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

Revisiting GDF9 variants in primary ovarian insufficiency: A shift from dominant to recessive pathogenicity?

BACKGROUND

Primary ovarian insufficiency (POI) affects around 2-4% of women before the age of 40. Genetic factors play an important role in POI. The GDF9 gene has been identified as a significant genetic contributor of POI. However, the pathogenicity and penetrance of GDF9 variants remain uncertain.

METHODS

A next-generation sequencing approach was employed to investigate the entire coding region of the GDF9 gene in a cohort of 1281 patients with POI or diminished ovarian reserve (DOR). The frequency of each identified GDF9 variant was then compared with that of the general population, taking into account the ethnicity of each individual.

RESULTS

By screening the entire coding region of the GDF9 gene, we identified 19 different variants, including 1 pathogenic frameshift variant. In total, 36 patients with POI/DOR (2.8%) carried at least one GDF9 variant. With regard to missense variants, no significant overrepresentation of the most common variants was observed in our POI/DOR cohort in comparison to the general or specific ethnic subgroups. Only one homozygous subject had a frameshift loss of function variant.

CONCLUSION

This epidemiological study suggests that the vast majority of heterozygous missense variants could be considered as variants of uncertain significance and the homozygous loss-of-function variant could be considered as a pathogenic variant. The identification of a novel case of a homozygous POI patient with a heterozygous mother carrying the same variant with normal ovarian function strongly suggests that GDF9 syndrome is an autosomal recessive disorder.

Current understanding of the genomic abnormities in premature ovarian failure: chance for early diagnosis and management

Premature ovarian failure (POF) is an insidious cause of female infertility and a devastating condition for women. POF also has a strong familial and heterogeneous genetic background. Management of POF is complicated by the variable etiology and presentation, which are generally characterized by abnormal hormone levels, gene instability and ovarian dysgenesis. To date, abnormal regulation associated with POF has been found in a small number of genes, including autosomal and sex chromosomal genes in folliculogenesis, granulosa cells, and oocytes. Due to the complex genomic contributions, ascertaining the exact causative mechanisms has been challenging in POF, and many pathogenic genomic characteristics have yet to be elucidated. However, emerging research has provided new insights into genomic variation in POF as well as novel etiological factors, pathogenic mechanisms and therapeutic intervention approaches. Meanwhile, scattered studies of transcriptional regulation revealed that ovarian cell function also depends on specific biomarker gene expression, which can influence protein activities, thus causing POF. In this review, we summarized the latest research and issues related to the genomic basis for POF and focused on insights gained from their biological effects and pathogenic mechanisms in POF. The present integrated studies of genomic variants, gene expression and related protein abnormalities were structured to establish the role of etiological genes associated with POF. In addition, we describe the design of some ongoing clinical trials that may suggest safe, feasible and effective approaches to improve the diagnosis and therapy of POF, such as Filgrastim, goserelin, resveratrol, natural plant antitoxin, Kuntai capsule et al. Understanding the candidate genomic characteristics in POF is beneficial for the early diagnosis of POF and provides appropriate methods for prevention and drug treatment. Additional efforts to clarify the POF genetic background are necessary and are beneficial for researchers and clinicians regarding genetic counseling and clinical practice. Taken together, recent genomic explorations have shown great potential to elucidate POF management in women and are stepping from the bench to the bedside.

Decreased GDF9 and BMP15 in follicle fluid and granulosa cells and outcomes of IVF-ET among young patients with low prognosis

PURPOSE

To analyze the level of growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) in follicle fluid (FF) and granulosa cells (GCs) derived from young patients with low prognosis for in vitro fertilization and embryo transfer (IVF-ET) treatment.

METHODS

A prospective cohort study was carried out by enrolling 52 young patients with low prognosis according to the POSEIDON classification group 3 (low prognosis group) and 51 young patients with normal ovarian reserve (control group). The concentration of the GDF9 and BMP15 proteins in FF was determined by enzyme-linked immunosorbent assay. The mRNA level of the GDF9 and BMP15 in the GCs was measured by quantitative real-time PCR.

RESULTS

The concentration of GDF9 (1026.72 ± 159.12 pg/mL vs. 1298.06 ± 185.41 pg/mL) and BMP15 (685.23 ± 143.91 pg/mL vs. 794.37 ± 81.79 pg/mL) in FF and the mRNA level of GDF9 and BMP15 in the GCs and the live birth rate per treatment cycle started (30.77% vs. 50.98%) and oocytes retrieved (4.25 ± 1.91 vs.12.04 ± 4.24) were significantly lower, whereas the canceled cycle rate was significantly higher (9.62% vs. 0) in the low prognosis group compared with the control group (P < 0.05). The expression of GDF9 and BMP15 in the ovary was positively correlated with live birth (P < 0.05).

CONCLUSION

The expression of GDF9 and BMP15 in the ovary was decreased in young patients with low prognosis accompanied by a poorer outcome of IVF-ET treatment.

TRIAL REGISTRATION

ChiCTR1800016107 (Chinese Clinical Trial Registry), May 11, 2018. ( http://www.chictr.org.cn/edit.aspx?pid=27216&htm=4 ).

Novel bone morphogenetic protein 15 (BMP15) gene variants implicated in premature ovarian insufficiency

BACKGROUND

Bone morphogenetic protein 15 (BMP15) is expressed in oocytes and plays a crucial role in the reproduction of mono-ovulating species. In humans, BMP15 gene mutations lead to imperfect protein function and premature ovarian insufficiency. Here we investigated the BMP15 gene variants in a population of Iranian women with premature ovarian insufficiency. We conducted predictive bioinformatics analysis to further study the outcomes of BMP15 gene alterations.

METHODS

Twenty-four well-diagnosed premature ovarian insufficiency cases with normal karyotype participated in this study. The entire coding sequence and exon-intron junctions of the BMP15 gene were analyzed by direct sequencing. In-silico analysis was applied using various pipelines integrated into the Ensembl Variant Effect Predictor online tool. The clinical interpretation was performed based on the approved guidelines.

RESULTS

By gene screening of BMP15, we discovered p.N103K, p.A180T, and p.M184T heterozygous variants in 3 unrelated patients. The p.N103K and p.M184T were not annotated on gnomAD, 1000 Genome and/or dbSNP. These mutations were not identified in 800 Iranians whole-exome sequencing that is recorded on Iranom database. We identified the p.N103K variant in a patient with secondary amenorrhea at the age of 17, elevated FSH and atrophic ovaries. The p.M184T was detected in a sporadic case with atrophic ovaries and very high FSH who developed secondary amenorrhea at the age of 31.

CONCLUSIONS

Here we newly identified p.N103K and p.M184T mutation in the BMP15 gene associated with idiopathic premature ovarian insufficiency. Both mutations have occurred in the prodomain region of protein. Despite prodomain cleavage through dimerization, it is actively involved in the mature protein function. Further studies elucidating the roles of prodomain would lead to a better understanding of the disease pathogenesis.

Alterations in follicular fluid BMP-15 RNA expression in women undergoing controlled ovarian hyperstimulation

Background/aim

Bone morphogenetic protein-15 (BMP-15) is one of the maturation indicators of the ovarian follicular pool. The aim of this study was to investigate the possible difference of follicular fluid (FF) BMP-15 RNA expression among low, normal, and high responder women attending controlled ovarian hyperstimulation-intracytoplasmic sperm injection (COH-ICSI) cycles.

Materials and methods

This cross-sectional study was conducted with 75 FFs of COH-ICSI cycles performed at the IVF Unit of University Hospital. Twenty FF from low response (group 1), 27 FF from normal response (group 2), and 28 FF from high response (group 3) were recruited for the study between September 2014 and February 2015. Cycle parameters were collected from patient files. FF BMP-15 RNA expression was evaluated with real-time polymerase chain reaction analysis. Statistical analysis was done with SPSS 16.0 version (SPSS Chicago, IL, USA).

Results

The mean age, infertility duration, and body mass index (BMI) of patients were 31.1 ± 4.4 years, 7.4 ± 4.5 years, and 25.6 ± 4.1 kg/m², respectively. There was no significant difference among groups for age, infertility duration, and BMI. There was no significant difference among groups for fertilization rate, implantation rate, pregnancy rate, and live birth rate. Among the 3 groups, FF BMP-15 RNA overexpression and lower expression rates were not significantly different. In all groups, overexpression showed dominance. The pregnancy rate was 45% among women with lower expression and the pregnancy rate among women with overexpression was 26% (P = 0.02). BMP-15 overexpression showed impact on becoming pregnant (OR = 3.7, 95% CI = 1.245–11.299, P = 0.019).

Conclusion

In this study, there was no significant difference in FF BMP-15 RNA expression levels among low, normal, and high responder women. However, overexpression of FF BMP-15 RNA showed a negative impact on pregnancy rates of women who attended COH-ICSI cycles.

Association between polymorphism in BMP15 and GDF9 genes and impairing female fecundity in diabetes type 2

Background

A shortened reproductive period and earlier menopause have been associated with type 2 diabetes. Growth differentiation factor 9(GDF9) and bone morphogenetic protein 15 (BMP15) gene mutations have been associated with earlier menopause. Therefore, this study aimed to evaluate the association between BMP15 and GDF9 mutations with impairing female fecundity in diabetic patients. The study subjects comprised 90 female diabetic patients and 60 female healthy controls. The physio-biochemical analysis was measured using enzymatic determination. A single-strand conformation polymorphism (SSCP) protocol was utilized to assess the pattern of genetic variations.

Results

Genotyping analysis of the BMP15 gene showed a heterogeneous pattern with the presence of two genotypes: AA and AC genotypes. Five novel missense single nucleotide polymorphisms (SNPs) were identified in the BMP15 gene: four SNPs detected in both genotypes, and Met4Leu, a specific SNP, was detected only in the AC genotype. Cumulative in silico tools indicated a highly deleterious effect for the Met4Leu on the mutant protein structure, function, and stability. Diabetes patients showed a significantly higher frequency of genotype AC. The physio-biochemical analysis of fasting plasma glucose (FBG), glycosylated hemoglobin (HbA1c), and luteinizing hormone (LH) were significantly higher (P < 0.05) in AC genotype than AA genotype.

Conclusions

The current research provides the first indication regarding the tight association of BMP15 polymorphism with the impairing female fecundity in the diabetic. A pivotal role is played by the novel (Met4Leu) SNP that can be used as a predictor for the impairing female fecundity of diabetes, while no polymorphism was found in exon 4 of the GDF9 gene.

The novel T755C mutation in <i>BMP15</i> is associated with the litter size of Iranian Afshari, Ghezel, and Shal breeds

Abstract. The present study was conducted to determine the molecular genetic variation in bone morphogenetic protein 15 (BMP15) of some selected Iranian sheep breeds and aims to provide relevant genetic information for twin-birth lambing. Therefore, a total of 44 rams and 213 ewes with single-, twin-, and triplet-birth lambing were used from Shal, Ghezel, Afshari and Lori-Bakhtiari sheep breeds. Three primer pairs were used for amplification of exons 1 and 2 of the BMP15 gene. The sequencing result of distinctive single-strand conformation polymorphism (SSCP) patterns showed segregation of the T755C mutation and the ensuing non-conservative substitution of L252P in the BMP15 propeptide. All three ewes with triplet-birth lambing and two sterile ewes were heterozygotic for this mutation. Association analysis revealed that this mutation was significantly related to the ewe's litter size, so that ewes with the CT genotype had 0.24 and 0.30 more lambs than those with the CC (p < 0.05) and TT (p < 0.01) genotypes, respectively. The mutation effect on the litter size was incomplete dominance in Afshari breed and over-dominance in Shal and Ghezel breeds. In conclusion, the findings in this experiment suggested synergistic effects of the T755C mutation and other unknown mutations in other effective genes which cause infertility and higher litter size in two different ways.

Involvement of Bone Morphogenetic Proteins (BMP) in the Regulation of Ovarian Function

Primordial germ cells migrate to the fetal gonads and proliferate during gestation to generate a fixed complement of primordial follicles, the so-called ovarian reserve. Primordial follicles comprise an oocyte arrested at the diplotene stage of meiosis, surrounded by a layer of pregranulosa cells. Activation of primordial follicles to grow beyond this arrested stage is of particular interest because, once activated, they are subjected to regulatory mechanisms involved in growth, selection, maturation, and ultimately, ovulation or atresia. The vast majority of follicles succumb to atresia and are permanently lost from the quiescent or growing pool of follicles. The bone morphogenetic proteins (BMPs), together with other intraovarian growth factors, are intimately involved in regulation of follicle recruitment, dominant follicle selection, ovulation, and atresia. Activation of primordial follicles appears to be a continuous process, and the number of small antral follicles at the beginning of the menstrual cycle provides an indirect indication of ovarian reserve. Continued antral follicle development during the follicular phase of the menstrual cycle is driven by follicle stimulating hormone (FSH) and luteinizing hormone (LH) in conjunction with many intraovarian growth factors and inhibitors interrelated in a complex web of regulatory balance. The BMP signaling system has a major intraovarian role in many species, including the human, in the generation of transcription factors that influence proliferation, steroidogenesis, cell differentiation, and maturation prior to ovulation, as well as formation of corpora lutea after ovulation. At the anterior pituitary level, BMPs also contribute to the regulation of gonadotrophin production.

Primary ovarian insufficiency associated with autosomal abnormalities: from chromosome to genome-wide and beyond

OBJECTIVE

The pathophysiology of primary ovarian insufficiency (POI) is not well elucidated. Many candidate genetic aberrations are on the X-chromosome; on the contrary, many genetic perturbations are also on the autosomes. The aim of this review is to summarize the knowledge of genetic aberrations on autosomes from chromosomal rearrangement, gene abnormality, genome-wide association studies and epigenetics.

METHODS

Searches of electronic databases were performed. Articles and abstracts relevant to POI and genetic studies associated with autosomes were summarized in this interpretive literature review.

RESULTS

Various genetic aberrations located on the autosomes were found. These abnormalities are from chromosomal rearrangement, which might disrupt the critical region on chromosome loci or disturbance of the meiosis process. Specific gene aberrations are also identified. The genes that have functions in ovarian development, folliculogenesis, and steroidogenesis on autosomes are proposed to be involved from gene association studies. Gene-to-gene interaction or epistasis also might play a role in POI occurrence. Recently, genetic techniques to study the whole genome have emerged. Although no specific conclusion has been made, the studies using genome-wide association to find the specific aberration throughout the genome in POI have been published. Epigenetic mechanisms might also take part in the pathogenesis of POI.

CONCLUSIONS

The considerably complex process of POI is still not well understood. Further research is needed for gene functional validation studies to confirm the contribution of genes in POI, or additional genome-wide association studies using novel clustered regularly interspaced short palindromic repeat/Cas9 technique might make these mechanisms more comprehensible.

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.

Age-related expression of TGF beta family receptors in human cumulus oophorus cells

PURPOSE

During ovarian follicle growth, local cellular interactions are essential for oocyte quality acquisition and successful fertilization. While cumulus cells (CCs) nurture oocytes, they also deliver oocyte-secreted factors (OSFs) that activate receptors on CCs. We hypothesized that disturbance of those interactions contributes to age-related lower reproductive success in women submitted to assisted reproductive technology treatments.

METHODS

Women aged 27-48, without recognized personal reproductive disorder, were enrolled in the study and divided in <35- and ≥35-year-old groups. CCs collected upon follicle aspiration were processed for immunocytochemistry and RNA extraction. The expression patterns of OSF receptors BMPR2, ALK 4, ALK5, and activin receptor-like kinase (ALK6) were studied.

RESULTS

Independently of age, receptors were found mostly in the cell periphery. The quantitative assay revealed that in older women, BMPR2, ALK 4, and ALK6 were all significantly decreased, whereas ALK5 was slightly increased.

CONCLUSIONS

Female age imparts an effect on the expression of OSF receptors in CCs. The findings indicate that reproductive aging affects the local regulation of signaling pathways mediated by BMPR2, ALK6, and ALK4 receptor activation, suggesting their joint involvement.

Role of Growth Differentiation Factor 9 and Bone Morphogenetic Protein 15 in Ovarian Function and Their Importance in Mammalian Female Fertility - A Review

Growth factors play an important role during early ovarian development and folliculogenesis, since they regulate the migration of germ cells to the gonadal ridge. They also act on follicle recruitment, proliferation/atresia of granulosa cells and theca, steroidogenesis, oocyte maturation, ovulation and luteinization. Among the growth factors, the growth differentiation factor 9 (GDF9) and the bone morphogenetic protein 15 (BMP15), belong to the transforming growth factor beta (TGF-β) superfamily, have been implicated as essential for follicular development. The GDF9 and BMP15 participate in the evolution of the primordial follicle to primary follicle and play an important role in the later stages of follicular development and maturation, increasing the steroidogenic acute regulatory protein expression, plasminogen activator and luteinizing hormone receptor (LHR). These factors are also involved in the interconnections between the oocyte and surrounding cumulus cells, where they regulate absorption of amino acids, glycolysis and biosynthesis of cholesterol cumulus cells. Even though the mode of action has not been fully established, in vitro observations indicate that the factors GDF9 and BMP15 stimulate the growth of ovarian follicles and proliferation of cumulus cells through the induction of mitosis in cells and granulosa and theca expression of genes linked to follicular maturation. Thus, seeking greater understanding of the action of these growth factors on the development of oocytes, the role of GDF9 and BMP15 in ovarian function is summarized in this brief review.

Genetics of primary ovarian insufficiency: new developments and opportunities

BACKGROUND

Primary ovarian insufficiency (POI) is characterized by marked heterogeneity, but with a significant genetic contribution. Identifying exact causative genes has been challenging, with many discoveries not replicated. It is timely to take stock of the field, outlining the progress made, framing the controversies and anticipating future directions in elucidating the genetics of POI.

METHODS

A search for original articles published up to May 2015 was performed using PubMed and Google Scholar, identifying studies on the genetic etiology of POI. Studies were included if chromosomal analysis, candidate gene screening and a genome-wide study were conducted. Articles identified were restricted to English language full-text papers.

RESULTS

Chromosomal abnormalities have long been recognized as a frequent cause of POI, with a currently estimated prevalence of 10-13%. Using the traditional karyotype methodology, monosomy X, mosaicism, X chromosome deletions and rearrangements, X-autosome translocations, and isochromosomes have been detected. Based on candidate gene studies, single gene perturbations unequivocally having a deleterious effect in at least one population include Bone morphogenetic protein 15 (BMP15), Progesterone receptor membrane component 1 (PGRMC1), and Fragile X mental retardation 1 (FMR1) premutation on the X chromosome; Growth differentiation factor 9 (GDF9), Folliculogenesis specific bHLH transcription factor (FIGLA), Newborn ovary homeobox gene (NOBOX), Nuclear receptor subfamily 5, group A, member 1 (NR5A1) and Nanos homolog 3 (NANOS3) seem likely as well, but mostly being found in no more than 1-2% of a single population studied. Whole genome approaches have utilized genome-wide association studies (GWAS) to reveal loci not predicted on the basis of a candidate gene, but it remains difficult to locate causative genes and susceptible loci were not always replicated. Cytogenomic methods (array CGH) have identified other regions of interest but studies have not shown consistent results, the resolution of arrays has varied and replication is uncommon. Whole-exome sequencing in non-syndromic POI kindreds has only recently begun, revealing mutations in the Stromal antigen 3 (STAG3), Synaptonemal complex central element 1 (SYCE1), minichromosome maintenance complex component 8 and 9 (MCM8, MCM9) and ATP-dependent DNA helicase homolog (HFM1) genes. Given the slow progress in candidate-gene analysis and relatively small sample sizes available for GWAS, family-based whole exome and whole genome sequencing appear to be the most promising approaches for detecting potential genes responsible for POI.

CONCLUSION

Taken together, the cytogenetic, cytogenomic (array CGH) and exome sequencing approaches have revealed a genetic causation in ∼20-25% of POI cases. Uncovering the remainder of the causative genes will be facilitated not only by whole genome approaches involving larger cohorts in multiple populations but also incorporating environmental exposures and exploring signaling pathways in intragenic and intergenic regions that point to perturbations in regulatory genes and networks.

A Major Gene for Bovine Ovulation Rate

Half-sib daughters sired by a bull believed to be a carrier of a major gene for high ovulation rate were evaluated for ovulation rate and genotyped in an effort to both test the hypothesis of segregation of a major gene and to map the gene’s location. A total of 131 daughters were produced over four consecutive years at a University of Wisconsin-Madison research farm. All were evaluated for ovulation rate over an average of four estrous cycles using transrectal ultrasonography. The sire and all daughters were genotyped using a 3K SNP chip and the genotype and phenotype data were used in a linkage analysis. Subsequently, daughters recombinant within the QTL region and the sire were genotyped successively with 50K and 777K SNP chips to refine the location of the causative polymorphism. Positional candidate genes within the fine-mapped region were examined for polymorphism by Sanger sequencing of PCR amplicons encompassing coding and 5’ and 3’ flanking regions of the genes. Sire DNA was used as template in the PCR reactions. Strong evidence of a major gene for ovulation rate was observed (p<1x10^-28) with the gene localized to bovine chromosome 10. Fine-mapping subsequently reduced the location to a 1.2 Mb region between 13.6 and 14.8 Mb on chromosome 10. The location identified does not correspond to that for any previously identified major gene for ovulation rate. This region contains three candidate genes, SMAD3, SMAD6 and IQCH. While candidate gene screening failed to identify the causative polymorphism, three polymorphisms were identified that can be used as a haplotype to track inheritance of the high ovulation rate allele in descendants of the carrier sire.

Evolutionary origin of bone morphogenetic protein 15 and growth and differentiation factor 9 and differential selective pressure between mono- and polyovulating species

Bone morphogenetic protein 15 (BMP15) and growth and differentiation factor 9 (GDF9) are TGFbeta-like oocyte-derived growth factors involved in ovarian folliculogenesis as critical regulators of many granulosa cell processes and ovulation rate. Ovarian phenotypic effect caused by alterations in BMP15 and GDF9 genes appears to differ between species and may be relevant to their mono- or polyovulating status. Through phylogenetic analysis we recently showed that these two paralogous genes are strongly divergent and in rapid evolution as compared to other members of the TGFbeta superfamily. Here, we evaluate the amino acid substitution rates of a set of proteins implicated in the ovarian function, including BMP15 and GDF9, with special attention to the mono- or polyovulating status of the species. Among a panel of mono- and polyovulating mammals, we demonstrate a better conservation of some areas in BMP15 and GDF9 within mono-ovulating species. Homology modeling of BMP15 and GDF9 homodimer and heterodimer 3-D structures was suggestive that these areas may be involved in dimer formation and stability. A phylogenetic study of BMP15/GDF9-related proteins reveals that these two genes diverged from the same ancestral gene along with BMP3 and GDF10, two other paralogous genes. A substitution rate analysis based on this phylogenetic tree leads to the hypothesis of an acquisition of BMP15/GDF9-specific functions in ovarian folliculogenesis in mammals. We propose that high variations observed in specific areas of BMP15 and GDF9 in polyovulating species change the equilibrium between homodimers and heterodimers, modifying the biological activity and thus allowing polyovulation to occur.

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.

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.

Species differences in the expression and activity of bone morphogenetic protein 15

Oocyte-derived bone morphogenetic protein 15 (BMP15) regulates ovulation rate and female fertility in a species-specific manner, being important in humans and sheep and largely superfluous in mice. To understand these species differences, we have compared the expression and activity of human, murine, and ovine BMP15. In HEK293F cells, human BMP15 is highly expressed (120 ng/ml), ovine BMP15 is poorly expressed (15 ng/ml), and murine BMP15 is undetectable. Because BMP15 synthesis is dependent upon interactions between the N-terminal prodomain and the C-terminal mature domain, we used site-directed mutagenesis to identify four prodomain residues (Glu(46), Glu(47), Leu(49), and Glu(50)) that mediate the high expression of human BMP15. Substituting these residues into the prodomains of murine and ovine BMP15 led to significant increases in growth factor expression; however, maximal expression was achieved only when the entire human prodomain was linked to the mature domains of the other species. Using these chimeric constructs, we produced and purified murine and ovine BMP15 and showed that in a COV434 granulosa cell bioassay, these molecules displayed little activity relative to human BMP15 (EC(50) 0.2nM). Sequence analysis suggested that the disparity in activity could be due to species differences at the type I receptor binding interface. Indeed, murine BMP15 activity was restored when specific residues through this region (Pro(329)/Tyr(330)) were replaced with the corresponding residues (Arg(329)/Asp(330)) from human BMP15. The identified differences in the expression and activity of BMP15 likely underlie the relative importance of this growth factor between species.

An update on primary ovarian insufficiency

Primary ovarian insufficiency (POI) occurs in about 1% of female population under the age of 40, leading to reproductive problems, an earlier encounter with menopausal symptoms, and complicated diseases. There are three presumable mechanisms involved in the development of POI, namely apoptosis acceleration, follicular maturation blocking and premature follicle activation, through the following studied causes: (i) chromosomal abnormalities or gene mutations: mostly involve X chromosome, such as FMR1 premutation; more and more potentially causal genes have been screened recently; (ii) metabolic disorders such as classic galactosaemia and 17-OH deficiency; (iii) autoimmune mediated ovarian damage: observed alone or with some certain autoimmune disorders and syndromes; but the specificity and sensitivity of antibodies towards ovary are still questionable; (iv) iatrogenic: radiotherapy or chemotherapy used in cancer treatment, as well as pelvic surgery with potential threat to ovaries' blood supply can directly damage ovarian function; (v) virus infection such as HIV and mumps; (vi) toxins and other environmental/lifestyle factors: cigarette smoking, toxins (e.g., 4-vinylcyclohexene diepoxide), and other environmental factors are associated with the development of POI. The etiology of a majority of POI cases is not identified, and is believed to be multifactorial. Strategies to POI include hormone replacement and infertility treatment. Assisted conception with donated oocytes has been proven to achieve pregnancy in POI women. Embryo cryopreservation, ovarian tissue cryopreservation and oocyte cryopreservation have been used to preserve ovarian reserve in women undergoing cancer treatments.

Identification and characterization of canine growth differentiation factor-9 and its splicing variant

Growth differentiation factor-9 (GDF-9), a member of the transforming growth factor-β (TGF-β) superfamily, is expressed exclusively in the oocyte within the ovary and plays essential roles in the ovarian function in mammals. However, a possible involvement of GDF-9 in canine ovarian physiology that has a unique ovulation process among mammals has not been studied. Interestingly, we have isolated two types of cDNA clones generated by an alternative splicing from a canine ovarian total RNA. The predominant long form cDNA shares a common precursor structure with GDF-9s in other species whereas the minor short form cDNA has a 172 amino acid truncation in the proregion. Using a transient expression system, we found that the long form cDNA has a defect in mature protein production whereas the short form cDNA readily produces mature protein. However, mutations at one or two N-glycosylation sites in the mature domain of the short form GDF-9 caused a loss in mature protein production. These results suggest that the prodomain and N-linked glycosylation of the mature domain regulate proper processing and secretion of canine GDF-9. Based on the biological functions of GDF-9, these characteristics of canine GDF-9 could be causatively linked to the unique ovulation process in the Canidae.

Unique bioactivities of bone morphogenetic proteins in regulation of reproductive endocrine functions

Remarkable progress has been made in understanding the mechanism by which growth factors and oocytes can regulate the development and function of granulosa cells. Insufficiency of two oocyte-specific growth factors, growth differentiation factor-9 and bone morphogenetic protein (BMP)-15, cause female infertility. Expression of mRNA and/or protein for the BMP system components, including ligands, receptors and intracellular signal transduction factors, was demonstrated in cell components of growing preantral follicles, and biofunctional experiments have further revealed many important roles of the BMP system in regulation of reproductive function. In this review, recent advances in studies on biological actions of BMPs in ovarian folliculogenesis and in related endocrine tissues are discussed.

Integral role of GDF-9 and BMP-15 in ovarian function

The oocyte plays an important role in regulating and promoting follicle growth, and thereby its own development, by the production of oocyte growth factors that predominantly act on supporting granulosa cells via paracrine signaling. Genetic studies in mice demonstrated critical roles of two key oocyte-derived growth factors belonging to the transforming growth factor-β (TGF-β) superfamily, growth and differentiation factor-9 (GDF-9) and bone morphogenetic protein-15 (BMP-15), in ovarian function. The identification of Bmp15 and Gdf9 gene mutations as the causal mechanism underlying the highly prolific or infertile nature of several sheep strains in a dosage-sensitive manner also highlighted the crucial role these two genes play in ovarian function. Similarly, large numbers of mutations in the GDF9 and BMP15 genes have been identified in women with premature ovarian failure and in mothers of dizygotic twins. The purpose of this article is to review the genetic studies of GDF-9 and BMP-15 mutations identified in women and sheep, as well as describing the various knockout and overexpressing mouse models, and to summarize the molecular and biological functions that underlie the crucial role of these two oocyte factors in female fertility.