Bmp15 mutations and ovarian function

Detection of Novel Variations Related to Litter Size in BMP15 Gene of Luzhong Mutton Sheep (Ovis aries)

Simple Summary

BMP15 is a critical gene in sheep reproduction. Most of its variations have been reported in European sheep. In this study, the entire open reading frame (ORF) region of BMP15 was sequenced in 154 Luzhong mutton sheep. Among 13 identified variations, six were novel. Four SNPs (ENSOART00000010201.1:c.352+342C>A, c.352+1232T>C, c.352+1165A>G and c.353-2036T>A) were significantly associated with litter size, and could be used as candidate genetic markers for improving litter size. The results also suggested possible interaction between BMP15 and FecB/GDF9.

Abstract

Litter size is an important economic trait in the mutton sheep industry. BMP15 is one of the key candidate genes for litter size in sheep. In this study, the entire ORF region of BMP15 was sequenced in 154 Luzhong mutton ewes, and the novel variations were determined. The association between polymorphism in BMP15 and litter size was analyzed using a general linear model. Six out of a total of thirteen variations were identified to be novel. Association analysis indicated that four (SNPs ENSOART00000010201.1:c.352+342C>A, c.352+1232T>C, c.352+1165A>G and c.353-2036T>A) were significantly associated with litter size. The joint analysis among three major genes (BMP15, BMPR1B and GDF9) exhibited significant interaction effects in three combinations (FecB and c.352+1232T>C of BMP15; FecB and c.352+1165A>G of BMP15; c.352+342C>A of BMP15 and ENSOART00000014382.1:c.994G>A of GDF9). For the SNPs c.352+1232T>C and c.352+342C>A, the global distribution of allele frequencies showed that the highest variation frequency occurs in Western Europe. In conclusion, the results demonstrated that BMP15 is a major gene for litter size in Luzhong mutton sheep and candidate SNPs associated with litter size were identified.

Effects of Human Endothelial Progenitor Cell and Its Conditioned Medium on Oocyte Development and Subsequent Embryo Development

Human endothelial progenitor cells (EPCs) secrete numerous growth factors, and they have been applied to regenerative medicine for their roles in angiogenesis as well as neovascularization. Angiogenesis is one of the essential factors for the maturation of ovarian follicles; however, the physiological function of EPCs or their derivatives on in vitro culture systems has not been fully understood. The aim of this study was to evaluate the effectiveness of EPCs and their conditioned medium (EPC-CM) on oocyte development and subsequent embryo development. In the results, the oocyte development and subsequent embryo development were significantly improved in EPCs and the EPC-CM group. In addition, markedly increased levels of growth factors/cytokines, such as basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), insulin growth factor-1 (IGF-1), interleukin-10 (IL-10), and epidermal growth factor (EGF), were observed in medium from the EPC-CM group. Additionally, EPC-CM after in vitro maturation (IVM) had significantly decreased reactive oxygen species (ROS) levels compared to those of other groups. Transcriptional levels of growth factor receptor-related genes (FGFR2, IGF1R) and anti-apoptotic-related gene (BCL2) were significantly upregulated in cumulus cells/oocytes from the EPC-CM group compared with those from the control. Furthermore, the expression levels of cumulus expansion-related genes (PTGS2, TNFAIP6, HAS2) and oocyte-maturation-related factors (GDF9, BMP15) were significantly enhanced in the EPC-CM group. Consequently, the present study provides the first evidence that EPC-CM contains several essential growth factors for oocyte development by regulating genes involved in oocyte maturation.

Use of the HRM Method in Quick Identification of FecXO Mutation in Highly Prolific Olkuska Sheep

Olkuska is a highly prolific sheep breed in Poland. Thanks to earlier identification of the genetic basis of its prolificacy, a mutation in the BMP-15 gene, we can use molecular biology tools to identify this causative mutation affecting prolificacy. In our research, we used the High-Resolution Melting (HRM) and Sanger sequencing methods to identify the genotypes of the studied animals. The result obtained by the HRM method is identical to those obtained by the sequencing method, which confirms the effectiveness of the HRM method and the possibility of quick and cheap identification of individuals with a FecXO mutation.

Effect of Melatonin on the In Vitro Maturation of Porcine Oocytes, Development of Parthenogenetically Activated Embryos, and Expression of Genes Related to the Oocyte Developmental Capability

Simple Summary

Exogenous melatonin has beneficial effects on improving cumulus oophorus expansion; mitochondrial distribution; intracellular level of glutathione; and first polar body extrusion rate of porcine oocytes derived from in vitro maturation. Moreover; melatonin supplementation increases relative abundances of BMP15 and CAT mRNA; and decreases intracellular levels of reactive oxygen species; and expression values of P53 and BAX genes; which are related to in vitro development of porcine oocytes.

Abstract

Melatonin treatment can improve quality and in vitro development of porcine oocytes, but the mechanism of improving quality and developmental competence is not fully understood. In this study, porcine cumulus–oocyte complexes were cultured in TCM199 medium with non-treated (control), 10⁻⁵ M luzindole (melatonin receptor antagonist), 10⁻⁵ M melatonin, and melatonin + luzindole during in vitro maturation, and parthenogenetically activated (PA) embryos were treated with nothing (control), or 10⁻⁵ M melatonin. Cumulus oophorus expansion, oocyte survival rate, first polar body extrusion rate, mitochondrial distribution, and intracellular levels of reactive oxygen species (ROS) and glutathione of oocytes, and cleavage rate and blastocyst rate of the PA embryos were assessed. In addition, expression of growth differentiation factor 9 (GDF9), tumor protein p53 (P53), BCL2 associated X protein (BAX), catalase (CAT), and bone morphogenetic protein 15 (BMP15) were analyzed by real-time quantitative PCR. The results revealed that melatonin treatment not only improved the first polar body extrusion rate and cumulus expansion of oocytes via melatonin receptors, but also enhanced the rates of cleavage and blastocyst formation of PA embryos. Additionally, melatonin treatment significantly increased intraooplasmic level of glutathione independently of melatonin receptors. Furthermore, melatonin supplementation not only significantly enhanced mitochondrial distribution and relative abundances of BMP15 and CAT mRNA, but also decreased intracellular level of ROS and relative abundances of P53 and BAX mRNA of the oocytes. In conclusion, melatonin enhanced the quality and in vitro development of porcine oocytes, which may be related to antioxidant and anti-apoptotic mechanisms.

Expression Analysis of the Prolific Candidate Genes, BMPR1B, BMP15, and GDF9 in Small Tail Han Ewes with Three Fecundity (FecB Gene) Genotypes

Simple Summary

As important prolific candidate genes, BMPR1B, BMP15, and GDF9 may affect the lambing performance of sheep. Therefore, regarding the three FecB genotypes of Small Tail Han (STH) sheep (FecB BB, FecB B+, and FecB ++), this study explored the gene expression characteristics of different tissues using reverse transcription PCR (RT-PCR) and real-time quantitative PCR (qPCR). The results showed that BMPR1B, BMP15, and GDF9 expression differed between the selected tissues, with all being highly expressed in the ovaries. Further analysis indicated that there was no significant difference in BMPR1B expression among the three FecB genotypes, but both GDF9 and BMP15 had the highest expression in FecB B+. As for other non-ovarian tissues, expression also varied. This study is relevant to understanding the high prolificacy of the STH breed.

Abstract

The expression characteristics of the prolific candidate genes, BMPR1B, BMP15, and GDF9, in the major visceral organs and hypothalamic–pituitary–gonadal (HPG) axis tissues of three FecB genotypes (FecB BB, FecB B+, and FecB ++) were explored in STH ewes using RT-PCR and qPCR. The results were as follows, BMPR1B was expressed in all FecB BB genotype (Han BB) tissues, and GDF9 was expressed in all selected tissues, but BMP15 was specifically expressed in the ovaries. Further study of ovarian expression indicated that there was no difference in BMPR1B expression between genotypes, but the FecB B+ genotype (Han B+) had greater expression of GDF9 and BMP15 than Han BB and FecB ++ genotype (Han ++) (p < 0.05, p < 0.01). BMP15 expression was lower in the ovaries of Han BB than in Han ++ sheep, but the reverse was shown for GDF9. The gene expression in non-ovarian tissues was also different between genotypes. Therefore, we consider that the three genes have an important function in ovine follicular development and maturation. This is the first systematic analysis of the tissue expression pattern of BMPR1B, BMP15, and GDF9 genes in STH sheep of the three FecB genotypes. These results contribute to the understanding of the molecular regulatory mechanism for ovine reproduction.

Interaction of the EGFR signaling pathway with porcine cumulus oocyte complexes and oviduct cells in a coculture system

It has become increasingly recognized that coculture has a beneficial effect on the in vitro maturation (IVM) of oocytes and embryo development in many species. However, these effects of coculture on IVM have been documented only for their positive conditioning roles without any evidence on the precise mechanisms underlying the action of coculture systems on the development of cumulus oocyte complexes (COCs). It has been suggested that the epidermal growth factor receptor (EGFR) signaling pathway is important for development of COCs, mediated by several epidermal growth factor (EGF)-like proteins with downstream mitogen-activated protein kinase 1/3 signaling. Therefore, we hypothesized that canine oviduct cells (OCs) in a coculture system, which shows improvement of oocyte quality in several species, are associated with EGFR signaling by exposure to progesterone (P4; imitating its production before ovulation and its continuous increase while oocytes reside in the oviduct to complete maturation in dogs). We designed three experimental groups: control, OCs coculture exposed to P4, and OCs coculture without exposure to P4. The result showed that the OCs coculture exposed to P4 strongly expressed EGF-like proteins and significantly improved COCs and subsequent embryo development. Furthermore, the expression of EGFR-related genes in cumulus cells and GDF9 and BMP15 in oocytes was upregulated in the P4-treated group. This study provides the first evidence that OCs exposed to P4 can induce strong expression of EGF-like proteins, and OCs effectively mediate improved porcine COCs development and subsequent embryo development by altering EGFR signaling related mRNA expression.

Acquisition of oocyte competence to develop as an embryo: integrated nuclear and cytoplasmic events

Infertility affects ~7% of couples of reproductive age with little change in incidence in the last two decades. ART, as well as other interventions, have made major strides in correcting this condition. However, and in spite of advancements in the field, the age of the female partner remains a main factor for a successful outcome. A better understanding of the final stages of gamete maturation yielding an egg that can sustain embryo development and a pregnancy to term remains a major area for improvement in the field. This review will summarize the major cellular and molecular events unfolding at the oocyte-to-embryo transition. We will provide an update on the most important processes/pathways currently understood as the basis of developmental competence, including the molecular processes involved in mRNA storage, its recruitment to the translational machinery, and its degradation. We will discuss the hypothesis that the translational programme of maternal mRNAs plays a key role in establishing developmental competence. These regulations are essential to assemble the machinery that is used to establish a totipotent zygote. This hypothesis further supports the view that embryogenesis begins during oogenesis. A better understanding of the events required for developmental competence will guide the development of novel strategies to monitor and improve the success rate of IVF. Using this information, it will be possible to develop new biomarkers that may be used to better predict oocyte quality and in selection of the best egg for IVF.

Effect of co-culture human endothelial progenitor cells with porcine oocytes during maturation and subsequent embryo development of parthenotes in vitro

Human endothelial progenitor cells (EPCs) have been applied to regenerative medicine for their roles in angiogenesis as well as neovascularization, and these angiogenetic functions have beneficial effects on maturation of ovarian follicles. However, little information is available on whether EPCs on culture systems affect oocyte maturation and subsequent embryo development. Therefore, the objective of this study was to investigate the effect of EPC co-culture on porcine oocytes during in vitro maturation (IVM) and subsequent embryo development, and to examine gene expression in cumulus cells, oocytes and blastocysts. The effect of co-culture using EPC on porcine oocyte IVM was investigated. Oocytes were activated using electrical stimulation and embryo developmental competence was estimated. The expression of the genes related to cumulus expansion, oocyte maturation, embryo development, and apoptosis were analyzed. In result, there was a significantly increased maturation rate in EPC group compared with control (p < 0.05). Also, oocytes co-cultured with EPCs exhibited significantly improved blastocyst formation rates (p < 0.05). The expression of mRNAs associated with cumulus expansion and apoptosis in cumulus cells was significantly up-regulated in EPC group. Also, markedly increased levels of GDF9, BMP15, and BCL2 were observed in oocytes from the EPC group. Blastocysts in the co-culture group showed significantly higher SOX2, OCT4, and NANOG levels. In conclusion, co-culturing porcine oocytes with EPCs improves their maturation by regulating genes involved in cumulus cell expansion, oocyte maturation, and apoptosis. Moreover, EPC co-culture during IVM enhanced embryo development as shown by increased blastocyst formation rate and pluripotency-related gene expression.

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.

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.

BMP15 regulates the inhibin/activin system independently of ovulation rate control in sheep

Polymorphisms in the gene encoding bone morphogenetic protein 15 (BMP15) have been associated with multiple ovulations in sheep. As BMP15 regulates inhibin expression in rodents, we assumed that the ovarian inhibin/activin system could mediate part of the effect of BMP15 mutations in the regulation of ovulation rate in sheep. To answer this question, we have studied the effects of two natural loss-of-function mutations of BMP15 on the expression of components of this system. The FecX^R and the FecX^Gr mutations, when present respectively in Rasa Aragonesa ewes at the heterozygous state and in Grivette ewes at the homozygous state, were associated with a twofold increase in ovulation rate. There were only small differences between mutant and wild-type ewes for mRNA expression of INHA, INHBA, ACVR1B, ACVR2A, FST or TGFBR3 in granulosa cells and inhibin A or activin A concentrations in follicular fluid. Moreover, the effects of mutations differed between breeds. In cultures of granulosa cells from wild-type ewes, BMP15, acting alone or in synergy with GDF9, stimulated INHA, INHBA and FST expression, but inhibited the expression of TGFBR3 Activin A did not affect INHBA expression, but inhibited the expression of ACVR2A also. The complexity of the inhibin/activin system, including positive and antagonistic elements, and the differential regulation of these elements by BMP15 and activin can explain that the effects of BMP15 mutations differ when present in different genetic backgrounds. In conclusion, the ovarian inhibin/activin system is unlikely to participate in the increase of ovulation rate associated with BMP15 mutations in sheep.

Characterization and Small RNA Content of Extracellular Vesicles in Follicular Fluid of Developing Bovine Antral Follicles

Exosomes and microvesicles (i.e., extracellular vesicles: EVs) have been identified within ovarian follicular fluid and recent evidence suggests that EVs are able to elicit profound effects on ovarian cell function. While existence of miRNA within EVs has been reported, whether EV size and concentration as well as their cargos (i.e., proteins and RNA) change during antral follicle growth remains unknown. Extracellular vesicles isolated from follicular fluid of small, medium and large bovine follicles were similar in size, while concentration of EVs decreased progressively as follicle size increased. Electron microscopy indicated a highly purified population of the lipid bilayer enclosed vesicles that were enriched in exosome biomarkers including CD81 and Alix. Small RNA sequencing identified a large number of known and novel miRNAs that changed in the EVs of different size follicles. Ingenuity Pathway Analysis (IPA) indicated that miRNA abundant in small follicle EV preparations were associated with cell proliferation pathways, while those miRNA abundant in large follicle preparations were related to inflammatory response pathways. These studies are the first to demonstrate that EVs change in their levels and makeup during antral follicle development and point to the potential for a unique vesicle-mediated cell-to-cell communication network within the ovarian follicle.

Effect of Anti-Müllerian hormone (AMH) and bone morphogenetic protein 15 (BMP-15) on steroidogenesis in primary-cultured human luteinizing granulosa cells through Smad5 signalling

PURPOSE

To determine if there is any effect of AMH and BMP-15 on estradiol and progesterone production from primary-cultured human luteinizing granulosa cells, to delineate what is the effect of FSH on their actions and which are the possible mechanisms involved.

METHODS

Luteinizing granulosa cells (GCs), obtained from follicular fluid of 30 women undergoing in vitro fertilization, were cultured, after a short 24-h preincubation period, in serum-free medium for 24 or/and 48 h in the presence/absence of various concentrations of AMH, BMP-15 and FSH alone or in combinations. Estradiol and progesterone production, SMAD5 phosphorylation and StAR expression were studied in parallel. Steroids were measured in culture-supernatant using enzyme-immunoassays, while Smad5-signaling pathway activation and StAR protein expression were assessed immunocytochemically.

RESULT(S)

We found that the treatment of AMH in GCs for 24/48 h attenuated FSH-induced estradiol production (p < 0.001), had no effect on basal estradiol levels, decreased basal progesterone production (p < 0.001) and FSH-induced StAR expression (p < 0.001). On the other hand, BMP-15 decreased basal estradiol levels (p < 0.001) and attenuated FSH-induced estradiol production (p < 0.001). Furthermore, BMP-15 reduced progesterone basal secretion (p < 0.001), an effect that was partially reversed by FSH (p < 0.01), probably via increasing StAR expression (p < 0.001). FSH-induced StAR expression was also attenuated by BMP-15 (p < 0.001). FSH, AMH and BMP-15 activated Smad-signaling pathway, as confirmed by the increase of phospo-Smad5 protein levels (p < 0.001 compared to control).

CONCLUSION(S)

AMH and BMP-15 by interacting with FSH affect the production of estradiol and progesterone from cultured luteinizing-granulosa cells possibly via Smad5-protein phosphorylation.

Creation of DNA aptamers against recombinant bone morphogenetic protein 15

The oocyte-derived growth factor bone morphogenetic protein (BMP) 15 plays important roles in fertility, but its mechanism of action differs between species. Generation of BMP15-binding molecules, as an essential investigation tool, would be helpful to provide valuable insight into the underlying biological features of BMP15. The BMP15-binding molecules could be antibodies or aptamers. Aptamers have many advantages over antibodies as macromolecular ligands for target proteins. DNA aptamers can be obtained by a method of Systematic Evolution of Ligands by EXponential enrichment (SELEX) beginning with a pool of random sequences. However, the success of this technique cannot be guaranteed if the initial pool lacks candidate sequences. Herein, we report on the creation of DNA aptamers by means of modified SELEX. The modification included enhanced mutation and progressive selection during an in vitro evolutionary process. As a proof-of-principle, we started from a single sequence instead of a multiple-sequence pool. Functional aptamers against the recombinant BMP15 were successfully created and identified.

Expression of maternally derived KHDC3, NLRP5, OOEP and TLE6 is associated with oocyte developmental competence in the ovine species

BACKGROUND

The sub-cortical maternal complex (SCMC), located in the subcortex of mouse oocytes and preimplantation embryos, is composed of at least four proteins encoded by maternal effect genes: OOEP, NLRP5/MATER, TLE6 and KHDC3/FILIA. The SCMC assembles during oocyte growth and was seen to be essential for murine zygote progression beyond the first embryonic cell divisions; although roles in chromatin reprogramming and embryonic genome activation were hypothesized, the full range of functions of the complex in preimplantation development remains largely unknown.

RESULTS

Here we report the expression of the SCMC genes in ovine oocytes and pre-implantation embryos, describing for the first time its expression in a large mammalian species. We report sheep-specific patterns of expression and a relationship with the oocyte developmental potential in terms of delayed degradation of maternal SCMC transcripts in pre-implantation embryos derived from developmentally incompetent oocytes. In addition, by determining OOEP full length cDNA by Rapid Amplification of cDNA Ends (RACE) we identified two different transcript variants (OOEP1 and OOEP2), both expressed in oocytes and early embryos, but with different somatic tissue distributions. In silico translation showed that 140 aminoacid peptide OOEP1 shares an identity with orthologous proteins ranging from 95% with the bovine to 45% with mouse. Conversely, OOEP2 contains a premature termination codon, thus representing an alternative noncoding transcript and supporting the existence of aberrant splicing during ovine oogenesis.

CONCLUSIONS

These findings confirm the existence of the SCMC in sheep and its key role for the oocyte developmental potential, deepening our understanding on the molecular differences underlying cytoplasmic vs nuclear maturation of the oocytes. Describing differences and overlaps in transcriptome composition between model organisms advance our comprehension of the diversity/uniformity between mammalian species during early embryonic development and provide information on genes that play important regulatory roles in fertility in nonmurine models, including the human.

Evidence supporting a functional requirement of SMAD4 for bovine preimplantation embryonic development: a potential link to embryotrophic actions of follistatin

Transforming growth factor beta (TGFbeta) superfamily signaling controls various aspects of female fertility. However, the functional roles of the TGFbeta-superfamily cognate signal transduction pathway components (e.g., SMAD2/3, SMAD4, SMAD1/5/8) in early embryonic development are not completely understood. We have previously demonstrated pronounced embryotrophic actions of the TGFbeta superfamily member-binding protein, follistatin, on oocyte competence in cattle. Given that SMAD4 is a common SMAD required for both SMAD2/3- and SMAD1/5/8-signaling pathways, the objectives of the present studies were to determine the temporal expression and functional role of SMAD4 in bovine early embryogenesis and whether embryotrophic actions of follistatin are SMAD4 dependent. SMAD4 mRNA is increased in bovine oocytes during meiotic maturation, is maximal in 2-cell stage embryos, remains elevated through the 8-cell stage, and is decreased and remains low through the blastocyst stage. Ablation of SMAD4 via small interfering RNA microinjection of zygotes reduced proportions of embryos cleaving early and development to the 8- to 16-cell and blastocyst stages. Stimulatory effects of follistatin on early cleavage, but not on development to 8- to 16-cell and blastocyst stages, were observed in SMAD4-depleted embryos. Therefore, results suggest SMAD4 is obligatory for early embryonic development in cattle, and embryotrophic actions of follistatin on development to 8- to 16-cell and blastocyst stages are SMAD4 dependent.

The endocrinology of the menstrual cycle

The ovulatory menstrual cycle is the result of the integrated action of the hypothalamus, pituitary, ovary, and endometrium. Like a metronome, the hypothalamus sets the beat for the menstrual cycle by the pulsatile release of gonadotropin-releasing hormone (GnRH). GnRH pulses occur every 1-1.5 h in the follicular phase of the cycle and every 2-4 h in the luteal phase of the cycle. Pulsatile GnRH secretion stimulates the pituitary gland to secrete luteinizing hormone (LH) and follicle stimulating hormone (FSH). The pituitary gland translates the tempo set by the hypothalamus into a signal, LH and FSH secretion, that can be understood by the ovarian follicle. The ovarian follicle is composed of three key cells: theca cells, granulosa cells, and the oocyte. In the ovarian follicle, LH stimulates theca cells to produce androstenedione. In granulosa cells from small antral follicles, FSH stimulates the synthesis of aromatase (Cyp19) which catalyzes the conversion of theca-derived androstenedione to estradiol. A critical concentration of estradiol, produced from a large dominant antral follicle, causes positive feedback in the hypothalamus, likely through the kisspeptin system, resulting in an increase in GnRH secretion and an LH surge. The LH surge causes the initiation of the process of ovulation. After ovulation, the follicle is transformed into the corpus luteum, which is stimulated by LH or chorionic gonadotropin (hCG) should pregnancy occur to secrete progesterone. Progesterone prepares the endometrium for implantation of the conceptus. Estradiol stimulates the endometrium to proliferate. Estradiol and progesterone cause the endometrium to become differentiated to a secretory epithelium. During the mid-luteal phase of the cycle, when progesterone production is at its peak, the secretory endometrium is optimally prepared for the implantation of an embryo. A diagrammatic representation of the intricate interactions involved in coordinating the menstrual cycle is provided in Fig. 1.

BMP15 suppresses progesterone production by down-regulating StAR via ALK3 in human granulosa cells

In addition to somatic cell-derived growth factors, oocyte-derived growth differentiation factor (GDF)9 and bone morphogenetic protein (BMP)15 play essential roles in female fertility. However, few studies have investigated their effects on human ovarian steroidogenesis, and fewer still have examined their differential effects or underlying molecular determinants. In the present study, we used immortalized human granulosa cells (SVOG) and human granulosa cell tumor cells (KGN) to compare the effects of GDF9 and BMP15 on steroidogenic enzyme expression and investigate potential mechanisms of action. In SVOG cells, neither GDF9 nor BMP15 affects the mRNA levels of P450 side-chain cleavage enzyme or 3β-hydroxysteroid dehydrogenase. However, treatment with BMP15, but not GDF9, significantly decreases steroidogenic acute regulatory protein (StAR) mRNA and protein levels as well as progesterone production. These suppressive effects, along with the induction of Sma and Mad-related protein (SMAD)1/5/8 phosphorylation, are attenuated by cotreatment with 2 different BMP type I receptor inhibitors (dorsomorphin and DMH-1). Furthermore, depletion of activin receptor-like kinase (ALK)3 using small interfering RNA reverses the effects of BMP15 on SMAD1/5/8 phosphorylation and StAR expression. Similarly, knockdown of ALK3 abolishes BMP15-induced SMAD1/5/8 phosphorylation in KGN cells. These results provide evidence that oocyte-derived BMP15 down-regulates StAR expression and decreases progesterone production in human granulosa cells, likely via ALK3-mediated SMAD1/5/8 signaling. Our findings suggest that oocyte may play a critical role in the regulation of progesterone to prevent premature luteinization during the late stage of follicle development.

Importance of the GDF9 signaling pathway on cumulus cell expansion and oocyte competency in sheep

Acquisition of developmental competency in cumulus oocyte complexes (COCs) is derived from endocrine hormones and oocyte secreted factors. The contribution of these factors in oocyte maturation and development is an active area of research. The objective of this research was to investigate whether growth differentiation factor 9 (GDF9) that is secreted by oocyte affects cumulus expansion and oocyte development in sheep. Immature ovine COCs were cultured in the presence of recombinant human GDF9 (rhGDF9), denuded oocytes, SB-431542, a specific inhibitor of activin-like kinase 4/5/7; or a combination of these factors. Routine in vitro maturation of COCs and denuded oocytes were used as external control samples. Cultured COCs were used for assessment of (1) cumulus expansion; (2) expression of cumulus-related transcripts including pentraxin 3, hyaluronan synthase 2 (HAS2), tumor necrosis factor alpha-induced protein 6, prostaglandin synthase 2, B-cell lymphoma 2 (BCL2), and Bcl2-associated X (BAX); and (3) yield and quality of embryo development. It was observed that cumulus expansion was not affected by any of these treatments. HAS2 mRNA expression confirmed this observation. In the presence of exogenous GDF9, cleavage rate was reduced, blastocyst rate did not differ from other groups, and trophectoderm cell number significantly increased. This suggests that exogenous GDF9 could improve embryo quality. It was also observed that oocyte secreted factors reduced proapoptotic BAX mRNA, and BCL2 mRNA expression was not significantly different from other groups. This study provides evidence that GDF9 signaling might have a minor influence on ovine cumulus expansion and oocyte development and that other signaling pathway(s) might have a dominant role.

Characterization of the exonic regions of the JY-1 gene in zebu cattle and buffaloes

Protein JY-1 is an oocyte-specific protein that plays an important regulatory role in the granulosa cell layer and during the early embryo development stages. It is the first specific protein of maternal origin discovered in a single-ovulating species. In this study, the exon regions of the JY-1 gene were characterized by sequencing in 20 unrelated cattle (Bos taurus indicus) and 20 unrelated buffaloes (Bubalus bubalis). Eighteen polymorphisms were detected in cattle and 10 polymorphisms in buffaloes. Some of the polymorphisms were identified in codifying regions and caused amino acid changes. The insertion of a thymine was detected in the codifying region of exon 3 of the buffalo sequence when compared to the cattle one. This insertion causes a change in the codons frameshift from this point onwards, modifying the 19 terminal amino acids of the buffalo protein and creating a premature stop codon. This finding may explain reproductive differences between cattle and buffaloes in terms of follicle recruitment, embryo development and incidence of twin pregnancies.

Ovarian reserve and anti-Mullerian hormone (AMH) in mothers of dizygotic twins

This study aimed to explore if natural dizygotic (DZ) twinning is associated with earlier menopause and lower anti-Mullerian hormone (AMH) values. We investigated if advanced biological reproductive aging, which can be responsible for the multiple follicle growth in familial twinning, is similar to mechanisms that occur in normal ovarian aging, reflected by earlier menopause in mothers of DZ twins and lower levels of AMH. A total of 16 mothers of DZ twins enrolled with the Netherlands Twin Register (average age at first assessment: 35.9 ± 3.0 years) and 14 control mothers (35.1 ± 3 years) took part in a prospective study. Fifteen years after entry into the study, which included follicle-stimulating hormone (FSH) assessment, AMH was measured in stored serum samples and menopause status was evaluated. Average AMH levels were not significantly different between DZ twin mothers and controls (2.1 ± 2.4 μg/L vs. 1.9 ± 1.9 μg/L). Among the 16 mothers of twins, 7 had an elevated (FSH) value over 10 U/L at first assessment. Their AMH levels were lower than the nine twin mothers with normal FSH values: 0.6 ± 0.4 versus 3.4 ± 2.6 μg/L (p = .01). Of the mothers of twins, eight mothers had entered menopause at the second assessment compared with only one control mother (p = .07). Thus, slightly more DZ mothers were in menopause than the control mothers, although this difference was not significant. The subgroup of DZ twin mothers who had an increased FSH concentration 15 years ago had a limited ovarian reserve as reflected by lower AMH levels. These data indicate that advanced ovarian aging can be a feature in familial DZ twinning, particularly with elevated early follicular phase FSH.

Quantitative analysis of bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) gene expression in calf and adult bovine ovaries

BACKGROUND

It has been reported that calf oocytes are less developmentally competent than oocytes obtained from adult cows. Bone morphogenetic protein 15 (BMP15) and growth and differentiation factor 9 (GDF9) play critical roles in folliculogenesis, follicular development and ovulation in mammalian ovaries. In the present study, we attempted to compare the expression patterns of BMP15 and GDF9 in the cells of calf and cow ovaries to determine a relationship between the level of these genes and the low developmental competence of calf oocytes.

METHODS

Bovine tissues were collected from 9-11 months-old calves and from 4-6 years-old cows. We characterized the gene expression of BMP15 and GDF9 in calf and adult bovine oocytes and cumulus cells using quantitative real-time reverse transcriptase polymerase chain reaction (QPCR) and in situ hybridization. Immunohistochemical analysis was also performed.

RESULTS

The expression of BMP15 and GDF9 in cumulus cells of adult ovaries was significantly higher than that in calf ovaries, as revealed by QPCR. GDF9 expression in the oocytes of calf ovaries was significantly higher than in those of the adult ovaries. In contrast, BMP15 expression in the oocytes of calf and adult ovaries was not significantly different. The localization of gene expression and protein were ascertained by histochemistry.

CONCLUSIONS

Our result showed for the first time BMP15 and GDF9 expression in bovine cumulus cells. BMP15 and GDF9 mRNA expression in oocytes and cumulus cells was different in calves and cows.

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.

Subfertility caused by altered follicular development and oocyte growth in female mice lacking PKB alpha/Akt1

Mammalian females are endowed with a finite number of primordial follicles at birth. Immediately following formation of the primordial follicle pool, cohorts of follicles are either culled from the ovary or are recruited to grow until the primordial follicle population is depleted. The majority of ovarian follicles, including the oocytes, undergo atresia through apoptotic cell death. As PKB alpha/Akt1 is known to regulate apoptosis, we asked whether Akt1 functioned in the regulation of folliculogenesis in the ovary. Akt1(-/-) females display reduced fertility and abnormal estrous cyclicity. At Postnatal Day (PND) 25, Akt1(-/-) ovaries possessed a reduced number of growing antral follicles, significantly larger primary and secondary oocytes, and an increase in the number of degenerate oocytes. By PND90, there was a significant decrease in the number of primordial follicles in Akt1(-/-) ovaries relative to Akt1(+/+). In vivo granulosa cell proliferation was reduced, as were expression levels of Kitl and Bcl2l1, two factors associated with granulosa cell proliferation/survival. No compensation was observed by Akt2 or Akt3 at the mRNA/protein level. Significantly higher serum LH and trends for lower FSH and higher inhibin A and lower inhibin B relative to Akt1(+/+) females were observed in Akt1(-/-) females. Exposure to exogenous gonadotropins resulted in an increase in the number of secondary follicles in Akt1(-/-) ovaries, but few mature follicles. Collectively, our results suggest that PKB alpha/Akt1 plays an instrumental role in the regulation of the growth and maturation of the ovary, and that the loss of PKB alpha/Akt1 results in premature ovarian failure.

BMP15 mutations associated with primary ovarian insufficiency cause a defective production of bioactive protein

Bone morphogenetic protein-15 (BMP15) is selectively synthesized by oocytes as a pre-proprotein and is considered an ovarian follicle organizer whose adequate function is critical for female fertility. Missense mutations were reported in primary ovarian insufficiency (POI) but their biological impact remained unexplored. Here, screening of 300 unrelated idiopathic overt POI women with primary or secondary amenorrhea (SA) led to the identification of six heterozygous BMP15 variations in 29 of them. All alterations are nonconservative and include one insertion of three nucleotides (p.L262_L263insL) and five missense substitutions. Except for the p.S5R located in the signal sequence, the other variants (p.R68W, p.R138H, p.L148P, and p.A180T) localize in the proregion, which is essential for the processing and secretion of bioactive dimers. The mutations p.R68W, p.L148P, and the novel p.R138H lead to marked reductions of mature protein production. Their biological effects, evaluated by a novel luciferase-reporter assay in a human granulosa cell (GC) line, were significantly reduced. Cotransfection experiments of defective mutants with equal amounts of wild-type BMP15 cDNA, thus reproducing the heterozygous state seen in patients, did not generate a complete recovery of wild-type activity. No or minor deleterious effects were detected for the variants p.L262_L263insL, p.A180T, or p.S5R. In conclusion, heterozygous BMP15 mutations associated with the early onset of overt POI lead to defective secretion of bioactive dimers. These findings support the concept that an adequate amount of BMP15 secreted in the follicular fluid is critical for female fertility. We propose to consider the screening of BMP15 mutations among the analyses for the prediction of POI risk.

Polymorphisms in GDF9 and BMP15 associated with fertility and ovulation rate in Moghani and Ghezel sheep in Iran

The genetic base of fertility and ovulation rate in Moghani and Ghezel sheep in northwestern Iran and northeastern Turkey is important because of their fat-tailed meat and carpet quality wool. The genes encoding bone morphogenetic (BM) protein 15 and growth differentiation (GD) factor 9, respectively BMP15 and GDF9 have been shown to affect female productivity in domesticated sheep. Recently, numerous investigations have been performed on a variety of breeds to determine the association between mutations in these genes and fertility. Thus, in this study, we assessed such mutations in the Moghani and Ghezel breeds using polymerase chain reaction (PCR)-based restriction fragment length polymorphism (RFLP) with appropriate enzymes. Our data were similar to those of the previous studies showing that the genotypes were heterozygous for GD (G -->A) and BM (C -->T) mutations. These heterozygous genotypes resulted in higher ovulation rates, illustrating that one copy of each of the BMP15 and GDF9 mutations had equivalent effects on the ovulation rate. We demonstrate for the first time that the BM variant may not be sufficient on its own for infertility. In addition, although the previous studies have shown no notable relationship between the GD variant, known as the non-effecting mutation and sterility, we report that this mutation has an important role in the Moghani and Ghezel breeds.

Bone morphogenetic protein 15 expression in human ovaries from fetuses, girls, and women

OBJECTIVE

To investigate, for the first time, the protein expression of bone morphogenetic protein (BMP) 15 in human ovaries from fetuses, girls/women as well as its mRNA transcripts in ovaries from fetuses and girls.

DESIGN

Controlled immunohistochemical and in situ hybridization study of expression of BMP-15 protein and mRNA transcripts in human ovaries.

SETTING

Major tertiary care academic center.

PATIENT(S)

Nine patients that underwent pregnancy terminations at 21-33 gestational weeks and 18 girls and women aged 5-39 years that underwent ovarian laparoscopies.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Immunohistochemistry (protein detection) in all specimens and in situ hybridization (mRNA detection) in specimens from fetuses and girls. Both procedures were conducted on paraffin sections.

RESULT(S)

The expression of the BMP-15 protein and its mRNA was identified already from primordial stages. Protein expression was detected in all oocytes and stroma cells from both ovarian sources, and in granulosa cells of specimens from girls and women. The mRNA transcripts were detected in the oocyte, granulosa, and stroma cells from fetuses and girls.

CONCLUSION(S)

The BMP-15 protein is expressed already at primordial stages in fetuses, girls, and women, and its mRNA transcripts in fetuses and girls. Further studies should be conducted to elucidate if indeed BMP-15 is involved in the activation of human primordial follicles.

[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.

Postnatal uterine development in Inverdale ewe lambs

Postnatal development of the uterus involves, particularly, development of uterine glands. Studies with ovariectomized ewe lambs demonstrated a role for ovaries in uterine growth and endometrial gland development between postnatal days (PNDs) 14 and 56. The uterotrophic ovarian factor(s) is presumably derived from the large numbers of growing follicles in the neonatal ovary present after PND 14. The Inverdale gene mutation (FecXI) results in an increased ovulation rate in heterozygous ewes; however, homozygous ewes (II) are infertile and have 'streak' ovaries that lack normal developing of preantral and antral follicles. Uteri were obtained on PND 56 to determine whether postnatal uterine development differs between wild-type (++) and II Inverdale ewes. When compared with wild-type ewes, uterine weight of II ewes was 52% lower, and uterine horn length tended to be shorter, resulting in a 68% reduction in uterine weight:length ratio in II ewes. Histomorphometrical analyses determined that endometria and myometria of II ewes were thinner and intercaruncular endometrium contained 38% fewer endometrial glands. Concentrations of estradiol in the neonatal ewes were low and not different between ++ and II ewes, but II ewes had lower concentrations of testosterone and inhibin-alpha between PNDs 14 and 56. Receptors for androgen and activin were detected in the neonatal uteri of both ++ and II ewes. These results support the concept that developing preantral and/or antral follicles of the ovary secrete uterotrophic factors, perhaps testosterone or inhibin-alpha, that acts in an endocrine manner to stimulate uterine growth and endometrial gland development in the neonatal ewes.

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.

JY-1, an oocyte-specific gene, regulates granulosa cell function and early embryonic development in cattle

Oocyte-specific gene products play a key role in regulation of fertility in mammals. Here, we describe the discovery, molecular characterization, and function of JY-1, a bovine oocyte-expressed gene shown to regulate both function of ovarian granulosa cells and early embryogenesis in cattle and characteristics of JY-1 loci in other species. The JY-1 gene encodes for a secreted protein with multiple mRNA transcripts containing an identical ORF but differing lengths of 3' UTR. JY-1 mRNA and protein are oocyte-specific and detectable throughout folliculogenesis. Recombinant JY-1 protein regulates function of follicle-stimulating hormone-treated ovarian granulosa cells, resulting in enhanced progesterone synthesis accompanied by reduced cell numbers and estradiol production. JY-1 mRNA of maternal origin is also present in early bovine embryos, temporally regulated during the window from meiotic maturation through embryonic genome activation, and is required for blastocyst development. The JY-1 gene has three exons and is located on bovine chromosome 29. JY-1-like sequences are present on syntenic chromosomes of other vertebrate species, but lack exons 1 and 2, including the protein-coding region, suggestive of species specificity in evolution and function of this oocyte-specific gene.

Heterozygote advantage for fecundity

Heterozygote advantage, or overdominance, remains a popular and persuasive explanation for the maintenance of genetic variation in natural populations in the face of selection. However, despite being first proposed more than 80 years ago, there remain few examples that fit the criteria for heterozygote advantage, all of which are associated with disease resistance and are maintained only in the presence of disease or other gene-by-environment interaction. Here we report five new examples of heterozygote advantage, based around polymorphisms in the BMP15 and GDF9 genes that affect female fecundity in domesticated sheep and are not reliant on disease for their maintenance. Five separate mutations in these members of the transforming growth factor beta (TGFbeta) superfamily give phenotypes with fitness differentials characteristic of heterozygous advantage. In each case, one copy of the mutant allele increases ovulation rate, and ultimately litter size per ewe lambing, relative to the wildtype. However, homozygous ewes inheriting mutant alleles from both parents have impaired oocyte development and maturation, which results in small undeveloped ovaries and infertility. Using data collected over many years on ovulation rates, litter size, and lambing rates, we have calculated the equilibrium solution for each of these polymorphisms using standard population genetic theory. The predicted equilibrium frequencies obtained for these mutant alleles range from 0.11 to 0.23, which are amongst the highest yet reported for a polymorphism maintained by heterozygote advantage. These are amongst the most frequent and compelling examples of heterozygote advantage yet described and the first documented examples of heterozygote advantage that are not reliant on a disease interaction for their maintenance.

Differential gene expression of bone morphogenetic protein 15 and growth differentiation factor 9 during in vitro maturation of porcine oocytes and early embryos

Bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) belong to the TGF-beta superfamily and are involved in the regulation of folliculogenesis. Though there are many reports concerning the expression and regulation of GDF9 in the process of oocyte maturation, expression of BMP15 during oocyte maturation is still not clearly understood. It has been reported that BMP15 and GDF9 expression is important in folliculogeneiss and that the regulation of these two proteins is complex and species-specific. In this report, we investigated the expression of BMP15 and GDF9 genes during in vitro maturation (IVM) at 0, 6, 12, 18, 24, 30, 36, 42 and 48 h for porcine oocytes. Porcine GDF9 gene was found to be highly expressed in immature oocytes and declined slowly during the oocyte maturation process. BMP15mRNA and its encoded protein were expressed at low levels in immature oocytes and increased to the highest level at 18 h of IVM, which coincides with the time of cumulus cell expansion. Thus, these two genes were differentially expressed during the oocyte maturation process and BMP15 is specifically expressed during cumulus cell expansion in porcine oocytes.

Smad signalling in the ovary

It has now been a decade since the first discovery of the intracellular Smad proteins, the downstream signalling molecules of one of the most important growth factor families in the animal kingdom, the transforming growth factor beta (TGF-beta) superfamily. In the ovary, several TGF-beta superfamily members are expressed by the oocyte, granulosa and thecal cells at different stages of folliculogenesis, and they signal mainly through two different Smad pathways in an autocrine/paracrine manner. Defects in the upstream signalling cascade molecules, the ligands and receptors, are known to have adverse effects on ovarian organogenesis and folliculogenesis, but the role of the individual Smad proteins in the proper function of the ovary is just beginning to be understood for example through the use of Smad knockout models. Although most of the different Smad knockouts are embryonic lethal, it is known, however, that in Smad1 and Smad5 knockout mice primordial germ cell development is impaired and that Smad3 deficient mice harbouring a deletion in exon 8 exhibit impaired folliculogenesis and reduced fertility. In this minireview we discuss the role of Smad structure and function in the ovarian context.

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

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

Evidence for a functional bone morphogenetic protein (BMP) system in the porcine ovary

Bone morphogenetic proteins (BMPs) play important roles in controlling fertility and ovulation rate. There is however, little information on the BMP system in the ovary of a large polyovular species. The aims of the present study were to investigate BMP-2 and -6 protein expression in the porcine ovary, their effects on granulosa cells in culture and their mechanism of action. Cells and oocytes were recovered from healthy antral follicles 2-6mm in diameter. When assessed by Western blotting, oocytes and follicular fluid contained BMP-2 and -6. In addition, BMP-2 and -6 were observed in granulosa cells and BMP-2 was also found in theca cells. Granulosa cells were cultured in a serum-free system for 144 h in the presence of increasing doses (0, 3, 30 and 100 ng/ml) of BMP-2 or BMP-6. Both BMPs suppressed progesterone production in a dose-dependent manner after 48 h (P<0.001) and 144 h (P<0.05). Only BMP-6 stimulated cell proliferation at 100 ng/ml (P<0.05). Investigation into the mechanism of action found that BMP-2 and -6 decreased cyclic adenosine monophosphate (cAMP) production (P<0.01), expression of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) protein (P<0.001) and steroidogenic acute regulatory protein (StAR) (BMP-6 only; P<0.05). This supports the hypothesis that BMP-2 and -6 act as luteinization inhibitors. In conclusion, these findings provide evidence for the presence of a complex signalling mechanism in the porcine ovary and suggest that both BMP-2 and -6 may act in a paracrine manner to control granulosa cell function in this large polyovulatory species.

Molecular biology and physiological role of the oocyte factor, BMP-15

The oocyte factor, bone morphogenetic protein-15 (BMP-15) has proven to be critical for normal fertility in female mammals. The biological functions of recombinant BMP-15 demonstrate its capacity to promote granulosa cell processes involved in early follicle growth, while simultaneously acting to restrict follicle-stimulating hormone (FSH)-induced granulosa cell differentiation. The in vitro biological activities of BMP-15 demonstrate its role in promoting early follicle growth through the stimulation of granulosa cell mitosis while simultaneously restricting FSH-induced follicle development through the suppression of FSH receptor mRNA expression. The in vivo relevance of the role of BMP-15 was established by the identification of naturally occurring BMP-15 mutations in sheep, which cause infertility in homozygous carrier ewes and, in striking contrast, increased fecundity in heterozygous carrier ewes due to an increase in ovulation quota. The necessity of BMP-15 for folliculogenesis in women has been recently established by the discovery of a BMP-15 mutation that is associated with ovarian dysgenesis. In contrast to the pronounced effects that the BMP-15 mutations have on folliculogenesis in sheep and humans, mice, which are homozygous for targeted deletions of BMP-15 exhibit only minimal defects in the ovulation process, leading to the proposal that there may be causal differences in the BMP-15 system of mono- and polyovulatory animals. Collectively, recent research on the oocyte-secreted factor BMP-15 has provided exciting new opportunities for understanding ovarian physiology and female fertility.

Posttranslational processing of mouse and human BMP-15: potential implication in the determination of ovulation quota

There has been significant attention to the growing recognition that oocytes have a critical capacity to organize and govern surrounding somatic cells. Bone morphogenetic protein 15 (BMP-15) is an oocyte-secreted factor that has raised particular interest due to its established role in determining ovulation quota and female fertility in mammals. As a first step in determining whether there are species-specific differences in the BMP-15 system that may play causal roles in the differences in ovulation quota observed in different mammalian species, we here compare the molecular characteristics of BMP-15 of polyovulatory mice with that of monoovulatory humans. We found that, although human BMP-15 mature protein is readily produced, there are defects in the production of mouse BMP-15 mature protein in an in vitro system of transfected cells. The generation of chimeric constructs consisting of different combinations of mouse and human BMP-15 proregions, cleavage sites, and mature regions indicates that the defects in the production of mouse BMP-15 mature protein depend on the presence of the mouse BMP-15 proregion. The mouse proregion also caused a significant reduction in the production of human BMP-15 mature protein. The coexpression with a convertase cleavage enzyme, furin, results in complete processing of all these chimeras; however, no mouse mature protein is detected in either secreted or cell-confined forms except when associated with the human proregion. Based on the biological role of BMP-15, defects in the production of mouse BMP-15 mature protein could correlate with the high ovulation quota and litter size observed in mice.

Are BMP-15 and GDF-9 primary determinants of ovulation quota in mammals?

How do mammals control the number of eggs that are ovulated during the estrous and menstrual cycles? Our understanding of this fundamental process has grown in recent years as a result of intense efforts to identify and characterize the genes that control the ovulation quota. An increasing body of evidence shows that two oocyte-specific factors, bone morphogenetic protein-15 (BMP-15) and growth and differentiation factor-9 (GDF-9), play crucial roles in determining folliculogenesis, ovulation rate and litter size in sheep and mice. In this article, we review recent advances on the physiological, cellular and molecular roles of BMP-15 and GDF-9, which, potentially, link these oocyte-secreted factors to the species-specific determination of ovulation quota and litter size in mammals.

Growth Differentiation Factor-9 and Stem Cell Factor Promote Primordial Follicle Formation in the Hamster: Modulation by Follicle-Stimulating Hormone1

Growth differentiation factor-9 (GDF-9) and stem cell factor (SCF) influence follicle formation beyond the primary stage; however, factors influencing the formation of primordial follicles remain elusive. To determine whether GDF-9 and SCF promoted primordial follicle formation during ovarian morphogenesis in the hamster, and whether FSH had any modulatory influence, fetal ovaries were collected on Gestation Day 15 from pregnant hamsters treated with or without an FSH antiserum on Gestation Day 12 and cultured in vitro up to Day 9 with SCF, GDF-9, or FSH. The percentages and diameters of primordial, primary, and secondary follicles and their oocytes were determined by morphometric evaluation, and the expression of GDF-9 was detected by immunolocalization. SCF, GDF-9, and FSH promoted primordial and primary follicle formation, but GDF-9 was more efficient. The diameters of the follicles developed under GDF-9 or FSH, but not SCF, compared well with those developed in vivo. FSH- and GDF-9-induced folliculogenesis was attenuated by the SCF antibody. Similarly, in vitro formation of primordial follicles decreased markedly in ovaries exposed to the FSH antiserum in utero, which was reversed by SCF, GDF-9, or FSH; however, GDF-9 had a profound effect on follicular development. GDF-9 protein appeared exclusively in the oocytes on Postnatal Day 4; however, it appeared in vitro by 48 h, and the expression was upregulated by FSH. These results suggest that although SCF-induced primordial follicle formation constitutes primarily somatic cell development, GDF-9 influences both the oocyte and its companion somatic cells. FSH plays an important role in primordial folliculogenesis in the hamster via GDF-9 and SCF.

The bone morphogenetic protein system in mammalian reproduction

Using molecular, cellular, and genetic approaches, recent studies examining the role of the bone morphogenetic protein (BMP) family of growth factors in the reproductive system have led to significant breakthroughs in our understanding of mammalian reproduction and fertility. Gene expression studies have revealed that key components of the BMP system (ligands, receptors, signaling molecules, and binding proteins) exhibit coordinated spatial and temporal expression patterns in fundamental cell types throughout the reproductive system. Availability of recombinant BMPs has enabled functional studies that have demonstrated important biological activities of BMPs in controlling cellular proliferation, differentiation, and apoptosis in reproductive tissues. The physiological importance of the BMP system for mammalian reproduction has been further highlighted by the elucidation of the aberrant reproductive phenotypes of animals with naturally occurring mutations or targeted deletions of certain BMP family genes. Collectively, these studies have established the concept that the BMP system plays a crucial role in fertility in female and male mammals. The purpose of this article is to review the evidence underpinning the importance of the BMP system in mammalian reproduction.

Towards an embryocentric world: the current and potential uses of embryo technologies in dairy production

Structural features of the dairy industry make it well situated to use embryo technologies as tools for enhancing the genetic merit of dairy cattle and improving fertility. Technologies dependent upon embryo transfer have the potential to increase the efficiency of quantitative genetic selection as well as marker-assisted selection, simplify cross-breeding and germplasm conservation procedures and allow incorporation of transgenes into dairy cattle. In addition, embryo technologies may prove useful in improving fertility in infertile populations of lactating cows. The realisation of the promise of embryo technologies has been constrained by suboptimal efficiency in the production of embryos, alterations in embryonic and fetal survival and development associated with in vitro embryo production and cloning, as well as other technical and societal concerns. Solutions to many of these constraints are possible and the use of embryo technologies in both nucleus and commercial herds is likely to increase. Eventually, embryo transfer may compete with artificial insemination as a dominant method for establishing pregnancies in dairy cattle.

Novel perspective: focusing on the X chromosome in reproductive cancers

In an XX female, one of the two X chromosomes has been inactivated during early embryonic life to achieve a compensation of X-linked gene products between males and females, leaving only one allele of X-linked genes functional. There are some X-linked genes escaping the X-inactivation, i.e., being expressed from both alleles. Escape from X-inactivation varies at different levels; some genes have both alleles active in some women but only one allele active in others, whereas some other genes have both alleles active in neoplastic tissue but only one allele active normally. The X-inactivation may be considered functionally equivalent to a loss of heterozygosity (LOH) for some genes, whereas escape from X-inactivation may be equivalent to functional gene amplification for others. The physiological LOH may make X-linked tumor suppressor genes lose their function more easily, compared with autosomal tumor suppressor genes, thus predisposing women to cancer formation more easily. Moreover, the human X chromosome contains many genes related to cancer or to sex and reproduction. All these properties of the X chromosome suggest that it may play more important roles than any autosomal chromosome in the development and progression of reproductive and urologic cancers.

Ovarian follicle growth and consequences for fertility in sheep

Understanding the pattern of ovarian follicle development is seen as an important step leading to the development of techniques that maximise fertility in sheep. Repeated observations of the growth of individual follicles have led to the understanding that follicles develop in a wave-like pattern during the oestrous cycle, with two to four waves per cycle being the most common. The ease with which follicle waves are described seems to depend on the their frequency and the number of follicles per wave. There is evidence for the largest follicle(s) of a follicle wave inhibiting the development of other follicles; however, in some cases this is not apparent as other follicle waves emerge when a previous large, healthy follicle is still present. Follicle development can be manipulated using exogenous gonadotrophins or progestagens and these have been shown to alter the number or age profile of developing follicles. The ovulation of aged follicles in cattle clearly has a detrimental effect on fertility, but this relationship is less clear and seems to be less critical in sheep. Recent findings at the molecular level show that the bone morphogenetic proteins (BMP) and their receptors are critically involved in the control of ovulation rate, but fully understanding their mechanism remains to be described. This highlights the potential for the integration of molecular and physiological findings to better develop methods to manipulate follicle development and reproduction in sheep.

Developmental and molecular aberrations associated with deterioration of oogenesis during complete or partial follicle-stimulating hormone receptor deficiency in mice

Targeted disruption of the mouse FSH receptor gene (FSH-R) that mediates the action of the FSH results in a gene dose-related ovarian phenotype in the developing as well as the adult animal. While null females (FORKO) are sterile, the haplo-insufficient mice experience early reproductive senescence. The purpose of this study was to first record changes in oocyte development in the null FORKO and haplo-insufficient mice. Oocyte growth is significantly retarded in the null mutants with thinner zona pellucida in preantral follicles, but thicker zona pellucida in secondary follicles. This morphometric change indicates developmental aberrations in coordination of the germ cell (oocyte) and the somatic granulosa cell (GC) compartments. Markers for primordial germ cell proliferation and oocyte growth, such as the c-Kit/Kit-ligand and bone morphogenetic protein-15 (BMP-15) were downregulated in both null and +/- ovaries, suggesting disrupted communication between oocyte and GCs. Extensive changes in the expression of other oocyte-specific gene products like the zona pellucida glycoproteins (zona pellucida A, B, and C) indicate major alteration in the extracellular matrix surrounding the germ cells. This led to leaky germ cells that allowed infiltration of somatic cells. These results show that the loss of FSH-R signaling alters the follicular environment, where oocyte-granulosa interactions are perturbed, creating an out-of-phase germ cell and somatic cell development. We believe that these data provide an experimental paradigm to explore the mechanisms responsible for preserving the structural integrity and quality of oocytes at different ages.