or with (G4) a GC line.

PARTICIPANTS/MATERIALS, SETTING, METHODS

To confirm TC differentiation, relative mRNA levels for LH receptor (Lhr), steroidogenic acute regulatory protein (Star), cholesterol side-chain cleavage enzyme (Cyp11a1), cytochrome P450 17A1 (Cyp17a1), hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 1 (Hsd3b1) and hydroxy-delta-5-steroid dehydrogenase, 3 beta- and steroid delta-isomerase 2 (Hsd3b2) were assessed. Immunohistochemistry was also performed for their protein detection and a specific marker was identified for TCs (aminopeptidase-N, CD13), as were markers for theca and small luteal cells (dipeptidyl peptidase IV (CD26) and Notch homolog 1, translocation-associated (NOTCH1)). Finally, we analyzed cell ultrastructure before (Day 0) and after in vitro culture (Day 8), and dehydroepiandrosterone (DHEA) and progesterone levels in the medium using transmission electron microscopy (TEM) and ELISA, respectively.

MAIN RESULTS AND THE ROLE OF CHANCE

Results obtained from qPCR showed a significant increase (P < 0.05) in mRNA levels of Lhr in F2 (floating cells in G2) and G4, Cyp17a1 in G1 and F1 (floating cells in G1) and Hsd3b2 in G1, G2, G3 and G4. Immunohistochemistry confirmed expression of each enzyme involved in the steroidogenic pathway at the protein stage. However, apart from G1, all other groups exhibited a significant (P < 0.05) rise in the number of CD13-positive cells. There was also a significant increase (P < 0.05) in NOTCH1-positive cells in G3 and G4. Ultrastructure analyses by TEM showed a distinct difference between groups and also versus Day 0. A linear trend with time revealed a significant gain (q < 0.001) in DHEA concentrations in the medium during the culture period in G1, G2, G3 and G4. It also demonstrated a statistical increase (q < 0.001) in G2, G3 and G4 groups, but G1 remained the same throughout culture in terms of progesterone levels.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Shorter periods of in vitro culture (e.g. 2, 4 and 6 days) could have led to increased concentrations of differentiated TCs in G2, G3 and G4. In addition, a group of cells cultured in BM and accompanied by COV434 cells would be necessary to understand their role in the differentiation process. Finally, while our results demonstrate that TCs can be differentiated in vitro from cells isolated from the cortical layer of postmenopausal ovaries, we do not know if these cells are differentiated from a subpopulation of precursor TCs present in ovarian cortex or ovarian SCs in general. It is therefore necessary to identify specific markers for precursor TCs in human ovaries to understand the origin of these cells.

WIDER IMPLICATIONS OF THE FINDINGS

This is a promising step toward understanding TC ontogenesis in the human ovary. Moreover, in vitro-generated human TCs can be used for studies on drug screening, as well as to understand TC-associated pathologies, such as androgen-secreting tumors and polycystic ovary syndrome.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by grants from the Fonds National de la Recherche Scientifique de Belgique (FNRS) (C.A.A. is an FRS-FNRS Research Associate; grant MIS #F4535 16 awarded to C.A.A.; grant 5/4/150/5 awarded to M.M.D.; grant ASP-RE314 awarded to P.A.) and Foundation Against Cancer (grant 2018-042 awarded to A.C.). The authors declare no competing interests.

Evaluation of expression and serum concentration of anti-Mullerian hormone as a follicle growth marker following consumption of fennel and flaxseed extract in first-generation mice pups

Background

The aim of the present study was to assess the expression and serum level of AMH in first-generation female mice pups following fennel and flaxseed consumption.

Methods

Twenty pregnant NMRI mice were allocated into four groups including control (CTL), fennel (FV), flaxseed (LU) and FV+ LU. Sixty-four female offsprings after lactation period, received the same regimen as their mothers for 56 and 240 days. The ovarian follicles development, serum concentration of AMH, as well as gene and protein expression of AMH were evaluated in the female offsprings at post-natal day 56 (PND56) and 240 (PND240).

Results

The number of total growing follicles were raised in the FV group in compression to the all experimental groups. In contrast, LU group showed a marked decrease in their numbers. The highest level of serum AMH was seen in the FV-diet mice, whereas LU negatively affected it. The expression level of AMH also increased in the FV and FV + LU groups, while a reduction was observed in the LU group. As well, IHC data showed that the number of AMH-positive cells in almost ovarian follicles of FV and FV + LU-treated mice was in compared to those of the LU group.

Conclusions

The overall effect of fennel treatment (alone and in combination with flaxseed) on ovary might be maintain primordial follicle storage through increased expression and serum level of AMH.

In vitro activation of cryopreserved ovarian tissue: A single-arm meta-analysis and systematic review

OBJECTIVE

Primordial follicles in premature ovarian failure (POF) patients are very difficult to be activated spontaneously, so that mature oocytes are difficult to be obtained for in vitro fertilization. The aim of our review is to analyze and to systematize the published data regarding effectiveness of different strategies for in vitro activation of cryopreserved ovarian tissue.

STUDY DESIGN

According to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a review of the literature was performed for all relevant full-text articles published in PubMed in English. Meta-analysis conducted using STATA 14.0. The random-effects model was used to combine 8 study results because the examination of heterogeneity was minimal.

RESULTS

One hundred and seventy seven patients after in vitro activation treatment (IVA) of ovarian tissue had accumulatively 26 pregnancies through IVF or natural pregnancy and then produced 18 live births. The random-effects model showed that the total clinical pregnancy and baby born rates reported in 8 studies evidence about effectiveness of IVA.

CONCLUSION

In vitro activation of primordial follicles as a new potential treatment for ovarian disorder patients, can be a promising option for fertility preservation. Drug-free activation of ovarian tissue in comparison with drug-included activation seemed to be more efficient.

The Factors and Pathways Regulating the Activation of Mammalian Primordial Follicles in vivo

Mammalian ovaries consist of follicles as basic functional units. Each follicle comprised an innermost oocyte and several surrounding flattened granulosa cells. Unlike males, according to the initial size of the primordial follicle pool and the rate of its activation and depletion, a female's reproductive life has been determined early in life. Primordial follicles, once activated, will get into an irreversible process of development. Most follicles undergo atretic degeneration, and only a few of them could mature and ovulate. Although there are a lot of researches contributing to exploring the activation of primordial follicles, little is known about its underlying mechanisms. Thus, in this review, we collected the latest papers and summarized the signaling pathways as well as some factors involved in the activation of primordial follicles, hoping to lead to a more profound understanding of the cellular and molecular mechanisms of primordial follicle activation.

In vivo and in vitro activation of dormant primordial follicles by EGF treatment in mouse and human

In the mammalian ovaries, dormant primordial follicles represent the reproductive reserve of individual females. Recently, stimulating the activation of primordial follicles in vitro has been practiced, making the utilization of those dormant follicles to treat female infertility possible. However, there are still lacks of effective upstream molecule and strategy to elevate follicle activation in vivo. In the current study, we revealed that growth factor EGF improved a transiently primordial follicle activation in mice by elevating the CDC42-PI3K signaling activity, and EGF treatment also improved the activation and development of human follicles in ovarian cortical pieces. Using a liquid-solid phase transition bio-gel as a carrier, an efficient in vivo activation system was established by ovarian topical EGF administration to living mice. We found that EGF treatment led to an increase of primordial follicle activation in short time but had no effect on long-term fertility in females. By establishing an inducible premature ovarian insufficiency (POI) mouse model through selectively ablating growing follicles in Zp3-Cre;iDTR mice, we further revealed that our in vivo EGF treatment system improved primordial follicle activation and ovulation of POI ovaries significantly. Taken together, our results revealed that in situ ovarian EGF administration could improve the activation of primordial follicles in living animals, and manipulating activation and development of primordial follicles in vivo might be an efficient approach to improve reproductive health in women.

The combination of basic fibroblast growth factor and kit ligand promotes the proliferation, activity and steroidogenesis of granulosa cells during human ovarian cortical culture

Different factors, such as basic fibroblast growth factor (bFGF) and kit ligand (KL), are used in ovarian cortical culture to promote activation of primordial follicles. In the present study, the effects of bFGF and KL, alone and in combination, were evaluated on human follicular activation and growth during in-situ cortical culture. Slow frozen-thawed human ovarian cortical tissues (n = 6) were cultured in 4 different groups: 1) control (base medium), 2) KL (base medium; BM + 100 ng/ml KL), 3) bFGF (BM + 100 ng/ml bFGF) and 4) bFGF + KL (BM + 100 ng/ml KL + 100 ng/ml bFGF) for a week. The proportion of morphologically normal and degenerated follicles at different developmental stages, secreted hormonal levels and specific gene expressions were compared. Although the proportion of growing follicles was higher than primordial counterpart in all cultured groups, no significant differences were observed among the cultured groups. In all cultured groups, anti-Müllerian hormone (AMH), progesterone and estradiol hormones levels increased after 7 days of culture; however, this increase was only significant for estradiol in the bFGF + KL group. The expression of Ki67 gene indicated an increase in ovarian cell proliferation in the three experimental groups compared to the control group, however this increment was only significant for the bFGF + KL group. It can be concluded that KL and bFGF factors individually have no beneficial effects on in-situ follicular growth, but their combination positively influences steroidogenesis of granulosa cells without significantly increasing the number of growing follicles.

Regulation of Folliculogenesis by Growth Factors in Piglet Ovary Exposed Prenatally to β-Hydroxy-β-Methylbutyrate (HMB)

Β-hydroxy-β-methylbutyrate (HMB) is one of the leucine metabolites with protein anabolic effects which makes it very popular among athletes. Previously, it was shown that HMB administered during the prenatal period reduced the pool of primordial follicles and increased the proportion of developing follicles in newborn piglets. This work is a further step to understand these morphological alterations. Therefore, the aim of this study was to examine the effect of prenatal HMB treatment on the expression of the Kit ligand, BMP-4, bFGF, and the IGF-1/IGF-1R system which are the main growth factors controlling follicular development. Excised ovaries from 12 newborn piglets, originated from the control (n=6) and HMB-treated (n=6) sows were used for immunohistochemical and western-blot analysis. The tested proteins were localized within egg nests and ovarian follicles. Furthermore, the western-blot assay indicated higher BMP-4, Kit ligand, and IGF-1R expression, while the level of bFGF and IGF-1 proteins decreased after HMB dietary treatment. These findings show that HMB included into sow diet can modulate the expression of growth factors and thereby alter ovarian morphology in offspring. Therefore, this study opens a discussion about the benefits and risks of the diet supplemented with HMB and its potential application in medicine and animal husbandry, and further research is necessary in this area.

Crosstalk between PTEN/PI3K/Akt Signalling and DNA Damage in the Oocyte: Implications for Primordial Follicle Activation, Oocyte Quality and Ageing

The preservation of genome integrity in the mammalian female germline from primordial follicle arrest to activation of growth to oocyte maturation is fundamental to ensure reproductive success. As oocytes are formed before birth and may remain dormant for many years, it is essential that defence mechanisms are monitored and well maintained. The phosphatase and tensin homolog of chromosome 10 (PTEN)/phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB, Akt) is a major signalling pathway governing primordial follicle recruitment and growth. This pathway also contributes to cell growth, survival and metabolism, and to the maintenance of genomic integrity. Accelerated primordial follicle activation through this pathway may result in a compromised DNA damage response (DDR). Additionally, the distinct DDR mechanisms in oocytes may become less efficient with ageing. This review considers DNA damage surveillance mechanisms and their links to the PTEN/PI3K/Akt signalling pathway, impacting on the DDR during growth activation of primordial follicles, and in ovarian ageing. Targeting DDR mechanisms within oocytes may be of value in developing techniques to protect ovaries against chemotherapy and in advancing clinical approaches to regulate primordial follicle activation.

Increased supply from blood vessels promotes the activation of dormant primordial follicles in mouse ovaries

The controlled activation of dormant primordial follicles is important for the maintenance of periodic ovulation. Previous reports have clearly identified the signaling pathway in granulosa cells and oocytes that controls the activation of primordial follicles; however, the exact cue for the in vivo activation of dormant primordial follicles is yet to be elucidated. In this study, we found that almost all activated primordial follicles made contact with blood vessels. Based on this result, we speculated that the contact between primordial follicles and blood vessels may provide a cue for the activation of dormant primordial follicles. To confirm this hypothesis, we attempted to activate dormant primordial follicles within the ovaries by inducing angiogenesis through the use of biodegradable gels containing recombinant vascular endothelial growth factor and in cultured ovarian tissues by increasing the serum concentration within the culture medium. The activation of dormant primordial follicles was promoted in both experiments, and our results indicated that an increase in the supply of the serum component, from new blood vessels formed via angiogenesis, to the dormant primordial follicles is the cue for their in vivo activation. In the ovaries, angiogenesis often occurs during every estrous cycle, and it is therefore likely that angiogenesis is the crucial event that influences the activation of primordial follicles.

Folliculogenesis-Associated Genes Expression in Human Vitrified Ovarian Tissue after Xenotransplantation in γ-Irradiated Mice

Objective

Autograft transplantation of vitrified cortical ovarian tissue is an acceptable clinical technique for fertility preservation in women. Xenograft transplantation into animal models could be useful for evaluating the safety of human vitrified ovarian tissue. This study targeted to evaluate impact of vitrification on expression of the genes associated with folliculogenesis after xenograft transplantation of human vitrified ovarian tissue to γ-irradiated mice.

Materials and Methods

In this experimental study, ovarian biopsies were gathered from six transsexual persons. The cortical section of ovarian biopsies was separated and chopped into small pieces. These pieces were randomly divided into vitrified and non-vitrified groups. In each group some pieces were considered as non-transplanted tissues and the others were transplanted to γ-irradiated female National Medical Research Institute (NMRI) mice. Before and after two weeks of xenograft transplantation, histological assessment and evaluation of the expression of folliculogenesis- associated genes (FIGLA, GDF-9, KL and FSHR) were performed in both vitrified and non-vitrified groups.

Results

Percentage of the normal follicles and expression of the all examined genes from transplanted and non- transplanted tissue were similar in both vitrified and non-vitrified groups (P>0.05). After transplantation, the normal follicle rate was significantly decreased and among the folliculogenesis-associated genes, expression of GDF-9 gene was significantly increased, rather than before transplantation in vitrified and non-vitrified tissues (P<0.05).

Conclusion

The vitrification method using dimethyl solphoxide and ethylene glycol (EG) had no remarkable effect on the normal follicular rate and expression of folliculogenesis-associated genes after two weeks human ovarian tissue xenografting. In addition, transplantation process can cause a significant decrease in normal follicular rate and expression of GDF-9 gene.

Environmental toxicant induced epigenetic transgenerational inheritance of ovarian pathology and granulosa cell epigenome and transcriptome alterations: ancestral origins of polycystic ovarian syndrome and primary ovarian insufiency

Two of the most prevalent ovarian diseases affecting women's fertility and health are Primary Ovarian Insufficiency (POI) and Polycystic Ovarian Syndrome (PCOS). Previous studies have shown that exposure to a number of environmental toxicants can promote the epigenetic transgenerational inheritance of ovarian disease. In the current study, transgenerational changes to the transcriptome and epigenome of ovarian granulosa cells are characterized in F3 generation rats after ancestral vinclozolin or DDT exposures. In purified granulosa cells from 20-day-old F3 generation females, 164 differentially methylated regions (DMRs) (P < 1 x 10-6) were found in the F3 generation vinclozolin lineage and 293 DMRs (P < 1 x 10-6) in the DDT lineage, compared to controls. Long noncoding RNAs (lncRNAs) and small noncoding RNAs (sncRNAs) were found to be differentially expressed in both the vinclozolin and DDT lineage granulosa cells. There were 492 sncRNAs (P < 1 x 10-4) in the vinclozolin lineage and 1,085 sncRNAs (P < 1 x 10-4) in the DDT lineage. There were 123 lncRNAs and 51 lncRNAs in the vinclozolin and DDT lineages, respectively (P < 1 x 10-4). Differentially expressed mRNAs were also found in the vinclozolin lineage (174 mRNAs at P < 1 x 10-4) and the DDT lineage (212 mRNAs at P < 1 x 10-4) granulosa cells. Comparisons with known ovarian disease associated genes were made. These transgenerational epigenetic changes appear to contribute to the dysregulation of the ovary and disease susceptibility that can occur in later life. Observations suggest that ancestral exposure to toxicants is a risk factor that must be considered in the molecular etiology of ovarian disease.

Nuclear exclusion of SMAD2/3 in granulosa cells is associated with primordial follicle activation in the mouse ovary

Maintenance and activation of the limited supply of primordial follicles in the ovary are important determinants of reproductive lifespan. Currently, the molecular programme that maintains the primordial phenotype and the early events associated with follicle activation are not well defined. Here, we have systematically analysed these events using microscopy and detailed image analysis. Using the immature mouse ovary as a model, we demonstrate that the onset of granulosa cell (GC) proliferation results in increased packing density on the oocyte surface and consequent GC cuboidalization. These events precede oocyte growth and nuclear translocation of FOXO3a, a transcription factor important in follicle activation. Immunolabelling of the TGFβ signalling mediators and transcription factors SMAD2/3 revealed a striking expression pattern specific to GCs of small follicles. SMAD2/3 were expressed in the nuclei of primordial GCs but were mostly excluded in early growing follicles. In activated follicles, GC nuclei lacking SMAD2/3 generally expressed Ki67. These findings suggest that the first phenotypic changes during follicle activation are observed in GCs, and that TGFβ signalling is fundamental for regulating GC arrest and the onset of proliferation.

Assessing recrudescence of photoregressed Siberian hamster ovaries using in vitro whole ovary culture

In vitro culture has been used to study different aspects of ovarian function; however, this technique has not been applied to study recrudescence, or the return of ovarian function in seasonally breeding species. In Siberian hamsters, exposure to inhibitory photoperiods induces declines in ovarian function, which are restored with photostimulation. Because these changes are mediated by changes in systemic gonadotropin (GT) secretion, we hypothesized that culturing photoregressed ovaries with GT would restore aspects of function and induce expression of key folliculogenic factors. Adult female Siberian hamsters were exposed to either long-day (LD; 16L:8D) or short-day (SD; 8L:16D) photoperiods for 14 weeks to maintain in vivo cyclicity or induce gonadal regression, respectively. Isolated ovaries were then cultured for 10 days with or without GT. Ovarian mass and messenger RNA (mRNA) expression of mitotic marker Pcna were increased in cultured SD ovaries (cSD) ovaries with GT as compared to without GT, with no changes noted among cultured LD (cLD) ovaries. Media estradiol and progesterone concentrations increased in both cLD and cSD ovaries cultured with GT as compared to without GT. No differences in follicle numbers or incidence of apoptosis were noted across groups. In addition, differential mRNA expression of folliculogenic growth factors ( Bmp-4, Ntf-3, Inh-α, Gdf-9, Igf-1, Has-2, and Cox-2) was observed in cSD treated with or without GT. Together, these results suggest that this in vitro model could be a useful tool to (a) study the return of function in photoregressed ovaries, and (b) to identify the specific roles folliculogenic factors play in ovarian recrudescence.

Micro-RNAs involved in cellular proliferation have altered expression profiles in granulosa of young women with diminished ovarian reserve

PURPOSE

The study aims to determine differences in micro-RNA (miRNA) expression in granulosa (GC) and cumulus cells (CC) between young women with diminished ovarian reserve (DOR) or normal ovarian reserve (NOR). Secondary objective was to identify downstream signaling pathways that could ultimately indicate causes of lower developmental competence of oocytes from young women with DOR.

METHODS

The method of the study is prospective cohort study.

RESULTS

Of the miRNA, 125 are differentially expressed in GC between DOR and NOR. Only nine miRNA were different in CC; therefore, we focused analysis on GC. In DOR GC, miR-100-5p, miR-16-5p, miR-30a-3p, and miR-193a-3p were significantly downregulated, while miR-155-5p, miR-192-5p, miR-128-3p, miR-486-5p, miR130a-3p, miR-92a-3p, miR-17-3p, miR-221-3p, and miR-175p were increased. This pattern predicted higher cell proliferation in the DOR GC. The primary pathways include MAPK, Wnt, and TGFbeta.

CONCLUSIONS

The miRNA pattern identified critical functions in cell proliferation and survival associated with DOR. GC in women with DOR seems to respond differently to the LH surge.

Ovarian Tissue Culture to Visualize Phenomena in Mouse Ovary

Mammalian females periodically ovulate an almost constant number of oocytes during each estrus cycle. To sustain such regularity and periodicity, regulation occurs at the hypothalamic-pituitary-gonadal axis level and on developing follicles in the ovary. Despite active studies, follicle development mechanisms are not clear because of the several steps involved from the dormant primordial follicle activation to ovulation, and because of the regulation complexity that differs at each follicular stage. To investigate the mechanisms of follicle development, and the dynamics of follicles throughout the estrus cycle, we developed a mouse ovarian tissue culture model that can be used to observe follicle development using a microscope. Systematic follicle development, periodical ovulation, and follicle atresia can all be reproduced in the cultured ovary model, and the culture conditions can be experimentally modulated. Here, we demonstrate the usefulness of this method in the study of the regulatory mechanisms of follicle development and other ovarian phenomena.

Folliculogenic factors in photoregressed ovaries: Differences in mRNA expression in early compared to late follicle development

The early stages of ovarian folliculogenesis generally progress independent of gonadotropins, whereas later stages require signaling initiated by FSH. In Siberian hamsters, cycles of folliculogenesis are mediated by changes in photoperiod which depress the hypothalamic pituitary gonadal axis. Reduced gonadotropins lead to decreases in mature follicle development and ovulation; however, early stages of folliculogenesis have not been explored in regressed ovaries. We hypothesized that intraovarian factors that contribute predominantly to later stages of folliculogenesis would react to changes in photoperiod, whereas factors contributing to earlier stages would not change. To probe if the early stages of folliculogenesis continue in the photoinhibited ovary while late stages decline, we measured the mRNA abundance of factors that interact with FSH signaling (Fshr, Igf1, Cox2) and factors that can function independently of FSH (c-Kit, Kitl, Foxo3, Figla, Nobox, Sohlh1, Lhx8). While plasma FSH, antral follicles, and corpora lutea numbers declined with exposure to inhibitory photoperiod, the numbers of primordial, primary, and secondary follicles did not change. Expression of factors that interact with FSH signaling changed with changes in photoperiod; however, expression of factors that do not interact with FSH were not significantly altered. These results suggest that the photoinhibited ovary is not completely quiescent, as factors important for follicle selection and early follicle growth are still expressed in regressed ovaries. Instead, the lack of gonadotropin support that characterizes the non-breeding season appears to inhibit only final stages of folliculogenesis in Siberian hamsters.

Glial cell line-derived neurotrophic factor supplementation promotes bovine in vitro oocyte maturation and early embryo development

Paracrine factors such as glial cell line-derived neurotrophic factor (GDNF), which was originally derived from the supernatants of a rat glioma cell line, play pivotal roles in oocyte maturation and early embryo development in mammals, such as mice, rats, pigs, sheep, and even humans. However, whether GDNF facilitates in vitro oocyte maturation or early embryo development in bovines is not yet known. We show for the first time that GDNF and its receptor, GDNF family receptor alpha-1 (GFRA1), are presented in ovarian follicles at different stages as well as during oocyte maturation and early embryo development. Immunostaining results revealed the subcellular localizations of GDNF and GFRA1 in oocytes throughout follicle development, first in germinal vesicles and during blastocyst embryo stages. The ability of exogenously applied GDNF to promote oocyte maturation and early embryo development was evaluated in culture, where we found that an optimal concentration of 50 ng/mL promotes the maturation of cumulus-oocyte complexes and the nuclei of denuded oocytes as well as the development of embryos after IVF. To further investigate the potential mechanism by which GDNF promotes oocyte maturation, bovine oocytes were treated with morpholinos targeting Gfra1. The suppression of GFRA1 presence blocked endogenous and exogenous GDNF functions, indicating that the effects of GDNF that are essential and beneficial for bovine oocyte maturation and early embryo development occur through this receptor. Furthermore, we show that supplementation with GDNF improves the efficiency of bovine IVF embryo production.

Quadrupling efficiency in production of genetically modified pigs through improved oocyte maturation

Assisted reproductive technologies in all mammals are critically dependent on the quality of the oocytes used to produce embryos. For reasons not fully clear, oocytes matured in vitro tend to be much less competent to become fertilized, advance to the blastocyst stage, and give rise to live young than their in vivo-produced counterparts, particularly if they are derived from immature females. Here we show that a chemically defined maturation medium supplemented with three cytokines (FGF2, LIF, and IGF1) in combination, so-called "FLI medium," improves nuclear maturation of oocytes in cumulus-oocyte complexes derived from immature pig ovaries and provides a twofold increase in the efficiency of blastocyst production after in vitro fertilization. Transfer of such blastocysts to recipient females doubles mean litter size to about nine piglets per litter. Maturation of oocytes in FLI medium, therefore, effectively provides a fourfold increase in piglets born per oocyte collected. As they progress in culture, the FLI-matured cumulus-oocyte complexes display distinctly different kinetics of MAPK activation in the cumulus cells, much increased cumulus cell expansion, and an accelerated severance of cytoplasmic projections between the cumulus cells outside the zona pellucida and the oocyte within. These events likely underpin the improvement in oocyte quality achieved by using the FLI medium.

Conserved insulin signaling in the regulation of oocyte growth, development, and maturation

Insulin signaling regulates various aspects of physiology, such as glucose homeostasis and aging, and is a key determinant of female reproduction in metazoans. That insulin signaling is crucial for female reproductive health is clear from clinical data linking hyperinsulinemic and hypoinsulinemic condition with certain types of ovarian dysfunction, such as altered steroidogenesis, polycystic ovary syndrome, and infertility. Thus, understanding the signaling mechanisms that underlie the control of insulin-mediated ovarian development is important for the accurate diagnosis of and intervention for female infertility. Studies of invertebrate and vertebrate model systems have revealed the molecular determinants that transduce insulin signaling as well as which biological processes are regulated by the insulin-signaling pathway. The molecular determinants of the insulin-signaling pathway, from the insulin receptor to its downstream signaling components, are structurally and functionally conserved across evolution, from worms to mammals-yet, physiological differences in signaling still exist. Insulin signaling acts cooperatively with gonadotropins in mammals and lower vertebrates to mediate various aspects of ovarian development, mainly owing to evolution of the endocrine system in vertebrates. In contrast, insulin signaling in Drosophila and Caenorhabditis elegans directly regulates oocyte growth and maturation. In this review, we compare and contrast insulin-mediated regulation of ovarian functions in mammals, lower vertebrates, C. elegans, and Drosophila, and highlight conserved signaling pathways and regulatory mechanisms in general while illustrating insulin's unique role in specific reproductive processes.

Expression of kit ligand and insulin-like growth factor binding protein 3 during in vivo or in vitro development of ovarian follicles in sheep

Expression of Kit ligand (KL) and insulin-like growth factor binding protein (IGFBP3) genes was studied at different in vivo and corresponding in vitro stages of development of the ovarian follicles in sheep. The expression of both KL and IGFBP3 was significantly higher in the primordial follicles relative to any other stage of development. Compared to the other stages, the KL expression in the cumulus cells from in vivo grown large antral follicles and that of IGFBP3 in COCs' isolated from large antral follicles matured in vitro for 24 hr were significantly higher. In the oocytes from in vivo grown ovarian follicles, the expression of KL was the same at all the stages of development. Insulin-like growth factor binding protein 3 expression was also the same in the oocytes at all the stages of the development except for a significantly lower expression in those from antral follicles. The expression of KL in the cumulus cells decreased significantly in the in vitro grown early antral follicles but did not change further as the development progressed. The expression of IGFBP3 in the cumulus cells from in vitro grown ovarian follicles appeared to increase as the development progressed although the increase was not significant between any two consecutive stages of development. In the oocytes in in vitro grown ovarian follicles, the expression levels of KL and IGFBP3 genes did not change with development. It is concluded that (i) KL and IGFBP3 genes follow specific patterns of expression during ovarian folliculogenesis and (ii) in vitro culture of preantral follicles compromises the development potential through alterations in the stage-specific patterns of expression of these and other developmentally important genes.

The concentration-dependent effect of progesterone on follicle growth in the mouse ovary

Follicle growth in the mammalian ovary is coordinately controlled by multiple factors to sustain periodic ovulation. In this study, we investigated the role of progesterone on follicle growth in the mouse ovary. As the concentration of progesterone changes during the estrus cycle, we cultured the sliced mouse ovary in a medium containing 10 ng/ml, 100 ng/ml, and 1 μg/ml progesterone. Progesterone promoted the growth of primordial to primary follicles at 100 ng/ml, while it suppressed the growth of secondary follicles at 1 μg/ml. Follicles at other developmental stages in the cultured ovary were unaffected with different concentrations of progesterone. The number of ovulated oocytes increased in the medium containing 100 ng/ml progesterone but decreased in the presence of 1 μg/ml progesterone. Follicles expressed two types of progesterone receptors, progesterone receptor (PGR) and PGR membrane component 1 (PGRMC1). While PGR shows transient expression on granulosa cells of Graafian follicles, PGRMC1 expresses in granulosa cells of developing follicles. These results suggest that progesterone controls the growth of developing follicles through PGRMC1. Our study shows that the effect of progesterone on ovulation and follicle growth in mouse ovary is dependent on the concentration of progesterone and the follicle stage.

Cumulus cell-conditioned medium supports embryonic stem cell differentiation to germ cell-like cells

Cumulus cells provide cellular interactions and growth factors required for oogenesis. In vitro studies of oogenesis are limited primarily because of the paucity of their source, first trimester fetal gonads, and the small number of germ lineage precursor cells present within these tissues. In order to understand this obscure but vitally important process, the present study was designed to direct differentiation of embryonic stem (ES) cells into germ lineage cells. For this purpose, buffalo ES cells were differentiated, as embryoid bodies (EBs) and monolayer adherent cultures, in the presence of different concentrations of cumulus-conditioned medium (CCM; 10%, 20% and 40%) for different periods of culture (4, 8 and 14 days) to identify the optimum differentiation-inducing concentration and time. Quantitative polymerase chain reaction analysis revealed that 20%–40% CCM induced the highest expression of primordial germ cell-specific (deleted in Azoospermia- like (Dazl), dead (Asp-Glu-Ala-Asp) box polypeptide 4 (Vasa also known as DDX4) and promyelocytic leukemia zinc finger protein (Plzf)); meiotic (synaptonemal complex protein 3 (Sycp3), mutl homolog I (Mlh1), transition protein 1/2 (Tnp1/2) and protamine 2 (Prm2); spermatocyte-specific boule-like RNA binding protein (Boule) and tektin 1 (Tekt1)) and oocyte-specific growth differentiation factor 9 (Gdf9) and zona pellucida 2 /3 (Zp2/3)) genes over 8–14 days in culture. Immunocytochemical analysis revealed expression of primordial germ cell (c-KIT, DAZL and VASA), meiotic (SYCP3, MLH1 and PROTAMINE 1), spermatocyte (ACROSIN and HAPRIN) and oocyte (GDF9 and ZP4) markers in both EBs and monolayer differentiation cultures. Western blotting revealed germ lineage-specific protein expression in Day 14 EBs. The significantly lower (P < 0.05) concentration of 5-methyl-2-deoxycytidine in differentiated EBs compared to undifferentiated EBs suggests that methylation erasure may have occurred. Oocyte-like structures obtained in monolayer differentiation stained positive for ZONA PELLUCIDA protein 4 and progressed through various embryo-like developmental stages in extended cultures.

The spatiotemporal hormonal orchestration of human folliculogenesis, early embryogenesis and blastocyst implantation

The early reproductive events starting with folliculogenesis and ending with blastocyst implantation into the uterine endometrium are regulated by a complex interplay among endocrine, paracrine and autocrine factors. This review examines the spatiotemporal integration of these maternal and embryonic signals that are required for successful reproduction. In coordination with hypothalamic-pituitary-gonadal (HPG) hormones, an intraovarian HPG-like axis regulates folliculogenesis, follicular quiescence, ovulation, follicular atresia, and corpus luteal functions. Upon conception and passage of the zygote through the fallopian tube, the contribution of maternal hormones in the form of paracrine secretions from the endosalpinx to embryonic development declines, with autocrine and paracrine signaling becoming increasingly important as instructional signals for the differentiation of the early zygote/morula into a blastocyst. These maternal and embryonic signals include activin and gonadotropin-releasing hormone 1 (GnRH1) that are crucial for the synthesis and secretion of the 'pregnancy' hormone human chorionic gonadotropin (hCG). hCG in turn signals pre-implantation embryonic cell division and sex steroid production required for stem cell differentiation, and subsequent blastulation, gastrulation, cavitation and blastocyst formation. Upon reaching the uterus, blastocyst hatching occurs under the influence of decreased activin signaling, while the attachment and invasion of the trophoblast into the endometrium appears to be driven by a decrease in activin signaling, and by increased GnRH1 and hCG signaling that allows for tissue remodeling and the controlled invasion of the blastocyst into the uterine endometrium. This review demonstrates the importance of integrative endocrine, paracrine, and autocrine signaling for successful human reproduction.

Influence of follicle stage on artificial ovary outcome using fibrin as a matrix

STUDY QUESTION

Do primordial-primary versus secondary follicles embedded inside a fibrin matrix have different capabilities to survive and grow after isolation and transplantation?

SUMMARY ANSWER

Mouse primordial-primary follicles showed a lower recovery rate than secondary follicles, but both were able to grow.

WHAT IS KNOWN ALREADY

Fresh isolated mouse follicles and ovarian stromal cells embedded in a fibrin matrix are capable of surviving and developing after short-term autografting.

STUDY DESIGN, SIZE, DURATION

In vivo experimental model using 11 donor Naval Medical Research Institute (NMRI) mice and 11 recipient severe combined immunodeficiency (SCID) mice. Both ovaries from all NMRI mice were mechanically disrupted and primordial-primary and secondary follicles were isolated with ovarian stromal cells. They were then encapsulated in a fibrin matrix composed of 12.5 mg/ml of fibrinogen (F12.5) and 1 IU/ml of thrombin (T1) (F12.5/T1), and grafted to the inner part of the peritoneum of SCID mice for 2 and 7 days.

PARTICIPANTS/MATERIALS, SETTING, METHODS

This study was conducted at the Gynecology Research Unit, Université Catholique de Louvain. All materials were used to conduct histological (H-E staining) and immunohistochemical (Ki67, TUNEL) analyses.

MAIN RESULTS AND THE ROLE OF CHANCE

Although all grafted fibrin clots were recovered, the follicle recovery rate on day 2 was 16 and 40% for primordial-primary and secondary follicles respectively, while on day 7, it was 6 and 28%. The secondary group showed a significantly higher recovery rate than the primordial-primary group (23%, P-value <0.001). Follicles found in both groups were viable, as demonstrated by live/dead assays, and no difference was observed in the apoptosis rate between groups, as evidenced by TUNEL. Their growth to further stages was confirmed by Ki67 immunostaining.

LIMITATIONS, REASONS FOR CAUTION

As demonstrated by our results, secondary follicles appear to be more likely to survive and develop than primordial-primary follicles in a fibrin matrix after both periods of grafting. These findings may also be attributed to the specific features of the fibrin matrix, which could benefit larger follicles, but not smaller follicles.

WIDER IMPLICATIONS OF THE FINDINGS

This study is essential to understanding possible impairment caused by factors such as the isolation procedure or fibrin matrix composition to the survival and development of different follicle stages. It therefore provides the basis for further investigations with longer periods of grafting.

STUDY FUNDING/COMPETING INTERESTS

This study was supported by grants from the Fonds National de la Recherche Scientifique de Belgique (grant Télévie No. 7.4578.14 and 7.4627.13, grant 5/4/150/5 awarded to Marie-Madeleine Dolmans), Fonds Spéciaux de Recherche, Fondation St Luc, the Foundation Against Cancer, and the Region Wallone (Convention N°6519-OVART) and donations from Mr Pietro Ferrero, Baron Frère and Viscount Philippe de Spoelberch. None of the authors have any competing interests to declare.

Kit ligand promotes the transition from primordial to primary follicles afterin vitroculture of ovine ovarian tissue

This study evaluated the effects of kit ligand (KL) on the morphology and development of ovine preantral follicles (fresh control) and after 7 days ofin vitroculture in α-Minimal Essential Medium (α-MEM; control medium) or the presence of KL (1, 10, 50, 100 or 200 ng/ml). There was an increase in the percentage of primary follicles at the concentration of 100 ng/ml KL, compared with the fresh control, control medium (α-MEM) and the other KL concentrations. Follicle diameter was significantly higher than the control medium only at concentrations of 50 and 100 ng/ml KL. In conclusion, 100 ng/ml KL promoted the transition from primordial to primary follicles (follicular activation) afterin vitroculture of ovine ovarian tissue.

Analysis of the Effect of Leukemia Inhibitory Factor on Follicular Growth in Cultured Murine Ovarian Tissue

Leukemia inhibitory factor (LIF) is expressed in the ovary and controls follicular growth. LIF has been reported to accelerate the primordial to primary follicle transition, the growth of cultured preantral follicles, and the maturation of oocytes. Previous reports on factors that regulate follicular growth have largely employed cultured follicles. However, there are several types of follicles and somatic cells in the ovary that are likely to interact with one another to regulate follicular growth. Therefore, a novel approach is essential for understanding the function of factors that regulate follicular growth in the ovary. In this study, we evaluated the function of LIF using cultured ovarian tissue. Ovarian tissue slices were cultured in the presence or absence of recombinant LIF and neutralizing anti-LIF antibody to enable continuous monitoring of follicular growth within the context of the ovary as well as analysis of the process of follicular growth. The results revealed that LIF inhibited the growth of primary, secondary, and antral follicles. Furthermore, we verified the inhibitory function of LIF using the neutralizing antibody, which accelerated follicular growth. These results suggest that LIF is likely to coordinate follicular growth in the ovary. The culture and analysis methods employed in this study are thus effective for clarifying the tissue-level functions of factors that regulate follicular growth within the ovary.

Basic fibroblast growth factor promotes macaque follicle development in vitro

Fertility preservation is an important type of frontier scientific research in the field of reproductive health. The culture of ovarian cortices to i) initiate primordial follicle growth and ii) procure developing follicles for later oocyte maturation is a promising fertility preservation strategy, especially for older women or cancer patients. At present, this goal remains largely unsubstantiated in primates because of the difficulty in attaining relatively large follicles via ovarian cortex culture. To overcome this hurdle, we cultured macaque monkey ovarian cortices with FSH, kit ligand (KL), basic fibroblast growth factor (bFGF), and/or epidermal growth factor (EGF). The various factors and factor combinations promoted primordial follicle development to different extents. Notably, both bFF (bFGF, 100 ng/ml and FSH, 50 ng/ml) and KF (KL, 100 ng/ml and FSH, 50 ng/ml) contributed to the activation of primordial follicles at day 12 (D12) of culture, whereas at D18, the proportions of developing follicles were significantly higher in the bFF and KF groups relative to the other treatment groups, particularly in the bFF group. Estradiol and progesterone production were also highest in the bFF group, and primary follicle diameters were the largest. Up until D24, the bFF group still exhibited the highest proportion of developing follicles. In conclusion, the bFGF–FSH combination promotes nonhuman primate primordial follicle developmentin vitro, with the optimal experimental window within 18 days. These results provide evidence for the future success of human ovarian cortex culture and the eventual acquisition of mature human follicles or oocytes for fertility restoration.

Involvement of miRNAs and Cell-Secreted Vesicles in Mammalian Ovarian Antral Follicle Development

Ovarian follicular development is a controlled series of events culminating with an ovulatory or atretic follicle. MicroRNAs (miRNAs) are small noncoding RNAs involved in translational regulation of genes in different developmental processes. Deletion of Dicer in mice ovaries demonstrated the importance of miRNAs in reproduction, which led to infertility. The miRNAs were thought to act only within host cells; however, these molecules are also present in cell-secreted vesicles. These vesicles are present in body fluids such as milk, serum, and ovarian follicular fluid. Vesicles are secreted in extracellular fluids and travel from donor to target cells, mediating transfer of bioactive material. Herein we discuss the role of hormonal-regulated miRNAs within different ovarian follicular cells as well as cell-secreted vesicles participation in mammalian ovarian follicular fluid. Furthermore, we discuss the possibility of miRNAs transference mediated by cell-secreted vesicles present in ovarian follicular fluid, increasing the versatility of miRNA functions during antral follicle development.

Regulation of secondary follicle growth by theca cells and insulin-like growth factor 1

Ovaries contain follicles at various stages of development, including primordial, primary, secondary, antral and Graafian follicles. Although the growth of these follicles is controlled to maintain regular ovulation, the mechanism through which this occurs remains unclear. In our study, we found that the growth rate of cultured secondary follicles separated from mice ovaries differed between follicles. After 4 days of culture, the size of some secondary follicles was markedly increased, while that of others had either slightly increased, remained unchanged or shrunk. We compared the expression levels of growth factors between these secondary follicles and found that the growth rate of cultured secondary follicles correlated with the expression level of insulin-like growth factor 1 (Igf1) mRNA. Igf1 mRNA expression level in secondary follicles containing theca cells was higher than that in secondary follicles without theca cells, and the granulosa cell proliferation around follicles containing theca cells was increased. Furthermore, an IGF1 inhibitor also inhibited the granulosa cell proliferation, and administration of IGF1 to secondary follicles without growth promoted granulosa cell proliferation. These results indicated that the theca cells of secondary follicles induced the expression of IGF1 and promoted the follicle growth.

Three-dimensional systems for in vitro follicular culture: overview of alginate-based matrices

The in vitro culture of ovarian follicles has provided critical insight into the biology of the follicle and its enclosed oocyte and the physical interaction and communication between the theca and granulosa cells and the oocyte that is necessary to produce meiotically competent oocytes. Various two-dimensional (2D) and three-dimensional (3D) culture systems have been developed to evaluate the effect of growth factors, hormones, extracellular matrix components and culture conditions on follicle development and oocyte growth and maturation. Among these culture systems, 3D systems make it possible to maintain follicle structure and support communication between the various cell compartments within the follicle. In this review article, we will discuss the three main approaches to ovarian follicle culture: 2D attachment systems, 3D floating systems and 3D encapsulated systems. We will specifically emphasise the development of and advances in alginate-based encapsulated systems for in vitro follicle culture.

Fibrin-mediated delivery of an ovarian follicle pool in a mouse model of infertility

The cryopreservation and autotransplantation of ovarian tissue is emerging as a powerful approach for preserving fertility. However, for cancer patients, it may not be possible to transplant ovarian tissue due to the risk of re-seeding disease. We investigated strategies for transplantation of individually isolated follicles to minimize the risk of re-introducing cancer cells present within the vasculature of ovarian stroma. Procedures for large-scale isolation of early-stage follicles and their encapsulation into fibrin hydrogels were developed. For in vivo validation studies, mice were ovariectomized and transplanted with encapsulated follicles into the ovarian bursa. A substantial increase in the number of secondary follicles was observed in the graft at 9 days after transplantation, and antral follicles by day 21, demonstrating primordial follicle recruitment into the growing pool. Initially, elevated follicle-stimulating hormone levels declined substantially by day 21, indicating feedback from the graft; presence of corpora lutea showed the graft's capability of restoring hormone cyclicity. Taken together, the transplanted follicles were able to engraft, mature, and restore ovarian function in an infertile mouse. This biomaterial may, thus, provide a platform for follicle transplantation with a low risk of cancer contamination and for developing strategies that preserve fertility for women facing a cancer diagnosis.

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.

FOXL2: a central transcription factor of the ovary

Forkhead box L2 (FOXL2) is a gene encoding a forkhead transcription factor preferentially expressed in the ovary, the eyelids and the pituitary gland. Its germline mutations are responsible for the blepharophimosis ptosis epicanthus inversus syndrome, which includes eyelid and mild craniofacial defects associated with primary ovarian insufficiency. Recent studies have shown the involvement of FOXL2 in virtually all stages of ovarian development and function, as well as in granulosa cell (GC)-related pathologies. A central role of FOXL2 is the lifetime maintenance of GC identity through the repression of testis-specific genes. Recently, a highly recurrent somatic FOXL2 mutation leading to the p.C134W subtitution has been linked to the development of GC tumours in the adult, which account for up to 5% of ovarian malignancies. In this review, we summarise data on FOXL2 modulators, targets, partners and post-translational modifications. Despite the progresses made thus far, a better understanding of the impact of FOXL2 mutations and of the molecular aspects of its function is required to rationalise its implication in various pathophysiological processes.

Basic fibroblast growth factor promotes the development of human ovarian early follicles during growth in vitro

STUDY QUESTION

What is the effect of basic fibroblast growth factor (bFGF) on the growth of individual early human follicles in a three-dimensional (3D) culture system in vitro?

SUMMARY ANSWER

The addition of 200 ng bFGF/ml improves human early follicle growth, survival and viability during growth in vitro.

WHAT IS KNOWN ALREADY

It has been demonstrated that bFGF enhances primordial follicle development in human ovarian tissue culture. However, the growth and survival of individual early follicles in encapsulated 3D culture have not been reported.

STUDY DESIGN, SIZE, DURATION

The maturation in vitro of human ovarian follicles was investigated. Ovarian tissue (n= 11) was obtained from 11 women during laparoscopic surgery for gynecological disease, after obtaining written informed consent. One hundred and fifty-four early follicles were isolated by enzymic digestion and mechanical disruption. They were individually encapsulated into alginate (1% w/v) and randomly assigned to be cultured with 0, 100, 200 or 300 ng bFGF/ml for 8 days.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Individual follicles were cultured in minimum essential medium α (αMEM) supplemented with bFGF. Follicle survival and growth were assessed by microscopy. Follicle viability was evaluated under confocal laser scanning microscope following Calcein-AM and Ethidium homodimer-I (Ca-AM/EthD-I) staining.

MAIN RESULTS AND THE ROLE OF CHANCE

After 8 days in culture, all 154 follicles had increased in size. The diameter and survival rate of the follicles and the percentage with good viability were significantly higher in the group cultured with 200 ng bFGF/ml than in the group without bFGF (P < 0.05). The percentage of follicles in the pre-antral stage was significantly higher in the 200 ng bFGF/ml group than in the group without bFGF (P < 0.05), while the percentages of primordial and primary follicles were significantly lower (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

The study focuses on the effect of bFGF on the development of individual human early follicles in 3D culture in vitro and has limited ability to reveal the specific effect of bFGF at each different stage. The findings highlight the need to improve the acquisition and isolation of human ovarian follicles.

WIDER IMPLICATIONS OF THE FINDINGS

The in vitro 3D culture of human follicles with appropriate dosage of bFGF offers an effective method to investigate their development. Moreover, it allows early follicles to be cultured to an advanced stage and therefore has the potential to become an important source of mature oocytes for assisted reproductive technology; particularly as an option for fertility preservation in women, including patients with cancer.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Basic Research Program of China (2011|CB944504, 2011CB944503) and the National Natural Science Foundation of China (81200470, 81000275, 31230047, 8110197). There are no conflicts of interest to declare.