Comparison of recombinant growth differentiation factor-9 and oocyte regulation of KIT ligand messenger ribonucleic acid expression in mouse ovarian follicles

Essential Role of Granulosa Cell Glucose and Lipid Metabolism on Oocytes and the Potential Metabolic Imbalance in Polycystic Ovary Syndrome

Granulosa cells are crucial for the establishment and maintenance of bidirectional communication among oocytes. Various intercellular material exchange modes, including paracrine and gap junction, are used between them to achieve the efficient delivery of granulosa cell structural components, energy substrates, and signaling molecules to oocytes. Glucose metabolism and lipid metabolism are two basic energy metabolism pathways in granulosa cells; these are involved in the normal development of oocytes. Pyruvate, produced by granulosa cell glycolysis, is an important energy substrate for oocyte development. Granulosa cells regulate changes in intrafollicular hormone levels through the processing of steroid hormones to control the development process of oocytes. This article reviews the material exchange between oocytes and granulosa cells and expounds the significance of granulosa cells in the development of oocytes through both glucose metabolism and lipid metabolism. In addition, we discuss the effects of glucose and lipid metabolism on oocytes under pathological conditions and explore its relationship to polycystic ovary syndrome (PCOS). A series of changes were found in the endogenous molecules and ncRNAs that are related to glucose and lipid metabolism in granulosa cells under PCOS conditions. These findings provide a new therapeutic target for patients with PCOS; additionally, there is potential for improving the fertility of patients with PCOS and the clinical outcomes of assisted reproduction.

The effect of ACVR1B/TGFBR1/ACVR1C signaling inhibition on oocyte and granulosa cell development during in vitro growth culture

The signals of the transforming growth factor β (TGF-β) superfamily play a critical role in follicular development in mammals. ACVR1B/TGFBR1/ACVR1C receptors mediate the signaling of several TGF-β superfamily ligands in granulosa cells. Although the requirement for ACVR1B/TGFBR1/ACVR1C receptor signaling in follicular development has been confirmed using mutant mouse models, the detailed roles of the signaling in granulosa cell and oocyte development have not been clearly defined. In the present study, we examined the requirement for ACVR1B/TGFBR1/ACVR1C receptor signaling in granulosa cells using an in vitro growth culture of oocyte-granulosa cell complexes (OGCs) and SB431542, a potent inhibitor of the receptor signaling. Although cumulus-oocyte complexes isolated from the control OGCs were able to undergo cumulus expansion, those isolated from OGCs grown with the inhibitor were not competent, even in the presence of in vivo-grown oocytes. The diameter of the oocytes in the SB431542-treated OGCs was comparable with that of the control; however, these oocytes were not competent for complete meiotic maturation or preimplantation development. Therefore, ACVR1B/TGFBR1/ACVR1C receptor signaling is not required for oocytes to increase their volume but is essential for the normal development of cumulus cells and oocyte developmental competence.

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.

Transzonal projections: Essential structures mediating intercellular communication in the mammalian ovarian follicle

The development of germ cells relies on contact and communication with neighboring somatic cells that provide metabolic support and regulatory signals. In females, contact is achieved through thin cytoplasmic processes that project from follicle cells surrounding the oocyte, extend through an extracellular matrix (ECM) that lies between them, and reach its surface. In mammals, the ECM is termed the zona pellucida and the follicular cell processes are termed transzonal projections (TZPs). TZPs become detectable when the zona pellucida is laid down during early folliculogenesis and subsequently increase in number as oocyte growth progresses. They then rapidly disappear at the time of ovulation, permanently breaking germ-soma contact. Here we review the life cycle and functions of the TZPs. We begin with an overview of the morphology and cytoskeletal structure of TZPs, in the context of actin- and tubulin-based cytoplasmic processes in other cell types. Next, we review the roles played by TZPs in mediating progression through successive stages of oocyte development. We then discuss two mechanisms that may generate TZPs-stretching at pre-existing points of granulosa cell-oocyte contact and elaboration of new processes that push through the zona pellucida-as well as gene products implicated in their formation or function. Finally, we describe the signaling pathways that cause TZPs to be retracted in response to signals that also trigger meiotic maturation and ovulation of the oocyte. The principles and mechanisms that govern TZP behavior may be relevant to understanding communication between physically separated cells in other physiological contexts.

Oocyte maturation abnormalities - A systematic review of the evidence and mechanisms in a rare but difficult to manage fertility pheneomina

A small proportion of infertile women experience repeated oocyte maturation abnormalities (OMAS). OMAS include degenerated and dysmorphic oocytes, empty follicle syndrome, oocyte maturation arrest (OMA), resistant ovary syndrome and maturation defects due to primary ovarian insufficiency. Genetic factors play an important role in OMAS but still need specifications. This review documents the spectrum of OMAS and to evaluate the multiple subtypes classified as OMAS. In this review, readers will be able to understand the oocyte maturation mechanism, gene expression and their regulation that lead to different subtypes of OMAs, and it will discuss the animal and human studies related to OMAS and lastly the treatment options for OMAs. Literature searches using PubMed, MEDLINE, Embase, National Institute for Health and Care Excellence were performed to identify articles written in English focusing on Oocyte Maturation Abnormalities by looking for the following relevant keywords. A search was made with the specified keywords and included books and documents, clinical trials, animal studies, human studies, meta-analysis, randomized controlled trials, reviews, systematic reviews and options written in english. The search detected 3,953 sources published from 1961 to 2021. After title and abstract screening for study type, duplicates and relevancy, 2,914 studies were excluded. The remaining 1,039 records were assessed for eligibility by full-text reading and 886 records were then excluded. Two hundred and twenty seven full-text articles and 0 book chapters from the database were selected for inclusion. Overall, 227 articles, one unpublished and one abstract paper were included in this final review. In this review study, OMAS were classified and extensively evaluatedand possible treatment options under the light of current information, present literature and ongoing studies. Either genetic studies or in vitro maturation studies that will be handled in the future will lead more informations to be reached and may make it possible to obtain pregnancies.

The ovarian reserve as target of insulin/IGF and ROS in metabolic disorder-dependent ovarian dysfunctions

It is known for a long time that metabolic disorders can cause ovarian dysfunctions and affect a woman’s fertility either by direct targeting follicular cells and/or the oocytes or by indirect interference with the pituitary-hypothalamic axis, resulting in dysfunctional oogenesis. Such disorders may also influence the efficiency of the embryo implantation and the quality of the embryo with permanent effects on the fertility and health of the offspring. Thanks to the expanding knowledge on the molecular mechanisms governing oogenesis and folliculogenesis in mammals, we are beginning to understand how such disorders can negatively affect this process and consequently fertility in women. In the present review, we point out and discuss how the disturbance of insulin/IGF-dependent signalling and increased reactive oxygen species (ROS) level in the ovary typically associated to metabolic disorders such as type II diabetes and obesity can dysregulate the dynamics of the ovarian reserve and/or impair the survival and competence of the oocytes.

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.

Effects of Stem Cell Factor/c-Kit Signaling on In Vitro Maturation of Porcine Oocytes and Subsequent Developmental Competence After Fertilization

Stem cell factor (SCF), also known as c-Kit ligand, plays an important role in the proliferation of primordial germ cells and the survival of oocytes during follicular development. The aim of this study was to investigate the effect of SCF/c-Kit signaling on in vitro maturation (IVM) of porcine oocytes by analyzing nuclear and cytoplasmic maturation, oocyte size, cumulus cell expansion, and developmental competence to the blastocyst stage. Moreover, mRNA expression patterns of porcine cumulus cells and oocytes were evaluated using qRT-PCR. Following 42 h of IVM, 10 and 50 ng/mL SCF-treated groups exhibited significantly (P < 0.05) increased polar body extrusion rates and intracellular glutathione levels compared with the control group. The cumulus expansion index significantly (P < 0.05) increased in all SCF-treated groups compared with the control samples. mRNA levels of the proapoptotic gene Bax and apoptosis-related cysteine peptidase Caspase3 were lower in SCF-treated cumulus cells than in the control group. Notably, the diameter of oocytes after IVM, the mRNA expression of well-known oocyte-secreted factors (GDF9 and BMP15), and an oocyte-specific protein essential for ovulation and oocyte health (YBX2) were significantly (P < 0.05) higher in SCF-treated than in non-treated oocytes. Inhibition of c-Kit during porcine IVM using ACK2, an antagonistic blocker of c-Kit, significantly (P < 0.05) decreased the polar body extrusion rate compared with the control, as well as blastocyst formation rate compared with the 10 ng/mL SCF-treated group. In conclusion, the effect of SCF/c-Kit-mediated signaling during porcine IVM could be ascribed to the reduced expression of apoptosis-related genes and higher expression of oocyte-specific/secreted factors.

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.

The regulatory role of miR-20a in bovine cumulus cells and its contribution to oocyte maturation

Dynamic changes in microRNAs in oocyte and cumulus cells before and after maturation may explain the spatiotemporal post-transcriptional gene regulation within bovine follicular cells during the oocyte maturation process. miR-20a has been previously shown to regulate proliferation and differentiation as well as progesterone levels in cultured bovine granulosa cells. In the present study, we aimed to demonstrate the function of miR-20a during the bovine oocyte maturation process. Maturation of cumulus-oocyte complexes (COCs) was performed at 39°C in an humidified atmosphere with 5% CO2 in air. The expression of miR-20a was investigated in the cumulus cells and oocytes at 22 h post culture. The functional role of miR-20a was examined by modulating the expression of miR-20a in COCs during in vitro maturation (IVM). We found that the miR-20a expression was increased in cumulus cells but decreased in oocytes after IVM. Overexpression of miR-20a increased the oocyte maturation rate. Even though not statistically significant, miR-20a overexpression during IVM increased progesterone levels in the spent medium. This was further supported by the expression of STAR and CYP11A1 genes in cumulus cells. The phenotypes observed due to overexpression of miR-20a were validated by BMP15 supplementation during IVM and subsequent transfection of BMP15-treated COCs using miR-20a mimic or BMPR2 siRNA. We found that miR-20a mimic or BMPR2 siRNA transfection rescued BMP15-reduced oocyte maturation and progesterone levels. We concluded that miR-20a regulates oocyte maturation by increasing cumulus cell progesterone synthesis by simultaneous suppression of BMPR2 expression.

Abnormal early folliculogenesis due to impeded pyruvate metabolism in mouse oocytes†

Fetal ovarian germ cells show characteristic energy metabolism status, such as enhanced mitochondrial metabolism as well as glycolysis, but their roles in early folliculogenesis are unclear. We show here that inhibition of pyruvate uptake to mitochondria by UK5099 in organ cultures of fetal mouse ovaries resulted in repressed early folliculogenesis without affecting energy production, survival of oocytes, or meiosis. In addition, the abnormal folliculogenesis by UK5099 was partially rescued by α-ketoglutarate and succinate, intermediate metabolites in the TCA cycle, suggesting the importance of those metabolites. The expression of TGFβ-related genes Gdf9 and Bmp15 in ovarian germ cells, which are crucial for folliculogenesis, was downregulated by UK5099, and the addition of recombinant GDF9 partially rescued the abnormal folliculogenesis induced by UK5099. We also found that early folliculogenesis was similarly repressed, as in the culture, in the ovaries of a germ cell-specific knockout of Mpc2, which encodes a mitochondria pyruvate carrier that is targeted by UK5099. These results suggest that insufficient Gdf9 expression induced by abnormal pyruvate metabolism in oocytes results in early follicular dysgenesis, which is a possible cause of defective folliculogenesis in humans.

Activation-induced cytidine deaminase is a possible regulator of cross-talk between oocytes and granulosa cells through GDF-9 and SCF feedback system

Activation-induced cytidine deaminase (AID, Aicda) is a master gene regulating class switching of immunoglobulin genes. In this study, we investigated the significance of AID expression in the ovary. Immunohistological study and RT-PCR showed that AID was expressed in murine granulosa cells and oocytes. However, using the Aicda-Cre/Rosa-tdRFP reporter mouse, its transcriptional history in oocytes was not detected, suggesting that AID mRNA in oocytes has an exogenous origin. Microarray and qPCR validation revealed that mRNA expressions of growth differentiation factor-9 (GDF-9) in oocytes and stem cell factor (SCF) in granulosa cells were significantly decreased in AID-knockout mice compared with wild-type mice. A 6-h incubation of primary granuloma cells markedly reduced AID expression, whereas it was maintained by recombinant GDF-9. In contrast, SCF expression was induced by more than threefold, whereas GDF-9 completely inhibited its increase. In the presence of GDF-9, knockdown of AID by siRNA further decreased SCF expression. However, in AID-suppressed granulosa cells and ovarian tissues of AID-knockout mice, there were no differences in the methylation of SCF and GDF-9. These findings suggest that AID is a novel candidate that regulates cross-talk between oocytes and granulosa cells through a GDF-9 and SCF feedback system, probably in a methylation-independent manner.

Control of Mammalian Oocyte Development by Interactions with the Maternal Follicular Environment

Development of animal germ cells depends critically on continuous contact and communication with the somatic compartment of the gonad. In females, each oocyte is enclosed within a follicle, whose somatic cells supply nutrients that sustain basal metabolic activity of the oocyte and send signals that regulate its differentiation. This maternal microenvironment thus plays an indispensable role in ensuring the production of fully differentiated oocytes that can give rise to healthy embryos. The granulosa cells send signals, likely membrane-associated Kit ligand, which trigger oocytes within resting-stage primordial follicles to initiate growth. During growth, the granulosa cells feed amino acids, nucleotides, and glycolytic substrates to the oocyte. These factors are necessary for the oocyte to complete its growth and are delivered via gap junctions that couple the granulosa cells to the oocyte. In a complementary manner, growing oocytes also release growth factors, notably growth-differentiation factor 9 and bone morphogenetic protein 15, which are necessary for proper differentiation of the granulosa cells and for these cells to support oocyte growth. During the late stages of oocyte growth, cyclic GMP that is synthesized by the granulosa cells and diffuses into the oocyte is required to prevent its precocious entry into meiotic maturation. Finally, at the early stages of maturation, granulosa cell signals promote the synthesis of a subset of proteins within the oocyte that enhance their ability to develop as embryos. Thus, the maternal legacy of the follicular microenvironment is witnessed by the fertilization of the ovulated oocyte and subsequent birth of healthy offspring.

Regulation of germ cell development by intercellular signaling in the mammalian ovarian follicle

Prior to ovulation, the mammalian oocyte undergoes a process of differentiation within the ovarian follicle that confers on it the ability to give rise to an embryo. Differentiation comprises two phases-growth, during which the oocyte increases more than 100-fold in volume as it accumulates macromolecules and organelles that will sustain early embryogenesis; and meiotic maturation, during which the oocyte executes the first meiotic division and prepares for the second division. Entry of an oocyte into the growth phase appears to be triggered when the adjacent granulosa cells produce specific growth factors. As the oocyte grows, it elaborates a thick extracellular coat termed the zona pellucida. Nonetheless, cytoplasmic extensions of the adjacent granulosa cells, termed transzonal projections (TZPs), enable them to maintain contact-dependent communication with the oocyte. Through gap junctions located where the TZP tips meet the oocyte membrane, they provide the oocyte with products that sustain its metabolic activity and signals that regulate its differentiation. Conversely, the oocyte secretes diffusible growth factors that regulate proliferation and differentiation of the granulosa cells. Gap junction-permeable products of the granulosa cells prevent precocious initiation of meiotic maturation, and the gap junctions also enable oocyte maturation to begin in response to hormonal signals received by the granulosa cells. Development of the oocyte or the somatic compartment may also be regulated by extracellular vesicles newly identified in follicular fluid and at TZP tips, which could mediate intercellular transfer of macromolecules. Oocyte differentiation thus depends on continuous signaling interactions with the somatic cells of the follicle. WIREs Dev Biol 2018, 7:e294. doi: 10.1002/wdev.294 This article is categorized under: Gene Expression and Transcriptional Hierarchies > Cellular Differentiation Signaling Pathways > Cell Fate Signaling Early Embryonic Development > Gametogenesis.

Inside the granulosa transcriptome

The somatic component of follicular structure is a mixture of different cell types, represented by Granulosa cells (GCs) that are the paracrine regulators of the oocyte growth. GCs finely support this process by a continuous bidirectional talk with oocyte, which ensure oocyte quality and competence. Specific pathways are involved in the cross-talk and in both GCs and oocyte development. This review summarizes data from GCs gene expression analysis concerning both their physiological role and their interaction with oocyte. We also explore the CGs transcriptome modifications induced by controlled ovarian stimulation (COS) or pathological conditions and their impact in reproduction. The transcriptome analysis of GCs could be a powerful tool to improve our knowledge about the pathways involved in oocyte development. This approach, associated with new technologies as RNA-seq could allow the identifications of new noninvasive biological markers of oocyte quality to increase the efficiency of clinical IVF. Moreover, GCs expression analysis could be useful to shed light on new therapeutic targets by providing new options for the treatment of infertility.

Effect of kit ligand on natriuretic peptide precursor C and oocyte maturation in cattle

In vitro maturation (IVM) of oocytes in cattle is inefficient, and there is great interest in the development of approaches to improve maturation and fertilization rates. Intraovarian signalling molecules are being explored as potential additives to IVM media. One such factor is kit ligand (KITL), which stimulates the growth of oocytes. We determined if KITL enhances oocyte maturation in cattle. The two main isoforms of KITL (KITL1 and KITL2) were expressed in bovine cumulus–oocyte complexes (COC), and levels of mRNA increased during FSH-stimulated IVM. The addition of KITL to the culture medium increased the percentage of oocytes that reached meiosis II but did not affect cumulus expansion after 22 h of IVM. Addition of KITL reduced the levels of mRNA encoding natriuretic peptide precursor C (NPPC), a protein that holds oocytes in meiotic arrest, and increased the levels of mRNA encoding YBX2, an oocyte-specific factor involved in meiosis. Removal of the oocyte from the COC resulted in increased KITL mRNA levels and decreased NPPC mRNA levels in cumulus cells, and addition of denuded oocytes reversed these effects. Taken together, our results suggest that KITL enhances bovine oocyte nuclear maturation through a mechanism that involves NPPC, and that the oocyte regulates cumulus expression of KITL mRNA.

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.

Simulated Microgravity Using a Rotary Culture System Compromises the In Vitro Development of Mouse Preantral Follicles

Background

Growing cells in simulated weightlessness condition might be a highly promising new technique to maintain or generate tissue constructs in a scaffold-free manner. There is limited evidence that microgravity condition may affect development of ovarian follicles. The objective of the present study was to investigate the effects of simulated microgravity on the in vitro development of mouse preantral follicles.

Methods and Results

Ovarian tissue from 14-day-old mice, or preantral follicles mechanically isolated from 14-day-old mouse ovaries were cultured at a simulated microgravity condition generated using a rotating wall vessel apparatus. Follicle survival was assessed quantitatively using H&E staining. Follicle diameter and oocyte diameter were measured under an inverted microscope. Ultrastructure of oocytes was evaluated using transmission electron microscopy. We observed that simulated microgravity compromised follicle survival in vitro, downregulated PCNA and GDF-9 expressions, and caused ultrastructural abnormalities in oocytes.

Conclusion

This study showed for the first time that three-dimensional culture condition generated by simulated microgravity is detrimental to the initial stage development of mouse preantral follicles in vitro. The experimental setup provides a model to further investigate the mechanisms involved in the in vitro developmental processes of oocytes/granulosa cells under the microgravity condition.

GDF9 is transiently expressed in oocytes before follicle formation in the human fetal ovary and is regulated by a novel NOBOX transcript

During human fetal ovary development, the process of primordial follicle formation is immediately preceded by a highly dynamic period of germ cell and somatic cell reorganisation. This is regulated by germ-cell specific transcription regulators, by the conserved RNA binding proteins DAZL and BOLL and by secreted growth factors of the TGFβ family, including activin βA: these all show changing patterns of expression preceding follicle formation. In mice, the transcription factor Nobox is essential for follicle formation and oocyte survival, and NOBOX regulates the expression of GDF9 in humans. We have therefore characterised the expression of GDF9 in relation to these known key factors during follicle formation in the human fetal ovary. mRNA levels of GDF9, BMP15 and NOBOX were quantified by qRT-PCR and showed dramatic increases across gestation. GDF9 protein expression was localised by immunohistochemistry to the same population of germ cells as those expressing activin βA prior to follicle formation but did not co-localise with either BOLL or DAZL. A novel NOBOX isoform was identified in fetal ovary that was shown to be capable of up-regulating the GDF9 promoter in reporter assays. Thus, during oogenesis in humans, oocytes go through a dynamic and very sharply demarcated sequence of changes in expression of these various proteins, even within individual germ cell nests, likely to be of major functional significance in determining selective germ cell survival at this key stage in ovarian development. Transcriptional variation may contribute to the range of age of onset of POI in women with NOBOX mutations.

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.

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.

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.

New molecular markers for the evaluation of gamete quality

PURPOSE

Only 30 % of IVF cycles result in a pregnancy, so that multiple embryos need to be replaced, per treatment cycle, to increase pregnancy rates, resulting in a multiple gestation rate of 25 %. The use of new markers in the gamete selection, could reduce the number of the oocytes to be fertilized and embryos to be produced, but the tools to evidence the gamete competence remain unavailable and more studies are needed to identify bio-markers to select the best oocyte and sperm to produce embryos with higher implantation potentiality.

METHODS

To define oocyte competence, the apoptosis of the surrounding cumulus cells and the oxygen consumption rates for individual oocytes before fertilization seems to provide a non-invasive marker of oocyte competence and hence a quantitative assessment of the reproductive potential for the oocyte. The chromatin integrity seems to be used also as biological marker of sperm competence, together with the morphological evaluation of large vacuoles in the head.

RESULTS

The apoptosis rate of cumulus cells lower than 25 % and an higher oxygen consumption could be an evidence of an overall metabolic activity, related to a better fertilization ability and embryo cleavage quality. The apoptosis rate of the sperm chromatin, evaluated by direct Tunel in situ analysis, seems to be, also for the male gamete, a marker of competence and implantation potentiality, in particular when it is lower than 20 %. The evaluation of the presence of large vacuoles in the sperm head prior to perform ICSI seems to increase the implantation rate, but it is not associated to chromatin integrity.

CONCLUSIONS

The biological concept of competence appears unrelated to any morphological parameters, so that it is necessary to investigate new molecular markers in the gamete selection. Apoptosis of cumulus cells in the oocytes and spermatozoa, revealing the presence of large vacuoles, could help to determine the competence of the gamete to be fertilize.

Investigations of TGF-β signaling in preantral follicles of female mice reveal differential roles for bone morphogenetic protein 15

Bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) are 2 closely related TGF-β ligands implicated as key regulators of follicle development and fertility. Animals harboring mutations of these factors often exhibit a blockage in follicle development beyond the primary stage and therefore little is known about the role of these ligands during subsequent (preantral) stages. Preantral follicles isolated from immature mice were cultured with combinations of BMP15, GDF9, and activin receptor-like kinase (ALK) inhibitors. Individually, GDF9 and BMP15 promoted follicle growth during the first 24 hours, whereas BMP15 subsequently (48-72 h) caused follicle shrinkage and atresia with increased granulosa cell apoptosis. Inhibition of ALK6 prevented the BMP15-induced reduction in follicle size and under basal conditions promoted a rapid increase in granulosa cell proliferation, suggesting BMP15 signals through ALK6, which in turn acts to restrain follicle growth. In the presence of GDF9, BMP15 no longer promoted atresia and in fact follicle growth was increased significantly more than with either ligand alone. This cooperative effect was accompanied by differential expression of Id1-3, Smad6-7, and Has2 and was blocked by the same ALK5 inhibitor used to block GDF9 signaling. Immunostaining for SMAD2/3 and SMAD1/5/8, representing the 2 main branches of TGF-β signaling, supported the fact that both canonical pathways have the potential to be active in growing follicles, whereas primordial follicles only express SMAD2/3. Overall results highlight differential effects of the 2 main TGF-β signaling pathways during preantral follicle growth.

The impact of culture conditions on early follicle recruitment and growth from human ovarian cortex biopsies in vitro

OBJECTIVE

To investigate the effects of a dynamic fluidic culture system on early in vitro folliculogenesis in standardized ovarian cortex biopsies.

DESIGN

Cortical small strips were cultured for 6 days in a conventional static or in a dynamic fluidic culture system.

SETTING

University-affiliated laboratory with an associated cryobank facility.

PATIENT(S)

Ovarian cortex from postpuberal female cancer patients (26.1 ± 1.3 y) who opted for cryopreservation of their tissue for fertility protection before gonadotoxic cancer therapy. With informed consent of the Institutional Ethics Committee, part of the tissue was available for patient-related research studies.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The viability and proliferative capacity of the cortex biopsies were evaluated by chemiluminescent microparticle immunoassay for detection of in vitro produced E2 and P in the supernate, by viable follicle counting via calcein staining, by histologic analyses, and by total RNA preparation and reverse transcription for real-time polymerase chain reaction of selected early folliculogenesis genes.

RESULT(S)

The data support the notion that early follicle development can be better achieved in vitro in a dynamic fluidic culture system. The findings are based on the presence of more viable follicles, higher expression levels of early folliculogenesis genes KIT-L, INHB, and GDF9, and the absence of premature luteinization of follicles.

CONCLUSION(S)

This study provides evidence that dynamic fluidic culture is a promising approach for investigating early follicular recruitment and growth in cortical biopsies. It may serve as a first step in a multistep culture system to design a complex in vitro system for complete folliculogenesis.

GDF9 modulates the reproductive and tumor phenotype of female inha-null mice

Intraovarian factors play important roles in coordinating germ cell and somatic cell growth in the ovary. Prior to the onset of gonadotropin stimulation and reproductive cyclicity, follicle development is dependent upon locally produced growth factors, such as the transforming growth factor beta family members inhibin, activin, and GDF9. In the absence of inhibin in prepubertal mice (Inha(-/-)), there are marked alterations in preantral follicle growth, but no evidence of ovarian tumors characteristic of adult Inha-null mice. To ascertain the contribution of GDF9 to the Inha-null phenotype, we analyzed folliculogenesis in postnatal Inha Gdf9 double knockout mice. Deletion of Gdf9 from Inha(-/-) rescues the initial growth defects found at early follicle stages in Inha(-/-) ovaries, but surprisingly enhances the onset of pretumor lesions. The normalization of growth dynamics between granulosa cells and oocytes of Inha Gdf9 double knockout mice is also accompanied by a reduction in levels of the activin/inhibin beta B subunit, Inhbb, which is upregulated in Inha(-/-) ovaries. However, at later ages, Inha Gdf9 double knockout ovaries are similar to Inha(-/-) ovaries, and show upregulation of the activin/inhibin subunits and downregulation of the growth factor, kit ligand, thus resulting in a local environment that is growth-promoting for granulosa cells but growth-inhibitory for oocytes. These data suggest a sequential mechanism of action initiated by GDF9 in the Inha knockout mouse that promotes defective folliculogenesis. These studies thus provide a novel role for GDF9 in causing reproductive defects and suppressing tumor initiation in the Inha(-/-) mouse model.

Isolation of ovarian components essential for growth and development of mammalian oocytes in vitro

Mammalian ovaries contain a large number of oocytes, most of which degenerate either before or at various stages of growth. Dynamic and precise regulation in the ovary involves many factors, each with a unique role. Identifying the single most important factor is impossible; however, it may be possible to identify factors essential for oocyte growth. It is evident that oocytes can grow into competent ova in vitro; however, how faithfully the follicle should mimic the in vivo conditions remains unclear. In the culture system discussed in this review, bovine and mouse oocyte-granulosa cell complexes, at approximately the late mid-growth stage, spread on a substratum without the involvement of theca cells. The structural simplicity of this system is advantageous because it reduces the basic conditions essential for regulation of oocyte growth. Apart from biological factors, high concentrations of polyvinylpyrrolidone (molecular weight: 360000) improved oocyte growth. Among ovarian factors, androstenedione was used to compensate for the absence of theca cells, and it promoted both follicular growth and acquisition of oocyte meiotic competence. Most oocytes cultured in a group were viable after long-term culture, suggesting that unlike ovarian events, there was no exhaustive follicle selection. Collectively, oocytes and their associated granulosa cells can establish independent units capable of supporting oocyte growth in appropriately modified culture media.

Expression and regulation of Kit ligand in the ovary of the hen

The Kit system, composed of Kit ligand (KL) and its tyrosine kinase receptor, cKit, has been well characterized in mammals. Studies have shown that it is involved in signaling between the oocyte and somatic cells during the process of follicle maturation. We characterized KL mRNA expression during follicle maturation in the domestic hen, examined regulation of KL and a possible function of the Kit system. KL mRNA expression was assessed using quantitative PCR (n=4 replicates) in follicles of various sizes (1, 3, 5, 6-12 mm, F1). Expression of KL mRNA decreased significantly (p<0.01) with follicle development and was highest in <1 mm follicles, which contained the theca as well as granulosa layers, with high levels also found in the granulosa layer of 3 mm follicles and ovarian stroma. To study regulation of KL mRNA, granulosa cells from 6-8 mm follicles (n=4 replicates) were plated in M199 plus 0.1% BSA in the presence of various treatments including: oocyte conditioned medium (OCM), Vitamin D(3), FSH, estradiol, progesterone and testosterone. OCM caused a dose-related increase (p<0.05) in expression of KL mRNA; Vitamin D(3) increased and FSH decreased expression of KL mRNA. cKit was detected (at the expected size) in the theca layer of 3-5 mm follicles and in a lysate of whole <1mm follicles. Culture of granulosa cells in the presence of OCM resulted in a decrease of P4 secretion, an effect blocked by pre-incubation of OCM with cKit antibody. Although OCM caused a dose-related increase in E2 secretion from theca, this was not blocked by cKit antibody.

Regulation of the ovarian reserve by members of the transforming growth factor beta family

Genetic or environmental factors that affect the endowment of oocytes, their assembly into primordial follicles, or their subsequent entry into the growing follicle pool can disrupt reproductive function and may underlie disorders such as primary ovarian insufficiency. Mouse models have been instrumental in identifying genes important in ovarian development, and a number of genes now associated with ovarian dysfunction in women were first identified as causing reproductive defects in knockout mice. The transforming growth factor beta (TGFB) family consists of developmentally important growth factors that include the TGFBs, anti-Müllerian hormone (AMH), activins, bone morphogenetic proteins (BMPs), and growth and differentiation factor 9 (GDF9). The ovarian primordial follicle pool is the source of oocytes in adults. Development of this pool can be grossly divided into three key processes: (1) establishment of oocytes during embryogenesis followed by (2) assembly and (3) activation of the primordial follicle. Disruptions in any of these processes may cause reproductive dysfunction. Most members of the TGFB family show pivotal roles in each of these areas. Understanding the phenotypes of various mouse models for this protein family will be directly relevant to understanding how disruptions in TGFB family signaling result in reproductive diseases in women and will present new areas for development of tailored diagnostics and interventions for infertility.

Regulatory role of kit ligand-c-kit interaction and oocyte factors in steroidogenesis by rat granulosa cells

Although kit ligand (KL)-c-kit interaction is known to be critical for oogenesis and folliculogenesis, its role in ovarian steroidogenesis has yet to be elucidated. We studied the impact of KL-c-kit interaction in regulation of steroidogenesis using rat oocyte/granulosa cell co-culture. In the presence of oocytes, soluble KL suppressed FSH-induced estradiol production and aromatase mRNA expression without affecting FSH-induced progesterone production. The KL effect on steroidogenesis was interrupted by an anti-c-kit neutralizing antibody, suggesting that KL-c-kit interaction is involved in suppression of estrogen by granulosa cells through oocyte c-kit action. The cAMP-PKA pathway activity was not directly involved in the estrogen regulation by KL-c-kit action. It was of note that KL treatment increased the expression levels of oocyte-derived FGF-8, GDF-9 and BMP-6, while it reduced the expression levels of oocyte-derived BMP-15 in the oocyte-granulosa cell co-culture. Given the findings that FGF-8, but not GDF-9, BMP-6 or -15, suppressed FSH-induced estrogen production by granulosa cells, oocyte-derived FGF-8 is linked to suppression of FSH-induced estrogen production through the KL-c-kit interaction. Furthermore, the suppression of FSH-induced estrogen production by KL in the co-culture was reversed by a FGF receptor kinase inhibitor and the effect of the inhibitor was enhanced in combination with extracellular-domain protein of BMPRII, which interferes with BMP-15 and GDF-9 activities. Thus, the actions of endogenous oocyte factors including FGF-8 and BMP-15/GDF-9 were involved in the KL activity that inhibited FSH-induced estradiol production. Collectively, the results indicate that KL-c-kit interaction plays a role in estrogenic regulation through oocyte-granulosa cell communication.

Conditions affecting growth and developmental competence of mammalian oocytes in vitro

Mammalian ovaries contain a large number of oocytes at different stages of growth. To utilize potential female gametes, it is important to develop culture systems that permit oocytes to achieve full growth and competence in order to undergo maturation, fertilization and development. The desired culture systems should meet at least the following three conditions: (i) oocytes remain healthy and functional so that they can execute intrinsic programs that direct their growth and development; (ii) granulosa cells that are adjacent to oocytes proliferate efficiently to prevent oocytes from becoming denuded; and (iii) granulosa cells maintain (and develop) appropriate associations with oocytes during the culture period. For this reason, several systems have been developed, and they can be classified into four categories based on the structure and components of the follicle/oocyte-granulosa cell complex and the location of the oocyte in the physical organization of the complex. The resultant diverse morphologies are due to multiple factors, including the method for initial isolation of follicles, the culture substrate, and hormones and other factors added into the medium. It is important to find an optimal combination of such factors involved in the process to facilitate future research efforts.

[Progress in exploring genes for high fertility in ewes]

Fecundity trait in sheep is regulated by some major genes. Among them, BMPR-IB, BMP-15, and GDF-9 are most distinguishing. The mutant FecB of BMPR-IB has multiplicative effects on ovulation. GDF-9's mutants FecGH, FecI, and BMP-15's mutants FecXI, FecXH, FecXG, FecXB, FecXL, and FecXR increase ovulation rate in the heterozygote but result in sterile phenotypes in the homozygote, while GDF-9's mutant, FecGE, only increases ovulation rate in the homozygote. In addition, Woodlands and Lacaune are known as inheritable major genes. Woodlands gene is an X-linked maternally imprinted gene, and Lacaune is similar to FecB with a multiplicative effect on ovulation rate. The size of the effect of one copy of a mutation on ovulation rate ranges from an extra 0.4 ovulations for the woodlands mutation to an extra 1.5 ovulations for the BMPR-IB and Lacaune mutation. Investigation into these genes will not only help to select breeds with high fertility, but also give a chance to further elucidate the mechanism involved in the phenomenon. This review summaries the source, location, phenotype, and mechanism of the major genes in all breeds of sheep.

Transcriptome profiling of sheep granulosa cells and oocytes during early follicular development obtained by laser capture microdissection

Background

Successful achievement of early folliculogenesis is crucial for female reproductive function. The process is finely regulated by cell-cell interactions and by the coordinated expression of genes in both the oocyte and in granulosa cells. Despite many studies, little is known about the cell-specific gene expression driving early folliculogenesis. The very small size of these follicles and the mixture of types of follicles within the developing ovary make the experimental study of isolated follicular components very difficult.

The recently developed laser capture microdissection (LCM) technique coupled with microarray experiments is a promising way to address the molecular profile of pure cell populations. However, one main challenge was to preserve the RNA quality during the isolation of single cells or groups of cells and also to obtain sufficient amounts of RNA.

Using a new LCM method, we describe here the separate expression profiles of oocytes and follicular cells during the first stages of sheep folliculogenesis.

Results

We developed a new tissue fixation protocol ensuring efficient single cell capture and RNA integrity during the microdissection procedure. Enrichment in specific cell types was controlled by qRT-PCR analysis of known genes: six oocyte-specific genes (SOHLH2, MAEL, MATER, VASA, GDF9, BMP15) and three granulosa cell-specific genes (KL, GATA4, AMH).

A global gene expression profile for each follicular compartment during early developmental stages was identified here for the first time, using a bovine Affymetrix chip. Most notably, the granulosa cell dataset is unique to date. The comparison of oocyte vs. follicular cell transcriptomes revealed 1050 transcripts specific to the granulosa cell and 759 specific to the oocyte.

Functional analyses allowed the characterization of the three main cellular events involved in early folliculogenesis and confirmed the relevance and potential of LCM-derived RNA.

Conclusions

The ovary is a complex mixture of different cell types. Distinct cell populations need therefore to be analyzed for a better understanding of their potential interactions. LCM and microarray analysis allowed us to identify novel gene expression patterns in follicular cells at different stages and in oocyte populations.

Oocyte growth in vitro: potential model for studies of oocyte-granulosa cell interactions

Various factors such as gonadotrophins, growth factors, and steroid hormones play important roles in the regulation of oocyte/follicular growth in mammalian ovaries. In addition to these factors, there is a bidirectional interaction between oocytes and granulosa cells that is essential for achieving optimal oocyte developmental competence. Oocytes play a key role in this interaction by secreting paracrine factors that alter the activities of neighboring cumulus cells, such as the expression of a specific amino acid transporter, cholesterol biosynthesis, and levels of glycolysis in the cumulus cells. Among the known oocyte-derived factors, growth differentiation factor 9 (GDF9) is the dominant factor mediating the regulation by oocytes leading to cumulus expansion and granulosa cell proliferation. GDF9 frequently interacts with other oocyte-derived factors in a synergistic manner. It seems reasonable to speculate that oocytes growing in vitro require interactions similar to those in vivo. Some of the oocyte-mediated regulations have been confirmed in vitro, providing evidence of the usefulness of culture systems as a strong tool for such studies. This review discusses in vitro culture of growing oocytes in terms of oocyte-granulosa cell interactions.

Transcriptome dynamics and molecular cross-talk between bovine oocyte and its companion cumulus cells

BACKGROUND

The bi-directional communication between the oocyte and its companion cumulus cells (CCs) is crucial for development and functions of both cell types. Transcripts that are exclusively expressed either in oocytes or CCs and molecular mechanisms affected due to removal of the communication axis between the two cell types is not investigated at a larger scale. The main objectives of this study were: 1. To identify transcripts exclusively expressed either in oocyte or CCs and 2. To identify those which are differentially expressed when the oocyte is cultured with or without its companion CCs and vice versa.

RESULTS

We analyzed transcriptome profile of different oocyte and CC samples using Affymetrix GeneChip Bovine Genome array containing 23000 transcripts. Out of 13162 genes detected in germinal vesicle (GV) oocytes and their companion CCs, 1516 and 2727 are exclusively expressed in oocytes and CCs, respectively, while 8919 are expressed in both. Similarly, of 13602 genes detected in metaphase II (MII) oocytes and CCs, 1423 and 3100 are exclusively expressed in oocytes and CCs, respectively, while 9079 are expressed in both. A total of 265 transcripts are differentially expressed between oocytes cultured with (OO+CCs) and without (OO-CCs) CCs, of which 217 and 48 are over expressed in the former and the later groups, respectively. Similarly, 566 transcripts are differentially expressed when CCs mature with (CCs+OO) or without (CCs-OO) their enclosed oocytes. Of these, 320 and 246 are over expressed in CCs+OO and CCs-OO, respectively.While oocyte specific transcripts include those involved in transcription (IRF6, POU5F1, MYF5, MED18), translation (EIF2AK1, EIF4ENIF1) and CCs specific ones include those involved in carbohydrate metabolism (HYAL1, PFKL, PYGL, MPI), protein metabolic processes (IHH, APOA1, PLOD1), steroid biosynthetic process (APOA1, CYP11A1, HSD3B1, HSD3B7). Similarly, while transcripts over expressed in OO+CCs are involved in carbohydrate metabolism (ACO1, 2), molecular transport (GAPDH, GFPT1) and nucleic acid metabolism (CBS, NOS2), those over expressed in CCs+ OO are involved in cellular growth and proliferation (FOS, GADD45A), cell cycle (HAS2, VEGFA), cellular development (AMD1, AURKA, DPP4) and gene expression (FOSB, TGFB2).

CONCLUSION

In conclusion, this study has generated large scale gene expression data from different oocyte and CCs samples that would provide insights into gene functions and interactions within and across different pathways that are involved in the maturation of bovine oocytes. Moreover, the presence or absence of oocyte and CC factors during bovine oocyte maturation can have a profound effect on transcript abundance of each cell types, thereby showing the prevailing molecular cross-talk between oocytes and their corresponding CCs.

Bidirectional communication between oocytes and follicle cells: ensuring oocyte developmental competence

Female fertility is determined to a large extent by the quality (developmental competence) of the oocyte as reflected in its ability to undergo meiosis, be fertilized, and give rise to a healthy embryo. Growth of the mammalian oocyte is coordinated with that of the follicle that encloses it by the actions of signals that pass in both directions between the germline and somatic components. This review summarizes what is known about the roles played by 2 different modes of intrafollicular signalling in oogenesis: paracrine factors activating receptors on the opposite cell type, and direct sharing of small molecules throughout the follicle via gap junction channels. Recent evidence indicates that these 2 modes of signalling interact to regulate oocyte growth and granulosa cell proliferation and that defects in either can contribute to female infertility.

Theca: the forgotten cell of the ovarian follicle

Theca cells function in a diverse range of necessary roles during folliculogenesis; to synthesize androgens, provide crosstalk with granulosa cells and oocytes during development, and provide structural support of the growing follicle as it progresses through the developmental stages to produce a mature and fertilizable oocyte. Thecal cells are thought to be recruited from surrounding stromal tissue by factors secreted from an activated primary follicle. The precise origin and identity of these recruiting factors are currently not clear, but it appears that thecal recruitment and/or differentiation involves not just one signal, but a complex and tightly controlled combination of multiple factors. It is clear that thecal cells are fundamental for follicular growth, providing all the androgens required by the developing follicle(s) for conversion into estrogens by the granulosa cells. Their function is enabled through the establishment of a vascular system providing communication with the pituitary axis throughout the reproductive cycle, and delivering essential nutrients to these highly active cells. During development, the majority of follicles undergo atresia, and the theca cells are often the final follicular cell type to die. For those follicles that do ovulate, the theca cells then undergo hormone-dependent differentiation into luteinized thecal cells of the corpus luteum. While the theca is an essential component of follicle development and ovulation, we do not yet fully understand the control of recruitment and function of theca cells, an important consideration since their function appears to be altered in certain causes of infertility.

Stability of housekeeping genes and expression of locally produced growth factors and hormone receptors in goat preantral follicles

The aim of the present study was to investigate the stability of six housekeeping genes, and the relative expression of growth factors (EGF, GDF-9, BMP-15, VEGF, FGF-2, BMP-6, IGF-1 and KL) and hormone receptors (FSH, LH and GH) in goat preantral follicles. To evaluate to stability of housekeeping genes micro-dissected fresh follicles (150–200 μm) as well as follicles that have been in vitro cultured for 12 days were used. In addition, isolated fresh follicles were used to compare expression of various growth factors and hormone receptors before culture. Both fresh and cultured follicles were subjected to total RNA extraction and synthesis of cDNA. After amplification of cDNA by real-time PCR, the geNorm software program was used to evaluate the stability of glyceraldehyde-2-phosphate dehydrogenase (GAPDH), β-tubulin, β-actin, phosphoglycerokinase (PGK), 18S rRNA, ubiquitin (UBQ) and ribosomal protein 19 (RPL-19). In addition, follicular steady-state levels of mRNA from the various growth factors under study were compared. Results demonstrated that, in goat preantral follicles, UBQ and β-actin were the most suitable reference genes and thus could be used as parameters to normalize data from future in vitro studies. In contrast, 18S RNA appeared the least stable gene among the tested housekeeping genes. Analysis of mRNA for several hypophyseal hormone receptors in fresh preantral follicles showed significantly higher FSH-R mRNA levels than those of LH-R and GH-R, and no difference between GH-R and LH-R mRNA levels. In regard growth factor mRNA expression in goat preantral follicles, EGF mRNA levels appeared significantly lower than those of the other studied growth factors. Increasingly higher relative mRNA levels were observed for GDF-9, BMP-15, BMP-6, FGF-2, VEGF, Kl and IGF-1, successively. In conclusion, UBQ and β-actin are the most stable housekeeping genes in fresh and 12-days cultured caprine preantral follicles. Furthermore, in fresh follicles, high levels of FSH-R mRNA are detected while among eight growth factors, IGF-1 is the most highly expressed and EGF the weakest expressed compound.

Human ovarian follicular development: from activation of resting follicles to preovulatory maturation

By integrating morphometrical and endocrinological data, as well as biological effects of various molecules synthesized by the human follicle, we propose a dynamic view of the follicle growth within the human ovary. Folliculogenesis starts with entry of resting follicles into the growth phase, a process where the kit system plays a key role. Several months are required for a new growing follicle to reach the preantral stage (0.15mm), then 70 additional days to reach the size of 2mm. Early growing follicle growth is regulated by subtle interactions between follicle-stimulating hormone (FSH) and local factors produced by theca and granulosa cells (GCs), as well as the oocyte. From the time they enter the selectable stage during the late luteal phase, follicles become sensitive to cyclic changes of FSH in terms of granulosa cell proliferation. During the early follicular phase, the early selected follicle grows very quickly and estradiol is present in the follicular fluid. However, the total steroid production remains moderate. From the mid-follicular phase, the preovulatory follicle synthesizes high quantities of estradiol, then after the mid-cycle gonadotropin surge, very large amounts of progesterone. At this stage of development, the responsiveness of the follicle to gonadotropins is maximum, especially to luteinizing hormone (LH) that triggers granulosa wall dissociation and cumulus expansion as well as oocyte nuclear maturation. Thus, as the follicle develops, its responsiveness to gonadotropins progressively increases under the control of local factors acting in an autocrine/paracrine fashion.

Inhibition of oocyte growth factors in vivo modulates ovarian folliculogenesis in neonatal and immature mice

Growth differentiation factor-9 (GDF9) and bone morphogenetic protein-15 (BMP15) are among the key regulators transmitting the signaling between the oocyte and the surrounding granulosa cells. Previously, it has been shown that a recombinant BMP type II receptor ectodomain-Fc fusion protein (BMPR2ecd-Fc) is able to inhibit the actions of GDF9 and BMP15 in vitro. Here, we have produced bioactive BMPR2ecd-Fc, which was injected i.p. into neonatal mice. Early folliculogenesis was first studied by injecting mice five times with various doses of BMPR2ecd-Fc during the postnatal days 4-12. Folliculogenesis was affected dose dependently, as evidenced by a decreased mitogenesis of granulosa cells of the growing follicles. Furthermore, we also noticed a decrease in the number of secondary and tertiary follicles as well as an increase in the oocyte size. Electron microscopic analysis revealed that the ultrastructure of the granulosa cells of the primary follicles was not affected by the BMPR2ecd-Fc treatment. A second study was conducted to investigate whether a longer treatment with 12 injections during postnatal days 4-28 would inhibit folliculogenesis. Similar effects were observed in the two studies on the early follicular developmental stages. However, in the long-term study, later stages of folliculogenesis were not blocked but rather increased numbers of antral follicles, preovulatory follicles, and corpora lutea were found. We conclude that BMPR2ecd-Fc is a potent modulator of ovarian folliculogenesis in vivo, and thus, is a valuable tool for studying the physiology and downstream effects of oocyte-derived growth factors in vivo.

The mammalian ovary from genesis to revelation

Two major functions of the mammalian ovary are the production of germ cells (oocytes), which allow continuation of the species, and the generation of bioactive molecules, primarily steroids (mainly estrogens and progestins) and peptide growth factors, which are critical for ovarian function, regulation of the hypothalamic-pituitary-ovarian axis, and development of secondary sex characteristics. The female germline is created during embryogenesis when the precursors of primordial germ cells differentiate from somatic lineages of the embryo and take a unique route to reach the urogenital ridge. This undifferentiated gonad will differentiate along a female pathway, and the newly formed oocytes will proliferate and subsequently enter meiosis. At this point, the oocyte has two alternative fates: die, a common destiny of millions of oocytes, or be fertilized, a fate of at most approximately 100 oocytes, depending on the species. At every step from germline development and ovary formation to oogenesis and ovarian development and differentiation, there are coordinated interactions of hundreds of proteins and small RNAs. These studies have helped reproductive biologists to understand not only the normal functioning of the ovary but also the pathophysiology and genetics of diseases such as infertility and ovarian cancer. Over the last two decades, parallel progress has been made in the assisted reproductive technology clinic including better hormonal preparations, prenatal genetic testing, and optimal oocyte and embryo analysis and cryopreservation. Clearly, we have learned much about the mammalian ovary and manipulating its most important cargo, the oocyte, since the birth of Louise Brown over 30 yr ago.

Longer CAG repeat length in the androgen receptor gene is associated with premature ovarian failure

BACKGROUND

Premature ovarian failure (POF) is a disorder characterized by lack of ovulation and elevated serum gonadotrophin levels before the age of 40 years. The cause of POF in most cases is unknown. As mice lacking the Androgen receptor (Ar) gene reportedly have a POF-like phenotype, we hypothesize that, variations in the AR gene maybe one of the causative factors for POF in humans. Thus the objective of the study is to evaluate the number of CAG repeats in exon 1 of the AR gene in non-familial, non-syndromic cases of POF.

METHODS

A clinic-based case-control study. Seventy-eight patients with non-familial, non-syndromic POF, and 90 controls were recruited to investigate the CAG repeat numbers in exon 1 of the AR gene by PCR and Gene Scan analysis.

RESULTS

The mean CAG repeat length in exon 1 of the AR gene of women with POF was 23.6 +/- 3.8, which was significantly higher than controls (20.08 +/- 3.45) (P < 0.001). The biallelic mean CAG repeat ranged from 11 to 32 in the control women, compared to 16 to 30 in the POF patients. The 22 CAG repeat allele followed by the 24 CAG repeat allele was found to be at highest frequency (15.38 and 12.8%) in POF cases, although the 19 CAG repeat allele was observed at highest frequency (12.2%) in controls.

CONCLUSIONS

The observation suggests that the CAG repeat length is increased in women with POF as compared with controls, and may be pathogenic for POF, at least in a subset of Indian women.

Kit ligand promotes first polar body extrusion of mouse preovulatory oocytes

BACKGROUND

Shortly after stimulation by the preovulatory surge of luteinizing hormone (LH), oocytes arrested at the late prophase I resume meiosis characterized by germinal vesicle breakdown (GVBD), chromosome condensation, and extrusion of the first polar body in preparation for fertilization and early embryonic development. However, oocytes express few or no LH receptors and are insensitive to direct LH stimulation. Thus, factors released by granulosa or theca cells expect to convey the LH stimuli to oocytes. To identify candidate ligand-receptor pairs potentially involved in the process of oocyte maturation, we performed DNA microarray analyses of ovarian transcripts in mice and identified Kit ligand (Kitl) as an ovarian factor stimulated by the LH/hCG surge. The purpose of this study is to investigate the roles of KITL in the nuclear and cytoplasmic maturation of preovulatory mouse oocytes.

METHODS

The levels of Kitl and c-kit transcripts in mouse ovaries and isolated ovarian cells were determined by real-time RT-PCR, while expression of KITL protein was examined by immunohistochemistry. Follicle culture, cumulus-oocyte complexes (COC) and denuded oocytes culture were used to evaluate the effect of KITL on mouse oocyte nuclear maturation. To assess the effect of KITL treatment on the cytoplasmic maturation of preovulatory oocytes, we performed in vitro maturation of oocytes followed by in vitro fertilization.

RESULTS

Major increase of Kitl transcripts in granulosa cells and mouse ovaries, and predominant expression of c-kit in preovulatory oocytes were identified by real-time RT-PCR. Predominant expression of KITL protein was found in granulosa cells of preovulatory and small antral follicles at 4 h after hCG treatment. In vitro cultures demonstrated that treatment with KITL enhanced first polar body extrusion in a dose-dependent manner. Moreover, treatment of COC with KITL enhanced first polar body extrusion with increase in cyclin B1 synthesis which is important for the progression of meiotic maturation after GVBD. In contrast, treatment of cultured preovulatory follicles with KITL did not affect GVBD and KITL has no effect on cytoplasmic maturation of preovulatory oocytes.

CONCLUSION

Our findings suggest potential paracrine roles of KITL in the nuclear maturation of preovulatory oocytes by promoting first polar body extrusion.

Revisiting oocyte-somatic cell interactions: in search of novel intrafollicular predictors and regulators of oocyte developmental competence

Prediction and improvement of oocyte competence are two critical issues in assisted reproductive technology to improve infertility therapy. The lack of reliable and objective predictors of oocyte developmental competence for oocyte/embryo selection during in vitro fertilization hampers the effectiveness of this technology. Likewise, the low pregnancy rate resulting from in vitro maturation of human oocytes represents a major obstacle for its clinical application. Oocyte competence is progressively acquired during follicular development, and the oocyte plays a dominant role in regulating granulosa cell functions and maintaining the microenvironment appropriate for the development of its competence. Hence, granulosa cell functions are reflective of oocyte competence, and molecular markers of granulosa cells are potentially reliable predictors of oocyte quality. With the advent of the functional genomics era, the transcriptome of granulosa cells has been extensively characterized. Experimental data supporting granulosa cell markers as predictors of oocyte competence are now emerging in both animal models and humans. Future efforts should focus on integrating granulosa cell genetic markers as parameters for oocyte/embryo selection. Moreover, novel in vitro evidence highlights the effectiveness of exogenous oocyte-secreted factors in promoting oocyte developmental competence in animal models. The challenge in evaluating the effect of oocyte-secreted factors on oocyte quality in a clinical setting is to standardize the various preparations of these recombinant proteins and decipher their complex interactions/cooperativity within the germline-somatic cell regulatory loop.

Oogenesis: Prospects and challenges for the future

Oogenesis serves a singular role in the reproductive success of plants and animals. Of their remarkable differentiation pathway what stands out is the ability of oocytes to transform from a single cell into the totipotent lineages that seed the early embryo. As our understanding that commonalities between diverse organisms at the genetic, cellular and molecular levels are conserved to achieve successful reproduction, the notion that embryogenesis presupposes oogenesis has entered the day-to-day parlance of regenerative medicine and stem cell biology. With emphasis on the mammalian oocyte, this review will cover (1) current concepts regarding the birth, survival and growth of oocytes that depends on complex patterns of cell communication between germ line and soma, (2) the notion of "maternal inheritance" from a genetic and epigenetic perspective, and (3) the relative value of model systems with reference to current clinical and biotechnology applications.