Functional and Molecular Characterization of Naturally Occurring Mutations in the Oocyte-secreted Factors Bone Morphogenetic Protein-15 and Growth and Differentiation Factor-9

Molecular forms of BMP15 and GDF9 in mammalian species that differ in litter size

Bone morphogenetic protein (BMP15) and growth differentiation factor (GDF9) are critical for ovarian follicular development and fertility and are associated with litter size in mammals. These proteins initially exist as pre-pro-mature proteins, that are subsequently cleaved into biologically active forms. Thus, the molecular forms of GDF9 and BMP15 may provide the key to understanding the differences in litter size determination in mammals. Herein, we compared GDF9 and BMP15 forms in mammals with high (pigs) and low to moderate (sheep) and low (red deer) ovulation-rate. In all species, oocyte lysates and secretions contained both promature and mature forms of BMP15 and GDF9. Whilst promature and mature GDF9 levels were similar between species, deer produced more BMP15 and exhibited, together with sheep, a higher promature:mature BMP15 ratio. N-linked glycosylation was prominant in proregion and mature GDF9 and in proregion BMP15 of pigs, and present in proregion GDF9 of sheep. There was no evidence of secreted native homo- or hetero-dimers although a GDF9 dimer in red deer oocyte lysate was detected. In summary, GDF9 appeared to be equally important in all species regardless of litter size, whilst BMP15 levels were highest in strict monovulatory species.

Genome-Wide Identification of a Regulatory Mutation in BMP15 Controlling Prolificacy in Sheep

The search for the genetic determinism of prolificacy variability in sheep has evidenced several major mutations in genes playing a crucial role in the control of ovulation rate. In the Noire du Velay (NV) sheep population, a recent genetic study has evidenced the segregation of such a mutation named FecL L . However, based on litter size (LS) records of FecL L non-carrier ewes, the segregation of a second prolificacy major mutation was suspected in this population. In order to identify this mutation, we have combined a case/control genome-wide association study with ovine 50k SNP chip genotyping, whole genome sequencing, and functional analyses. A new single nucleotide polymorphism (OARX:50977717T > A, NC_019484) located on the X chromosome upstream of the BMP15 gene was evidenced to be highly associated with the prolificacy variability (P = 1.93E-11). The variant allele was called FecX N and shown to segregate also in the Blanche du Massif Central (BMC) sheep population. In both NV and BMC, the FecX N allele frequency was estimated close to 0.10, and its effect on LS was estimated at +0.20 lamb per lambing at the heterozygous state. Homozygous FecX N carrier ewes were fertile with increased prolificacy in contrast to numerous mutations affecting BMP15. At the molecular level, FecX N was shown to decrease BMP15 promoter activity and supposed to impact BMP15 expression in the oocyte. This regulatory action was proposed as the causal mechanism for the FecX N mutation to control ovulation rate and prolificacy in sheep.

Role of certain growth factors and hormones in folliculogenesis

Folliculogenesis is an inextricable process associated with female fertility and infertility cases. This process involves many events at cellular and molecular level in a highly orchestrated fashion which culminates with ovulation. Various factors like hormonal factors, growth factors, role of ovarian micro environment, diseases of reproductive tract etc. influence the process of folliculogenesis in systematic manner. The function and mechano-biology of these growth factors and hormones have been studied by many researchers. This review discusses about those hormonal and growth factors which are involved in folliculogenesis process.

Impairment of ovaries by 2,3,7,8-tetrachlorobenzo-p-dioxin (TCDD) exposure in utero associated with BMP15 and GDF9 in the female offspring rat

2,3,7,8-Tetrachlorobenzo-p-dioxin (TCDD) exposure in utero had been shown to affect ovarian development and functions. However, its mechanism remained unknown. In this study, to investigate the effect of maternal exposure to TCDD on ovaries, the pregnant Sprague Dawley (SD) rats were treated with TCDD (100 ng/kg or 500 ng/kg) or only vehicle and corn oil on the day 8-14 of gestation through the gavage with a stainless-steel feeding needle (once a day). The vaginal opening and estrous cycle of female offspring rats (F1) were monitored twice a day. The ovarian histology, follicle counts, real-time PCR, western blotting and DNA methylation analysis about Gdf9 and Bmp15 were carried out in F1 rats. The results showed that exposure to TCDD (especially the dose of 500 ng/kg) in utero on GD8-14 might change the ovary weight, the concentration of E2 and FSH, the estrous cycles and the numbers of primordial and secondary follicles of the offspring rats. In addition, the mRNA and protein expression of GDF9 and BMP15 was down-regulated, while the methylation patterns of Gdf9 and Bmp15 were not affected. In conclusion, maternal exposure to TCDD could affect the ovary development and functions which were possibly associated with down-regulation of mRNA and protein expression of GDF9 and BMP15. However, the down-regulation was not related to the pattern of methylation of Gdf9 and Bmp15.

MicroRNA-21 plays a pivotal role in the oocyte-secreted factor-induced suppression of cumulus cell apoptosis

It is known that oocytes and cumulus cells (CCs) are more resistant to apoptosis than other compartments of the antral follicle. However, although oocyte-secreted factors (OSFs) have been found to be involved in suppressing bovine CC apoptosis, little is known about the intracellular mechanisms by which OSFs render CCs resistant to apoptosis. Here, we show that coculture with mouse or pig cumulus-denuded oocytes, culture with recombinant mouse growth differentiation factor-9 (GDF-9), or culture in pig oocyte-conditioned medium (POCM) significantly inhibited CC apoptosis of mouse oocytectomized cumulus oophorus complexes (OOXs). The POCM contained both GDF-9 and bone morphogenetic protein-15, and their levels remained constant during culture of OOXs. The level of microRNA-21 (miR-21) was significantly lower in OOXs than in COCs after culture in a simplified α-MEM medium, but increased significantly when OOXs were cultured with GDF-9 or in POCM. The level of miR-21 in OSF-treated CCs was correlated with that of Dicer1 but not that of Drosha mRNA. Inhibiting activin receptor-like kinase 5 or SMAD3 completely abolished the beneficial effects of GDF-9 or POCM on CC apoptosis and miR-21 levels. Up- and downregulating miR-21 expression significantly reduced and increased CC apoptosis, respectively. The OSF-upregulated miR-21 expression suppressed CC apoptosis with activation of the PI3K/Akt signaling. In conclusion, miR-21 plays a pivotal role in the OSF suppression of CC apoptosis. OSFs upregulated miR-21 expression through the TGF-β superfamily signaling, which worked through DICER. MicroRNA-21 prevented apoptosis via the PI3K/Akt signaling.

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.

α-SNAP is expressed in mouse ovarian granulosa cells and plays a key role in folliculogenesis and female fertility

The balance between ovarian folliculogenesis and follicular atresia is critical for female fertility and is strictly regulated by a complex network of neuroendocrine and intra-ovarian signals. Despite the numerous functions executed by granulosa cells (GCs) in ovarian physiology, the role of multifunctional proteins able to simultaneously coordinate/modulate several cellular pathways is unclear. Soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein (α-SNAP) is a multifunctional protein that participates in SNARE-mediated membrane fusion events. In addition, it regulates cell-to-cell adhesion, AMPK signaling, autophagy and apoptosis in different cell types. In this study we examined the expression pattern of α-SNAP in ovarian tissue and the consequences of α-SNAP (M105I) mutation (hyh mutation) in folliculogenesis and female fertility. Our results showed that α-SNAP protein is highly expressed in GCs and its expression is modulated by gonadotropin stimuli. On the other hand, α-SNAP-mutant mice show a reduction in α-SNAP protein levels. Moreover, increased apoptosis of GCs and follicular atresia, reduced ovulation rate, and a dramatic decline in fertility is observed in α-SNAP-mutant females. In conclusion, α-SNAP plays a critical role in the balance between follicular development and atresia. Consequently, a reduction in its expression/function (M105I mutation) causes early depletion of ovarian follicles and female subfertility.

BMP15 in catfish testis: Cellular distribution, seasonal variation, and its role in steroidogenesis

Considering the absence of information on testicular growth factors in fishes, present study was aimed to elucidate the existence of BMP15, an important member of TGF-β superfamily, in the testis of a seasonally breeding freshwater catfish, Clarias batrachus and its role in regulation of testicular activities. The study demonstrated the expression of BMP15 in the somatic cells (Sertoli and interstitial cells) in fish testis. The expression varied with changing testicular activity; the expression was very high in the quiescent and early recrudescing testis coinciding with the renewal of spermatogonial cells. Expression then declined gradually with progression of spermatogenesis and steroidogenesis. Expression of BMP15 showed positive correlation with seasonally changing testicular 17β-estradiol but negatively with testicular testosterone and 11-ketotestosterone. In vitro treatment of testis with recombinant human BMP15 enhanced the production of estradiol-17β but concurrently suppressed the production of testosterone and 11-ketotestosterone in testis. Though BMP15 did not alter the expression of StAR protein in the testis, it promoted the expression of 3β-hydroxysteroid dehydrogenase and aromatase in fish testis. Thus the present study for the first time demonstrates that fish testis is capable of producing BMP15 and is expressed by the somatic cells unlike mammals wherein it is produced exclusively by germ cells. Study also suggests that BMP15 may modulate the testicular steroidogenesis by altering the expression of steroidogenic enzymes. BMP15 also appears to play crucial role in renewal of spermatogial cells by augmenting the testicular production of 17β-estradiol.

Survey of mutations in prolificacy genes in Santa Ines and Morada Nova sheep

ABSTRACT Polymorphisms in the BMP-15 gene related to Galway (FecXG) and Inverdale (FecXI) and in the BMPR-1B gene known as Booroola (FecB) mutations were investigated using the Polymerase Chain Reaction - Restriction Fragment Length Polymorphism (PCR-RFLP) method, on sheep from the breeds Santa Inês (n= 574) and Morada Nova (n=282). DNA was extracted and amplified through PCR with specific primers that introduced a restriction site in association with the mutation. The PCR products were submitted to endonucleases. The experiment found no FecXG and FecXI mutations. Six samples of animals with multiple offspring/birth history presented polymorphism for FecB similar to control samples, but this pattern was not confirmed by nucleotide sequencing. Although the absence of these mutations in the studied breeds, other factors related to prolificacy should be investigated to explain the inherent prolificity mechanisms.

Genetic polymorphism of growth differentiation factor 9 (GDF9) gene related to fecundity in two Egyptian sheep breeds

PURPOSE

This study explores polymorphisms in the growth differentiation factor 9 (GDF9) gene (exon 1) with respect to fertility in Egyptian sheep.

METHODS

Blood samples were collected, and genomic DNA was extracted from 24 Saidi and 13 Ossimi ewes. A 710 bp portion of the GDF9 gene, was amplified using specific primers, and the sequence was analyzed to clarify the phylogenetic relationship of Egyptian breed sheep. In addition, the PCR-RFLP method using Pst1 or Msp1 restriction enzymes was used to mask polymorphisms of partial exon 1 of GDF9 gene to establish molecular markers for twinning.

RESULTS

The lambing rate percentage and litter size showed significant difference between ewes, which produce single and twin lamb for each breed individually, whereas the coefficient of variation of the Saidi breed is greater than that of the Ossimi breed. The results suggested that the GDF9 gene shared a similarity in sequence compared to six accession numbers of Ovis aries found in GenBank. Molecular phylogenetic analyses were performed based on nucleotide sequences in order to examine the position of the Egyptian breeds among many other sheep breeds. The results indicate that accession number AF078545 of O. aries is closely related with Saidi and Ossimi ewes that produce single or twin lamb using the unweighted pair group method with arithmetic mean (UPGMA) analysis. Results showed that Msp1 enzyme digestion revealed polymorphic restriction pattern consisting of one band with 710 bp for ewes producing single lamb and two bands with 710 and 600 bp for ewes producing twin lamb in Saidi sheep breed.

CONCLUSION

Sequence analysis and diversity of polymorphisms in the GDF9 gene (exon 1) have a novel base substitution (A-T) for detection of Fec^G mutations that serve as a molecular marker for twinning.

Oocyte-somatic cell interactions in the human ovary-novel role of bone morphogenetic proteins and growth differentiation factors

BACKGROUND

Initially identified for their capability to induce heterotopic bone formation, bone morphogenetic proteins (BMPs) are multifunctional growth factors that belong to the transforming growth factor β superfamily. Using cellular and molecular genetic approaches, recent studies have implicated intra-ovarian BMPs as potent regulators of ovarian follicular function. The bi-directional communication of oocytes and the surrounding somatic cells is mandatory for normal follicle development and oocyte maturation. This review summarizes the current knowledge on the physiological role and molecular determinants of these ovarian regulatory factors within the human germline-somatic regulatory loop.

OBJECTIVE AND RATIONALE

The regulation of ovarian function remains poorly characterized in humans because, while the fundamental process of follicular development and oocyte maturation is highly similar across species, most information on the regulation of ovarian function is obtained from studies using rodent models. Thus, this review focuses on the studies that used human biological materials to gain knowledge about human ovarian biology and disorders and to develop strategies for preventing, diagnosing and treating these abnormalities.

SEARCH METHODS

Relevant English-language publications describing the roles of BMPs or growth differentiation factors (GDFs) in human ovarian biology and phenotypes were comprehensively searched using PubMed and the Google Scholar database. The publications included those published since the initial identification of BMPs in the mammalian ovary in 1999 through July 2016.

OUTCOMES

Studies using human biological materials have revealed the expression of BMPs, GDFs and their putative receptors as well as their molecular signaling in the fundamental cells (oocyte, cumulus/granulosa cells (GCs) and theca/stroma cells) of the ovarian follicles throughout follicle development. With the availability of recombinant human BMPs/GDFs and the development of immortalized human cell lines, functional studies have demonstrated the physiological role of intra-ovarian BMPs/GDFs in all aspects of ovarian functions, from follicle development to steroidogenesis, cell–cell communication, oocyte maturation, ovulation and luteal function. Furthermore, there is crosstalk between these potent ovarian regulators and the endocrine signaling system. Dysregulation or naturally occurring mutations within the BMP system may lead to several female reproductive diseases. The latest development of recombinant BMPs, synthetic BMP inhibitors, gene therapy and tools for BMP-ligand sequestration has made the BMP pathway a potential therapeutic target in certain human fertility disorders; however, further clinical trials are needed. Recent studies have indicated that GDF8 is an intra-ovarian factor that may play a novel role in regulating ovarian functions in the human ovary.

WIDER IMPLICATIONS

Intra-ovarian BMPs/GDFs are critical regulators of folliculogenesis and human ovarian functions. Any dysregulation or variations in these ligands or their receptors may affect the related intracellular signaling and influence ovarian functions, which accounts for several reproductive pathologies and infertility. Understanding the normal and pathological roles of intra-ovarian BMPs/GDFs, especially as related to GC functions and follicular fluid levels, will inform innovative approaches to fertility regulation and improve the diagnosis and treatment of ovarian disorders.

Conversion of Goat Fibroblasts into Lineage-Specific Cells Using a Direct Reprogramming Strategy

Direct reprogramming is an efficient strategy to convert one cell type to another. In this study, due to the failure of maintaining the undifferentiated state of goat embryotic stem- and induced pluripotent stem-like cells in vitro, we explored an alternative way to directly convert goat fibroblasts to lineage-specific cells. The 'Yamanaka factors' was ectopically expressed in fibroblasts for a short term to situate cells in a metastable state. By culturing with lineage-specific media for 1-2 weeks, the cardiomyocyte-like cells and neurocyte-like cells were generated and confirmed by the quantitative RT-PCR and immunocytochemical staining. The metastable-state cells could also be converted into oocyte-like cells (OLCs) after culturing in media with retinoic acid (RA) and bovine follicular fluid (bFF) for 2-3 weeks. The generated OLCs were surrounded by cumulus granulosa cell-like cells and formed a structure resembling goat cumulus-oocyte complex from ovaries. This primary follicular structure could be developed further in oocyte mature medium and expressed germ cell-specific markers. In addition, we found that the induction efficiency was higher and OLC cell size was bigger in bFF than in RA treatment. Altogether, the direct reprogramming of goat fibroblasts into lineage-specific cells can facilitate stem cell research in domestic animals.

Growth and differentiation factor 9 promotes oocyte growth at the primary but not the early secondary stage in three-dimensional follicle culture

PURPOSE

Factors that differentially regulate oocyte and granulosa cell growth within the early preantral follicle and how these factors differ at each stage of follicle growth remain poorly understood. The aim of this study was to isolate and evaluate the effect of recombinant growth and differentiation factor 9 (GDF9) on oocyte and granulosa cell growth at the primary and early secondary stages of preantral follicle growth during in vitro culture.

METHODS

Primary stage follicles (diameters of 50-89 μm) and early secondary stage follicles (diameters of 90-120 μm) were isolated from immature mice, and individual, intact follicles were cultured in vitro in the presence and absence of recombinant GDF9. The effects of GDF9 on follicle growth were determined by the assessment of changes in the follicle volume during culture. The growth of the granulosa cell and oocyte compartments of the follicles was evaluated separately at each stage.

RESULTS

GDF9 significantly increased the growth of isolated follicles at both the primary and early secondary follicle stages. Independent evaluation of the granulosa cell and oocyte compartments revealed that, while GDF9 promoted granulosa cell growth at both stages of folliculogenesis, oocyte growth was stage specific. GDF9 promoted growth of the oocyte at the primary, but not the early secondary, follicle stage.

CONCLUSIONS

These findings demonstrate a stage-specific role for GDF9 in the regulation of oocyte and granulosa cell growth at the primary and early secondary stages of preantral follicle development.

Driving folliculogenesis by the oocyte-somatic cell dialog: Lessons from genetic models

This review focuses on the role of the dialog between the oocyte and its companion somatic cells in driving folliculogenesis from the primordial to the preovulatory follicle stage. Mouse and sheep genetic models have brought complementary evidence of these cell interactions and their consequences for ovarian function. In mouse, the deletion of genes encoding connexins has shown that functional gap junction channels between oocytes and granulosa cells and between granulosa cells themselves maintain the follicle in a functionally integrated state. Targeted deletions in oocytes or granulosa cells have revealed the cell- and stage-specific role of ubiquist factors belonging to the phosphatidylinositol 3 kinase signaling pathway in primordial follicle activation, oocyte growth and follicle survival. Various models of transgenic mice and sheep carrying natural loss-of-function mutations associated with sterility have established that the oocyte-derived factors, bone morphogenetic protein (BMP) 15 and growth differentiation factor 9 orchestrate follicle development, support cumulus metabolism and maturation and participate in oocyte meiosis arrest. Unexpectedly in sheep, mutations resulting in the attenuation of BMP signaling lead to enhanced ovulation rate, likely resulting from a lowered follicular atresia rate and the enhancement of FSH-regulated follicular maturation. Both the activation level of BMP signaling and an adequate equilibrium between BMP15 and growth differentiation factor 9 determine follicle survival, maturation, and development toward ovulation. The physiological approaches which were implemented on genetic animal models during the last 20 years have opened up new perspectives for female fertility by identifying the main signaling pathways of the oocyte-somatic cell dialog.

Kisspeptin receptor haplo-insufficiency causes premature ovarian failure despite preserved gonadotropin secretion

Premature ovarian failure (POF) affects 1% of women in reproductive age, but its etiology remains uncertain. Whereas kisspeptins, the products of Kiss1 that act via Kiss1r (aka, Gpr54), are known to operate at the hypothalamus to control GnRH/gonadotropin secretion, additional actions at other reproductive organs, including the ovary, have been proposed. Yet, their physiological relevance is still unclear. We present here a series of studies in Kiss1r haplo-insufficient and null mice suggesting a direct role of kisspeptin signaling in the ovary, the defect of which precipitates a state of primary POF. Kiss1r hypomorph mice displayed a premature decline in ovulatory rate, followed by progressive loss of antral follicles, oocyte loss, and a reduction in all categories of preantral follicles. These alterations were accompanied by reduced fertility. Because of this precocious ovarian ageing, mice more than 48 weeks of age showed atrophic ovaries, lacking growing follicles and corpora lutea. This phenomenon was associated with a drop in ovarian Kiss1r mRNA expression, but took place in the absence of a decrease in circulating gonadotropins. In fact, FSH levels increased in aged hypomorph animals, reflecting loss of follicular function. In turn, Kiss1r-null mice, which do not spontaneously ovulate and have arrested follicular development, failed to show normal ovulatory responses to standard gonadotropin priming and required GnRH prestimulation during 1 week in order to display gonadotropin-induced ovulation. Yet, the magnitude of such ovulatory responses was approximately half of that seen in control immature wild-type animals. Altogether, our data are the first to demonstrate that Kiss1r haplo-insufficiency induces a state of POF, which is not attributable to defective gonadotropin secretion. We also show that the failure of follicular development and ovulation linked to the absence of Kiss1r cannot be fully rescued by (even extended) gonadotropin replacement. These findings suggest a direct ovarian role of kisspeptin signaling, the perturbation of which may contribute to the pathogenesis of POF.

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.

Using sheep lines with mutations in single genes to better understand ovarian function

Livestock populations have been subjected to strong selection pressure to improve reproductive success, and this has led to the identification of lines of animals with increased fecundity. These animals provide a rich biological resource for discovery of genes and regulatory mechanisms that underpin improved reproductive success. To date, three genes, all related to the transforming growth factor β pathway, have been identified as having mutations that lead to alterations in ovulation in sheep. In addition, several other sheep lines have been identified with putative mutations in single genes with major effects on ovulation rate. This review is focused on the identification of the mutations affecting ovulation rate and how these discoveries have provided new insights into control of ovarian function.

Genome-wide association studies identify two novel BMP15 mutations responsible for an atypical hyperprolificacy phenotype in sheep

Some sheep breeds are naturally prolific, and they are very informative for the studies of reproductive genetics and physiology. Major genes increasing litter size (LS) and ovulation rate (OR) were suspected in the French Grivette and the Polish Olkuska sheep populations, respectively. To identify genetic variants responsible for the highly prolific phenotype in these two breeds, genome-wide association studies (GWAS) followed by complementary genetic and functional analyses were performed. Highly prolific ewes (cases) and normal prolific ewes (controls) from each breed were genotyped using the Illumina OvineSNP50 Genotyping Beadchip. In both populations, an X chromosome region, close to the BMP15 gene, harbored clusters of markers with suggestive evidence of association at significance levels between 1E(-05) and 1E(-07). The BMP15 candidate gene was then sequenced, and two novel non-conservative mutations called FecX(Gr) and FecX(O) were identified in the Grivette and Olkuska breeds, respectively. The two mutations were associated with the highly prolific phenotype (p FecX (Gr) = 5.98E(-06) and p FecX(O) = 2.55E(-08)). Homozygous ewes for the mutated allele showed a significantly increased prolificacy (FecX(Gr)/FecX(Gr), LS = 2.50 ± 0.65 versus FecX(+)/FecX(Gr), LS = 1.93 ± 0.42, p<1E(-03) and FecX(O)/FecX(O), OR = 3.28 ± 0.85 versus FecX(+)/FecX(O), OR = 2.02 ± 0.47, p<1E(-03)). Both mutations are located in very well conserved motifs of the protein and altered the BMP15 signaling activity in vitro using a BMP-responsive luciferase test in COV434 granulosa cells. Thus, we have identified two novel mutations in the BMP15 gene associated with increased LS and OR. Notably, homozygous FecX(Gr)/FecX(Gr) Grivette and homozygous FecX(O)/FecX(O) Olkuska ewes are hyperprolific in striking contrast with the sterility exhibited by all other known homozygous BMP15 mutations. Our results bring new insights into the key role played by the BMP15 protein in ovarian function and could contribute to a better understanding of the pathogenesis of women's fertility disorders.

Members of the DAN family are BMP antagonists that form highly stable noncovalent dimers

Signaling of bone morphogenetic protein (BMP) ligands is antagonized by a number of extracellular proteins, including noggin, follistatin and members of the DAN (differential screening selected gene abberative in neuroblastoma) family. Structural studies on the DAN family member sclerostin (a weak BMP antagonist) have previously revealed that the protein is monomeric and consists of an eight-membered cystine knot motif with a fold similar to transforming growth factor-β ligands. In contrast to sclerostin, certain DAN family antagonists, including protein related to DAN and cerberus (PRDC), have an unpaired cysteine that is thought to function in covalent dimer assembly (analogous to transforming growth factor-β ligands). Through a combination of biophysical and biochemical studies, we determined that PRDC forms biologically active dimers that potently inhibit BMP ligands. Furthermore, we showed that PRDC dimers, surprisingly, are not covalently linked, as mutation of the unpaired cysteine does not inhibit dimer formation or biological activity. We further demonstrated that the noncovalent PRDC dimers are highly stable under both denaturing and reducing conditions. This study was extended to the founding family member DAN, which also forms noncovalent dimers that are highly stable. These results demonstrate that certain DAN family members can form both monomers and noncovalent dimers, implying that biological activity of DAN family members might be linked to their oligomeric state.

The function of bone morphogenetic proteins in the human ovary

The gonadotropins, follicle-stimulating hormone (FSH), and luteinizing hormone (LH), are of particular importance in ovarian physiology. However, FSH receptors and LH receptors are not expressed until the secondary follicle stage, indicating that initiation of follicular growth is independent of the gonadotropins. Among many intra-ovarian growth factors, many studies have shown that bone morphogenetic proteins (BMPs) play pivotal roles in regulating the early phases of follicular growth. The BMP system induces the gonadotropin system by modulating gonadotropin receptors in early-stage follicles. Interestingly, the BMP system also prevents precocious maturation of the follicle by suppressing luteinization. Signals provoked by the preovulatory LH surge eliminate BMPs, enabling luteinization to progress. Thus, the BMP system and the gonadotropin system seem to cooperate in regulating follicular development, maturation, and luteinization.

Impaired production of BMP-15 and GDF-9 mature proteins derived from proproteins WITH mutations in the proregion

Mutations in the bone morphogenetic protein-15 (BMP-15) and growth and differentiation factor-9 (GDF-9) genes have been identified in women with primary ovarian insufficiency (POI) and mothers of dizygotic twins. Here, we show that biological activities of the conditioned media from human embryonic kidney 293F cells transfected with two representative BMP-15 and GDF-9 mutants identified in the affected women have significantly reduced biological activities compared with the corresponding wild-type. Moreover, this difference is due to decreased production of the mature proteins, attributed most likely to impaired posttranslational processing of the proprotein. As genetic studies of the BMP-15 and/or GDF-9 genes in ewes established that a reduction of these proteins is associated with an increased ovulation rate, it is conceivable that women affected with these mutations may have an increased probability of bearing dizygotic twins during active reproductive ages before diagnosis with POI at later ages due to an earlier exhaustion of ovarian reserve.

Identification of novel missense mutations of GDF9 in Chinese women with polycystic ovary syndrome

The gene for growth differentiation factor 9 (GDF9) is expressed in human oocytes and has an important function in regulating early follicle growth and fertility. Polycystic ovary syndrome (PCOS) is one of the common defects that causes ovary dysfunction and is linked to aberrant processes in folliculogenesis. Previous studies have discovered several mutations in the screening of GDF9 in premature ovarian failure but none in PCOS. This current study focused on the mutational analysis of the coding region of GDF9 among 216 Chinese PCOS patients. Of the 10 different variants found in this study, five novel missense mutations in GDF9 were discovered namely c.15C>G, c.118T>G, c.133A>G, c.1025A>T and c.1275C>A. The above-mentioned mutations indicate GDF9 may be potentially associated with PCOS patients. As far as is known, this study is the first to provide evidence for such an association.

Variants of the BMP15 gene in a cohort of patients with premature ovarian failure

BACKGROUND

Bone morphogenetic protein 15 (BMP15) is an oocyte-derived growth factor acting as a major player in follicle differentiation in mammals. Mutations in the BMP15 gene, some of which lead to defective secretion of bioactive dimers, have been associated with premature ovarian failure (POF) in humans.

METHODS

Fifty patients diagnosed with POF with a normal karyotype were included in the study. After DNA extraction and amplification by PCR, the entire coding sequence and intron-exon junctions of BMP15 gene were analysed in the cohort of POF patients and in a control group of 214 patients.

RESULTS

Nine variants of the BMP15 gene including six missense substitutions and one insertion of three nucleotides were identified in the POF group. Three of them were previously described as single nucleotide polymorphisms and were also found in the control group. Two variants (H81R and G199R) have not been previously described and were not identified among controls but were not predicted to be deleterious. One variant (A180T) was identified among two POF cases, and also in two controls. One variant (F194S), predicted as potentially deleterious, was identified for the first time in a POF patient but also identified in one control. One variant (L148P), potentially deleterious, previously reported in POF patients, was identified for the first time among controls. The variant 788insTCT, previously identified among POF patients, probably has a low biological impact as it was also found in control patients and is a common polymorphism in sub-Saharan African populations.

CONCLUSIONS

Various missense variants of the BMP15 gene were identified among patients with POF. For most variants, the impact of the amino-acid substitution on the protein structure and function was predicted to be low. The two variants predicted as potentially deleterious were also identified among controls and could be considered as rare polymorphisms. Although some of these variants could contribute to the development of POF in a complex manner, the demonstration of their role in the pathogenesis of POF requires additional functional studies.

Oocyte numbers in the mouse increase after treatment with 5-aminoisoquinolinone: a potent inhibitor of poly(ADP-ribosyl)ation

Poly(ADP-ribosyl)ation is a posttranslational protein modification carried out by a family of enzymes referred to as poly(ADP-ribose) polymerases (PARPs). It has been proposed that the broad nuclear distribution of PARPs may allow them to modulate gene expression in addition to their more accepted role as DNA repair mediators. The role of poly(ADP-ribosyl)ation during oogenesis and folliculogenesis is unknown. Here we found that when 3- to 4-wk-old mice were injected with 5-amninoisoquinolinone, a water soluble inhibitor of poly(ADP-ribosyl)ation, it leads to considerably increased oocyte numbers and a dramatic increase in primordial follicle numbers. Furthermore, we show that inhibition of poly(ADP-ribosyl)ation leads to an increased expression of specific genes and pathways in mouse ovaries, in particular, transforming growth factor superfamily members. Our results demonstrate that poly(ADP-ribosyl)ation, is important in oogenesis and folliculogenesis, and it may have a differential role in regulating gene expression, DNA repair, and apoptosis. The novel function of poly(ADP-ribosyl)ation in oogenesis and folliculogenesis sheds light on the alternative role that DNA repair mediators may play in cellular development and differentiation.

Multiple endocrine regulation by bone morphogenetic protein system

Bone morphogenetic proteins (BMPs) were originally identified with regard to their actions to regulate ectopic formation of bone and cartilage and early embryonic development. Subsequently, our research program has investigated a BMP system that exists in the mammalian ovary and plays roles in regulating numerous granulosa cell functions. BMP ligands including BMP-2, -4, -6, -7 and -15 were found to inhibit gondotropin-dependent progesterone synthesis by granulosa cells, which led to the hypothesis that BMPs are a physiological luteinization inhibitor in growing ovarian follicles during the follicular phase of the ovarian cycle. The physiological importance of the BMP system for normal mammalian reproduction has been further recognized by the discovery of aberrant reproductive phenotypes of female sheep and humans having mutated genes encoding BMP-15. Physiological roles of BMPs in the pituitary, hypothalamus, adrenal and other tissues have also been discovered. Here we discuss recent advances in the understanding of autocrine/paracrine actions of BMPs in the systemic regulation of endocrine function.

Homozygosity for a single base-pair mutation in the oocyte-specific GDF9 gene results in sterility in Thoka sheep

The control of fecundity is critical in determining mammalian offspring survival. It is regulated principally by the ovulation rate, so that primates and large farm species commonly have a single offspring. Previously, several mutations have been identified in sheep which increase the naturally low ovulation rate; although in some cases homozygous ewes are infertile. In the present study we present a detailed characterization of a novel mutation in growth differentiation factor 9 (GDF9), found in Icelandic Thoka sheep. This mutation is a single base change (A1279C) resulting in a nonconservative amino acid change (S109R) in the C-terminus of the mature GDF9 protein, which is normally expressed in oocytes at all stages of development. Genotyping all animals for which reproductive records were available confirmed this mutation to be associated with increased fecundity in heterozygous ewes and infertility in homozygotes. Analysis of homozygote ovarian morphology and a number of genes normally activated in growing follicles showed that GDF9 was not involved in oocyte activation, but in subsequent development of the follicle. This study highlights the importance of oocyte factors in regulating fertility and provides new information for structural analysis and investigation of the potentially important sites of dimerization or translational modifications required to produce biologically active GDF9. It also provides the basis for the utilization of these animals to enhance sheep production.

Mutation of the bone morphogenetic protein GDF3 causes ocular and skeletal anomalies

Ocular mal-development results in heterogeneous and frequently visually disabling phenotypes that include coloboma and microphthalmia. Due to the contribution of bone morphogenetic proteins to such processes, the function of the paralogue Growth Differentiation Factor 3 was investigated. Multiple mis-sense variants were identified in patients with ocular and/or skeletal (Klippel-Feil) anomalies including one individual with heterozygous alterations in GDF3 and GDF6. These variants were characterized, individually and in combination, through integrated biochemical and zebrafish model organism analyses, demonstrating appreciable effects with western blot analyses, luciferase based reporter assays and antisense morpholino inhibition. Notably, inhibition of the zebrafish co-orthologue of GDF3 accurately recapitulates patient phenotypes. By demonstrating the pleiotropic effects of GDF3 mutation, these results extend the contribution of perturbed BMP signaling to human disease and potentially implicate multi-allelic inheritance of BMP variants in developmental disorders.

Oocyte peptides as paracrine tools for ovarian stimulation and oocyte maturation

Recent studies report the production and isolation of a stable bioactive recombinant human bone morphogenetic protein 15 (rhBMP15) that is appropriately processed in HEK-293 cells and activates the SMAD 1/5/8 pathway in mouse granulosa cell cultures. Further, the purified rhBMP15 induces the expression of genes associated with cumulus expansion. Thanks to recent research, we have a greater understanding of the importance of the dialogue that occurs between the oocyte and the granulosa cell layer with regard to regulating folliculogenesis and the acquisition of oocyte developmental competence and maturation. BMP15 is one of the critical components of these intra-follicular communication pathways. The production of recombinant human BMP15 is important for understanding the biochemistry of this specific pathway and for also fully understanding its functional contributions to mediating oocyte development. The production of a stable recombinant human BMP15 is also important for use in experiments aimed at optimizing ovarian stimulation protocols and in vitro oocyte maturation methods. This is required to improve oocyte and embryonic developmental competence and increase our ability to effectively use in vitro methods for animal production and the treatment of human infertility.

Compartmentalizing VEGF-induced ERK2/1 signaling in placental artery endothelial cell caveolae: a paradoxical role of caveolin-1 in placental angiogenesis in vitro

On vascular endothelial growth factor (VEGF) stimulation, both VEGF R1 and R2 receptors were phosphorylated in ovine fetoplacental artery endothelial (oFPAE) cells. Treatment with VEGF stimulated both time- and dose-dependent activation of ERK2/1 in oFPAE cells. VEGF-induced ERK2/1 activation was mediated by VEGFR2, but not VEGFR1, and was linked to intracellular calcium, protein kinase C, and Raf-1. VEGF stimulated oFPAE cell proliferation, migration, and tube formation in vitro. Blockade of ERK2/1 pathway attenuated VEGF-induced cell proliferation and tube formation but failed to inhibit migration in oFPAE cells. Disruption of caveolae by cholesterol depletion with methyl-beta-cyclodextrin or by down-regulation of its structural protein caveolin-1 blunted VEGF-induced ERK2/1 activation, proliferation, and tube formation in oFPAE cells, indicating an essential role of integral caveolae in these VEGF-induced responses. Adenoviral overexpression of caveolin-1 and addition of a caveolin scaffolding domain peptide also inhibited VEGF-stimulated ERK2/1 activation, cell proliferation, and tube formation in oFPAE cells. Furthermore, molecules comprising the ERK2/1 signaling module, including VEGFR2, protein kinase Calpha, Raf-1, MAPK kinase 1/2, and ERK2/1, resided with caveolin-1 in caveolae. VEGF transiently stimulated ERK2/1 activation in the caveolae similarly as in intact cells. Caveolae disruption greatly diminished ERK2/1 activation by VEGF in oFPAE cell caveolae. We conclude that caveolae function as a platform for compartmentalizing the VEGF-induced ERK2/1 signaling module. Caveolin-1 and caveolae play a paradoxical role in regulating VEGF-induced ERK2/1 activation and in vitro angiogenesis as evidenced by the similar inhibitory effects of down-regulation and overexpression of caveolin-1 and disruption of caveolae in oFPAE cells.

[Genetic analysis of premature ovarian failure: role of forkhead and TGF-beta genes]

Premature ovarian failure is a common pathology affecting 1% of women. Although multiple etiologies have been described the majority of cases are idiopathic. Forkhead transcription factors as FOXL2 and FOXO3A are of particular interest in the research of genetic factors related with the pathology as they are present in diverse developmental pathways and ovarian physiology. Similarly, some TGF-beta factors (i.e. BMP 15 and GDF-9) have been demonstrated to play a key role in the regulation, at ovarian level, of female reproduction. In recent years numerous studies have been performed in order to elucidate the implication of these factors in the ovarian physiopathology. The aim of this manuscript is to describe some of these advances in the context of premature ovarian failure.

Hormonal regulation of proprotein convertase subtilisin/kexin type 5 expression during ovarian follicle development in the rat

The proprotein convertase subtilisin/kexin (PCSKs), a family of subtilisin-like proteases, is the processing enzymes for the activation of many hormone precursors. The present study was designed to identify the PCSK isoform expressed in the ovary and to examine its expression in gonadotropin-stimulated rat ovary. Northern blot analysis of ovaries obtained from prepubertal rats revealed an increased expression of Pcsk5 messenger RNA (mRNA) during development with the highest levels at 21 days of age. Treatment of immature rats with PMSG further increased ovarian Pcsk5 expression, and in situ hybridization analysis revealed the localization of Pcsk5 mRNA in theca-interstitial cells of follicles in different sizes. Interestingly, treatment of PMSG-primed rats with hCG resulted in a transient stimulation of ovarian Pcsk5 mRNA levels within 3-6 h. In addition to theca-interstitial cells, hCG treatment induced the expression of Pcsk5 in granulosa cells of preovulatory follicles. Pcsk1, 2 and 4 mRNAs were not detected whereas Pcsk7 mRNA was slightly expressed. Injection of a progestin antagonist RU486 or an inhibitor of 3beta-hydroxysteroid dehydrogenase epostane at 1h before hCG treatment inhibited hCG-induced Pcsk5 mRNA levels. Treatment with LH stimulated both Pcsk5 mRNA and protein levels in preovulatory follicles cultured in vitro. In addition, forskolin but not TPA stimulated Pcsk5 mRNA levels. RNase protection assay revealed that the soluble Pcsk5A variant was the predominant form stimulated by gonadotropins in the ovary. Finally, the predicted proprotein substrates cleaved by PCSK5 were analyzed in preovulatory follicles using regular expressions. The present study demonstrates PCSK5A as the gonadotropin-regulated PCSK isoform in the ovary, and its possible contribution to ovulation by processing pro-TGFbeta and matrix metalloproteinase family.

The proregion of mouse BMP15 regulates the cooperative interactions of BMP15 and GDF9

Bone morphogenetic protein 15 (BMP15) and growth and differentiation factor 9 (GDF9) are secreted by the mammalian oocyte and are essential for ovarian follicular development, ovulation, and fertility. However, the secreted forms of the BMP15 and GDF9 proteins and the nature of cooperative molecular interactions between BMP15 and GDF9 previously reported have not been fully characterized. In this study, we found that recombinant mouse BMP15 and GDF9 are secreted as cleaved mature and proregion proteins, with BMP15 also secreted as uncleaved promature protein. Noncovalent interactions were identified between the mature and proregion proteins of each growth factor. Moreover, GDF9 mature protein was found to coimmunoprecipitate with the BMP15 proregion, suggestive of a heteromeric association between BMP15 and GDF9. Mouse GDF9 was found to exist mostly as a dimer of mature protein, in both the presence and absence of BMP15. In contrast, BMP15 formed mostly multimers of proregion and mature protein when combined with GDF9, providing further evidence for heteromeric interaction. Mouse BMP15 was found to act cooperatively with GDF9 in a rat granulosa cell thymidine incorporation bioassay and to signal through the BMPR2 and ACVR1B/TGFBR1/ACVR1C receptor-mediated pathways. Immunoneutralization experiments using GDF9 mature protein antibody indicated that these cooperative interactions are species specific. Additionally, immunoneutralization with proregion antibodies highlighted the involvement of the BMP15 proregion in BMP15/GDF9 cooperative interactions. Taken together, these findings support a novel hypothesis where the extracellular cooperative interactions of recombinant mouse BMP15 and GDF9 are multimeric, involving the proregion of BMP15, and may well be species specific.

Variation in bone morphogenetic protein 15 is not associated with spontaneous human dizygotic twinning

BACKGROUND

Spontaneous dizygotic (DZ) twinning in humans is under genetic control. In sheep, heterozygous loss of function mutations in bone morphogenetic protein 15 (BMP15) increase ovulation and hence twinning rates.

METHODS

To investigate the role of BMP15 in human twinning, we typed 14 common variants, 4 rare novel variants initially detected by sequencing 279 mothers of DZ twins (MODZT) and 17 variants previously associated with premature ovarian failure (POF) in 933 DZ twinning families. We also typed five additional POF associated GDF9 variants.

RESULTS

There was some evidence for association between DZ twinning and a common intronic BMP15 variant (rs3897937), but this was not significant after correction for multiple testing. Three of the four novel variants (p.Pro174Ser, p.Ala311Thr and p.Arg392Thr) occurred in 1-5 MODZT but were not detected in 1512 controls. We also detected three POF associated mutations in both BMP15 and GDF9 at low frequencies in MODZT and controls.

CONCLUSIONS

We conclude that neither rare nor common BMP15 variants play a significant role in the variation in human DZ twinning.

Phosphorylation of bone morphogenetic protein-15 and growth and differentiation factor-9 plays a critical role in determining agonistic or antagonistic functions

Two highly homologous oocyte-secreted growth factors, bone morphogenetic protein (BMP)-15 and growth and differentiation factor (GDF)-9, are known to control folliculogenesis and ovulation through direct effects on granulosa cells in the developing follicles. Although much is known about the expression and biology of these proteins, the impact of posttranslational modifications of BMP-15 and GDF-9 is unknown. Here, we report that: 1) recombinant human (rh) BMP-15 and rhGDF-9 are phosphorylated; 2) the phosphorylation is essential for bioactivity; and 3) the dephosphorylated forms of rhBMP-15 and rhGDF-9 can abolish the bioactivity of rhBMP-15, rhGDF-9, and rhBMP-7, but not rh activin A. These results indicate that the phosphorylation state of rhBMP-15 and rhGDF-9 is a determinant of their agonistic and antagonistic activities.

Recent advances in the study of genes involved in non-syndromic premature ovarian failure

Premature ovarian failure (POF) is a common pathology leading to infertility affecting about 1% of women under 40 years old. In POF patients, the ovarian dysfunction is characterized by the lack of the ovarian response to close a negative feedback loop on the synthesis of pituitary gonadotropins. Although the majority of cases are considered as idiopathic, diverse aetiologies have been associated, including genetic factors. Up to now, the potential genetic causes of non-syndromic POF have been established mainly by genetic linkage analysis of familial cases or by the screening of mutations in candidate genes based on animal models. Here, we review recent advances in the study of candidate genes.

Oocyte-derived BMP15 and FGFs cooperate to promote glycolysis in cumulus cells

Mammalian oocytes are deficient in their ability to carry out glycolysis. Therefore, the products of glycolysis that are necessary for oocyte development are provided to oocytes by companion cumulus cells. Mouse oocytes secrete paracrine factors that promote glycolysis in cumulus cells. The objective of this study was to identify paracrine factors secreted by oocytes that promote glycolysis and expression of mRNA encoding the glycolytic enzymes PFKP and LDHA. Candidates included growth differentiation factor 9 (GDF9), bone morphogenetic protein 15 (BMP15) and fibroblast growth factors (FGFs). Bmp15-/- and Gdf9+/- Bmp15-/- (double mutant, DM) cumulus cells exhibited reduced levels of both glycolysis and Pfkp and Ldha mRNA, and mutant oocytes were deficient in promoting glycolysis and expression of Pfkp and Ldha mRNA in cumulus cells of wild-type (WT) mice. Alone, neither recombinant BMP15, GDF9 nor FGF8 promoted glycolysis and expression of Pfkp and Ldha mRNA in WT cumulus cells. Co-treatment with BMP15 and FGF8 promoted glycolysis and increased expression of Pfkp and Ldha mRNA in WT cumulus cells to the same levels as WT oocytes; however, the combinations of BMP15/GDF9 or GDF9/FGF8 did not. Furthermore, SU5402, an FGF receptor-dependent protein kinase inhibitor, inhibited Pfkp and Ldha expression in cumulus cells promoted by paracrine oocyte factors. Therefore, oocyte-derived BMP15 and FGFs cooperate to promote glycolysis in cumulus cells.

Analyses of GDF9 mutation in 100 Chinese women with premature ovarian failure

We screened growth differentiation factor 9 coding regions for mutations in a Chinese sample of 100 women with premature ovarian failure and discovered four novel single-nucleotide polymorphisms: c.436C>T (p.Arg146Cys), c.588A>C (silent), c.712A>G (p.Thr238Ala), and c.1283G>C (p.Ser428Thr). Nonsynonymous single-nucleotide polymorphisms c.436C>T and c.1283G>C were also detected in the control population. The c.712A>G perturbation results in a missense mutation (p.Thr238Ala) and was not present in any of 96 controls. Substitution of the hydrophobic amino acid residue alanine for hydrophilic threonine may disrupt growth differentiation factor 9 function.

Infertility caused by retardation of follicular development in mice with oocyte-specific expression of Foxo3a

In recent years, mammalian oocytes have been proposed to have important roles in the orchestration of ovarian follicular development and fertility. To determine whether intra-oocyte Foxo3a, a component of the phosphatidylinositol 3-kinase (PI3K) signaling pathway, influences follicular development and female fertility, a transgenic mouse model was generated with constitutively active Foxo3a expressed in oocytes. We found that the female transgenic mice were infertile, which was caused by retarded oocyte growth and follicular development, and anovulation. Further mechanistic studies revealed that the constitutively active Foxo3a in oocytes caused a dramatic reduction in the expression of bone morphogenic protein 15 (Bmp15), connexin 37 and connexin 43, which are important molecules for the establishment of paracrine and gap junction communications in follicles. Foxo3a was also found to facilitate the nuclear localization of p27(kip1) in oocytes, a cyclin-dependent kinase (Cdk) inhibitor that may serve to inhibit oocyte growth. The results from the current study indicate that Foxo3a is an important intra-oocyte signaling molecule that negatively regulates oocyte growth and follicular development. Our study may therefore give some insight into oocyte-borne genetic aberrations that cause defects in follicular development and anovulation in human diseases, such as premature ovarian failure.

Growth differentiating factor-9 mutations may be associated with premature ovarian failure

OBJECTIVE

To determine whether perturbations of the growth differentiating factor-9 (GDF9) gene are associated with premature ovarian failure (POF).

DESIGN

Mutational analysis of the GDF9 gene in 61 women with POF.

SETTING

Academic institution.

PATIENT(S)

Sixty-one women with POF; 60 control women.

INTERVENTION(S)

Peripheral blood sampling, genomic DNA extraction, mutational screening, and DNA sequencing.

MAIN OUTCOME MEASURE(S)

Genetic perturbations in GDF9 that are associated with POF.

RESULT(S)

A single missense mutation, substitution of a cytosine residue with thymidine in exon 1 of GDF9, was found in a white woman in whom POF developed at age 22. This mutation occurred in a highly conserved proprotein region and resulted in replacement of a nonpolar amino acid (proline) with a polar amino acid (serine) at position 103. Neither 60 control women nor 60 other women with POF demonstrated this genetic perturbation. Exon 2 showed only previously recognized single nucleotide polymorphisms.

CONCLUSION(S)

GDF9 mutations may be one explanation for POF, albeit uncommon.

A novel mutation in the bone morphogenetic protein 15 gene causing defective protein secretion is associated with both increased ovulation rate and sterility in Lacaune sheep

Genetic mutations with major effects on ovulation rate and litter size in sheep were recently identified in three genes belonging to the TGFbeta superfamily pathway: the bone morphogenetic protein 15 (BMP15, also known as GDF9b), growth differentiation factor 9 (GDF9), and BMP receptor type IB (also known as activin-like kinase 6). Homozygous BMP15 or GDF9 mutations raise female sterility due to a failure of normal ovarian follicle development, whereas heterozygous animals for BMP15 or GDF9 as well as heterozygous and homozygous animals for BMP receptor type IB show increased ovulation rates. In the present work, a new naturally occurring mutation in the BMP15 gene in the high prolific Lacaune sheep breed is described. The identified variant is a C53Y missense nonconservative substitution leading to the aminoacidic change of a cysteine with a tyrosine in the mature peptide of the protein. As for other mutations found in the same gene, this is associated with an increased ovulation rate and sterility in heterozygous and homozygous animals, respectively. Further in vitro studies showed that the C53Y mutation was responsible for the impairment of the maturation process of the BMP15 protein, resulting in a defective secretion of both the precursor and mature peptide. Overall, our findings confirm the essential role of the BMP15 factor in the ovarian folliculogenesis and control of ovulation rate in sheep.

BMP-15 regulation of ovulation quota in mammals

Naturally occurring mutations in the oocyte-specific factor, bone morphogenetic protein-15 (BMP-15), cause infertility in women and in ewes. In contrast to these monoovulatory mammals, the targeted deletion of BMP-15 in polyovulatory mice results in subfertility with only minimal defects in the ovulation process. Given the established role of BMP-15 in governing the progression of folliculogenesis, it is hypothesized that species-specific differences in the BMP-15 system are involved in species-specific determination of ovulation quota and litter size. Recent data using in vitro cell transfection methodology indicate that, in contrast to human BMP-15 which is successfully processed and secreted, the mouse BMP-15 proprotein is resistant to proteolytic cleavage. Thus, no functional mature BMP-15 is secreted in vitro. Further studies have shown that the functional mature form of BMP-15 is barely detectable in mouse oocytes in vivo until just before ovulation, when it is markedly increased. The general hypothesis to emerge from these observations is that the species-specific differences in the defects caused by mutations in the bmp15 gene between monoovulatory ewes and women and polyovulatory mice might be attributed to the timing of the production of BMP-15 mature protein. (Reprod Med Biol 2006; 5: 245-248).

The effects of immunizing sheep with different BMP15 or GDF9 peptide sequences on ovarian follicular activity and ovulation rate

The aims of these studies were to determine the abilities of antisera against different regions of ovine bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) to inhibit ovarian follicular activity, estrus (mating), and ovulation in sheep. The 9-15-mer peptides were conjugated to keyhole limpet hemocyanin (KLH) and used to generate antibodies against the flexible N-terminal regions of the mature protein as well as against regions in which dimerization of the protein or interaction with a type 1 BMP or a type 2 TGFB or BMP receptor was predicted to occur. Ewes (n = 10 per treatment group) were vaccinated with KLH or the KLH-BMP15 (n = 9 different peptides) or KLH-GDF9 (n = 10) peptides in Freund adjuvant at five consecutive monthly intervals. Overall, antisera generated against peptides that corresponded to amino acid residues 1-15 of the N-terminus of the BMP15 or GDF9 mature protein or GDF9 amino acid residues 21-34 were the most potent at inhibiting ovulation following primary and single booster vaccination. Several other BMP15 (8/9) or GDF9 (6/10) treatment groups, but not KLH alone, also produced significant reductions in the numbers of animals that ovulated, although 2, 3 or 4 booster vaccinations were required. Anovulation was commonly associated with the inhibition of normal ovarian follicular development and anestrus. The in vitro neutralization studies with IgG from the BMP15 or GDF9 immunized ewes showed that the mean inhibition of BMP15 plus GDF9 stimulation of (3)H-thymidine uptake by rat granulosa cells was approximately 70% for animals without corpora lutea (CL), whereas for animals with one to three CL or more than three CL, the inhibition was 24%-33% or 27%-42%, respectively. In summary, these data suggest that reagents that block the biological actions of BMP15 or GDF9 at their N-termini have potential as contraceptives or sterilizing agents.

Novel variants in growth differentiation factor 9 in mothers of dizygotic twins

CONTEXT

Genes from the ovarian bone morphogenetic signaling pathway (GDF9 and BMP15) are critical for normal human fertility. We previously identified a deletion mutation in GDF9 in sisters with spontaneous dizygotic (DZ) twins, but the prevalence of rare GDF9 variants in twinning families is unknown.

OBJECTIVE

The objective was to evaluate the frequency of rare variants in GDF9 in families with a history of DZ twinning.

DESIGN AND SUBJECTS

We recruited 3450 individuals from 915 DZ twinning families (1693 mothers of twins) and 1512 controls of Caucasian origin. One mother of DZ twins was selected from 279 of the 915 families, and a DNA sample was screened for rare variants in GDF9 using denaturant HPLC. Variants were confirmed by DNA sequencing and genotyped in the entire sample by matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry.

RESULTS

We found two novel insertion/deletions (c.392-393insT, c.1268-1269delAA) and four missense alterations in the GDF9 sequence in mothers of twins. Two of the missense variants (c.307C > T, p.Pro103Ser and c.362C > T, p.Thr121Leu) were located in the pro-region of GDF9 and two (c.1121C > T, p.Pro374Leu and c.1360C > T, p.Arg454Cys) in the mature protein region. For each variant, the frequencies were higher in cases compared with controls. The proportion of mothers of DZ twins carrying any variant (4.12%) was significantly higher (P < 0.0001) than the proportion of carriers in controls (2.29%).

CONCLUSION

We describe new variants in the GDF9 gene that are significantly more common in mothers of DZ twins than controls, suggesting that rare GDF9 variants contribute to the likelihood of DZ twinning.