Stepwise requirement of c-kit tyrosine kinase in mouse ovarian follicle development

Asprosin-mediated regulation of ovarian functions in mice: an age-dependent study

Asprosin is a recently discovered adipokine reported to be involved in the modulation of mammalian gonadal functions. Preliminary investigations suggest its role in regulation of ovarian functions in rodents as well as bovids. In addition, increased levels of the adipokine during human ovarian pathophysiologies implicate it in disease progression and severity. The present study evidenced high expression of asprosin in ovaries of juvenile, pubertal and adult mice while expression was significantly low in ageing ovaries. Further, asprosin stimulated expression of markers for ovarian folliculogenesis (Scf, c-Kit, Gdf9, Bmp6, Fshr, Lhr) and steroidogenesis (3β-Hsd) in adult mice. In addition to exploring concentration-dependent effect of asprosin, the study implicates asprosin as an age-dependent modulator of ovarian functions as treatment of ovaries with asprosin led to upregulation of Fshr, c-Kit, Bmp6, and Gdf9 in both adult and juvenile ovaries, Lhr only in adults while that of Scf only in juvenile ovaries. The current study is first to report an age-dependent expression and role of asprosin in murine ovaries.

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.

KIT in oocytes: a key factor for oocyte survival and reproductive lifespan

BACKGROUND

The KITL-KIT interaction is known as an important initiator in oocyte activation through the downstream pathway of PI3K-AKT-FOXO3 signalling. Previous studies utilising germ cell-specific Kit mutant knockin and kinase domain knockout models with Vasa-Cre suggested the crucial role of KIT in oocyte activation at the primordial follicle stage.

METHODS

We utilised mice with complete postnatal deletion of KIT expression in oocytes via Gdf9-iCre and conducted analyses on ovarian follicle development, specific markers, hormone assays, and fertility outcomes.

FINDINGS

Our findings reveal contrasting phenotypes compared to previous mouse models with prenatal deletion of Kit. Specifically, postnatal deletion of Kit exhibit no defects in germ cell nest breakdown, follicle activation, and folliculogenesis during development. Remarkably, upon reaching full maturity, mice with postnatal deletion of Kit experience a complete loss of ovarian reserve, growing follicles, and ovarian function. Furthermore, mice display smaller ovarian size and weight, delayed folliculogenesis, and phenotypes indicative of primary ovarian insufficiency (POI), including elevated serum levels of FSH, reduced AMH, and absence of ovarian follicles, ultimately resulting in infertility. Additionally, the ovaries exhibit randomly distributed expression of granulosa and theca cell markers such as Inhibin α, ACVR2B, and LHR. Notably, there is the uncontrolled expression of p-SMAD3 and Ki67 throughout the ovarian sections, along with the widespread presence of luteinised stroma cells and cleaved Caspase-3-positive dying cells.

INTERPRETATION

These genetic studies underscore the indispensable role of KIT in oocytes for maintaining the survival of ovarian follicles and ensuring the reproductive lifespan.

FUNDING

This work was supported by National Institutes of Health grant R01HD096042 and startup funds from UNMC (S.Y.K.).

Mouse oocytes sequester aggregated proteins in degradative super-organelles

Oocytes are among the longest-lived cells in the body and need to preserve their cytoplasm to support proper embryonic development. Protein aggregation is a major threat for intracellular homeostasis in long-lived cells. How oocytes cope with protein aggregation during their extended life is unknown. Here, we find that mouse oocytes accumulate protein aggregates in specialized compartments that we named endolysosomal vesicular assemblies (ELVAs). Combining live-cell imaging, electron microscopy, and proteomics, we found that ELVAs are non-membrane-bound compartments composed of endolysosomes, autophagosomes, and proteasomes held together by a protein matrix formed by RUFY1. Functional assays revealed that in immature oocytes, ELVAs sequester aggregated proteins, including TDP-43, and degrade them upon oocyte maturation. Inhibiting degradative activity in ELVAs leads to the accumulation of protein aggregates in the embryo and is detrimental for embryo survival. Thus, ELVAs represent a strategy to safeguard protein homeostasis in long-lived cells.

Making a good egg: human oocyte health, aging, and in vitro development

Mammalian eggs (oocytes) are formed during fetal life and establish associations with somatic cells to form primordial follicles that create a store of germ cells (the primordial pool). The size of this pool is influenced by key events during the formation of germ cells and by factors that influence the subsequent activation of follicle growth. These regulatory pathways must ensure that the reserve of oocytes within primordial follicles in humans lasts for up to 50 years, yet only approximately 0.1% will ever be ovulated with the rest undergoing degeneration. This review outlines the mechanisms and regulatory pathways that govern the processes of oocyte and follicle formation and later growth, within the ovarian stroma, through to ovulation with particular reference to human oocytes/follicles. In addition, the effects of aging on female reproductive capacity through changes in oocyte number and quality are emphasized, with both the cellular mechanisms and clinical implications discussed. Finally, the details of current developments in culture systems that support all stages of follicle growth to generate mature oocytes in vitro and emerging prospects for making new oocytes from stem cells are outlined.

Antagonism between DDX6 and PI3K-AKT signaling is an oocyte-intrinsic mechanism controlling primordial follicle growth†

Oocyte maturation and subsequent ovulation during the reproductive lifespan ensure long-term reproduction in mammalian females. This is achieved by tight regulation for the maintenance and growth of primordial follicles. However, the underlying mechanisms remain unsolved. We herein report that posttranscriptional gene regulation mediated by an RNA helicase, DEAD-box helicase 6 (DDX6), and phosphoinositide-3-kinase (PI3K)-AKT signaling exhibits an antagonistic interaction in mouse primordial follicles. DDX6 forms P-body-like cytoplasmic foci in oocytes, which colocalize to a P-body component, DCP1A. Interestingly, the P-body-like granules predominantly assemble in primordial follicles, but disperse once follicle growth is initiated, suggesting that they play a role in the maintenance of primordial follicles. Oocyte-specific knockout of Ddx6 using Gdf9-iCre revealed that Ddx6-deficient oocytes are defective in foci assembly and are abnormally enlarged, resulting in premature depletion of primordial follicles. These results indicate that DDX6 is required to maintain primordial follicles. The abnormal oocyte enlargement is because of enhanced PI3K-AKT signaling, a pivotal signaling pathway in the growth of primordial follicles. Conversely, the forced activation of PI3K-AKT signaling by knocking out Pten disassembles P-body-like granules in primordial follicles. These data suggest that DDX6 and PI3K-AKT signaling mutually antagonize the assembly of P-body-like granules and the growth of primordial follicles. We propose this mutual antagonism as an oocyte-intrinsic mechanism controlling the maintenance and growth of primordial follicles, ensuring the longevity of female reproduction.

Adenovirus-mediated gene delivery restores fertility in congenitally infertile female mice

Oogenesis depends on close interactions between oocytes and granulosa cells. Abnormal signaling between these cell types can result in infertility. However, attempts to manipulate oocyte-granulosa cell interactions have had limited success, likely due to the blood-follicle barrier (BFB), which prevents the penetration of exogenous materials into ovarian follicles. Here, we used adenoviruses (AVs) to manipulate the oocyte-granulosa cell interactions. AVs penetrated the BFB and transduced granulosa cells through ovarian microinjection. Although AVs caused transient inflammation, they did not impair fertility in wild-type mice. Introduction of Kitl-expressing AVs into congenitally infertile Kitl^Sl-t/Kitl^Sl-t mutant mouse ovaries, which contained only primordial follicles because of a lack of Kitl expression, restored fertility through natural mating. The offspring showed no evidence of AV integration and exhibited normal genomic imprinting patterns for imprinted genes. These results demonstrate the usefulness of AVs for manipulating oogenesis and suggest the possibility of gene therapies for human female infertility.

Signaling pathway intervention in premature ovarian failure

Premature ovarian failure (POF) is a multifactorial disease that refers to the occurrence of secondary amenorrhea, estrogen decrease, and gonadotropin increase in women under the age of 40. The prevalence of POF is increasing year by year, and the existing instances can be categorized as primary or secondary cases. This disease has adverse effects on both the physiology and psychology of women. Hormone replacement therapy is the recommended treatment for POF, and a multidisciplinary strategy is required to enhance the quality of life of patients. According to recent studies, the primary mechanism of POF is the depletion of ovarian reserve function as a result of increased primordial follicular activation or primordial follicular insufficiency. Therefore, understanding the processes of primordial follicle activation and associated pathways and exploring effective interventions are important for the treatment of POF.

Gene therapy for female infertility: A farfetched dream or reality?

A major cause of infertility in women is impaired ovulation or oogenesis. In this issue of Cell Reports Medicine, Kanatsu-Shinohara et al.1 demonstrate the potential of gene delivery with adeno-associated virus that can cross the blood-follicle barrier and restore oogenesis in congenitally infertile mice.

Adeno-associated-virus-mediated gene delivery to ovaries restores fertility in congenital infertile mice

Oocytes and granulosa cells closely interact with each other during follicular development, and a lack of appropriate signaling between them results in infertility. Attempts to manipulate oocyte microenvironment have been impeded by the impermeability of the blood-follicle barrier (BFB). To establish a strategy for manipulating oogenesis, we use adeno-associated viruses (AAVs), which have a unique ability of transcytosis. Microinjecting of AAVs into the ovarian stroma penetrates the BFB and achieves long-term gene expression. Introduction of an AAV carrying the mouse Kitl gene restores oogenesis in congenitally infertile KitlSl-t/KitlSl-t mutant mouse ovaries, which lack Kitl expression but contain only primordial follicles. Healthy offspring without AAV integration are born by natural mating. Therefore, AAV-mediated gene delivery not only provides a means for studying oocyte-granulosa interactions through the manipulation of the oocyte microenvironment but could also be a powerful method to treat female infertility resulting from somatic cell defects.

The role of Hippo pathway signaling and A-kinase anchoring protein 13 in primordial follicle activation and inhibition

OBJECTIVE

To determine whether the mechanotransduction and pharmacomanipulation of A-kinase anchoring protein 13 (AKAP13) altered Hippo signaling pathway transcription and growth factors in granulosa cells. Primary ovarian insufficiency is the depletion or dysfunction of primordial ovarian follicles. In vitro activation of ovarian tissue in patients with primary ovarian insufficiency alters the Hippo and phosphatase and tensin homolog/phosphatidylinositol 3-kinase/protein kinase B/forkhead box O3 pathways. A-kinase anchoring protein 13 is found in granulosa cells and may regulate the Hippo pathway via F-actin polymerization resulting in altered nuclear yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif coactivators and Tea domain family (TEAD) transcription factors.

DESIGN

Laboratory studies.

SETTING

Translational science laboratory.

PATIENT(S)

None.

INTERVENTION(S)

COV434 cells, derived from a primary human granulosa tumor cell line, were studied under different cell density and well stiffness conditions. Cells were transfected with a TEAD-luciferase (TEAD-luc) reporter as well as expression constructs for AKAP13 or AKAP13 mutants and then treated with AKAP13 activators, inhibitors, and follicle-stimulating hormone.

MAIN OUTCOME MEASURE(S)

TEAD gene activation or inhibition was measured by TEAD-luciferase assays. The messenger ribonucleic acid levels of Hippo pathway signaling molecules, including connective tissue growth factor (CTGF), baculoviral inhibitors of apoptosis repeat-containing 5, Ankyrin repeat domain-containing protein 1, YAP1, and TEAD1, were measured by quantitative real-time polymerase chain reaction. Protein expressions for AKAP13, CTGF, YAP1, and TEAD1 were measured using Western blot.

RESULT(S)

Increased TEAD-luciferase activity and expression of markers for cellular growth were associated with decreased cell density, increased well stiffness, and AKAP13 activator (A02) treatment. Additionally, decreased TEAD-luc activity and expression of markers for cellular growth were associated with AKAP13 inhibitor (A13) treatment, including a reduced expression of the BIRC5 and ANKRD1 (YAP-responsive genes) transcript levels and CTGF protein levels. There were no changes in TEAD-luc with follicle-stimulating hormone treatment, supporting Hippo pathway involvement in the gonadotropin-independent portion of folliculogenesis.

CONCLUSION(S)

These findings suggest that AKAP13 mediates Hippo-regulated changes in granulosa cell growth via mechanotransduction and pharmacomanipulation. The AKAP13 regulation of the Hippo pathway may represent a potential target for regulation of follicle activation.

Single-nucleotide polymorphisms in <i>FLT3</i>, <i>NLRP5</i>, and <i>TGIF1</i> are associated with litter size in Small-tailed Han sheep

Previous studies have indicated that FLT3, NLRP5, and TGIF1 play a pivotal role in sheep fecundity. Nevertheless, little is known about the association of the polymorphisms of these genes with litter size (LS). In this study, the selected single-nucleotide polymorphisms (SNPs) were genotyped using a Sequenom MassARRAY® platform, and the distribution of different genotypes of the SNPs in the seven sheep breeds (Small-tailed Han, Hu, Cele Black, Suffolk, Tan, Prairie Tibetan, and Sunite sheep) were analyzed. The reliability of the estimated allele frequency for all seven SNPs was at least 0.9545. Given the association of the TGIF1 g.37866222C > T polymorphism with LS in Small-tailed Han sheep (p<0.05), fecundity differences might be caused by the change in amino acid from proline (Pro) to serine (Ser), which has an impact on secondary, tertiary protein structures with concomitant TGIF1 functionality changes. The FLT3 rs421947730 locus has a great effect on the LS (p<0.05), indicating that the locus of FLT3 in synergy with KILTG is likely to facilitate ovarian follicle maturation and ovulation. Moreover, NLRP5 rs426897754 is associated with the LS of the second and third parities (p<0.05). We speculate that a synonymous variant of NLRP5 may be involved in folliculogenesis accompanied by BMP15, FSHR, BMPR1B, AMH, and GDF9, resulting in the different fecundity of Small-tailed Han sheep. Our studies provide valuable genetic markers for sheep breeding.

Regulation of mouse primordial follicle formation by signaling through the PI3K pathway

Cell signaling mediated by the KIT receptor is critical for many aspects of oogenesis including the proliferation and migration of primordial germ cells, as well as the survival, growth, and maturation of ovarian follicles. We previously showed that KIT regulates cyst breakdown and primordial follicle formation, and in this study, have investigated the mechanisms downstream of the receptor by modulating the activity of two downstream signaling cascades: the phosphoinositide 3-kinase (PI3K) and the mitogen-activated protein kinase (MAPK) pathways. E17.5 ovaries were cultured for five days with a daily dose of media supplemented with either the PI3K inhibitor LY294002, the MEK inhibitor U0126, or a DMSO vehicle control. Our histological observations aligned with the established role of PI3K in oocyte growth and primordial follicle activation but also revealed that LY294002 treatment delayed the processes of cyst breakdown and primordial follicle formation. U0126 treatment also led to a reduction in oocyte growth and follicle development but did not appear to affect cyst breakdown. The delay in cyst breakdown was mitigated when ovaries were dually dosed with LY294002 and KITL, suggesting that while KIT may signal through PI3K to promote cyst breakdown, other signaling networks downstream of the receptor could compensate. These observations unearth a role for PI3K signaling in the establishment of the ovarian reserve and suggest that PI3K might be the primary mediator of KIT-induced cyst breakdown and primordial follicle formation in the mouse ovary.

Leukaemia inhibitory factor modulates the differentiation of granulosa cells during sheep in vitro preantral to antral follicle development and improves oocyte meiotic competence

In vitro follicle development from cryopreserved ovarian tissue could become an invaluable assisted reproduction technology for women with early ovarian failure. The challenge lies in producing, from small follicles present in the ovarian cortex, high-quality mature oocytes able to sustain embryo development. In vivo, an optimal combination of hormones and other factors coordinates the development of follicles and their enclosed oocyte. We have investigated the effect of the leukaemia inhibitory factor (LIF) cytokine, alone or in combination with FSH, on sheep in vitro follicle development from the preantral stage onwards. LIF did not alter follicle growth or antrum formation, but it modulated the differentiation of granulosa cells, as revealed by decreased production of anti-Müllerian hormone and abolished FSH-induced stimulation of oestradiol secretion. This modulatory role was also reflected in the abundance of mRNA from 35 genes, analysed by reverse-transcription coupled to microfluidic quantitative PCR. LIF stimulated or at least maintained the expression of genes involved in the dialogue between the oocyte and granulosa cells, through gap junctions (GJA4 encoding connexin 37) or paracrine signalling (Bone morphogenetic protein 15, KIT ligand and their receptors). Finally, the presence of both LIF and FSH during follicle growth strongly improved oocyte meiotic competence: most oocytes (56%) underwent subsequent nuclear maturation, a significant increase compared with their counterparts from follicles of similar size (550-900 µm) cultured with FSH only (28%) or developed in vivo (9%). Their ability to sustain embryo development remains to be evaluated. Combined supplementation with FSH and LIF certainly merits investigation with human follicles.

Human Granulosa Cells-Stemness Properties, Molecular Cross-Talk and Follicular Angiogenesis

The ovarian follicle is the basic functional unit of the ovary, comprising theca cells and granulosa cells (GCs). Two different types of GCs, mural GCs and cumulus cells (CCs), serve different functions during folliculogenesis. Mural GCs produce oestrogen during the follicular phase and progesterone after ovulation, while CCs surround the oocyte tightly and form the cumulus oophurus and corona radiata inner cell layer. CCs are also engaged in bi-directional metabolite exchange with the oocyte, as they form gap-junctions, which are crucial for both the oocyte’s proper maturation and GC proliferation. However, the function of both GCs and CCs is dependent on proper follicular angiogenesis. Aside from participating in complex molecular interplay with the oocyte, the ovarian follicular cells exhibit stem-like properties, characteristic of mesenchymal stem cells (MSCs). Both GCs and CCs remain under the influence of various miRNAs, and some of them may contribute to polycystic ovary syndrome (PCOS) or premature ovarian insufficiency (POI) occurrence. Considering increasing female fertility problems worldwide, it is of interest to develop new strategies enhancing assisted reproductive techniques. Therefore, it is important to carefully consider GCs as ovarian stem cells in terms of the cellular features and molecular pathways involved in their development and interactions as well as outline their possible application in translational medicine.

Revisiting the Impact of Local Leptin Signaling in Folliculogenesis and Oocyte Maturation in Obese Mothers

The complex nature of folliculogenesis regulation accounts for its susceptibility to maternal physiological fitness. In obese mothers, progressive expansion of adipose tissue culminates with severe hyperestrogenism and hyperleptinemia with detrimental effects for ovarian performance. Indeed, maternal obesity is associated with the establishment of ovarian leptin resistance. This review summarizes current knowledge on potential effects of impaired leptin signaling throughout folliculogenesis and oocyte developmental competence in mice and women.

Expression patterns of ZO-1/2 and their effects on porcine oocyte in vitro maturation and early embryonic development

Zonula occludens (ZO)-1 and ZO-2 are involved in epithelial polarity maintenance, gene transcription, cell proliferation and tumor cell metastasis. Regulating ZO-1/2 expression influences the early embryonic development of mice, but whether they are involved in oocyte maturation is still poorly understood. In the present study, the expression patterns of ZO-1 and ZO-2 in porcine cumulus cells and oocytes matured in vitro and early embryos from parthenogenetic activation were detected by qRT-PCR or Western blot, and then their roles in porcine oocyte maturation and early embryo development were investigated by shRNA technology. ZO-1 and ZO-2 were found to be expressed in cumulus cells, oocytes and early embryos, while ZO-1α⁺ was expressed only in cumulus cells, morula and blastocysts. During in vitro maturation (IVM), the abundance of ZO-1 and ZO-2 in oocytes was significantly higher than that in cumulus cells at 0 h (P < 0.01), and their mRNA and protein levels displayed relatively higher expression at 0 and 18 h, respectively. Compared with the control groups, cumulus cell expansion, oocyte nucleus maturation, and subsequent cleavage were not influenced by treatment of the cumulus-oocyte complexes (COCs) with ZO-1-shRNA1, ZO-2-shRNA2 or combined ZO-1-shRNA1 and ZO-2-shRNA2 lentivirus (P > 0.05). However, the blastocyst rate was reduced by treatment of COCs with ZO-1-shRNA1 but not ZO-2-shRNA2. The total cell number of blastocysts was decreased by downregulation of ZO-1 and ZO-2 (P < 0.05). Downregulation of ZO-1 and ZO-2 also resulted in a significant decrease (P < 0.05) in the expression of Cx43, Cx45, PTX3 and PTGS2 in cumulus cells, Cx45, BMP15, ZP3 and C-KIT in MII oocytes, and Nanog in blastocysts, with the exception of HAS2 expression in cumulus cells and Oct4 expression in blastocysts (P > 0.05). Altogether, the above results indicate that ZO-1 and ZO-2 display similar expression patterns during porcine oocyte IVM and are critical to porcine oocyte maturation and early embryonic development.

A novel variant in the promoter region of miR-9 gene strongly affects litter size in Markhoz goats

This study aimed to identify and evaluate the effects of single nucleotide polymorphisms (SNPs) within miR-9 and miR-27a genes and their promoters, as well as 3'UTR regions of KITLG and IGF1 genes on litter size in Markhoz goats. PCR-SSCP analysis revealed different band patterns and sequencing results confirmed four SNPs including a C/A, a A/G, a C/T and a A/G substitution located in the promoter region of miR-9 gene, 48 bp upstream of miR-9 seed region within the 3'UTR of KITLG gene, 37 bp downstream of miR-27a gene and 39 bp upstream of miR-9 seed region within the 3'UTR of IGF1 gene, respectively. The results of the least-square analyses indicated that AA genotype of miR-9 gene strongly and positively affects litter size in Markhoz goats (P < 0.01). Furthermore, the results of the logistic regression analyses confirmed that the A allele of miR-9 gene has a tremendous impact on litter size in Markhoz goats (P < 0.01). Scanning the promoter region of miR-9 gene showed that changing C allele to A may prevent HES1, HES2, NRF1 and TCFL5 transcription factors (TFs) from binding to the promoter, which can reduce the expression of miR-9 gene. Principle component analysis (PCA) showed that approximately 60% of the variation of the data set was explained by two of four SNPs. Also, the biplot from the PCA showed a strong association between litter size and C/A polymorphism of miR-9 promoter. Linkage disequilibrium analysis revealed a very slight linkage among investigated loci.

Effects of stem cell factor on in vitro growth of buffalo oocytes

Stem cell factor (SCF) plays important roles in primordial follicle activation, oocyte growth and survival, granulosa cell proliferation, theca cell recruitment, and ovarian steroidogenesis. The aim of this study was to investigate the effect of SCF on in vitro growth of buffalo oocytes. Oocyte-granulosa cell complexes (OGCs) were dissected from early antral follicles of slaughtered buffalo ovaries and cultured for 6 days in media supplemented with 0, 50 or 100 ng/mL SCF. In vitro grown oocytes were further cultured for in vitro maturation for 24 h. The results showed that SCF significantly (P < 0.05) increased oocyte diameter in vitro. The percentages of surviving oocytes were 60, 81 and 92 in 0, 50 and 100 ng/mL SCF supplemented group, respectively. SCF promoted formation of antrum-like structures in culture. The results also showed that SCF enhanced the maturation of in vitro grown buffalo oocytes. Here, 14% in vitro grown oocytes reached metaphase II (MII) stage in 50 ng/mL SCF supplemented group, whereas the percentage was increased to 26% in 100 ng/mL SCF treated group. These results show that SCF supports the growth, viability and nuclear maturation of buffalo oocytes in vitro.

Effect of caloric restriction and rapamycin on ovarian aging in mice

Caloric restriction (CR) increases the preservation of the ovarian primordial follicular reserve, which can potentially delay menopause. Rapamycin also increases preservation on the ovarian reserve, with similar mechanism to CR. Therefore, the aim of our study was to evaluate the effects of rapamycin and CR on metabolism, ovarian reserve, and gene expression in mice. Thirty-six female mice were allocated into three groups: control, rapamycin-treated (4 mg/kg body weight every other day), and 30% CR. Caloric restricted females had lower body weight (P < 0.05) and increased insulin sensitivity (P = 0.003), while rapamycin injection did not change body weight (P > 0.05) and induced insulin resistance (P < 0.05). Both CR and rapamycin females displayed a higher number of primordial follicles (P = 0.02 and 0.04, respectively), fewer primary, secondary, and tertiary follicles (P < 0.05) and displayed increased ovarian Foxo3a gene expression (P < 0.05). Despite the divergent metabolic effects of the CR and rapamycin treatments, females from both groups displayed a similar increase in ovarian reserve, which was associated with higher expression of ovarian Foxo3a.

Primordial follicle activation as new treatment for primary ovarian insufficiency

Primordial follicle activation is a process in which individual primordial follicles leave their dormant state and enter a growth phase. While existing hormone stimulation strategies targeted the growing follicles, the remaining dormant primordial follicles were ruled out from clinical use. Recently, in vitro activation (IVA), which is a method for controlling primordial follicle activation, has provided an innovative technology for primary ovarian insufficiency (POI) patients. IVA was developed based on Hippo signaling and phosphatase and tensin homolog (PTEN)/phosphatidylinositol-3-kinase (PI3K)/protein kinase B (AKT)/forkhead box O3 (FOXO3) signaling modulation. With this method, dormant primordial follicles are activated to enter growth phase and developed into competent oocytes. IVA has been successfully applied in POI patients who only have a few remaining remnant primordial follicles in the ovary, and healthy pregnancies and deliveries have been reported. IVA may also provide a promising option for fertility preservation in cancer patients and prepubertal girls whose fertility preservation choices are limited to tissue cryopreservation. Here, we review the basic mechanisms, translational studies, and current clinical results for IVA. Limitations and further study requirements that could potentially optimize IVA for future use will also be discussed.

A way for in vitro/ex vivo egg production in mammals

Eggs are female germ cells that are required for producing offspring through sexual reproduction. In mammals, eggs are produced in the ovary and ovulated into the oviduct. It is well known that over 99% of eggs are degenerated without ovulation, so that many studies have attempted in vitro folliculogenesis to produce many eggs in different species for a few decades. Although many methods have been developed, a success of in vitro egg production with the resultant live birth of offspring has been limited, especially in livestock animals. More recently, we have succeeded in producing live pups derived from in vitro/ex vivo egg production in mice. This review aims to introduce our recent findings with a brief history of in vitro/ex vivo culture systems for follicles and ovaries.

Follicle development as an orchestrated signaling network in a 3D organoid

The ovarian follicle is the structural and functional unit of the ovary, composed of the female gamete (the oocyte) and supportive somatic cells. Follicles are not only the source of a female's germ cell supply, but also secrete important hormones necessary for proper endocrine function. Folliculogenesis, the growth and maturation of the follicular unit, is a complex process governed by both intrafollicular crosstalk and pituitary-secreted hormones. While the later stages of this process are gonadotropin-dependent, early folliculogenesis appears to be controlled by the ovarian microenvironment and intrafollicular paracrine and autocrine signaling. In vitro follicle culture remains challenging because of the limited knowledge of growth factors and other cytokines influencing early follicle growth. Here we discuss the current state of knowledge on paracrine and autocrine signaling influencing primary follicles as they develop into the antral stage. Given the importance of intrafollicular signaling and the ovarian microenvironment, we reviewed the current engineering approaches for in vitro follicle culture, including 3D systems using natural hydrogels such as alginate and synthetic hydrogels such as poly(ethylene glycol). Our discussion is focused on what drives the proliferation of granulosa cells, development of the thecal layer, and antrum formation-three processes integral to follicle growth up to the antral stage. Further research in this area may reveal the mechanisms behind these complex signaling relationships within the follicle, leading to more successful and physiologically-relevant in vitro culture methods that will translate well to clinical applications.

Primordial follicle activation is affected by the absence of Sohlh1 in mice

Previous studies have reported that only primordial follicles and empty follicles can be found in 7.5 days postparturition (dpp) Sohlh1^-/- mouse ovaries and females are infertility. There appears to be a defect in follicle development during the primordial-to-primary follicle transition in Sohlh1^-/- mouse ovaries. However, detailed analyses of these phenomena have not been performed. In this study, we used Sohlh1^-/- transgenic mice to explore the role of Sohlh1 in folliculogenesis. The results showed that only primordial follicles and empty follicles can be observed in Sohlh1^-/- ovaries from 0.5 to 23.5 dpp. The expression of Foxo3 and FOXO3 was downregulated; nucleocytoplasmic shuttling of FOXO3 was normal in 7.5-dpp Sohlh1^+/+ but not Sohlh1^-/- ovaries; and primordial follicle activation (PFA) was not observed in 7.5-dpp Sohlh1^-/- mice. The expression levels of KIT, AKT, and P308-AKT were downregulated (p < 0.05), whereas that of P473-AKT was not significantly changed (p > 0.05). The KIT/PI3K/AKT pathway was inhibited. Furthermore, we conducted a dual luciferase assay and chromatin immunoprecipitation. The results showed that SOHLH1 can upregulate the Kit gene by binding to the -3698 bp E-box motif. The absence of Sohlh1 may affect PFA in mouse ovaries via downregulation of Kit and inhibition of the KIT/PI3K/AKT pathway.

Progressive obesity alters ovarian insulin, phosphatidylinositol-3 kinase, and chemical metabolism signaling pathways and potentiates ovotoxicity induced by phosphoramide mustard in mice

Mechanisms underlying obesity-associated reproductive impairment are ill defined. Hyperinsulinemia is a metabolic perturbation often observed in obese subjects. Insulin activates phosphatidylinositol 3-kinase (PI3K) signaling, which regulates ovarian folliculogenesis, steroidogenesis, and xenobiotic metabolism. The impact of progressive obesity on ovarian genes encoding mRNA involved in insulin-mediated PI3K signaling and xenobiotic biotransformation [insulin receptor (Insr), insulin receptor substrate 1 (Irs1), 2 (Irs2), and 3 (Irs3); kit ligand (Kitlg), stem cell growth factor receptor (Kit), protein kinase B (AKT) alpha (Akt1), beta (Akt2), forkhead transcription factor (FOXO) subfamily 1 (Foxo1), and subfamily 3 (Foxo3a), microsomal epoxide hydrolase (Ephx1), cytochrome P450 family 2, subfamily E, polypeptide 1 (Cyp2e1), glutathione S-transferase (GST) class Pi (Gstp1) and class mu 1 (Gstm1)] was determined in normal wild-type nonagouti (a/a; lean) and lethal yellow mice (KK.CG-Ay/J; obese) at 6, 12, 18, or 24 weeks of age. At 6 weeks, ovaries from obese mice had increased (P < 0.05) Insr and Irs3 but decreased (P < 0.05) Kitlg, Foxo1, and Cyp2e1 mRNA levels. Interestingly, at 12 weeks, an increase (P < 0.05) in Kitlg and Kit mRNA, pIRS1Ser302, pAKTThr308, EPHX1, and GSTP1 protein level was observed due to obesity, while Cyp2e1 mRNA and protein were reduced. A phosphoramide mustard (PM) challenge increased (P < 0.05) ovarian EPHX1 protein abundance in lean but not obese females. In addition, lung tissue from PM-exposed animals had increased (P < 0.05) EPHX1 protein with no impact of obesity thereon. Taken together, progressive obesity affected ovarian signaling pathways potentially involved in obesity-associated reproductive disorders.

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.

Untapped Reserves: Controlling Primordial Follicle Growth Activation

Even with the benefit of assisted reproductive technologies (ART), many women are unable to conceive and deliver healthy offspring. One common cause of infertility is the inability to produce eggs capable of contributing to live birth. This can occur despite standard-of-care treatment to maximize the recovery of eggs from growing ovarian follicles. Dormant primordial follicles in the human ovary are a 'reserve ' that can be exploited clinically to overcome this problem. We discuss how controlling primordial follicle growth activation (PFGA) can produce increased numbers of high-quality eggs available for fertility treatment(s). We consider the state of the art in interventions used to control PFGA, and consider genetic and epigenetic strategies on the horizon that might improve compromised oocyte quality to increase live births.

Ring Finger Protein 6 Mediates Androgen-Induced Granulosa Cell Proliferation and Follicle Growth via Modulation of Androgen Receptor Signaling

The destiny of the ovarian follicle (growth or atresia) is tightly regulated by the actions and interactions of endocrine, paracrine, and autocrine factors. Although androgens are known to be important in the regulation of folliculogenesis, whether they facilitate or suppress follicular growth has been controversial, and the mechanisms involved are not fully understood. Moreover, the role and regulation of androgen receptor (AR) in mediating androgen signaling during follicular development is not clear. Here, we report that the active androgen dihydrotestosterone upregulates the expression of AR and its E3 ligase ring finger protein 6 (RNF6), increasing site-specific AR polyubiquitination and AR transcriptional activity for soluble Kit ligand (sKit-L) expression in preantral follicle growth. RNF6 silencing suppressed dihydrotestosterone-induced AR ubiquitination (lysine residue 63) and proliferation and suppressed apoptosis in preantral granulosa cells, with these responses being overcome by the presence of exogenous sKit-L. Taken together, our findings support the notion that RNF6 plays an important role in androgen-induced, follicle-stage-dependent follicle growth and that it acts by facilitating AR-mediated granulosa cell sKit-L expression and proliferation. Our findings offer insights into the regulatory mechanism of androgen action in ovarian follicular growth.

Increased SCF in Follicular Fluid and Granulosa Cells Positively Correlates With Oocyte Maturation, Fertilization, and Embryo Quality in Humans

Stem cell factor (SCF), which is derived from granulosa cells (GCs), plays a key role in the process of follicular development and oocyte maturation. The present study aimed to explore whether the levels of SCF in follicular fluid (FF) and GCs can be used as a potential marker for predicting oocyte developmental potential. Follicular fluid and GC samples from 150 female patients undergoing intracytoplasmic sperm injection were collected in this study. The SCF concentrations in FFs and SCF messenger RNA (mRNA) in GCs were evaluated by using enzyme-linked immunosorbent assay and real-time polymerase chain reaction, respectively. The results showed that the levels of SCF protein and mRNA were significantly associated with oocyte maturation, normal fertilization, cleavage, and embryo quality. Moreover, the levels of SCF protein and mRNA in pregnancy group were also higher than those in the nonpregnancy group. The cutoff value of SCF in FF for predicting high-quality embryo was 1.346, with a sensitivity of 57.8% and a specificity of 72.4%, and the cutoff value of SCF in GCs for predicting high-quality embryo was 6.650, with a sensitivity of 64.4% and a specificity of 78.1%. In conclusion, our results showed a positive and statistically significant relationship between SCF level and oocyte maturation, normal fertilization, cleavage, embryo quality, and clinical pregnancy. Therefore, the levels of SCF in FF and GCs might be considered as a new marker for predicting oocyte developmental potential.

New approaches to increasing oocyte yield from ruminants

Artificial insemination, superovulation and embryo transfer have had beneficial impacts on animal production but a limiting factor to realizing the full potential of these techniques and of other reproductive technologies is the availability of fertile oocytes. To overcome this problem, methods for maturing oocytes in vitro (IVM) have been developed. The production of bovine embryos by IVM is in commercial use but the rate of success and quality of embryos is low. The lack of success may be due to the quality of oocytes that are being matured and it would be preferable to utilize the abundant source of immature oocytes from preantral and primordial follicles by developing systems for in vitro growth (IVG). Several culture systems that utilize early growing follicles as a source of oocytes have been developed for laboratory species and these have been successful in producing live young. IVG in association with IVM and cryopreservation have the potential to maximize the genetic potential of high genetic merit females and shorten generation intervals. This paper presents the current status of technology for the in vitro growth and development of immature oocytes, in vitro maturation and cryopreservation of germ cells in domestic ruminants.

The effect of FSH and activin A on Akt and MAPK1/3 phosphorylation in cultured bovine ovarian cortical strips

Background

rhFSH and rhActA have been used in mammalian ovarian follicle culture systems for activation of follicular growth in vitro and suggested to be responsible for primordial follicle survival through MAPK and Akt pathways. The aim of our study was to determine the effects of rhFSH and rhActA on Akt, pAkt, MAPK1/3 and pMAPK1/3 protein levels in bovine ovarian cortical strips cultured in vitro.

Methods

Ovarian cortical strips from heifers were cultured in the presence of rhFSH (50 ng/mL), rhActA (100 ng/mL) or combination of these factors for 6 days. The strips were embedded in paraffin for histological observations and homogenized for western blot to determine Akt, pAkt, MAPK1/3 and pMAPK1/3 protein levels after the culture. Determination of primordial, primary and secondary follicle proportions at the end of culture as well as comparison of healthy follicle for each developmental stage after the culture was performed to quantify follicle survival and activation.

Results

pAkt protein levels were significantly lower in rhFSH + rhActA group among the other groups, whereas pMAPK1/3 levels were not significantly changed. Follicular activation and survival was measured to be significantly lower in rhFSH + rhActA group. Percentage of healthy primordial follicles was higher in control group whereas healthy secondary follicle proportion was higher in both rhActA and rhFSH groups. rhActA alone had a better impact on follicular activation, since the percentage of the secondary follicles was significantly higher than other treatment groups.

Conclusions

The use of rhActA and rhFSH alone or in the combined form results in differential levels of Akt and MAPK proteins. Both rhActA and rhFSH alone has a remarkable contribution in survival and activation of the follicles in accordance with higher levels of these proteins. Thus, the manipulation of Akt and MAPK pathways with appropriate activators might contribute to proper activation and development of ovarian follicles in vitro.

Control of Oocyte Growth and Development by Intercellular Communication Within the Follicular Niche

In the mammalian ovary, each oocyte grows and develops within its own structural and developmental niche-the follicle. Together with the female germ cell in the follicle are somatic granulosa cells, specialized companion cells that surround the oocyte and provide support to it, and an outer layer of thecal cells that serve crucial roles including steroid synthesis. These follicular compartments function as a single physiological unit whose purpose is to produce a healthy egg, which upon ovulation can be fertilized and give rise to a healthy embryo, thus enabling the female germ cell to fulfill its reproductive potential. Beginning from the initial stage of follicle formation and until terminal differentiation at ovulation, oocyte and follicle growth depend absolutely on cooperation between the different cellular compartments. This cooperation synchronizes the initiation of oocyte growth with follicle activation. During growth, it enables metabolic support for the follicle-enclosed oocyte and allows the follicle to fulfill its steroidogenic potential. Near the end of the growth period, intra-follicular interactions prevent the precocious meiotic resumption of the oocyte and ensure its nuclear differentiation. Finally, cooperation enables the events of ovulation, including meiotic maturation of the oocyte and expansion of the cumulus granulosa cells. In this chapter, we discuss the cellular interactions that enable the growing follicle to produce a healthy oocyte, focusing on the communication between the germ cell and the surrounding granulosa cells.

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.

The influence of N-acetyl-l-cysteine on damage of porcine oocyte exposed to zearalenone in vitro

Zearalenone (ZEA), one of the mycotoxins produced by Fusarium fungi, impacts porcine reproduction by interfering with the estrogen signaling pathway. Previous studies have shown that ZEA inhibits porcine oocyte maturation through the formation of aberrant spindle. To explore the effect of ZEA on porcine oocyte meiotic maturation, the extent of both nuclear and cytoplasmic maturation was examined in this study. Compared with control group, presence of ZEA (3 μM) during oocyte maturation, significantly inhibited the polar body extrusions from 71% to 51%, and significantly increased intracellular reactive oxygen species (ROS) level (12.01 vs. 5.89). Intracellular glutathione (GSH) content in ZEA treatment group was lower than in the control group (1.08 pmol/oocyte vs. 0.18 pmol/oocyte), and cortical granules of cortical area distributed oocytes were reduced (88% vs. 62%). ZEA decreases cumulus expansion in both morphology and mRNA level (HAS2, PTX3, TNFAIP6 and CX43). Addition of N-acetyl-l-cysteine (NAC) to the oocyte maturation media reversed the ZEA-induced inhibition of polar body extrusion (from 69% to 81%), up-regulated ROS (from 7.9 to 6.5), down-regulated GSH content (from 0.16 to 0.82 pmol/oocyte) and recovered cumulus cells expansion in morphology and mRNA level. It is concluded that ZEA affects both oocyte nucleus and cytoplasmic maturation during in vitro maturation, and NAC can reverse these damages to some extent.

Two mutations in the 5'-flanking region of the KITLG gene are associated with litter size of dairy goats

In this study, Xinong Saanen (SN) and Guanzhong (GZ) dairy goat breeds were used to detect single nucleotide polymorphisms (SNPs) in the 5'-flanking region of the KITLG gene by DNA sequencing and primer-introduced restriction analysis-polymerase chain reaction. Two novel SNPs (g.13090G>T and g.13664C>A) were identified (GenBank Accession no. KM658964). Furthermore, g.13090G>T and g.13664C>A loci were closely linked in SN and GZ breeds (r(2) > 0.33). Association analysis results showed that g.13090G>T and g.13664C>A SNPs significantly affected litter size (P < 0.05). The litter size of individuals with the combined genotype GG/CC from both dairy goat breeds was greater than that of individuals with TT/AA in average parity (P < 0.05). Known biochemical and physiological functions, along with our results, indicated that GG/CC could be used in marker-assisted selection to choose individuals with greater litter size from both breeds. These results extend the spectrum of genetic variation in the caprine KITLG gene and may contribute to genetic resources and breeding of goats.

MicroRNA-378 regulates oocyte maturation via the suppression of aromatase in porcine cumulus cells

We sought to investigate whether miR-378 plays a role in cumulus cells and whether the manipulation of miRNA levels in cumulus cells influences oocyte maturation in vitro. Cumulus-oocyte complexes (COCs) from ovarian follicles had significantly lower levels of precursor and mature miR-378 in cumulus cells surrounding metaphase II (MII) oocytes than cumulus cells surrounding germinal vesicle (GV) oocytes, suggesting a possible role of miR-378 during COC maturation. Overexpression of miR-378 in cumulus cells impaired expansion and decreased expression of genes associated with expansion (HAS2, PTGS2) and oocyte maturation (CX43, ADAMTS1, PGR). Cumulus cell expression of miR-378 also suppressed oocyte progression from the GV to MII stage (from 54 ± 2.7 to 31 ± 5.1%), accompanied by a decrease of growth differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15), zona pellucida 3 (ZP3), and CX37 in the oocytes. Subsequent in vitro fertilization resulted in fewer oocytes from COCs overexpressing miR-378 reaching the blastocyst stage (7.3 ± 0.7 vs. 16.6 ± 0.5%). miR-378 knockdown led to increased cumulus expansion and oocyte progression to MII, confirming a specific effect of miR-378 in suppressing COC maturation. Aromatase (CYP19A1) expression in cumulus cells was also inhibited by miR-378, leading to a significant decrease in estradiol production. The addition of estradiol to IVM culture medium reversed the effect of miR-378 on cumulus expansion and oocyte meiotic progression, suggesting that decreased estradiol production via suppression of aromatase may be one of the mechanisms by which miR-378 regulates the maturation of COCs. Our data suggest that miR-378 alters gene expression and function in cumulus cells and influences oocyte maturation, possibly via oocyte-cumulus interaction and paracrine regulation.

Mouse GDF9 decreases KITL gene expression in human granulosa cells

Kit ligand (KITL) is an important granulosa cell-derived growth factor in ovarian folliculogenesis, but its expression and function in human granulosa cells are currently poorly understood. Based on studies performed in animal models, it was hypothesised that KITL gene expression in human granulosa cells is regulated by androgens and/or growth differentiation factor 9 (GDF9). We utilised two models of human granulosa cells, the KGN granulosa tumour cell line and cumulus granulosa cells obtained from preovulatory follicles of women undergoing assisted reproduction. Cells were treated with combinations of 5α-dihydrotestosterone (DHT), recombinant mouse GDF9, and the ALK4/5/7 inhibitor SB431542. KITL mRNA levels were measured by quantitative real-time PCR. No change in KITL mRNA expression was observed after DHT treatment under any experimental conditions, but GDF9 treatment resulted in a significant decrease in KITL mRNA levels in both KGN and cumulus cells. The effect of GDF9 was abolished by the addition of SB431542. These results indicate that KITL is not directly regulated by androgen signalling in human granulosa cells. Moreover, this study provides the first evidence that GDF9 negatively regulates KITL gene expression in human granulosa cells providing new information on the regulation of these important growth factors in the human ovary.

Differential regulation of kit ligand A (kitlga) expression in the zebrafish ovarian follicle cells--evidence for the existence of a cyclic adenosine 3', 5' monophosphate-mediated binary regulatory system during folliculogenesis

Kit ligand (Kitl) is an important paracrine factor involved in the activation of primordial follicles from the quiescent pool and in the maintenance of meiotic arrest before germinal vesicle breakdown (GVBD). It has been reported that follicle-stimulating hormone (FSH) stimulates but luteinizing hormone (LH) suppresses the expression of Kitl in the granulosa cells in mammals. Considering that both gonadotropins signal in the follicle cells mainly by activating cyclic adenosine 3', 5'-monophosphate (cAMP) pathway, we are intrigued by how cAMP differentially regulates Kitl expression. In the present study, we demonstrated that both human chorionic gonadotropin (hCG) and pituitary adenylate cyclase activating polypeptide (PACAP) inhibited insulin-like growth factor I (IGF-I)-induced Akt phosphorylation and kitlga expression in the zebrafish follicle cells. Further experiments showed that cAMP was involved in regulating the expression of kitlga. However, two cAMP-activated effectors, protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac), had converse effects. PKA promoted whereas Epac inhibited the expression of kitlga, as demonstrated by the respective activators. Interestingly, cAMP also appeared to exert differential effects on kitlga expression at different stages of follicle development during folliculogenesis, significantly stimulating kitlga expression at the early growth stage but suppressing it at the full-grown stage before final oocyte maturation, implying a potential mechanism for differential effects of the same pathway at different stages. The inhibitory effect of forskolin (activator of adenylate cyclase) and H89 (inhibitor of PKA) on IGF-I-induced expression of kitlga suggested cross-talk between the cAMP and IGF-I-activated PI3K-Akt pathways. This study, together with our previous findings on IGF-I regulation of kitlga expression, provides important clues to the underlying mechanism that regulates Kit ligand expression during folliculogenesis in the ovary.

Association analysis between variants in KITLG gene and litter size in goats

Xinong Saanen (SN) and Guanzhong (GZ) goat breeds were used to detect single nucleotide polymorphisms (SNPs) in the coding regions with their intron-exon boundaries and the proximal flanking regions of KITLG gene by DNA sequencing and genotyped by PCR-restriction fragment (PCR-RFLP). Four novel SNPs (g.12654G>A, g.12772G>A, g.12829T>C and g.23683C>T) were identified (GenBank accession No. KM609289). It was shown that Xinong Saanen and Guanzhong goat breeds were in Hardy-Weinberg disequilibrium at g.12654G>A, g.12772G>A and g.12829T>C loci (P<0.05). The g.12654G>A, g.12772G>A and g.12829T>C loci were closely linked in both goat breeds (r(2)>0.33). Results of an association analysis indicated that SNPs g.12654G>A, g.12772G>A and g.12829T>C had significant effects on litter size (P<0.05). The combined genotypes of four SNP loci also affected litter size with the C7(GG/GG/CC/CC) genotype in the SN goat breed and C1(AA/GG/CC/CC) and C7(GG/GG/CC/CC) genotypes in the GZ goat breed having the highest litter size. The biochemical and physiological functions, together with the results obtained in our investigation, suggest that C7(GG/GG/CC/CC) could be used in marker-assisted selection to select the individuals with higher litter size in both goat breeds. The results extend the spectrum of genetic variation of the caprine KITLG gene, which might contribute to goat genetic resources and breeding.

Antimüllerian hormone regulates stem cell factor expression in human granulosa cells

OBJECTIVE

To determine whether there is a correlation between antimüllerian hormone (AMH) and stem cell factor (SCF) in serum, follicular fluid (FF), and granulosa cells (GCs), and to investigate a possible regulatory mechanism of AMH on SCF in human granulosa cells.

DESIGN

Prospective clinical and experimental study.

SETTING

Academic center.

PATIENT(S)

163 women undergoing IVF.

INTERVENTION(S)

Serum, FF, and GCs obtained in all women, primary cultures of human GCs.

MAIN OUTCOME MEASURE(S)

AMH and SCF were analyzed in serum, FF, and GCs, using enzyme-linked immunosorbent assay, reverse-transcription polymerase chain reaction, and immunoblotting.

RESULT(S)

There was a significant negative correlation between AMH and SCF protein level in FF, and in the mRNA expression of AMH and SCF in GCs. Conversely, there was no correlation between AMH and SCF levels in serum. In primary cultures of human GCs, SCF was down-regulated by treatment with recombinant human AMH and was increased by cyclic adenosine 3':5' monophosphate (cAMP) in a dose-dependent manner. A protein kinase A (PKA) inhibitor (H89) significantly reversed the effects of recombinant human AMH and cAMP on SCF mRNA and protein expression.

CONCLUSION(S)

This is the first report on a modulatory role for AMH as an ovarian/follicular autocrine/paracrine factor controlling SCF expression via the cAMP/PKA pathway.

Acute 7,12-dimethylbenz[a]anthracene exposure causes differential concentration-dependent follicle depletion and gene expression in neonatal rat ovaries

Chronic exposure to the polycyclic aromatic hydrocarbon 7,12-dimethylbenz[a]anthracene (DMBA), generated during combustion of organic matter including cigarette smoke, depletes all ovarian follicle types in the mouse and rat, and in vitro models mimic this effect. To investigate the mechanisms involved in follicular depletion during acute DMBA exposure, two concentrations of DMBA at which follicle depletion has (75 nM) and has not (12.5 nM) been observed were investigated. Postnatal day four F344 rat ovaries were maintained in culture for four days before a single exposure to vehicle control (1% DMSO; CT) or DMBA (12 nM; low-concentration or 75 nM; high-concentration). After four or eight additional days of culture, DMBA-induced follicle depletion was evaluated via follicle enumeration. Relative to control, DMBA did not affect follicle numbers after 4 days of exposure, but induced large primary follicle loss at both concentrations after 8 days; while, the low-concentration DMBA also caused secondary follicle depletion. Neither concentration affected primordial or small primary follicle number. RNA was isolated and quantitative RT-PCR performed prior to follicle loss to measure mRNA levels of genes involved in xenobiotic metabolism (Cyp2e1, Gstmu, Gstpi, Ephx1), autophagy (Atg7, Becn1), oxidative stress response (Sod1, Sod2) and the phosphatidylinositol 3-kinase (PI3K) pathway (Kitlg, cKit, Akt1) 1, 2 and 4 days after exposure. With the exception of Atg7 and cKit, DMBA increased (P < 0.05) expression of all genes investigated. Also, BECN1 and pAKT(Thr308) protein levels were increased while cKIT was decreased by DMBA exposure. Taken together, these results suggest an increase in DMBA bioactivation, add to the mechanistic understanding of DMBA-induced ovotoxicity and raise concern regarding female low concentration DMBA exposures.

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.

Differential regulation of Kit ligand A expression in the ovary by IGF-I via different pathways

Kit ligand (KITL) plays indispensable roles both in primordial follicle activation and in the maintenance of meiotic arrest of the oocyte. The regulation of KITL expression in the ovary, however, remains largely unknown. In the zebrafish, there are 2 paralogues of KITL, kitlga and kitlgb, and 2 Kit receptors, kita and kitb. Consistent with the situation in mammals, kitlga is only expressed in the ovarian follicle cells, and its cognate receptor kita is expressed in the oocyte. In the present study, we demonstrated that the expression of kitlga was promoted by IGF-I through its receptor IGF-IR. The stimulation involved transcription but not translation, suggesting that the kitlga gene is likely a direct downstream target of IGF-I signaling. Further experiments showed that the stimulatory effect of IGF-I was mediated by phosphatidyl inositol 3-kinase (PI3K)-Akt pathway. IGF-I also activated MEK-ERK pathway; however, this pathway suppressed kitlga expression. The regulation of kitlga expression by IGF-I appeared to depend on the stage of follicle development with a greater induction at early stage than late stage. This may be related to changes in IGF-I signaling pathways and/or local paracrine environment. In support of this were the differential expression of IGF-I receptors (igf1ra and igf1rb) and responsiveness of IGF-I signaling pathways, especially the PI3K-Akt pathway. Furthermore, the IGF-I-induced kitlga expression was inhibited by epidermal growth factor, an oocyte-derived paracrine factor in the zebrafish follicle. This study provides evidence for a controlling mechanism underlying the regulation of KITL expression in the ovary.