In vitro production of meiotically competent oocytes from early antral follicles in sheep

The potential of using long in vitro culture (LIVC) of cumulus-oocyte complexes (COCs) from early antral follicles (EAFs) as an assisted reproductive technology in cattle has shown promising results. This study explored the feasibility of applying this technology to sheep as seasonal breeding animals. Ovaries from sheep were collected during both the breeding and non-breeding seasons. COCs were isolated from EAFs (350-450 μm) and cultured in TCM199 medium supplemented with 0.15 μg/mL Zn sulfate, 10-4IU/mL FSH, 10 ng/mL estradiol, 50 ng/mL testosterone, 50 ng/mL progesterone, and 5 μM Cilostamide. After five days of LIVC, the COCs were submitted to an in vitro maturation procedure. The results indicate successful in vitro development of COCs, evidenced by a significant increase in oocyte diameter (p < 0.000) and the preservation of gap junction communication between oocyte and cumulus cells. The gradual uncoupling was accompanied by a progressive chromatin transition from the non-surrounded nucleolus (NSN) to the surrounded nucleolus (SN) (p < 0.000), coupled with a gradual decrease in global transcriptional activity and an increase in oocyte meiotic competence (p < 0.000). Maintenance of oocyte-cumulus investment architecture, viability, and metaphase II capability was significantly higher in COCs collected during the breeding season (p < 0.000), suggesting higher quality than those obtained during the non-breeding season. In conclusion, our study confirms LIVC feasibility in sheep, emphasizing increased effectiveness during the breeding season in isolating higher-quality COCs from EAFs. These findings can influence improving the LIVC system in mammals with seasonal reproduction.

Oocyte and cumulus cell cooperativity and metabolic plasticity under the direction of oocyte paracrine factors

Mammalian oocytes develop and mature in a mutually dependent relationship with surrounding cumulus cells. The oocyte actively regulates cumulus cell differentiation and function by secreting soluble paracrine oocyte-secreted factors (OSFs). We characterized the molecular mechanisms by which two model OSFs, cumulin and BMP15, regulate oocyte maturation and cumulus-oocyte cooperativity. Exposure to these OSFs during mouse oocyte maturation in vitro altered the proteomic and multispectral autofluorescence profiles of both the oocyte and cumulus cells. In oocytes, cumulin significantly upregulated proteins involved in nuclear function. In cumulus cells, both OSFs elicited marked upregulation of a variety of metabolic processes (mostly anabolic), including lipid, nucleotide, and carbohydrate metabolism, whereas mitochondrial metabolic processes were downregulated. The mitochondrial changes were validated by functional assays confirming altered mitochondrial morphology, respiration, and content while maintaining ATP homeostasis. Collectively, these data demonstrate that cumulin and BMP15 remodel cumulus cell metabolism, instructing them to upregulate their anabolic metabolic processes, while routine cellular functions are minimized in the oocyte during maturation, in preparation for ensuing embryonic development.NEW & NOTEWORTHY Oocyte-secreted factors (OSFs) promote oocyte and cumulus cell cooperativity by altering the molecular composition of both cell types. OSFs downregulate protein catabolic processes and upregulate processes associated with DNA binding, translation, and ribosome assembly in oocytes. In cumulus cells, OSFs alter mitochondrial number, morphology, and function, and enhance metabolic plasticity by upregulating anabolic pathways. Hence, the oocyte via OSFs, instructs cumulus cells to increase metabolic processes on its behalf, thereby subduing oocyte metabolism.

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

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

Application of specific ELISAs for BMP15 and GDF9 to cumulus cell extracts from infertile women

Bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) are oocyte-specific paracrine factors which regulate ovarian cumulus cell (CC) functions. This study aimed to investigate if BMP15 and GDF9 bound to CCs can be characterized, quantified, and show an association with IVF outcomes in infertile women. BMP15 and GDF9 ELISAs were validated and applied to discarded CC extracts. Pooled CCs from individual patients were collected from 120 (cohort 1; BMP15 only) and 81 infertility patients (cohort 2; BMP15 and GDF9) undergoing superovulation. BMP15 and GDF9 levels expressed per CC DNA were correlated with maternal age, clinical and embryology data. Total BMP15 and GDF9 were highly correlated with each other (r = 0.9, p < 0.001). The GDF9:BMP15 ratio was unrelated to oocyte number or age. BMP15/CC DNA and GDF9/CC DNA were unaffected by the type of superovulation and were not related to oocyte/embryo outcomes.

Idebenone relieves the damage of heat stress on the maturation and developmental competence of porcine oocytes

The reproductive function of animals is often affected by climatic conditions. High-temperature conditions can cause damage to oocyte maturation and embryonic development in a variety of ways. The purpose of this study was to prove that supplementation idebenone (IDB) to the maturation medium can improve the maturation and development of porcine oocytes after heat stress (HS). Porcine cumulus-oocyte complexes (COCs) were cultured in the maturation medium with different concentrations of IDB (0, 0.1, 1 and 10 μM) for 44 hr at either 38.5°C or under the HS conditions. The cumulus oophorus expansion, nuclear maturation and blastocyst rate after parthenogenetic activation (PA) were measured. We found that HS (in vitro maturation 20-24 hr, 42°C) exposure significantly reduced cumulus expansion index and maturation rate of oocytes and the blastocyst rate of PA embryos, while IDB supplementation significantly improved oocyte maturation and development to the blastocysts stage after PA. Moreover, the addition of IDB decreased the intracellular level of ROS and increased GSH content, hence enhancing the antioxidant capacity of oocytes under HS. Meanwhile, IDB treatment also obviously improved the mitochondrial membrane potential and ATP synthesis of oocytes under HS conditions. Furthermore, IDB treatment increased the expression of GDF9 and BMP15 in IVM oocytes which attribute to improve the quality and outcome of IVM oocytes and the development competence of PA embryos in pigs. In summary, we demonstrated that IDB supplementation into the maturation medium exerted protective effects and improved the ability of maturation and developmental competence of porcine oocytes exposed to HS.

Effects of selected hormones and their combination on progesterone and estradiol production and proliferation of feline granulosa cells cultured in vitro

Little is known about the hormonal regulation of feline ovarian granulosa cell proliferation and steroidogenesis. The present study aimed to develop a hormone responsive granulosa cell culture system to measure steroidogenic and cell proliferation responses to help identify factors that might regulate ovarian function in queens. Five experiments were conducted each with 75 or more ovaries, three in spring and two in fall seasons. Granulosa cells were isolated and treated in vitro with various hormones in serum-free medium for 48 h after an initial 48 h plating in 10% fetal calf serum. In granulosa cells isolated from spring and fall collected feline ovaries, IGF1 alone and combined with FSH stimulated (P < 0.05) cell proliferation, whereas FSH alone had no effect (P > 0.10) on cell proliferation. Also, in granulosa cells collected in spring and fall, IGF1 alone and FSH alone increased (P < 0.05) estradiol production by severalfold, and a combination of FSH and IGF1 increased (P < 0.05) estradiol production above either FSH or IGF1 treatment alone. The FSH plus IGF1 treatment increased (P < 0.05) CYP19A1 mRNA abundance by 27-fold. In contrast, EGF decreased (P < 0.05) FSH plus IGF1-induced estradiol production by over 80% in granulosa cells of both spring and fall collected ovaries. In granulosa cells isolated from spring and fall collected ovaries, IGF1 plus FSH inhibited (P < 0.05) progesterone production. Melatonin increased (P < 0.05) FSH plus IGF1-induced cell proliferation and amplified (P < 0.05) the FSH plus IGF1-induced inhibition of progesterone production. However, melatonin and GH had no effect (P > 0.10) on estradiol production either alone or in combination with FSH plus IGF1 in both spring and fall. Prolactin, FGF9 and activin had no effect (P > 0.10) on cell proliferation or steroidogenesis. FGF2 decreased (P < 0.05) estradiol production without affecting progesterone production or cell numbers. Growth differentiation factor 9 (GDF9) increased (P < 0.05) progesterone production but had no effect (P > 0.10) on granulosa cell proliferation or estradiol production. In conclusion, the in vitro system described herewithin may be useful to assess and evaluate ovarian function in feline species and has identified EGF, FSH and IGF1 as major regulators of feline ovarian follicular function.

Mutations in NLRP5 and NLRP9 are Associated with Litter Size in Small Tail Han Sheep

Previous studies showed that the NLR family pyrin domain-containing 5 (NLRP5) and NLRP9 genes are two important reproductive genes; however, their effects on sheep litter size are unknown. Therefore, in this study, we first genotyped seven sheep breeds via the MassARRAY^® SNP system at the loci g.60495375A > G, g.60495363G > A, and g.60499690C > A in NLRP5, and g.59030623T > C and g.59043397A > C in NLRP9. Our results revealed that each locus in most sheep breeds contained three genotypes. Then, we conducted population genetic analysis of single nucleotide polymorphisms in NLRP5 and NLRP9, and we found that the polymorphism information content value in all sheep breeds ranged from 0 to 0.36, and most sheep breeds were under Hardy-Weinberg equilibrium (p > 0.05). Furthermore, association analysis in Small Tail Han sheep indicated that two loci, g.60495363G > A in NLRP5 and g.59030623T > C in NLRP9, were highly associated with litter size. The mutation in g.60495363G > A may decrease interactions of NLRP5 with proteins, such as GDF9, whereas the mutation in g.59030623T > C may enhance the combining capacity of NLRP9 with these proteins; consequently, these mutations may influence the ovulation rate and even litter size. The findings of our study provide valuable genetic markers that can be used to improve the breeding of sheep and even other mammals.

Serum Concentrations of Oocyte-Secreted Factors BMP15 and GDF9 During IVF and in Women With Reproductive Pathologies

Oocyte-secreted factors bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) are critical for folliculogenesis and fertility. This study developed ELISAs for the measurement of BMP15 and GDF9 in serum and investigated their usefulness as biomarkers of female reproductive function. Serum samples were obtained from women undergoing infertility treatments (n = 154) and from perimenopausal and postmenopausal women (n = 28). Serum concentrations of BMP15 and GDF9 were analyzed in women relative to age, anti-Müllerian hormone, number of oocytes retrieved, and polycystic ovary syndrome (PCOS) after superovulation for in vitro fertilization. BMP15 and GDF9 immunoassays were validated for specificity, sensitivity (24 and 26 pg/mL, respectively), and reproducibility. BMP15 and GDF9 were detectable in 61% and 29% of women, respectively. BMP15 and GDF9 varied 64-fold and 15-fold, respectively, between women, but they did not change within subjects following ovarian stimulation with gonadotropins. Serum GDF9 concentration, but not BMP15 concentration, was associated with oocyte number retrieved in patients without PCOS (P = 0.018). GDF9 and BMP15 associations with oocyte number differed significantly (P < 0.05) with PCOS status. GDF9 concentrations were lower in poor responders (women with fewer than four oocytes retrieved or with cancelled cycles; P = 0.020). Serum BMP15, but not GDF9, was lower in women >55 years of age, compared with women of reproductive age (P < 0.01). This study develops and validates immunoassays to quantitate BMP15 and GDF9 in human serum and to correlate concentrations with female reproductive potential. Although assay sensitivities require improvement, this study demonstrates the diagnostic potential of oocyte-secreted BMP15 and GDF9 as serum biomarkers in reproductive medicine.

Influence of growth differentiation factor 9 and bone morphogenetic protein 15 on in vitro maturation of canine oocytes

Growth differentiation factor 9 (GDF-9) and bone morphogenetic protein 15 (BMP-15) have pivotal roles in oocyte development in many species, therefore the aim was to investigate these factors during in vitro maturation (IVM) of canine oocytes. Canine cumulus oocytes complexes (COCs) were cultured in six groups for 72 hr in a supplemented TCM199-Hepes medium as (a) Control group; (b) GDF-9 antibody (Ab); (c) BMP-15 Ab; (d) recombinant human (rh) GDF-9; (e) rh BMP-15 or (f) rh BMP-15 and GDF-9. Data were evaluated by ANOVA. The Abs against GDF-9 or BMP-15 had a negative impact on meiotic development. Higher (p < 0.05) number of oocytes was arrested at GVBD stage when they were incubated with either GDF-9 Ab (64.4 ± 2.1%) or BMP-15 Ab (67.2%± 4.9%) in comparison to those in control group (32.4 ± 7.8%). In contrast, more (p < 0.05) oocytes in control group reached MI (37.4 ± 1.3%) and MII stages (10.2 ± 2.1%) comparing to those groups with GDF-9 Ab (23.1 ± 4.7% MI; 0.0% MII) or BMP-15 Ab (16.4 ± 2.4%MI; 5.9% ± 2.1 MII). Higher rates (p < 0.05) of oocytes in control group stayed still arrested at GV (19.9 ± 8.6%) in comparison to those cultured with either rhGDF-9 (3.7 ± 0.4%) or rhBMP-15 (10.9 ± 0.7%). However, there were no differences in MII rates between oocytes cultured with GDF-9 (14.7 ± 3.1) and BMP-15 (7.8 ± 2.5) separately. But, more oocytes (p < 0.05) reached the MII stage (20.5 ± 3.8%) compared to those exposed to each protein separately and to the control group. These results suggest that these proteins likely contribute to the meiotic development in dogs.

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

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

Molecular forms of ruminant BMP15 and GDF9 and putative interactions with receptors

Bone morphogenetic factor 15 (BMP15) and growth differentiation factor 9 (GDF9) are oocyte-secreted factors with demonstrable effects on ovarian follicular development and ovulation rate. However, the molecular forms of BMP15 and GDF9 produced by oocytes remain unclear. The aims herein, using Western blotting (WB) procedures with specific monoclonal antibodies (mabs), were to identify the molecular forms of BMP15 and GDF9 synthesised and secreted by isolated ovine (o) and bovine (b) oocytes in vitro The mabs were known to recognise the biological forms of BMP15 or GDF9 since they had previously been shown to inhibit their bioactivities in vitro and in vivo Using recombinant variants of oBMP15 and oGDF9, including a cysteine mutant form of oBMP15 (S356C) and a human (h) BMP15:GDF9 heterodimer (cumulin), it was established that the mabs were able to identify monomeric, dimeric, promature and higher-molecular-weight forms of BMP15 and GDF9 and cumulin (GDF9 mab only). After using non-reducing, reducing and reducing + cross-linking conditions, the major oocyte-secreted forms of o and b BMP15 and GDF9 were the cleaved and uncleaved monomeric forms of the promature proteins. There was no evidence for dimeric or heterodimeric forms of either mature BMP15 or GDF9. From in silico modelling studies using transforming growth factor beta (TGFB), activin or BMP crystal templates, and both present and previously published data, a model is proposed to illustrate how the monomeric forms of BMP15 and GDF9 may interact with their type II and type I cell-surface receptors to initiate the synergistic actions of these growth factors.

Signalling pathways involved in the synergistic effects of human growth differentiation factor 9 and bone morphogenetic protein 15

Growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) act synergistically to regulate granulosa cell proliferation and steroid production in several species. Several non-Sma and mothers against decapentaplegic (SMAD) signalling pathways are involved in the action of murine and ovine GDF9 and BMP15 in combination, with the pathways utilised differing between the two species. The aims of this research were to determine if human GDF9 and BMP15 also act in a synergistic manner to stimulate granulosa cell proliferation and to identify which non-SMAD signalling pathways are activated. Human GDF9 with BMP15 (GDF9+BMP15) stimulated an increase in (3)H-thymidine incorporation (P<0.001), which was greater than the increase with BMP15 alone, while GDF9 alone had no effect. The stimulation of (3)H-thymidine incorporation by GDF9+BMP15 was reduced by the addition of inhibitors to the SMAD2/3, nuclear factor-KB (NF-KB) and c-Jun N-terminal kinase (JNK) signalling pathways. Inhibitors to the SMAD1/5/8, extracellular signal-regulated kinase mitogen-activated protein kinase (ERK-MAPK) or p38-MAPK pathways had no effect. The addition of the BMP receptor 2 (BMPR2) extracellular domain also inhibited stimulation of (3)H-thymidine incorporation by GDF9+BMP15. In conclusion, human GDF9 and BMP15 act synergistically to stimulate granulosa cell proliferation, a response that also involves species-specific non-SMAD signalling pathways.

ATF6 knockdown decreases apoptosis, arrests the S phase of the cell cycle, and increases steroid hormone production in mouse granulosa cells

Activating transcription factor 6 (ATF6), a sensor protein located in the endoplasmic reticulum (ER) membrane, is an important factor in the ER stress signaling pathway. ER stress is known to be involved in folliculogenesis, follicular growth, and ovulation; however, the physiological function of ATF6 in mouse granulosa cells remains largely unknown. The aim of this study was to assess the role of ATF6 in mouse granulosa cells with respect to apoptosis, the cell cycle, and steroid hormone production, as well as several key genes related to follicular development, via RNA interference, immunohistochemical staining, real-time quantitative PCR, Western blotting, flow cytometry, terminal deoxynucleotidyltransferase-mediated deoxy-UTP nick end labeling (TUNEL) assay, and ELISA. Immunohistochemical staining revealed that ATF6 was extensively distributed in the granulosa cells of various ovarian follicles and oocytes in adult female mice. FSH or LH treatment significantly increased ATF6 protein levels in mouse granulosa cells. In the meantime, a recombinant plasmid was used to deplete ATF6 successfully using short hairpin RNA-mediated interference technology, which was verified at both the mRNA and protein levels. Flow cytometry and TUNEL assay analysis indicated that ATF6 depletion decreased apoptosis and arrested the S phase of the cell cycle in mouse granulosa cells. Consistent with these results, p53, caspase-3, B cell lymphoma 2 (Bcl-2)-associated X protein, CCAAT-enhancer-binding protein homologous protein, cyclin A1, cyclin B1, and cyclin D2 mRNA expression decreased, whereas Bcl-2 and glucose-regulated protein 78 kDa mRNA expression increased. Interestingly, ATF6 knockdown obviously increased progesterone and estradiol production in mouse granulosa cells. Cytochrome P450 1b1 (Cyp1b1) mRNA levels were downregulated, whereas Cyp11a1, steroidogenic acute regulatory, and Cyp19a1 mRNA levels were upregulated, in keeping with the changes in steroid hormones. Furthermore, ATF6 disruption remarkably increased insulin-like growth factor binding protein4 (Igfbp4) expression and decreased hyaluronan synthase 2 (Has2), prostaglandin-endoperoxide synthase 2 (Ptgs2), and prostaglandin F receptor (Ptgfr) expression in mouse granulosa cells, which are proteins crucial for follicular development. But, after treating with tunicamycin, the levels of Has2, Ptgs2, and Ptgfr increased relatively, whereas Igfbp4 expression decreased. Collectively, these results imply that ATF6, as a key player in ER stress signaling, may regulate apoptosis, the cell cycle, steroid hormone synthesis, and other modulators related to folliculogenesis in mouse granulosa cells, which may indirectly be involved in the development, ovulation, and atresia of ovarian follicles by affecting the physiological function of granulosa cells. The present study extends our understanding and provides new insights into the physiological significance of ATF6, a key signal transducer of ER stress, in ovarian granulosa cells.

Forkhead box O member FOXO1 regulates the majority of follicle-stimulating hormone responsive genes in ovarian granulosa cells

FSH promotes maturation of ovarian follicles. One pathway activated by FSH in granulosa cells (GCs) is phosphatidylinositol-3 kinase/AKT. The AKT target FOXO1 is reported to function primarily as a repressor of FSH genes, including Ccnd2 and Inha. Based on its broad functions in other tissues, we hypothesized that FOXO1 may regulate many more GC genes. We transduced GCs with empty adenovirus or constitutively active FOXO1 followed by treatment with FSH for 24 h, and conducted RNA deep sequencing. Results show that FSH regulates 3772 genes ≥2.0-fold; 60% of these genes are activated or repressed by FOXO1. Pathway Studio Analysis revealed enrichment of genes repressed by FOXO1 in metabolism, signaling, transport, development, and activated by FOXO1 in signaling, cytoskeletal functions, and apoptosis. Gene regulation was verified by q-PCR (eight genes) and ChIP analysis (two genes). We conclude that FOXO1 regulates the majority of FSH target genes in GCs.

Oocyte expression, secretion and somatic cell interaction of mouse bone morphogenetic protein 15 during the peri-ovulatory period

Bone morphogenetic protein 15 (BMP15) is a key intraovarian growth factor regulating mammalian fertility, yet expression and localisation of different BMP15 protein forms within ovarian follicles around the time of the preovulatory LH surge remains unclear. Using immunoblotting and immunocytochemistry, the present study identified that post-translationally processed BMP15 proregion and mature proteins are increasingly expressed and localised with cumulus and granulosa cells from mice treated with pregnant mare’s serum gonadotropin (PMSG) + human chorionic gonadotrophin (hCG). However, this increased expression was absent in cumulus–oocyte complexes matured in vitro. Pull-down assays further revealed that the recombinant BMP15 proregion is capable of specific interaction with isolated granulosa cells. To verify an oocyte, and not somatic cell, origin of Bmp15 mRNA and coregulated growth differentiation factor 9 (Gdf9), in situ hybridisation and quantitative polymerase chain reaction results confirmed the exclusive oocyte localisation of Bmp15 and Gdf9, regardless of treatment or assay method. Relative oocyte expression levels of Bmp15 and Gdf9 decreased significantly after PMSG + hCG treatment; nevertheless, throughout all treatments, the Bmp15 : Gdf9 mRNA expression ratio remained unchanged. Together, these data provide evidence that the preovulatory LH surge leads to upregulation of several forms of BMP15 protein secreted by the oocyte for putative sequestration and/or interaction with ovarian follicular somatic cells.

Oocytes lacking O-glycans alter follicle development and increase fertility by increasing follicle FSH sensitivity, decreasing apoptosis, and modifying GDF9:BMP15 expression

The number of eggs ovulated varies within and between species and is influenced by many variables. However, the regulatory mechanisms remain poorly understood. We previously demonstrated a key role for the oocyte because mice generating oocytes deficient in core 1-derived O-glycans ovulate ∼40-50% more eggs than Controls. Here we analyze the basis of this phenotype using Mutant [core 1 β1,3-galactosyltransferase 1 (C1galt1)(FF):zona pellucida glycoprotein 3 Cre (ZP3Cre)] and Control (C1galt1(FF)) female mice. In culture, Mutant follicles exhibited delayed antrum formation [indicative of follicle stimulant hormone (FSH) dependence] and increased sensitivity to FSH. Although the Mutant estrous cycle was extended, comprehensive endocrine changes were not observed; rather FSH, LH, inhibin B, and anti-Mullerian hormone were temporally altered, revealing estrous cycle stage-specific modifications to the hypothalamic-pituitary-gonadal axis. At proestrus, when FSH levels were decreased in Mutants, ovaries contained more, smaller, preantral follicles. Mutant follicles exhibited reduced levels of apoptosis, and both B-cell lymphoma 2 (Bcl-2) and BCL-2-associated X protein (Bax) were altered compared with Controls. Mutant ovaries also had an increase in the expression ratio of growth differentiation factor 9 (GDF9):bone morphogenetic protein 15 (BMP15) at diestrus. On the basis of these data, we propose that modified oocyte glycoproteins alter GDF9:BMP15 expression modifying follicle development resulting in the generation of more follicles. Thus, the oocyte is a key regulator of follicle development and has a crucial role in determining ovulation rate.

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

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Effects of differing oocyte-secreted factors during mouse in vitro maturation on subsequent embryo and fetal development

PURPOSE

We hypothesised that varying native oocyte-secreted factor (OSF) exposure or using different recombinant OSF peptides would have differential effects on post-in vitro maturation (IVM) embryo and fetal development.

METHODS

Mouse cumulus oocyte complexes (COCs) were treated with the purified mature domain of GDF9 and/or BMP15 or were co-cultured with denuded oocytes (DOs) from 0 h or 3 h of IVM. DOs were matured for 3 h as either intact COCs+/-FSH before denuding, or as DOs + FSH. COCs were fertilised and blastocyst development was assessed on days 5 and 6, and either differentially stained for ICM numbers or vitrified/warmed embryos were transferred to recipients to assess implantation and fetal rates.

RESULTS

No improvement in embryo development was observed with the addition of GDF9 and/or BMP15 to IVM. In contrast, embryos derived from COCs co-cultured with DOs had significantly improved blastocyst rates and ICM numbers compared to controls (P < 0.05). The highest response was obtained when DOs were first added to COCs at 3 h of IVM, after being pre-treated (0-3 h) as COCs + FSH. Compared to control, co-culture with DOs from 3 h did not affect implantation rates but more than doubled fetal yield (21% vs 48%; P < 0.05). GDF9 Western blot analysis was unable to detect any differences in quantity or form of GDF9 (17 and 65 kDa) in extracts of DO at 0 h or 3 h.

CONCLUSIONS

This study provides new knowledge on means to improve oocyte quality in vitro which has the potential to significantly aid human infertility treatment and animal embryo production technologies.

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

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

Investigations of TGF-β signaling in preantral follicles of female mice reveal differential roles for bone morphogenetic protein 15

Bone morphogenetic protein 15 (BMP15) and growth differentiation factor 9 (GDF9) are 2 closely related TGF-β ligands implicated as key regulators of follicle development and fertility. Animals harboring mutations of these factors often exhibit a blockage in follicle development beyond the primary stage and therefore little is known about the role of these ligands during subsequent (preantral) stages. Preantral follicles isolated from immature mice were cultured with combinations of BMP15, GDF9, and activin receptor-like kinase (ALK) inhibitors. Individually, GDF9 and BMP15 promoted follicle growth during the first 24 hours, whereas BMP15 subsequently (48-72 h) caused follicle shrinkage and atresia with increased granulosa cell apoptosis. Inhibition of ALK6 prevented the BMP15-induced reduction in follicle size and under basal conditions promoted a rapid increase in granulosa cell proliferation, suggesting BMP15 signals through ALK6, which in turn acts to restrain follicle growth. In the presence of GDF9, BMP15 no longer promoted atresia and in fact follicle growth was increased significantly more than with either ligand alone. This cooperative effect was accompanied by differential expression of Id1-3, Smad6-7, and Has2 and was blocked by the same ALK5 inhibitor used to block GDF9 signaling. Immunostaining for SMAD2/3 and SMAD1/5/8, representing the 2 main branches of TGF-β signaling, supported the fact that both canonical pathways have the potential to be active in growing follicles, whereas primordial follicles only express SMAD2/3. Overall results highlight differential effects of the 2 main TGF-β signaling pathways during preantral follicle growth.

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

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