Positive selection in bone morphogenetic protein 15 targets a natural mutation associated with primary ovarian insufficiency in human

Adaptive evolution and functional significance of the PPARGC1A gene across diverse animal species

Codon-based analyses of the PPARGC1A gene across 38 vertebrate species were deployed to elucidate patterns of evolutionary change. Employing maximum likelihood assessments through MEGA, we scrutinized 447 codon positions addressing the entire coding region, excluding positions mired by gaps or missing data. Distinct codons manifested variance in selection pressures, particularly codons 4, 11, 66, and 123, which exhibited positive dN-dS values suggestive of positive selection. Codon 137 displayed the most pronounced dN-dS value, signifying intensified selective advantage. Meanwhile, codons 30 and 90 portrayed near-neutral scores, indicative of purifying selection. Complementary computational methods (IFEL, REL, FUBAR, and SLAC) confirmed positive selection at specific codon sites, with varying degrees of corroboration. The integration of mixed-effect modeling (MEME) identified episodic diversifying selection, pinpointing codons that underwent selection episodes in certain lineages. Refined codon model selection lent insight into substitution rates, revealing nuanced degrees of evolutionary conservation among different codons. Supporting these genetic insights, the phylogenetic analysis highlighted relationships among the PPARGC1A sequences and domain analysis confirmed conserved features across species, while protein-protein interaction networks suggested a complex web of functional interdependencies. These findings advance our understanding of the PPARGC1A gene's evolutionary trajectory and underscore the gene's potential adaptive significance within diverse vertebrate lineages.

Mechanism of Guilu Erxian ointment based on targeted metabolomics in intervening in vitro fertilization and embryo transfer outcome in older patients with poor ovarian response of kidney-qi deficiency type

OBJECTIVE

To study the effect of Guilu Erxian ointment on the outcome of IVF-ET in older patients with poor ovarian response infertility of kidney-qi deficiency type, and to verify and analyze the mechanism of action of traditional Chinese medicine on improving older patients with poor ovarian response infertility of kidney-qi deficiency type from the perspective of metabolomics using targeted metabolomics technology, identify the related metabolic pathways, and provide metabolic biomarker basis and clinical treatment ideas for improving older patients with poor ovarian response infertility.

METHODS

This study was a double-blind, randomized, placebo-controlled trial, and a total of 119 infertile patients who underwent IVF-ET at Shandong Center for Reproduction and Genetics of Integrated Traditional Chinese and Western Medicine were selected. Eighty older patients with infertility undergoing IVF were randomly divided into older treatment group and older placebo group, and another 39 young healthy women who underwent IVF-ET or ICSI due to male factors were selected as the normal control group. Flexible GnRH antagonist protocol was used for ovulation induction in all three groups, and Guilu Erxian ointment and placebo groups started taking Guilu Erxian ointment and placebo from the third day of menstruation until IVF surgery. And ultra-high performance liquid chromatography-triple quadrupole mass spectrometer (UHPLC-QTRAP MS) was used to detect metabolites in the three groups of samples.

RESULTS

Compared with the placebo group, the number of oocytes retrieved, 2PN fertilization, high-quality embryos, total number of available embryos and estrogen on HCG day were increased in the treatment group, and the differences were statistically significant (P > 0.05), but the clinical pregnancy rate of fresh embryos and frozen embryos were not statistically significant (P > 0.05). The results of targeted metabolomics analysis showed that follicular fluid in the treatment group clustered with the normal young group and deviated from the placebo group. A total of 55 significant differential metabolites were found in the follicular fluid of older patients with poor ovarian response of kidney-qi deficiency type and patients in the normal young group, after Guilu Erxian ointment intervention, Metabolites such as L-Aspartic acid, Glycine, L-Serine, Palmitoleic Acid, Palmitelaidic acid, L-Alanine, Gamma-Linolenic acid, Alpha-Linolenic Acid, and N-acetyltryptophan were down-regulated, mainly involving amino acid metabolism and fatty acid metabolism.

CONCLUSION

Guilu Erxian ointment can effectively improve the clinical symptoms and IVF outcomes of older patients with poor ovarian response of kidney-qi deficiency type. There were differences in follicular fluid metabolites between older patients with poor ovarian response of kidney-qi deficiency type and normal women. L-Aspartic acid, L-Alanine, Aminoadipic acid, L-Asparagine, L-Arginine, L-Serine, Gamma- Linolenic acid, Pentadecanoic acid and Alpha-Linolenic Acid are closely related to older patients with poor ovarian response due to deficiency of kidney-qi and may be inferred as biomarkers. The mechanism of Guilu Erxian ointment intervention may be mainly through amino acid metabolism and fatty acid metabolism regulation.

In Silico Study and Effects of BDMC33 on TNBS-Induced BMP Gene Expressions in Zebrafish Gut Inflammation-Associated Arthritis

The bone morphogenic protein (BMP) family is a member of the TGF-beta superfamily and plays a crucial role during the onset of gut inflammation and arthritis diseases. Recent studies have reported a connection with the gut-joint axis; however, the genetic players are still less explored. Meanwhile, BDMC33 is a newly synthesized anti-inflammatory drug candidate. Therefore, in our present study, we analysed the genome-wide features of the BMP family as well as the role of BMP members in gut-associated arthritis in an inflammatory state and the ability of BDMC33 to attenuate this inflammation. Firstly, genome-wide analyses were performed on the BMP family in the zebrafish genome, employing several in silico techniques. Afterwards, the effects of curcumin analogues on BMP gene expression in zebrafish larvae induced with TNBS (0.78 mg/mL) were determined using real time-qPCR. A total of 38 identified BMP proteins were revealed to be clustered in five major clades and contain TGF beta and TGF beta pro peptide domains. Furthermore, BDMC33 suppressed the expression of four selected BMP genes in the TNBS-induced larvae, where the highest gene suppression was in the BMP2a gene (an eight-fold decrement), followed by BMP7b (four-fold decrement), BMP4 (four-fold decrement), and BMP6 (three-fold decrement). Therefore, this study reveals the role of BMPs in gut-associated arthritis and proves the ability of BDMC33 to act as a potential anti-inflammatory drug for suppressing TNBS-induced BMP genes in zebrafish larvae.

Premature ovarian insufficiency - the need for a genomic map

Premature ovarian insufficiency (POI) is a life-long disorder of heterogeneous etiology, presenting as adolescent primary amenorrhea in its most severe form, with an overall incidence of 1%. Idiopathic POI accounts for up to 70% of women with POI; and genomic, genetic, epidemiological, familial and cohort studies demonstrate a genetic component to this condition. Currently, the only genetic tests routinely performed in non-syndromic POI are FMR1 premutation and cytogenetics, the latter specifically for X-chromosome abnormalities. However, a myriad of genetic aberrations has been identified and implicated, some of which act in a monogenic Mendelian fashion. The presence of multiple genetic aberrations and the complexity of POI genomics are hardly surprising since the embryological formation of the primordial oocyte pool, postnatal oogenesis and folliculogenesis are all highly complex pathways. With this review, the aim is to discuss the current genetic etiologies in the emerging field of POI genomics. Promising candidate genes include STAG3, SYCE1, FIGLA, NOBOX, FSHR, BMP15 and INHA. This area has the potential to progress rapidly in light of advances in genomic technologies. The development of a POI genomic map not only will assist in understanding the underlying molecular mechanisms affecting ovarian function but will also be essential in designing predictive and diagnostic gene panels as well as future novel therapeutic strategies.

Characterization of a novel mutation V136L in bone morphogenetic protein 15 identified in a woman affected by POI

Background

Premature ovarian insufficiency (POI) is an ovarian defect characterized by primary or secondary amenorrhea, hypergonadotropism and hypoestrogenism which occurs before the age of 40 years with a major genetic component. In this study we performed clinical evaluation and genetic analysis of a group of 18 patients with POI.

The study involved 18 consecutive women with POI. Karyotiping and genetic analysis for research of mutations in GDF9 (Growth Differentation Factor 9) and BMP15 (Bone morphogentic protein 15) genes and FMR1 (Fragile X Mental Retardation 1) premutation were carried out. In vitro functional study of the novel BMP15 mutation was performed using COV434 (Human ovarian granulosa tumour cells 434) cells of ovarian granulosa, which consistently express BMP responsive element, and luciferase reporter assay.

Results

Three patients (17%) had a family history of POI. Ten patients (56%) had a family history of autoimmune diseases and nine patients (50%) showed a personal history of one or more autoimmune diseases. Of patients for whom morphological assessment was available, almost half (44%) had poor follicle assets or small ovaries’s size at pelvic US. Two patients (13%) showed reduced bone density at DEXA (Dual Energy X-ray Absorptiometry). All the women had normal female kariotype and no mutations in the GDF-9 gene or FMR1 premutations were found. A novel heterozygous mutation c.406G > C (V136L) of BMP15 gene was identified in one patient. After transfection in COV434 cells, BMP15 variant showed a significantly reduced luciferase activity compared to wild type.

Conclusions

POI is a multifactorial disease with several health implications. Autoimmunity and genetics represent the most common aetiology. We identified and characterized a novel BMP15 mutation, providing an additional elucidation of molecular basis of this complex disorder.

Adaptive Molecular Evolution of AKT3 Gene for Positive Diversifying Selection in Mammals

The V-Akt Murine Thymoma Viral Oncogene Homolog 3 (AKT3) gene is of the serine/threonine-protein kinase family and influences the production of milk fats and cholesterol by acting on the sterol administrative area restricting protein (SREBP). The AKT3 gene is highly preserved in animals, and during lactation in cattle, its expression increases. The AKT3 gene is expressed in the digestive system, mammary gland, and immune cells. A phylogenetic investigation was performed to clarify the evolutionary role of AKT3, by maximum probability. The AKT3 gene sequence data of various mammalian species was evident even with animals undergoing breeding selection. From 39 mammalian species studied, there was a signal of positive diversifying selection with Hominidae at 13Q, 16G, 23R, 24P, 121P, 294K, 327V, 376L, 397K, 445T, and 471F among other codon sites of the AKT3 gene. These sites were codes for amino acids such as arginine, proline, lysine, and leucine indicating major roles for the function of immunological proteins, and in particular, the study highlighted the importance of changes in gene expression of AKT3 on immunity.

Oocyte-Secreted Factors Synergize With FSH to Promote Aromatase Expression in Primary Human Cumulus Cells

CONTEXT

The role of growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) on aromatase regulation is poorly understood in humans.

OBJECTIVE

Determine GDF9 and BMP15 effects on FSH stimulation of estradiol production in primary human cumulus granulosa cells (GCs). We hypothesized that the combination of GDF9 and BMP15 potentiates FSH-induced aromatase expression.

DESIGN

Primary human cumulus GCs in culture.

SETTING

University infertility center.

PATIENTS OR OTHER PARTICIPANTS

GCs of 60 women undergoing in vitro fertilization were collected.

INTERVENTIONS

Cells were treated with GDF9 and/or BMP15 (GB) in the presence or absence of FSH, dibutyryl cAMP, or SMAD inhibitors.

MAIN OUTCOME MEASURES

Promoter activity, mRNA, protein, and estradiol levels were quantified.

RESULTS

FSH and GB treatment increased CYP19A1 promoter activity, mRNA, and protein levels as well as estradiol when compared with cells treated with FSH only. GB treatment potentiated cAMP stimulation of aromatase and IGF2 stimulation by FSH. GB effects were inhibited by SMAD3 inhibitors and IGF1 receptor inhibitors. GB, but not FSH, stimulates SMAD3 phosphorylation.

CONCLUSION

The combination of GDF9 and BMP15 potently stimulates the effect of FSH and cAMP on CYP19a1 promoter activity and mRNA/protein levels. These effects translate into an increase in estradiol production. This potentiation seems to occur through activation of the SMAD2/3 and SMAD3 signaling pathway and involves, at least in part, the effect of the IGF system.

Connecting links between genetic factors defining ovarian reserve and recurrent miscarriages

PURPOSE

Approximately 1-2% of the women faces three or more successive spontaneous miscarriages termed as recurrent miscarriage (RM). Many clinical factors have been attributed so far to be the potential risk factors in RM, including uterine anomalies, antiphospholipid syndrome, endocrinological abnormalities, chromosomal abnormalities, and infections. However, in spite of extensive studies, reviews, and array of causes known to be associated with RM, about 50% cases encountered by treating physicians remains unknown. The aims of this study were to evaluate recent publications and to explore oocyte-specific genetic factors that may have role in incidence of recurrent miscarriages.

METHOD

Recent studies have identified common molecular factors contributing both in establishment of ovarian reserve and in early embryonic development. Also, studies have pointed out the relationship between the age-associated depletion of OR and increase in the risk of miscarriages, thus suggestive of an interacting biology. Here, we have gathered literature evidences in establishing connecting links between genetic factors associated with age induced or pathological OR depletion and idiopathic RM, which are the two extreme ends of female reproductive pathology.

CONCLUSION

In light of connecting etiological link between infertility and RM as reviewed in this study, interrogating the oocyte-specific genes with suspected roles in reproductive biology, in cases of unexplained RM, may open new possibilities in widening our understanding of RM pathophysiology.

GDF-9 and BMP-15 direct the follicle symphony

Understanding the physiology underlying the complex dialog between the oocyte and its surrounding somatic cells within the ovarian follicle has been crucial in defining optimal procedures for the development of clinical approaches in ART for women suffering from infertility and ovarian dysfunction. Recent studies have implicated oocyte-secreted factors like growth differentiation factor 9 (GDF-9) and bone morphogenetic protein 15 (BMP-15), members of the transforming growth factor-beta (TGFβ) superfamily, as potent regulators of folliculogenesis and ovulation. These two factors act as biologically active heterodimers or as homodimers in a synergistic cooperation. Through autocrine and paracrine mechanisms, the GDF-9 and BMP-15 system has been shown to regulate growth, differentiation, and function of granulosa and thecal cells during follicular development playing a vital role in oocyte development, ovulation, fertilization, and embryonic competence. The present mini-review provides an overview of recent findings relating GDF-9 and BMP-15 as fundamental factors implicated in the regulation of ovarian function and discusses their potential role as markers of oocyte quality in women.

"Evaluation of four genes associated with primary ovarian insufficiency in a cohort of Mexican women"

PURPOSE

Primary ovarian insufficiency (POI) is a clinical condition observed in women younger than 40 years of age, characterized by amenorrhea, hypoestrogenism, high levels of follicle-stimulating hormone (FSH), and infertility. Mutations in some master regulators of the development, maturation, and maintenance of ovarian follicles such as BMP15, FSHR, FOXL2, and GDF9 have been suggested as etiological factors in the development of POI. The aim of this study, the first in the Mexican population, is to evaluate the presence of mutations or polymorphisms in these four candidate genes.

METHODS

In a sample of 20 Mexican patients with idiopathic POI, we looked for and analyzed genetic variants in BMP15, FSHR, FOXL2, and GDF9 genes.

RESULTS

We observed two polymorphisms: a coding change, c.919G>A (p.Ala307Thr), in the FSHR gene and a synonymous variant, c.447C>T (p.Thr149Thr), in the GDF9 gene. These two variants have been reported previously as polymorphisms (rs6165 and rs254286, respectively). We observed no significant difference associated with POI in the patients when compared with a healthy control group (p > 0.05). Also, no exonic variants were found for the genes BMP15 and FOXL2 in the individuals tested.

CONCLUSIONS

The lack of association of the evaluated genes in this sample of Mexican women is consistent with the complex genetic etiology of POI that is observed across cohorts studied thus far.

A common African variant of human connexin 37 is associated with Caucasian primary ovarian insufficiency and has a deleterious effect in vitro

Folliculogenesis requires communication between granulosa cells and oocytes, mediated by connexin-based gap junctions. Connexin 37 (Cx37)-deficient female mice are infertile. The present study assessed Cx37 deficiency in patients with primary ovarian insufficiency (POI). A candidate gene study was performed in patients and controls from the National Genotyping Center (Evry, France) including 58 Caucasian patients with idiopathic isolated POI and 142 Caucasian controls. Direct genomic sequencing of the coding regions of the GJA4 gene (encoding Cx37) was performed with the aim to identify a deleterious variant associated with POI and absent in ethnically matched controls. A single Cx37 variant absent in the control population was identified, namely a c.946G>A heterozygous substitution leading to a p.Gly316Ser variant that was present in two POI patients. This variant was absent in all Caucasian controls from various databases, and has been observed exclusively in African populations. This variant was identified to have a dominant negative effect in HeLa cells in vitro to alter connexon function (by 67.2±7.17%), as determined by Gap-fluorescence recovery after photobleaching. The alteration principally resulted from a decrease of cell surface connexons due to altered trafficking (by 47.73±8.59%). In marked contrast to this observation, a p.Pro258Ser variant frequent in all ethnic populations in databases had no functional effect in vitro. In conclusion, the present study reported on a Cx37 variant in two Caucasian POI patients, which was absent in control Caucasian populations, and which had a deleterious effect in vitro. It is therefore suggested that in the genetic context of the Caucasian population, this variant may contribute to POI.

Maximum-likelihood approaches reveal signatures of positive selection in BMP15 and GDF9 genes modulating ovarian function in mammalian female fertility

Bone morphogenetic proteins (BMPs) and the growth factors (GDFs) play an important role in ovarian folliculogenesis and essential regulator of processes of numerous granulosa cells. BMP15 gene variations linked to various ovarian phenotypic consequences subject to the species, from infertility to improved prolificacy in sheep, primary ovarian insufficiency in women or associated with minor subfertility in mouse. To study the evolving role of BMP15 and GDF9, a phylogenetic analysis was performed. To find out the candidate gene associated with prolificacy in mammals, the nucleotide sequence of BMP15 and GDF9 genes was recognized under positive selection in various mammalian species. Maximum‐likelihood approaches used on BMP15 and GDF9 genes exhibited a robust divergence and a prompted evolution as compared to other TGFβ family members. Furthermore, among 32 mammalian species, we identified positive selection signals in the hominidae clade resulting to 132D, 147E, 163Y, 191W, and 236P codon sites of BMP15 and 162F, 188K, 206R, 240A, 244L, 246H, 248S, 251D, 253L, 254F and other codon sites of GDF9. The positively selected amino acid sites such as Alanine, Lucien, Arginine, and lysine are important for signaling. In conclusion, this study evidences that GDF9 and BMP15 genes have rapid evolution than other TGFß family members and was subjected to positive selection in the mammalian clade. Selected sites under the positive selection are of remarkable significance for the particular functioning of the protein and consequently for female fertility.

Genetics of primary ovarian insufficiency

Primary ovarian insufficiency (POI) is characterized by a loss of ovarian function before the age of 40 and account for one major cause of female infertility. POI relevance is continuously growing because of the increasing number of women desiring conception beyond 30 years of age, when POI prevalence is >1%. POI is highly heterogeneous and can present with ovarian dysgenesis and primary amenorrhea, or with secondary amenorrhea, and it can be associated with other congenital or acquired abnormalities. In most cases POI remains classified as idiopathic. However, the age of menopause is an inheritable trait and POI has a strong genetic component. This is confirmed by the existence of several candidate genes, experimental and natural models. The variable expressivity of POI defect may indicate that, this disease may frequently be considered as a multifactorial or oligogenic defect. The most common genetic contributors to POI are the X chromosome-linked defects. Here, we review the principal X-linked and autosomal genes involved in syndromic and non-syndromic forms of POI with the expectation that this list will soon be upgraded, thus allowing the possibility to predict the risk of an early age at menopause in families with POI.

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.

Association between BMP15 Gene Polymorphism and Reproduction Traits and Its Tissues Expression Characteristics in Chicken

BMP15 (Bone morphogenetic protein 15) is an oocyte-secreted growth factor required for ovarian follicle development and ovulation in mammals, but its effects on reproduction in chickens are unclear. In this study, the association between BMP15 polymorphisms and reproduction traits were analyzed, and its expression characteristics in different tissues were explored in LaiWu Black chickens. Three single nucleotide polymorphisms (SNPs) were identified in four hundred LaiWu Black chickens. One SNP (NC_006091.3:g.1773T>C) located in exon 2 which was significantly associated with egg weight at first egg (EWFE) (P = 0.0389), was novel. Diplotypes based on the three SNPs were found to be significantly associated with egg weight at age of 43W (EW43) (P = 0.0058). The chickens with H3H3 diplotype had their first egg 0.57 days later than chickens with H5H5 diplotype and 1.21 days-3.96 days earlier than the other five diplotype chickens. The egg production at age of 43W (E43), egg production at age of 46W (E46) and egg production at age of 48W (E48) for chickens with H3H3 diplotype were the highest among all the chickens, and the E48 of chickens with H3H3 diplotype had 11.83 eggs higher than chickens with H1H5 diplotype. RT-qPCR results showed that the expression level of BMP15 gene in ovarian follicle was in the order of 4 mm>6 mm -8 mm> 15 mm -19 mm> 23 mm -29 mm > 33 mm -34 mm in diameter. The mRNA level in follicles of 4 mm and 6-8 mm in diameter were significantly higher than that in the other follicles (P<0.01). In the same week, the highest mRNA level was found in the ovary, and it was significantly different from that found in the liver and oviduct (P<0.01). Our results indicate that BMP15 plays a vital role in the development of ovary and follicles, especially in the development of primary follicles. H3H3 may be an potential advantageous molecular marker for improving reproduction traits in chickens.

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.