Mouse oocytes regulate granulosa cell steroidogenesis

The multifaceted role of extracellular ATP in sperm function: From spermatogenesis to fertilization

Extracellular adenosine 5'-triphosphate (ATP) is a vital signaling molecule involved in various physiological processes within the body. In recent years, studies have revealed its significant role in male reproduction, particularly in sperm function. This review explores the multifaceted role of extracellular ATP in sperm function, from spermatogenesis to fertilization. We discuss the impact of extracellular ATP on spermatogenesis, sperm maturation and sperm-egg fusion, highlighting the complex regulatory mechanisms and potential clinical applications in the context of male infertility. By examining the latest research, we emphasize the crucial role of extracellular ATP in sperm function and propose future research directions to further.

Cooperative effects of oocytes and estrogen on the forkhead box L2 expression in mural granulosa cells in mice

Forkhead box L2 (FOXL2) plays a critical role in the development and function of mammalian ovaries. In fact, the causative effects of FOXL2 misregulations have been identified in many ovarian diseases, such as primary ovarian insufficiency and granulosa cell tumor; however, the mechanism by which FOXL2 expression is regulated is not well studied. Here, we showed that FOXL2 expression in ovarian mural granulosa cells (MGCs) requires stimulation by both oocyte-derived signals and estrogen in mice. In the absence of oocytes or estrogen, expression of FOXL2 and its transcriptional targets, Cyp19a1 and Fst mRNA, in MGCs were significantly decreased. Moreover, expression levels of Sox9 mRNA, but not SOX9 protein, were significantly increased in the FOXL2-reduced MGCs. FOXL2 expression in MGCs was maintained with either oocytes or recombinant proteins of oocyte-derived paracrine factors, BMP15 and GDF9, together with estrogen, and this oocyte effect was abrogated with an ALK5 inhibitor, SB431542. In addition, the FOXL2 level was significantly decreased in MGCs isolated from Bmp15^-/- /Gdf9^+/- mice. Therefore, oocyte, probably with estrogen, plays a critical role in the regulation of FOXL2 expression in mural granulosa cells in mice.

Mysteries and unsolved problems of mammalian fertilization and related topics

Mammalian fertilization is a fascinating process that leads to the formation of a new individual. Eggs and sperm are complex cells that must meet at the appropriate time and position within the female reproductive tract for successful fertilization. I have been studying various aspects of mammalian fertilization over 60 years. In this review, I discuss many different aspects of mammalian fertilization, some of my laboratory's contribution to the field, and discuss enigmas and mysteries that remain to be solved.

Expression and regulation of estrogen receptor 2 and its coregulators in mouse granulosa cells

The cooperative effects of estrogen and oocyte-derived paracrine factors (ODPFs) play critical roles in the normal development of ovarian follicles; however, the mechanism underlying this cooperation has not been well studied. The present study aimed to determine whether ODPFs affect estrogen signaling by regulating the expression of estrogen receptor (ESR) and its coregulators in mouse granulosa cells. Some transcripts encoding ESR coregulators were differentially expressed between cumulus and mural granulosa cells (MGCs). The transcript levels of ESR coregulators, including nuclear receptor corepressor 1 and activator 2, in cumulus cells were significantly suppressed by ODPFs; however, they increased when cumulus cell-oocyte complexes were treated with the transforming growth factor beta receptor I inhibitor, SB431542. Moreover, MGCs exhibited significantly higher ESR2 protein and transcript levels than those in cumulus cells. ODPFs promoted Esr2 expression in cumulus cells but had no effect on that in MGCs. Overall, regulation of the expression of ESR2 and its coregulators in cumulus cells by oocytes seems to be one of the mechanisms underlying estrogen-oocyte cooperation in well-developed antral follicles in mice.

CPEB3 deficiency in mice affect ovarian follicle development and causes premature ovarian insufficiency

Premature ovarian insufficiency (POI) is a heterogeneous and multifactorial disorder. In recent years, there has been an increasing interest in research on the pathogenesis and treatment of POI, owing to the implementation of the second-child policy in China. Cytoplasmic polyadenylation element-binding protein 3 (CPEB3) is an RNA-binding protein that can bind to specific RNA sequences. CPEB3 can bind to and affect the expression, cellular location, and stability of target RNAs. Cpeb3 is highly expressed in the ovary; however, its functions remain unknown. In this study, Cpeb3-mutant mice were used to characterize the physiological functions of CPEB3. Cpeb3-mutant female mice manifested signs of gradual loss of ovarian follicles, ovarian follicle development arrest, increased follicle atresia, and subfertility with a phenotype analogous to POI in women. Further analysis showed that granulosa cell proliferation was inhibited and apoptosis was markedly increased in Cpeb3-mutant ovaries. In addition, the expression of Gdf9, a potential target of CPEB3, was decreased in Cpeb3-mutant ovaries and oocytes. Altogether, these results reveal that CPEB3 is essential for ovarian follicle development and female fertility as it regulates the expression of Gdf9 in oocytes, disruption of which leads to impaired ovarian follicle development and POI.

Effects of oocyte-derived growth factors on the growth of porcine oocytes and oocyte-cumulus cell complexes in vitro

During oocyte growth and follicle development, oocytes closely communicate with cumulus cells. We examined the effects of oocyte-derived growth factors, growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15), on the growth and acquisition of meiotic competence of porcine oocytes collected from early antral follicles (1.2-1.5 mm). First, we confirmed that GDF9 and BMP15 mRNAs were expressed almost exclusively in the oocytes. Oocyte-cumulus cell complexes (OCCs) collected from early antral follicles were cultured in growth medium supplemented with 0-100 ng/ml of GDF9 or BMP15 for 5 days. GDF9 dose-dependently increased the OCC diameter, while BMP15 did not. GDF9 and BMP15 had no significant effects on oocyte growth (P > 0.05). When OCCs that had been cultured with 50 and 100 ng/ml BMP15 were subjected to a subsequent maturation culture, they expanded fully by gonadotropic stimulation and 49% and 61% of oocytes matured to metaphase II (MII), respectively. In contrast, GDF9 did not promote cumulus expansion, and < 10% of oocytes matured to MII. Based on the difference in cumulus expansion, we compared the expression of luteinizing hormone/choriogonadotropin receptor (LHCGR) and follicle stimulating hormone receptor (FSHR) mRNAs in cumulus cells. The level of LHCGR mRNA was increased in cumulus cells of the BMP15 group, although there were no significant differences in FSHR mRNA levels among the groups. These results suggest that GDF9 promotes the growth of OCCs and that BMP15 promotes LHCGR mRNA expression in cumulus cells during oocyte growth culture, which may contribute to cumulus expansion and oocyte maturation.

Effects of Growth and Differentiation Factor 9 and Bone Morphogenetic Protein 15 overexpression on the steroidogenic metabolism in bovine granulosa cells in vitro

Granulosa cells (GCs) play important roles in the regulation of ovarian functions, and in vitro culture is a relevant model for the study of steroidogenesis in ovarian follicles. Thus, growth factors secreted by the oocyte, like Growth and Differentiation Factor 9 (GDF9) and Bone Morphogenetic Protein 15 (BMP15), play an important part in the luteinization of granulosa cells. The aim of this work was to express GDF9 and BMP15 genes in bovine GCs in vitro and evaluate their effects on the luteinization process. Samples of culture medium and GCs transfected with GDF9 and BMP15 were obtained for 21 consecutive days to analyse the steroidogenic hormones' concentration (progesterone (P₄ ) and estradiol (E₂ )) and the expression of STAR, GDF9 and BMP15 and their respective receptors. The results demonstrated an inhibitory effect of GDF9 and BMPF15 on P₄ secretion in bovine GCs cultured in vitro. Moreover, our study demonstrated the entire expression of their respective receptors (TGFBR1, BMPR1B and BMPR2) and the inhibition of the steroidogenic marker, STAR gene. This work sheds light on a novel biological function of BMP15 and GDF9 in bovine GCs physiology, which could elucidate a non-described biological role for GDF9 and BMP15 in bovine granulosa cells' metabolism.

A Comparative Analysis of Oocyte Development in Mammals

Sexual reproduction requires the fertilization of a female gamete after it has undergone optimal development. Various aspects of oocyte development and many molecular actors in this process are shared among mammals, but phylogeny and experimental data reveal species specificities. In this chapter, we will present these common and distinctive features with a focus on three points: the shaping of the oocyte transcriptome from evolutionarily conserved and rapidly evolving genes, the control of folliculogenesis and ovulation rate by oocyte-secreted Growth and Differentiation Factor 9 and Bone Morphogenetic Protein 15, and the importance of lipid metabolism.

Molecular Mechanisms of Prophase I Meiotic Arrest Maintenance and Meiotic Resumption in Mammalian Oocytes

Mechanisms of meiotic prophase I arrest maintenance (germinal vesicle [GV] stage) and meiotic resumption (germinal vesicle breakdown [GVBD] stage) in mammalian oocytes seem to be very complicated. These processes are regulated via multiple molecular cascades at transcriptional, translational, and posttranslational levels, and many of them are interrelated. There are many molecular cascades of meiosis maintaining and meiotic resumption in oocyte which are orchestrated by multiple molecules produced by pituitary gland and follicular cells. Furthermore, many of these molecular cascades are duplicated, thus ensuring the stability of the entire system. Understanding mechanisms of oocyte maturation is essential to assess the oocyte status, develop effective protocols of oocyte in vitro maturation, and design novel contraceptive drugs. Mechanisms of meiotic arrest maintenance at prophase I and meiotic resumption in mammalian oocytes are covered in the present article.

Molecular Aspects and Clinical Relevance of GDF9 and BMP15 in Ovarian Function

Growth and differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) are oocyte-secreted factors with a leading role in the control of ovarian function in female reproduction, modulating both the cell fate of the somatic granulosa cells and the quality and developmental competence of the egg. This short review aims to consolidate the molecular aspects of GDF9 and BMP15 and their integral actions in female fertility to understand particularly their effects on oocyte quality and fetal growth. The significant consequences of mutations in the GDF9 and BMP15 genes in women with dizygotic twins as well as the clinical relevance of these oocyte factors in the pathogenesis of primary ovarian insufficiency and polycystic ovary syndrome are also addressed.

Low glucose availability stimulates progesterone production by mouse ovaries in vitro

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

Modifications of human growth differentiation factor 9 to improve the generation of embryos from low competence oocytes

Growth differentiation factor 9 (GDF9) is an oocyte-derived growth factor that plays a critical role in ovarian folliculogenesis and oocyte developmental competence and belongs to the TGF-β family of proteins. Recombinant human GDF9 (hGDF9) is secreted in a latent form, which in the case of the fully processed protein, has the proregion noncovalently associated with the mature region. In this study, we investigated a number of amino acid residues in the mature region of hGDF9 that are different from the corresponding residues in the mouse protein, which is not latent. We designed, expressed, and purified 4 forms of chimeric hGDF9 (M1-M4) that we found to be active in a granulosa cell bioassay. Using a porcine in vitro maturation model with inherent low developmental competence (yielding 10%-20% blastocysts), we tested the ability of the chimeric hGDF9 proteins to improve oocyte maturation and developmental competence. Interestingly, one of the chimeric proteins, M3, was able to significantly increase the level of embryo production using such low competence oocytes. Our molecular modeling studies suggest that in the case of hGDF9 the Gly(391)Arg mutation probably increases receptor binding affinity, thereby creating an active protein for granulosa cells in vitro. However, for an improvement in oocyte developmental competence, a second mutation (Ser(412)Pro), which potentially decreases the affinity of the mature region for the proregion, is also required.

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.

Bone morphogenetic protein 15 in the pro-mature complex form enhances bovine oocyte developmental competence

Developmental competence of in vitro matured (IVM) oocytes needs to be improved and this can potentially be achieved by adding recombinant bone morphogenetic protein 15 (BMP15) or growth differentiation factor (GDF9) to IVM. The aim of this study was to determine the effect of a purified pro-mature complex form of recombinant human BMP15 versus the commercially available bioactive forms of BMP15 and GDF9 (both isolated mature regions) during IVM on bovine embryo development and metabolic activity. Bovine cumulus oocyte complexes (COCs) were matured in vitro in control medium or treated with 100 ng/ml pro-mature BMP15, mature BMP15 or mature GDF9 +/− FSH. Metabolic measures of glucose uptake and lactate production from COCs and autofluorescence of NAD(P)H, FAD and GSH were measured in oocytes after IVM. Following in vitro fertilisation and embryo culture, day 8 blastocysts were stained for cell numbers. COCs matured in medium +/− FSH containing pro-mature BMP15 displayed significantly improved blastocyst development (57.7±3.9%, 43.5±4.2%) compared to controls (43.3±2.4%, 28.9±3.7%) and to mature GDF9+FSH (36.1±3.0%). The mature form of BMP15 produced intermediate levels of blastocyst development; not significantly different to control or pro-mature BMP15 levels. Pro-mature BMP15 increased intra-oocyte NAD(P)H, and reduced glutathione (GSH) levels were increased by both forms of BMP15 in the absence of FSH. Exogenous BMP15 in its pro-mature form during IVM provides a functional source of oocyte-secreted factors to improve bovine blastocyst development. This form of BMP15 may prove useful for improving cattle and human artificial reproductive technologies.

The fundamental role of bone morphogenetic protein 15 in ovarian function and its involvement in female fertility disorders

BACKGROUND

A large number of studies have contributed to understanding the general mechanisms driving ovarian folliculogenesis in humans and show a complex endocrine dialog between the central nervous system, the pituitary and the ovary, integrated by various intraovarian paracrine messages. The role of intraovarian paracrine regulation has acquired more relevance in the recent years owing to the discovery of previously unknown factors, such as the oocyte-derived bone morphogenetic protein (BMP)15.

METHODS

A thorough literature search was carried out in order to summarize what has been reported so far on the role of BMP15, and the BMP15 paralog, growth and differentiation factor 9 (GDF9), in ovarian function and female fertility. Research articles published in English until March 2014 were included.

RESULTS

The biological actions of BMP15 include: (i) the promotion of follicle growth and maturation starting from the primary gonadotrophin-independent phases of folliculogenesis; (ii) the regulation of follicular granulosa cell (GC) sensitivity to FSH action and the determination of ovulation quota; (iii) the prevention of GC apoptosis and (iv) the promotion of oocyte developmental competence. The existence of biologically active heterodimers with GDF9, and/or the synergistic co-operation of BMP15 and GDF9 homodimers are indeed relevant in this context. Experimental disruption of the bmp15 gene in mice resulted in a mild fertility defect limited to females, whereas natural missense mutations in ewes cause variable phenotypes (ranging from hyperprolificacy to complete sterility) depending on a fine gene dosage mechanism also involving GDF9. Strong evidence supports the concept that such a mechanism plays an important role in the regulation of ovulation rate across mammalian and non-mammalian species. Following the discovery of sheep fecundity genes, several research groups have focused on alterations in human BMP15 associated with primary ovarian insufficiency (POI) or polycystic ovary syndrome. Several variants of BMP15 are significantly associated with POI supporting their pathogenic role, but the underlying biological mechanism is still under investigation and of great interest in medicine. BMP15 maps to the Xp locus involved in the determination of the ovarian defect in Turner syndrome and significantly contributes to the determination of ovarian reserve. Pioneering studies in women undergoing controlled ovarian stimulation indicate that BMP15 may represent a marker of ovarian response or oocyte quality.

CONCLUSIONS

BMP15, an oocyte-derived growth and differentiation factor, is a critical regulator of folliculogenesis and GC activities. Variations in BMP15 gene dosage have a relevant influence on ovarian function and can account for several defects of female fertility. The modulation of BMP15 action may have interesting pharmacological perspectives and the analysis of BMP15 may become a useful marker in IVF procedures. Recent outcomes indicate that the close interactions of BMP15/GDF9 have a critical biological impact that should be taken into account in future studies.

Transactivation of micrornA-320 by microRNA-383 regulates granulosa cell functions by targeting E2F1 and SF-1 proteins

Our previous studies have shown that microRNA-320 (miR-320) is one of the most down-regulated microRNAs (miRNA) in mouse ovarian granulosa cells (GCs) after TGF-β1 treatment. However, the underlying mechanisms of miR-320 involved in GC function during follicular development remain unknown. In this study, we found that pregnant mare serum gonadotropin treatment resulted in the suppression of miR-320 expression in a time-dependent manner. miR-320 was mainly expressed in GCs and oocytes of mouse ovarian follicles in follicular development. Overexpression of miR-320 inhibited estradiol synthesis and proliferation of GCs through targeting E2F1 and SF-1. E2F1/SF-1 mediated miR-320-induced suppression of GC proliferation and of GC steroidogenesis. FSH down-regulated the expression of miR-320 and regulated the function of miR-320 in mouse GCs. miR-383 promoted the expression of miR-320 and enhanced miR-320-mediated suppression of GC proliferation. Injection of miR-320 into the ovaries of mice partially promoted the production of testosterone and progesterone but inhibited estradiol release in vivo. Moreover, the expression of miR-320 and miR-383 was up-regulated in the follicular fluid of polycystic ovarian syndrome patients, although the expression of E2F1 and SF-1 was down-regulated in GCs. These data demonstrated that miR-320 regulates the proliferation and steroid production by targeting E2F1 and SF-1 in the follicular development. Understanding the regulation of miRNA biogenesis and function in the follicular development will potentiate the usefulness of miRNA in the treatment of reproduction and some steroid-related disorders.

Transactivation of microRNA-383 by steroidogenic factor-1 promotes estradiol release from mouse ovarian granulosa cells by targeting RBMS1

Our previous studies have shown that microRNA-383 (miR-383) is one of the most down-regulated miRNA in TGF-β1-treated mouse ovarian granulosa cells (GC). However, the roles and mechanisms of miR-383 in GC function during follicular development remain unknown. In this study, we found that miR-383 was mainly expressed in GC and oocytes of mouse ovarian follicles. Overexpression of miR-383 enhanced estradiol release from GC through targeting RNA binding motif, single stranded interacting protein 1 (RBMS1). miR-383 inhibited RBMS1 by affecting its mRNA stability, which subsequently suppressed the level of c-Myc (a downstream target of RBMS1). Forced expression of RBMS1 or c-Myc attenuated miR-383-mediated steroidogenesis-promoting effects. Knockdown of the transcription factor steroidogenic factor-1 (SF-1) significantly suppressed the expression of Sarcoglycan zeta (SGCZ) (miR-383 host gene), primary and mature miR-383 in GC, indicating that miR-383 was transcriptionally regulated by SF-1. Luciferase and chromatin immunoprecipitation assays revealed that SF-1 specifically bound to the promoter region of SGCZ and directly transactivated miR-383 in parallel with SGCZ. In addition, SF-1 was involved in regulation of miR-383- and RBMS1/c-Myc-mediated estradiol release from GC. These results suggest that miR-383 functions to promote steroidogenesis by targeting RBMS1, at least in part, through inactivation of c-Myc. SF-1 acts as a positive regulator of miR-383 processing and function in GC. Understanding of regulation of miRNA biogenesis and function in estrogen production will potentiate the usefulness of miRNA in the control of reproduction and treatment of some steroid-related disorders.

[Reconsidering the roles of female germ cells in ovarian development and folliculogenesis]

The production of fertilizable ova is the consequence of multiple events that start as soon as ovarian development and culminate at the time of ovulation. Throughout their development, germ cells are associated with companion somatic cells, which ensure germ cell survival, growth and maturation. Data obtained in vitro and in vivo on several animal models of germ cell depletion have led to uncover the many roles of germ cells on both ovarian development and folliculogenesis. During ovarian development, germ cells become progressively enclosed within epithelial structures called "ovigerous cords" constituted by pregranulosa cells, lined by a basement membrane. At the end of ovarian development, ovigerous cords fragment into primordial follicles, which are epithelial units constituted by an oocyte surrounded by a single layer of granulosa cells. Germ cells are necessary for the fragmentation of ovigerous cords into follicles, since in their absence, no follicle will form. Germ cells also ensure the differentiation of the ovarian somatic lineage, and they may inhibit the testis-differentiating pathway by preventing the conversion of pregranulosa cells into Sertoli cells, their counterpart in the testis. Regularly, primordial follicles are recruited into the growing follicle pool and initiate their growth. They develop through primary, preantral, antral and preovulatory stages before being ovulated. Interestingly, the action of the oocyte on companion somatic cells tightly depends on the follicular stage. In primordial follicles, the oocyte prevents the transdifferentiation of granulosa cells into cells resembling Sertoli cells. By contrast, as soon as the follicle enters growth, the oocyte regulates the functional differentiation of granulosa cells and at the latest stages, it prevents their premature maturation into luteal cells. Overall, these data demonstrate that the female germ cell act on companion somatic cells to regulate ovarian development and folliculogenesis, thereby actively supporting its own maturation.

The porcine Gpr3 gene: molecular cloning, characterization and expression level in tissues and cumulus-oocyte complexes during in vitro maturation

G protein-coupled receptor 3 (Gpr3) is a member of G protein-coupled receptor rhodopsin family, which is present throughout the follicle within the ovary and functions as a critical factor for the maintenance of meiotic prophase arrest in oocytes by a Gs protein-mediated pathway. In the current paper, attempts were made to clone and characterize a gene encoding Gpr3 from pigs and investigate its expression pattern in tissues and the whole cumulus-oocyte complexes (COCs) in vitro maturation (IVM). Rapid amplification of cDNA ends and RT-PCR gave rise to the full sequence of Gpr3 gene with its length being 2101 bp nucleotides, including an open reading frame of 993 bp, encoding a 331 amino acid polypeptide with the molecular weight of 35.2 kDa. Homology search and sequence multi-alignment demonstrated that the putative porcine Gpr3 protein sequence shared a high identity with other animal Gpr3 orthologs, including several highly conservative motifs and amino acids. Real-time PCR analysis showed that the Gpr3 gene was expressed in tissues of cerebrum, cerebellum, hypothalamus, pituitary, ovary, oviduct, uterus, heart, liver, spleen, lung, kidney, muscle, fat, testis, thymus and granulosa cell, oocyte and COCs at different expression levels. The expression levels of this gene in oocyte, uterus, liver, fat, pituitary and brain were higher than that in other tissues. Interestingly, the mRNA and protein levels of Gpr3 in the whole COCs were down-regulated, and its mRNA expression levels were significantly and negatively correlated with the degrees of cumulus expansion (r = -0.937, P < 0.01) during IVM, suggesting its important roles in cumulus expansion and oocyte maturation.

Estradiol promotes and maintains cumulus cell expression of natriuretic peptide receptor 2 (NPR2) and meiotic arrest in mouse oocytes in vitro

Natriuretic peptide type C (NPPC) and its cognate receptor natriuretic peptide receptor 2 (NPR2) are essential for maintaining meiotic arrest in mouse oocytes residing in Graafian follicles. Cumulus cells, which are associated with the oocyte, express the receptor NPR2, a guanylyl cyclase, whereas mural granulosa cells express ligand NPPC. This study determined the temporal expression of Npr2 and the hormonal factors that participate in regulating its expression and, thereby, in oocyte meiotic arrest. Stimulation of follicular development in vivo with equine chorionic gonadotropin (eCG) promoted expression of Npr2 mRNA by cumulus cells and some periantral mural granulosa cells. However, FSH did not elevate the levels of Npr2 mRNA in cultured cumulus-oocyte complexes (COCs) isolated from mice not stimulated in vivo with eCG. Nevertheless, estradiol elevated expression of this transcript in vitro to the same steady-state level found in COCs isolated from eCG-stimulated follicles in vivo. Expression of Npr2 mRNA was rapidly reduced in COCs in vitro after isolation from eCG-primed mice unless maintained in culture with estradiol. The ability of NPPC to maintain meiotic arrest in cultured COCs was transient unless culture was in estradiol-containing medium. Ability of cumulus cells to produce cyclic GMP, which is required for the maintenance of meiotic arrest, was also lost in the absence of estradiol, indicating that estradiol is required to maintain functional NPR2 receptors on cumulus cells in vitro. It is concluded that estradiol promotes and maintains expression of NPR2 in cumulus cells and participates in NPPC-mediated maintenance of oocyte meiotic arrest in vitro.

Effect of oocyte-secreted factors on porcine in vitro maturation, cumulus expansion and developmental competence of parthenotes

The oocyte is known from recent studies in the mouse, cow, sheep and human to be a central regulator of follicular cell function. However, in the pig, little information is known about the regulation of cumulus expansion by oocyte-secreted factors and oocyte quality. We investigated the possible effects of oocyte-secreted factors during in vitro maturation on cumulus expansion and on porcine oocytes as judged by subsequent embryonic development after parthenogenetic activation. Cumulus-oocyte complexes (COC) from antral follicles of pig ovaries collected from a local abattoir were divided into control and treatment groups and were cultured in tissue culture medium 199 supplemented with follicle-stimulating hormone. Treatment groups consisted of increasing numbers of denuded oocytes (DO) co-cultured with COC (at ratios of COC to DO of 1:1, 1:2, 1:3, 1:4 and 1:5). After incubation for 44 h, cumulus expansion and maturation rates were assessed and oocytes were activated parthenogenetically. Cumulus expansion in the 1 COC:4 DO and 1 COC:5 DO groups was low and altered because full dispersion of the outer layer did not occur. Cell viability was not affected, as measured by the automated cell counter, but scanning electron microscopy revealed only a scanty extracellular matrix. Blastocyst rate was significantly higher in the 1 COC:4 DO (34.4%) and in the 1 COC:5 DO (34.9%) groups (p < 0.05) when compared with other groups. Maturation rate, cleavage rate and total cell number showed no significant difference between control and treatment groups. Amplification by reverse transcription polymerase chain reaction (RT-PCR) showed up-regulation of growth differentiation factor 9 (GDF9) in the cumulus cells in the 1 COC:4 DO group at 44 h. We conclude that denuded porcine oocytes could improve the maturation of COC as evidenced by increased blastocyst development in the 1 COC:4 DO, even though cumulus expansion was poor. This improvement could be a result of the GDF9 up-regulation.

Estrogen promotes the development of mouse cumulus cells in coordination with oocyte-derived GDF9 and BMP15

The differentiation and function of cumulus cells depend upon oocyte-derived paracrine factors, but studies on the estrogen receptor knockout mice suggested that estrogen also participates in these processes. This study investigates the possible coordination of estrogen and oocytes in the development and function of cumulus cells using cumulus expansion and the expression of transcripts required for expansion as functional endpoints. Preantral granulosa cell-oocyte complexes developed in vitro with 17β-estradiol (E2) exhibited increased levels of cumulus expansion and Has2 transcripts, encoding hyaluronan synthase 2, compared with those developed without E2. Moreover, cumulus cell-oocyte complexes (COCs) isolated from antral follicles and maintained in culture without E2 exhibited reduced cumulus expansion and Has2 mRNA levels compared with freshly isolated COCs. Exogenous E2, provided during the maintenance culture, alleviated these deficiencies. However, when oocytes were removed from COCs, E2 supplementation did not maintain competence to undergo expansion; the presence in culture of either fully grown oocytes or recombinant growth differentiation factor 9 (GDF9) was required. Recombinant bone morphogenetic protein 15, but not fibroblast growth factor 8, augmented the GDF9 effect. Oocytes or GDF9 suppressed cumulus cell levels of Nrip1 transcripts encoding nuclear receptor-interacting protein 1, a potential inhibitor of estrogen receptor signals. Therefore, E2 and oocyte-derived paracrine factors GDF9 and bone morphogenetic protein 15 coordinate to promote the development of cumulus cells and maintain their competence to undergo expansion. Furthermore, suppression of Nrip1 expression in cumulus cells by oocyte may be one mechanism mediating cross talk between oocyte and E2 signals that promotes follicular development.

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.

Oocyte secreted factors improve embryo developmental competence of COCs from small follicles in prepubertal goats

Oocytes secrete soluble paracrine factors called Oocyte Secreted Factors (OSFs) which regulate the cumulus cell phenotype. Follicle populations in ovaries from prepubertal females have smaller diameters than their adult counterparts. Oocytes from small follicles are less competent than those from large follicles. The aim of this study was to investigate, in prepubertal goats, the effect of OSFs secreted by denuded oocytes (DOs) from small (<3 mm) or large (>or=3 mm) follicles during IVM on embryo development and the blastocyst quality of cumulus-oocyte complexes (COCs) from small follicles and to determine if GDF9 participates in this process. Treatment groups were: (A) COCs non selected by their follicle size (control group); (B) cumulus oocytes complexes from small follicles (SFCOCs), (C) cumulus oocytes complexes from small follicles co-cultured with denuded oocytes from small follicles (SFCOCs + SFDOs), and (D) cumulus oocytes complexes from small follicles co-cultured with denuded oocytes from large follicles (SFCOCs + LFDOs). The effect of the addition of kinase inhibitor SB-431542, which antagonizes GDF9, was tested in A, C, and D treatment groups. Co-cultured SFCOCs with SFDOs or LFDOs significantly augmented the blastocyst rate in comparison to SFCOCs alone (15.77%, 17.39% vs. 10.31%, respectively). Blastocysts from SFCOCs + LFDOs group showed higher rates of tetraploid nuclei than blastocysts from SFCOCs and the control group (14.43% vs. 5.45% and 5.24%, respectively; P < 0.05). However, we did not observe differences in the hatching rate, mean cell number or embryo cryotolerance (P > 0.05) between the four treatment groups. The addition of SB-431542 during IVM did not have any effect on blastocyst rate (P > 0.05). In conclusion, in prepubertal goats, COCs with a low embryo developmental competence as a consequence of follicle size can be improved by coculturing them with denuded oocytes from both small and large follicles. GDF9 does not seem play a role in this improvement.

Portrait of an oocyte: our obscure origin

Oocytes play a pivotal role in the cycle of human life. As we discuss here, after emerging from germline stem cells in the fetus, they grow in a follicular niche in which development is harmonized for timely ovulation and hormone secretion after puberty. Most human oocytes have poor developmental competence and are peculiarly vulnerable to chromosomal malsegregation, especially as women pass the optimal years of fertility and may begin to turn to assisted reproductive technologies (ARTs) and egg donation. Research needs to focus on the molecular factors involved and the environmental niche required for optimal development of oocytes, with the aim of increasing their numbers and quality for ARTs, since these are the factors that so often limit human fertility.

Growth differentiation factor 9 enhances activin a-induced inhibin B production in human granulosa cells

Activin A or growth differentiation factor 9 (GDF9) alone can increase beta(B)-mRNA level in human granulosa-lutein cells from women undergoing in vitro fertilization, but their potential interactions and related cell signaling pathways involved are unknown. We therefore compared inhibin subunit and inhibin levels and activation of activin receptors (ACVRs) and Smad signaling pathway in these human granulosa-lutein cells with and without GDF9 and/or activin A treatment. Inhibin subunit (alpha, beta(A), beta(B)), ACVR, and Smad2/3/4/7 mRNA levels, inhibin A and B production, and Smad phosphorylation were assessed by real-time RT-PCR, ELISA, and immunoblotting, respectively. Data were analyzed by ANOVA followed by Tukey's test. Activin A (1-50 ng/ml) or GDF9 (1-200 ng/ml) alone had only little stimulatory effects on alpha- and beta(A)-mRNA levels. In contrast, GDF9 could stimulate beta(B)-subunit levels but to a lesser degree than the dose- and time-dependent effects of activin A. Compared with untreated cells, GDF9 pretreatment for 24 h significantly enhanced activin A-induced beta(B)-mRNA levels, inhibin B secretion, and Smad2/3 phosphorylation (effects attenuated by bone morphogenetic protein receptor 2 extracellular domain, a GDF9 antagonist); and induced ACVR2B/1B and Smad2/3 but reduced Smad7 (an inhibitory Smad) mRNA levels. We report here for the first time that GDF9 enhances cell response to activin A by modulating key components of the activin signaling pathway in regulating inhibin subunits and hence inhibin B production in human granulosa-lutein cells.

p38-Mitogen-activated protein kinase stimulated steroidogenesis in granulosa cell-oocyte cocultures: role of bone morphogenetic proteins 2 and 4

Roles of the p38-MAPK pathway in steroidogenesis were investigated using coculture of rat granulosa cells with oocytes. Activin and FSH readily phosphorylated p38 in granulosa cells. Activin effect on p38 phosphorylation was abolished by a selective activin receptor-like kinase-4, -5, and -7 inhibitor, SB431542. SB431542 decreased FSH-induced estradiol but had no effect on progesterone production with a marginal cAMP reduction, suggesting that endogenous activin is primarily involved in estradiol synthesis. FSH-induced p38 activation was not affected either by SB431542 or follistatin, suggesting that FSH activates p38 not through the endogenous activin. Bone morphogenetic protein (BMP)-2 and BMP-4 also enhanced FSH-induced p38 phosphorylation, which was augmented by oocyte action. A specific p38 inhibitor, SB203580, decreased FSH-induced estradiol production. However, FSH-induced cAMP accumulation was not changed by SB203580, suggesting that p38 activation is linked to estradiol synthesis independently of cAMP. BMP-2 and BMP-4 inhibited FSH- and forskolin (FSK)-induced progesterone and cAMP synthesis regardless of oocyte action. BMP-2, BMP-4, and activin increased FSH-induced estradiol production, which was enhanced in the presence of oocytes. In contrast to activin that enhanced FSK-induced estradiol, BMP-2 and BMP-4 had no effects on FSK-induced estradiol production, suggesting that BMP-2 and BMP-4 directly activate FSH-receptor signaling. Given that activin increased, but BMP-2 and BMP-4 decreased, FSH-induced cAMP, the effects of BMP-2 and BMP-4 on estradiol enhancement appeared to be diverged from the cAMP-protein kinase A pathway. Thus, BMP-2 and BMP-4 differentially regulate steroidogenesis by stimulating FSH-induced p38 and suppressing cAMP. The former is involved in estradiol production and enhanced by oocyte action, whereas the latter leads to reduction of progesterone synthesis.

Cell–cell interaction and oocyte growth

In most mammals, oocytes initiate meiosis in late fetal life; by the time of birthe they have already entered the diplotene stage of prophase I of meiosis and becaome arrested thereafter at the dictyate state(Baker, 1972). At this stage they became surrounded by a few nonproliferating flat follicle cells forming a unit called the resting or primordial follicle.

Oocyte-secreted factors: regulators of cumulus cell function and oocyte quality

Oocyte quality is a key limiting factor in female fertility, yet we have a poor understanding of what constitutes oocyte quality or the mechanisms governing it. The ovarian follicular microenvironment and maternal signals, mediated primarily through granulosa cells (GCs) and cumulus cells (CCs), are responsible for nurturing oocyte growth, development and the gradual acquisition of oocyte developmental competence. However, oocyte-GC/CC communication is bidirectional with the oocyte secreting potent growth factors that act locally to direct the differentiation and function of CCs. Two important oocyte-secreted factors (OSFs) are growth-differentiation factor 9 and bone morphogenetic protein 15, which activate signaling pathways in CCs to regulate key genes and cellular processes required for CC differentiation and for CCs to maintain their distinctive phenotype. Hence, oocytes appear to tightly control their neighboring somatic cells, directing them to perform functions required for appropriate development of the oocyte. This oocyte-CC regulatory loop and the capacity of oocytes to regulate their own microenvironment by OSFs may constitute important components of oocyte quality. In support of this notion, it has recently been demonstrated that supplementing oocyte in vitro maturation (IVM) media with exogenous OSFs improves oocyte developmental potential, as evidenced by enhanced pre- and post-implantation embryo development. This new perspective on oocyte-CC interactions is improving our knowledge of the processes regulating oocyte quality, which is likely to have a number of applications, including improving the efficiency of clinical IVM and thereby providing new options for the treatment of infertility.

Oocyte-directed depletion of connexin43 using the Cre-LoxP system leads to subfertility in female mice

Gap junctions, predominantly comprising connexin43 (Cx43), mediate cell-to-cell communication within the ovarian follicle. However, the partaking of Cx43 in the formation of the gap junction channels, between the oocyte and the somatic cells, is controversial. We addressed this dispute by crossing females that carry a Cx43 coding region, flanked by loxP recognition sites, with males expressing the Cre recombinase under the control of Zp3 promoter. Oocytes of the resultant Zp3Cre;Gja1(lox/lox) mice did not express Cx43 and were referred to as Cx43(del/del). Unexpectedly, a decrease in Cx43 was observed in cumulus/granulosa cells of some follicles as well. Nevertheless, no histological abnormalities were detected in the ovaries of the Zp3Cre;Gja1(lox/lox) mice. Furthermore, these mice ovulated normally and developed fully functional corpora lutea. Additionally, the ovarian Cx43(del/del) oocytes were meiotically arrested and transferred Lucifer yellow to the surrounding cumulus cells. However, mating Zp3Cre;Gja1(lox/lox) females with wild-type males resulted in a reduced rate of parturition and a substantial decrease in litter size. Further examination revealed that although preimplantation development of Zp3Cre;Gja1(lox/+) embryos was normal, the blactocysts exhibited impaired implantation. Our data suggest that total ablation of Cx43 in the oocyte, combined with its decrease in the surrounding somatic cells, allows normal oogenesis and folliculogenesis, ovulation and early embryonic development but severely impairs the implantation capacity of the resulting blactocysts.

Tissue-engineered follicles produce live, fertile offspring

Oocytes grown in vitro are of low quality and yield few live births, thus limiting the ability to store or bank the ova of women wishing to preserve their fertility. We applied tissue engineering principles to the culture of immature mouse follicles by designing an alginate hydrogel matrix to maintain the oocyte's 3- dimensional (3D) architecture and cell-cell interactions in vitro. A 3D culture mimics the in vivo follicle environment, and hydrogel-encapsulated follicles develop mature oocytes within the capacity for fertilization similar to that of oocytes matured in vivo. Embryos derived from cultured oocytes fertilized in vitro and transferred to pseudopregnant female mice were viable, and both male and female offspring were fertile. Our results demonstrate that alginate hydrogel-based 3D in vitro culture of follicles permits normal growth and development of follicles and oocytes. This system creates new opportunities for discovery in follicle biology and establishes a core technology for human egg banks for preservation of fertility.

Differential regulation of steroidogenesis by bone morphogenetic proteins in granulosa cells: involvement of extracellularly regulated kinase signaling and oocyte actions in follicle-stimulating hormone-induced estrogen production

In the present study, we investigated the cellular mechanism by which oocytes and bone morphogenetic proteins (BMPs) govern FSH-induced steroidogenesis using rat primary granulosa cells. BMP-6 and BMP-7 both inhibited FSH- and forskolin (FSK)-induced progesterone synthesis and reduced cAMP synthesis independent of the presence or absence of oocytes. BMP-7 also increased FSH-induced estradiol production, and the response was further augmented in the presence of oocytes. In contrast, BMP-6 had no impact on estradiol synthesis regardless of the presence of oocytes. Because BMP-7 changed neither FSK- nor cAMP-induced estradiol production, the BMP-7 action was mediated through a FSH receptor signaling mechanism that was independent of cAMP-protein kinase A pathway. Treatment with FSH but not cAMP activated ERK1/2 phosphorylation in granulosa cells, which was further accelerated by oocytes. A specific ERK inhibitor, U0126, increased estradiol production and decreased FSH- and FSK-induced progesterone production and cAMP synthesis. This suggests that ERK activation is directly linked to inhibition of estradiol synthesis and amplification of cAMP. Moreover, FSH-induced ERK1/2 phosphorylation was inhibited by BMP-7 but not influenced by BMP-6. In contrast, BMP signaling including Smad1/5/8 phosphorylation and Id-1 transcription was up-regulated by FSH and oocytes in granulosa cells through inhibition of Smad6/7 expression. Collectively, oocytes enhance FSH-induced MAPK activation and BMP signaling in granulosa cells, which leads to differential regulation of steroidogenesis elicited by BMPs in the presence of FSH in developing follicles.

Participation of mitogen-activated protein kinase in luteinizing hormone-induced differential regulation of steroidogenesis and steroidogenic gene expression in mural and cumulus granulosa cells of mouse preovulatory follicles

The LH surge induces the terminal differentiation and onset of luteinization in granulosa cells of preovulatory follicles, a process that involves the differential expression of genes essential for steroidogenesis and appears to be mediated by complex signaling pathways. The objective of this study was to investigate whether these processes that commonly occur in mural granulosa cells (MGCs) also occur in cumulus cells, and whether they are mediated by the mitogen-activated protein kinase (MAPK), specifically MAPK3/1 (also commonly known as extracellular signal-regulated kinase 1&2, ERK1/2). The standard superovulation model for premature female mice was used to obtain MGCs and cumulus-oocyte complexes (COCs), and sensitive real-time RT-PCR was used to simultaneously detect the expression levels of transcripts encoding key steroidogenic enzymes in the same sample. We observed significant downregulation of Cyp19a1 and upregulation of Star and Cyp11a1 mRNA expression in both COCs and MGCs after in vivo administration of hCG or in vitro treatment with gonadotropins or 8-Br-cAMP. This differential pattern of steroidogenic gene expression was correlated with the ultimate changes of circulating estradiol (E(2)) and progesterone (P(4)) levels after administration of hCG. In vitro, when MGCs and COCs were treated with U0126 - a specific inhibitor of MAPK3/1 activation - gonadotropin-induced P(4) production, 8-Br-cAMP-induced P(4) production, and expression of Star and Cyp11a1 mRNA were significantly downregulated, whereas the levels of E(2) and Cyp19a1 mRNA in the same samples were significantly upregulated. We conclude that the surge of preovulatory LH induces the differential expression of transcripts encoding key steroidogenic enzymes essential for E(2) and P(4) synthesis in both cumulus and MGCs, and this process is mediated by the MAPK3/1-dependent pathway.

Molecular basis of oocyte-paracrine signalling that promotes granulosa cell proliferation

Oocytes regulate follicle growth by secreting paracrine growth factors that act on neighbouring granulosa cells (GCs). Those factors identified to date are mainly members of the transforming growth factor-beta (TGFbeta) superfamily, but little is known about which specific receptor/signalling system(s) they employ. This study was conducted to determine the requisite pathways utilised by oocytes to promote GC proliferation. We used an established oocyte-secreted mitogen bioassay, where denuded mouse oocytes are co-cultured with mural GCs. Oocytes, growth differentiation factor-9 (GDF9), TGFbeta1 and activin-A all promoted GC DNA synthesis, but bone-morphogenetic protein 6 (BMP6) did not. Subsequently, we tested the capacity of various TGFbeta superfamily receptor ectodomains (ECD) to neutralise oocyte- or specific growth factor-stimulated GC proliferation. The BMP type-II receptor (BMPR-II) ECD antagonised oocyte and GDF9 bioactivity dose-dependently, but had no or minimal effect on TGFbeta1 and activin-A bioactivity, demonstrating its specificity. The TGFbetaR-II, activinR-IIA and activinR-IIB ECDs all failed to neutralise oocyte- or GDF9-stimulated GC DNA synthesis, whereas they did antagonise the activity of their respective native ligands. An activin receptor-like kinase (ALK) 4/5/7 inhibitor, SB431542, also antagonised both oocyte and GDF9 bioactivity in a dose-dependent manner. Consistent with these findings, oocytes, GDF9 and TGFbeta1 all activated SMAD2/3 reporter constructs in transfected GC, and led to phosphorylation of SMAD2 proteins in treated cells. Surprisingly, oocytes did not activate the SMAD1/5/8 pathway in transfected GCs although exogenous BMP6 did. This study indicates that oocyte paracrine factors primarily utilise a similar signalling pathway first identified for GDF9 that employs an unusual combination of TGFbeta superfamily receptors, the BMPR-II and a SMAD2/3 stimulatory ALK (4, 5 or 7), for transmitting their mitogenic actions in GC. This cell-signalling pathway may also have relevance in the hypothalamic-pituitary axis and in germ-somatic cell interactions in the testis.

Contribution of Germ Cells to the Differentiation and Maturation of the Ovary: Insights from Models of Germ Cell Depletion

In mammals, the role played by germ cells in ovarian differentiation and folliculogenesis has been the focus of an increasing number of studies over the last decades. From these studies, it has emerged that bidirectional communication between germ cells and surrounding companion cells is required as soon as the initial assembly of follicles. Models of germ cell depletion that arise from both spontaneous and experimentally induced mutations as well as irradiation or chemical treatments have been helpful in deciphering the role played by germ cells from the onset of ovarian differentiation onward. This review reports current knowledge and proposes novel hypotheses that can be formulated from these models about the contribution of germ cells to ovarian differentiation and folliculogenesis. In particular, it promotes the idea that the influence of germ cells on companion somatic cells varies within both ovarian differentiation and folliculogenesis.

Androgens Augment the Mitogenic Effects of Oocyte-Secreted Factors and Growth Differentiation Factor 9 on Porcine Granulosa Cells1

In this study, we test the hypothesis that the growth-promoting action of androgens on granulosa cells requires paracrine signaling from the oocyte. Mural granulosa cells (MGCs) from small antral (1-3 mm) prepubertal pig follicles were cultured in the presence or absence of denuded oocytes (DO) from the same follicles to determine whether mitogenic and/or steroidogenic responses, to combinations of FSH, insulin-like growth factor 1 (IGF1), and dihydrotestosterone (DHT) were influenced by oocyte-secreted factors (OSFs). To further explore the identity of such factors we performed the same experiments, substituting growth differentiation factor 9 (GDF9), a known OSF, for the DO. OSFs and GDF9 both potently enhanced IGF1-stimulated proliferation, and inhibited FSH-stimulated progesterone secretion. Alone, DHT had little effect on DNA synthesis, but significantly enhanced the mitogenic effects of OSFs or GDF9 in the presence of IGF1. Denuded oocytes, GDF9, and DHT independently inhibited FSH-stimulated progesterone secretion, and androgen, together with DO or GDF9, caused the most potent steroidogenic inhibition. Focusing on mitogenic effects, we demonstrate that both natural androgen receptor (AR) agonists, testosterone and DHT, dose-dependently augmented the mitogenic activity of DO or GDF9. Antiandrogen (hydroxyflutamide) treatment, which is used to block androgen receptor activity, opposed the interaction between androgen and GDF9. In conclusion, androgens stimulate porcine MGC proliferation in vitro by potentiating the growth-promoting effects of oocytes or GDF9, via a mechanism that involves the AR. These signaling pathways are likely to be important regulators of folliculogenesis in vivo, and may contribute to the excess follicle growth that is observed in androgen-treated female animals.

Essential role of the oocyte in estrogen amplification of follicle-stimulating hormone signaling in granulosa cells

The establishment of dominant ovarian follicles that are capable of ovulating fertilizable oocytes is a fundamental determinant of female fertility. This process is governed by pituitary gonadotropins as well as local ovarian factors. Within the follicle, estrogen acts in an autocrine/paracrine manner to enhance FSH action in the granulosa cells. These effects include the augmentation of P450aromatase expression and estradiol production. This feed-forward effect of estrogen is believed to play a key role in follicle dominance. Here we found the essential role of the oocyte in this physiological process using primary cultures of rat granulosa cells. In the presence, but not absence, of oocytes, estrogen amplified FSH-stimulated increases in mRNA expression of P450aromatase, FSH receptor, LH receptor, and inhibin alpha-, betaA-, and betaB-subunits as well as cAMP production. Thus, oocytes mediate the estrogen enhancement of FSH action in the granulosa cells. In comparison with FSH, cotreatment with estrogen and oocytes failed to amplify the stimulatory effects of forskolin or 8-bromoadenosine-cAMP on granulosa cell responses including P450aromatase mRNA expression and cAMP production, indicating that estrogen/oocytes amplify FSH action at a site upstream of adenylate cyclase. These findings support the novel conclusion that communication between the oocyte and granulosa cells plays a crucial role in mediating estrogen action during FSH-dependent folliculogenesis.

Role of oocyte-secreted growth differentiation factor 9 in the regulation of mouse cumulus expansion

Oocyte-secreted factors are required for expansion of the mouse cumulus-oocyte complex, which is necessary for ovulation. Oocyte-secreted growth differentiation factor 9 (GDF9) signals through the bone morphogenetic protein receptor II and is currently the primary candidate molecule for the cumulus-expansion enabling factor. This study was conducted to determine whether GDF9 is the mouse cumulus-expansion enabling factor. Cumulus-oocyte complexes were collected from mice, and the oocyte was microsurgically removed to generate an oocytectomized (OOX) complex. OOX complexes treated with FSH alone or recombinant mouse GDF9 alone failed to expand, whereas expansion was induced in the presence of FSH by GDF9, TGFbeta1, or coculture with oocytes. A specific GDF9-neutralizing antibody, mAb-GDF9-53, neutralized the expansion of OOX complexes in response to GDF9 but not the expansion of OOX complexes cocultured with oocytes. Using real-time RT-PCR, hyaluronan synthase 2 (HAS2) mRNA expression by OOXs was up-regulated 4- to 6-fold by oocytes and GDF9. Monoclonal neutralizing antibody-GDF9-53 attenuated GDF9-induced OOX HAS2 expression but not oocyte-induced HAS2 expression. A TGFbeta antagonist neutralized TGFbeta-induced, but not oocyte-induced, expansion of OOX complexes, and when combined with monoclonal neutralizing antibody-GDF9-53 also failed to neutralize oocyte-induced expansion. Furthermore, a soluble portion of the bone morphogenetic protein receptor II extracellular domain, which is a known GDF9 antagonist, completely antagonized GDF9-induced expansion but only partially neutralized oocyte-induced expansion. This study provides further evidence that like TGFbeta, GDF9 can enable FSH-induced cumulus expansion, but more importantly, demonstrates that neither GDF9 nor TGFbeta alone, nor the two in unison, account for the critical oocyte-secreted factors regulating mouse cumulus expansion.

Localization and gene expression of steroid sulfatase by RT-PCR in cumulus cells and relationship to serum FSH levels observed during in vitro fertilization

Background

The purpose of this study was to localize the expression of steroid sulfatase (STS) in cumulus cells and to determine the relationship between STS mRNA expression and the serum levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol and progesterone.

Methods

The subject group included 49 women (29 to 44 years old) for whom in vitro fertilization treatment was indicated. All subjects gave informed consent. One hundred fourteen samples of cumulus-oocyte complex (COC) were obtained under microscopic observation. Part of the COC was stained by STS antibody. RNA was extracted by phenol-chloroform method and real-time PCR was performed. Serum of each patient was collected and was measured by ELISA.

Results

Some of the cumulus samples were stained by STS antibody. The expression of STS mRNA in all samples was confirmed by quantitative RT-PCR. Although there was no significant correlation between the level of STS mRNA and the serum levels of estradiol, progesterone and LH, there was a statistically significant negative correlation between the level of STS mRNA expression and the serum level of FSH (n = 105, p = 0.018, r = -0.22).

Conclusion

These results have demonstrated for the first time the expression of STS in cumulus cells by immunohistological stainings and real-time RT-PCR. STS expression in cumulus cells may be related to the control of the local steroidal environment in the oocyte. Serum FSH may control STS mRNA expression from the results of RT-PCR, although the correlation was low.

Expression of Growth Differentiation Factor 9 Messenger RNA in Porcine Growing and Preovulatory Ovarian Follicles1

We have shown previously that porcine cumulus and mural granulosa cells produce a factor that is very similar, if not identical, to the oocyte-derived cumulus expansion-enabling factor (CEEF). Because growth differentiation factor 9 (GDF9) is the most likely candidate for the CEEF, in the present study we tested the hypothesis that GDF9 is expressed not only in oocytes in the pig but also in somatic follicular cells. In addition, we asked whether the relative abundance (RA) of GDF9 mRNA changes in oocytes and/or follicular cells during the periovulatory period or culture of oocyte-cumulus complexes (OCCs) in vitro. Denuded oocytes, OCCs, cumulus, and mural granulosa cells were isolated from growing and preovulatory follicles. Total RNA was extracted from the cells, and reverse transcription-polymerase chain reaction (RT-PCR) was carried out using specific oligonucleotide primers. The RT-PCR resulted in amplification of a product of expected size (277 base pairs) in samples prepared from all follicular cell types. The identity of the RT-PCR products with GDF9 was confirmed by analysis of their nucleotide sequence, which was 88% and 91% identical to human and ovine GDF9, respectively. The RA of GDF9 mRNA in the somatic follicular cells was approximately fourfold lower than in oocytes. Assessment of the RA of GDF9 mRNA during the periovulatory period and during culture and expansion of OCCs in vitro revealed that it remained stable in oocytes and mural granulosa cells and decreased significantly in expanding cumulus cells. We conclude that GDF9 mRNA can be produced by somatic follicular cells in the pig and that cumulus expansion is not preceded or accompanied by an increase in the RA of GDF9 mRNA in any of the tested cell types.

Immunoneutralization of Growth Differentiation Factor 9 Reveals It Partially Accounts for Mouse Oocyte Mitogenic Activity1

Paracrine factors secreted by oocytes play a pivotal role in promoting early ovarian follicle growth and in defining a morphogenic gradient in antral follicles, yet the exact identities of these oocyte factors remain unknown. This study was conducted to determine the extent to which the mitogenic activity of mouse oocytes can be attributed to growth differentiation factor 9 (GDF9). To do this, specific anti-human GDF9 monoclonal antibodies were generated. Based on epitope mapping and bioassays, a GDF9 neutralizing antibody, mAb-GDF9-53, was characterized with very low cross-reactivity with related transforming growth factor (TGF)beta superfamily members, including BMP15 (also called GDF9B). Pep-SPOT epitope mapping showed that mAb-GDF9-53 recognizes a short 4-aa sequence, and three-dimensional peptide modeling suggested that this binding motif lies at the C-terminal fingertip of mGDF9. As predicted by sequence alignments and modeling, the antibody detected recombinant GDF9, but not BMP15 in a Western blot and GDF9 protein in oocyte extract and oocyte-conditioned medium. In a mouse mural granulosa cell (MGC) bioassay, mAb-GDF9-53 completely abolished the mitogenic effects of GDF9, but had no effect on TGFbeta1 or activin A-stimulated MGC proliferation. An unrelated IgG at the same dose had no effect on GDF9 activity. This GDF9 neutralizing antibody was then tested in an established oocyte-secreted mitogen bioassay, where denuded oocytes cocultured with granulosa cells promote cell proliferation in a dose-dependent manner. The mAb-GDF9-53 dose dependently (0-160 microg/ml) decreased the mitogenic activity of oocytes but only by approximately 45% at the maximum dose of mAb. Just 5 microg/ml of mAb-GDF9-53 neutralized 90% of recombinant mGDF9 mitogenic activity, but only 15% of oocyte activity. Unlike mAb-GDF9-53, a TGFbeta pan-specific neutralizing antibody did not affect the mitogenic capacity of the oocyte, but completely neutralized TGF beta 1-induced DNA synthesis. This study has characterized a specific GDF9 neutralizing antibody. Our data provide the first direct evidence that the endogenous GDF9 protein is an important oocyte-secreted mitogen, but also show that GDF9 accounts for only part of total oocyte bioactivity.

A Novel PEPP Homeobox Gene, TOX, Is Highly Glutamic Acid Rich and Specifically Expressed in Murine Testis and Ovary1

The homeobox gene superfamily has been highly conserved throughout evolution. These genes act as transcription factors during several important developmental processes. To explore the functional roles of homeobox genes in spermatogenesis, we performed a degenerate oligonucleotide polymerase chain reaction (PCR) screening of a testis cDNA library and isolated a novel mouse homeobox gene. This gene, which we named Tox, encodes a homeodomain protein distantly related to members of the Paired/Pax (Prd/Pax) family. A phylogenetic analysis revealed Tox to be a member of the recently defined PEPP subfamily of Paired-like homeobox genes. Tox was mapped to chromosome X, with its homeodomain organized into three exons. A special feature of Tox is that the encoded protein sequence contains two poly-glutamic acid (poly E) stretches, which make Tox highly acidic. Tox transcripts were detected predominately in the testis and ovary of mice. Tox expression in testes was initiated soon after birth, mainly in Sertoli cells and spermatogonia; however, in adult mice, Tox expression shifts to the spermatids and spermatozoa. Tox expression in ovaries was detected in somatic cells of follicles, early on in theca cells, and in both granulosa and theca cells at the later stages of follicular development. Based on these results, Tox may play an important role during gametogenesis.

Correlations between steroids concentration in follicular fluid, pronuclear morphology and embryo qualities in in vitro fertilization

Background:  Several parameters of early embryo development are known as predictors of implantation success. Recently, zygote or embryo morphological assessments are thought to be a major method of selection in embryo transfer. We expected that the concentrations of the steroids in follicular fluid (FF) were associated with oocyte maturation and embryo quality. In the present paper, we evaluated the relationship of several parameters. Methods:  We investigated 105 samples of FF from 22 subjects by in vitro fertilization (IVF). We evaluated the correlations between the FF concentrations of estradiol (E₂) and progesterone (P₄), the diameter of the ovarian follicles, fertilization, and zygote assessment based on pronuclear morphology and day 3 embryo qualities (i.e. number of blastomeres and fragmentation rate). Results:  There was a positive correlation between the E₂ concentrations in FF and serum (r = 0.273, P < 0.01), but there was no correlation between follicular diameter and the FF concentration of each steroid. The concentration of E₂ in FF containing fertilized oocytes was not significantly different from that in FF containing unfertilized oocytes. At the pronuclear stage, the concentration of either steroid in FF did not differ among the morphological groups. The concentration of P₄ in FF was significantly lower in the group in which pronuclei were detected at 20 h after insemination than in the group in which pronuclei were not detected. The concentration of E₂ in FF was significantly related to the number of blastomeres (r = 0.271, P < 0.05) and furthermore, was significantly higher in FF from which morphologically good embryos were obtained at day 3 (P < 0.05). Conclusions:  The FF concentrations of the steroids did not affect the pronuclear pattern, but P₄ production may play a role in reducing the potential of the oocyte to develop pronuclei and the concentration of E₂ may predict the cleavage capability of the oocyte. (Reprod Med Biol 2003; 2: 171-176).

Plasma membrane channels formed by connexins: their regulation and functions

Members of the connexin gene family are integral membrane proteins that form hexamers called connexons. Most cells express two or more connexins. Open connexons found at the nonjunctional plasma membrane connect the cell interior with the extracellular milieu. They have been implicated in physiological functions including paracrine intercellular signaling and in induction of cell death under pathological conditions. Gap junction channels are formed by docking of two connexons and are found at cell-cell appositions. Gap junction channels are responsible for direct intercellular transfer of ions and small molecules including propagation of inositol trisphosphate-dependent calcium waves. They are involved in coordinating the electrical and metabolic responses of heterogeneous cells. New approaches have expanded our knowledge of channel structure and connexin biochemistry (e.g., protein trafficking/assembly, phosphorylation, and interactions with other connexins or other proteins). The physiological role of gap junctions in several tissues has been elucidated by the discovery of mutant connexins associated with genetic diseases and by the generation of mice with targeted ablation of specific connexin genes. The observed phenotypes range from specific tissue dysfunction to embryonic lethality.

Paracrine effects of oocyte secreted factors and stem cell factor on porcine granulosa and theca cells in vitro

Oocyte control of granulosa and theca cell function may be mediated by several growth factors via a local feedback loop(s) between these cell types. This study examined both the role of oocyte-secreted factors on granulosa and thecal cells, cultured independently and in co-culture, and the effect of stem cell factor (SCF); a granulosa cell derived peptide that appears to have multiple roles in follicle development. Granulosa and theca cells were isolated from 2-6 mm healthy follicles of mature porcine ovaries and cultured under serum-free conditions, supplemented with: 100 ng/ml LR3 IGF-1, 10 ng/ml insulin, 100 ng/ml testosterone, 0-10 ng/ml SCF, 1 ng/ml FSH (granulosa), 0.01 ng/ml LH (theca) or 1 ng/ml FSH and 0.01 ng/ml LH (co-culture) and with/without oocyte conditioned medium (OCM) or 5 oocytes. Cells were cultured in 96 well plates for 144 h, after which viable cell numbers were determined. Medium was replaced every 48 h and spent medium analysed for steroids. Oocyte secreted factors were shown to stimulate both granulosa cell proliferation (P < 0.001) and oestradiol production (P < 0.001) by granulosa cells throughout culture. In contrast, oocyte secreted factors suppressed granulosa cell progesterone production after both 48 and 144 hours (P < 0.001). Thecal cell numbers were increased by oocyte secreted factors (P = 0.02), together with a suppression in progesterone and androstenedione synthesis after 48 hours (P < 0.001) and after 144 hours (P = 0.02), respectively. Oocyte secreted factors also increased viable cell numbers (P < 0.001) in co-cultures together with suppression of progesterone (P < 0.001) and oestradiol (P < 0.001). In granulosa cell only cultures, SCF increased progesterone production in a dose dependent manner (P < 0.001), whereas progesterone synthesis by theca cells was reduced in a dose dependent manner (P = 0.002). Co-cultured cells demonstrated an increase in progesterone production with increasing SCF dose (P < 0.001) and an increase in oestradiol synthesis at the highest dose of SCF (100 ng/ml). In summary, these findings demonstrate the presence of a co-ordinated paracrine interaction between somatic cells and germ cells, whereby oocyte derived signals interact locally to mediate granulosa and theca cell function. SCF has a role in modulating this local interaction. In conclusion, the oocyte is an effective modulator of granulosa-theca interactions, one role being the inhibition of luteinization.