Extra-ovarian expression and activity of growth differentiation factor 9

Growth differentiation factor 9 (GDF9) produced within the ovary plays an essential role during follicle maturation through actions on granulosa cells, but extra-ovarian expression, signalling and actions of GDF9 are less well characterised. The present studies confirm GDF9 expression in the mouse testis, pituitary gland and adrenocortical cancer (AC) cells, and establish its expression in L beta T2 gonadotrophs, and in mouse adrenal glands, particularly foetal and neonatal cortical cells. AC, L beta T2, TM3 Leydig and TM4 Sertoli cells express the requisite GDF9 binding signalling components, particularly activin receptor-like kinase (ALK) 5 and the bone morphogenetic protein (BMP)/GDF type II receptor, BMPRII (BMPR2). We therefore compared GDF9 activation of these potential extra-ovarian target cell types with its activation of granulosa cells. Recombinant mouse GDF9 stimulated expression of activin/transforming growth factor-beta-responsive reporters, pGRAS-luc or pAR3-lux, in TM4 and AC cells (IC50=145 ng/ml in the latter case), and two granulosa cell lines, KGN and COV434. The ALK4/5/7 inhibitor, SB431542, blocked GDF9 activity in each case. By contrast, GDF9 lacked specific effects on TM3 cells and rat primary pituitary and mouse L beta T2 gonadotrophs. Our findings show that GDF9 regulates the expression of R-SMAD2/3-responsive reporter genes through ALK4, 5 or 7 in extra-ovarian (adrenocortical and Sertoli) cells with similar potency and signalling pathway to its actions on granulosa cells, but suggest that expression of BMPRII, ALK5 (TGFBR1) and R-SMADs 2 and 3 may not be sufficient for a cell to respond to GDF9.

Growth differentiation factor 9 is a germ cell regulator of Sertoli cell function

Oocyte-secreted growth differentiation factor (GDF) 9 and bone morphogenetic protein (BMP) 15 are critical regulatory factors in female reproduction. Together, they promote granulosa cell proliferation and stimulate the maturation of preovulatory follicles. Despite their importance in female fertility, GDF9 and BMP15 expression patterns and function during spermatogenesis have not been investigated. In this study we show that the expression and stage-specific localization of both factors are limited to the germ cells of the rat seminiferous epithelium, with GDF9 being principally localized in round spermatids and BMP15 in gonocytes and pachytene spermatocytes. To identify potential cellular targets for GDF9 actions, cells of the seminiferous tubule were isolated and screened for the expression of signaling receptors [activin-like kinase (ALK) 5, ALK6, and BMP receptor, type II)]. Individual receptor types were expressed throughout the seminiferous epithelium, but coexpression of ALK5 and BMP receptor, type II was limited to Sertoli cells and round spermatids. Based on the reproductive actions of related TGFbeta ligands in the ovary and testis, GDF9 was assessed for its ability to regulate tight junction function and inhibin B production in rat Sertoli cell cultures. When recombinant mouse GDF9 was added to immature Sertoli cell cultures, it inhibited membrane localization of the junctional proteins claudin-11, occludin, and zonula occludens-1, thereby disrupting tight junction integrity. Concomitantly, GDF9 up-regulated inhibin subunit expression and significantly stimulated dimeric inhibin B protein production. Together, these results demonstrate that GDF9 and BMP15 are germ cell-specific factors in the rat testis, and that GDF9 can modulate key Sertoli cell functions.

Disruption of bidirectional oocyte-cumulus paracrine signaling during in vitro maturation reduces subsequent mouse oocyte developmental competence

Oocyte-cumulus cell bidirectional communication is essential for normal development of the oocyte and cumulus cells (CCs) within the follicle. We showed recently that addition of recombinant growth differentiation factor 9 (GDF9), which signals through the SMAD2/3 pathway, during mouse oocyte in vitro maturation (IVM) increased fetal viability. This study thus aimed to observe the effects of disrupting oocyte-CC bidirectional communication during IVM on oocyte developmental competence and fetal outcomes. Cumulus-oocyte complexes (COCs) from equine chorionic gonadotropin-primed prepubertal (CBA/C57BL6) mice were cultured with or without 50 mIU/ml follicle-stimulating hormone (FSH) and 10 ng/ml epidermal growth factor (EGF) or 4 muM SMAD2/3 inhibitor SB-431542. Cumulus expansion and first polar body extrusion were then assessed, or COCs were fertilized and stained to evaluate sperm entry or cultured to the blastocyst stage. Embryo development and blastocyst quality were assessed, and Day 4.5 blastocysts were transferred to pseudopregnant recipients to analyze fetal outcomes. SMAD2/3 inhibition or FSH/EGF absence during IVM resulted in decreased cumulus expansion. First polar body extrusion and sperm entry were decreased in the absence of FSH/EGF, whereas only sperm entry was affected in SB-431542-matured COCs. Embryo development and blastocyst rates were unaffected; however, blastocyst quality was significantly altered, with reduced inner cell mass cell numbers in embryos derived from COCs matured in both treatments. When COCs were matured with SB-431542 in the absence of FSH/EGF, cumulus expansion was reduced, but fertilization, embryo development, and embryo quality were not. Inhibition of SMAD2/3 signaling in the presence of FSH/EGF significantly reduced fetal survival but had no effect on implantation or fetal and placental dimensions and morphology.

Characterization of novel phosphodiesterases in the bovine ovarian follicle

The phosphodiesterase (PDE) family is a group of enzymes that catalyzes the transformation of cyclic nucleotides into 5' nucleotides. Based on rodents, the current mammalian model of PDE distribution in the ovarian follicle predicts Pde3a in the oocyte and Pde4d in the somatic cells. Using bovine as an experimental model, the present results showed that PDE3 was the predominant PDE activity in oocytes. However, cumulus cell cAMP-PDE activity was predominantly resistant to inhibition by 3-isobutyl-methylxantine, indicating PDE8 activity (60% of total PDE activity) and a minor role for PDE4 (<5%). A total of 20% of total oocyte PDE activity was also attributed to PDE8. The PDE activity measurements in mural granulosa cells from 2 to 6 mm in diameter suggest the presence of PDE4 and PDE8. In granulosa cells from follicles >10 mm, total PDE and PDE8 activities along with PDE8A protein level were increased compared with smaller follicles. The RT-PCR experiments showed that cumulus cells expressed PDE8A, PDE8B, and PDE10A. Western blot experiments showed PDE8A, PDE8B, and PDE4D proteins in mural granulosa cells and cumulus-oocyte complexes. PDE8 inhibition using dipyridamole in a dose-dependent manner increased cAMP levels in the cumulus-oocyte complexes and delayed oocyte nuclear maturation. These results are the first to demonstrate the functional presence of PDE8 in the mammalian ovarian follicle. This challenges the recently described cell-specific expression of cAMP-PDEs in the ovarian follicle and the notion that PDE4 is the predominant granulosa/cumulus cell PDE. These findings have implications for our understanding of hormonal regulation of folliculogenesis and the potential application of PDE inhibitors as novel contraceptives.

Regulation of gap junctions in porcine cumulus-oocyte complexes: contributions of granulosa cell contact, gonadotropins, and lipid rafts

Gap-junctional communication (GJC) plays a central role in oocyte growth. However, little is known about the regulation of connexin 43 (Cx43)-based gap-junction channels in cumulus-oocyte complexes (COCs) during in vitro maturation. We show that rupture of COCs from mural granulosa cells up-regulates Cx43-mediated GJC and that gonadotropins signal GJC breakdown by recruiting Cx43 to lipid rafts when oocyte meiosis resumes. Oocyte calcein uptake through gap junctions increases during early in vitro oocyte maturation and remains high until 18 h, when it falls simultaneously with the oocyte germinal vesicle breakdown. Immunodetection of Cx43 and fluorescence recovery after photobleaching assays revealed that the increase of GJC is independent of gonadotropins but requires RNA transcription, RNA polyadenylation, and translation. GJC rupture, in contrast, is achieved by a gonadotropin-dependent mechanism involving recruitment of Cx43 to clustered lipid rafts. These results show that GJC up-regulation in COCs in in vitro culture is independent of gonadotropins and transcriptionally regulated. However, GJC breakdown is gonadotropin dependent and mediated by the clustering of Cx43 in lipid raft microdomains. In conclusion, this study supports a functional role of lipid raft clustering of Cx43 in GJC breakdown in the COCs during in vitro maturation.

Increased gonadotrophin stimulation does not improve IVF outcomes in patients with predicted poor ovarian reserve

PURPOSE

This retrospective study was carried out to evaluate whether increasing the starting dose of FSH stimulation above the standard dose of 150 IU/day in patients with low predicted ovarian reserve can improve IVF outcomes.

METHOD

A total of 122 women aged less than 36 years in their first cycle of IVF were identified as having likely low ovarian reserve based on a serum AMH measurement below 14 pmol/l. Thirty five women were administered the standard dose of 150 IU/day FSH, while the remaining 87 received a higher starting dose (200-300 IU/day FSH). There were no significant differences in age, BMI, antral follicle count, serum AMH, FSH or aetiology of infertility between the two dose groups.

RESULTS

No significant improvement in oocyte and embryo yield or pregnancy rates was observed following an upward adjustment of FSH starting dose. While increasing the dose of FSH above 150 IU/day did not produce any adverse events such as OHSS, it did consume an extra 1,100 IU of FSH per IVF cycle.

CONCLUSION

The upward FSH dose adjustment in anticipation of low ovarian reserve can not be advocated as it is both expensive and of no proven clinical value.

Oocyte-secreted factors: regulators of cumulus cell function and oocyte quality

Oocyte quality is a key limiting factor in female fertility, yet we have a poor understanding of what constitutes oocyte quality or the mechanisms governing it. The ovarian follicular microenvironment and maternal signals, mediated primarily through granulosa cells (GCs) and cumulus cells (CCs), are responsible for nurturing oocyte growth, development and the gradual acquisition of oocyte developmental competence. However, oocyte-GC/CC communication is bidirectional with the oocyte secreting potent growth factors that act locally to direct the differentiation and function of CCs. Two important oocyte-secreted factors (OSFs) are growth-differentiation factor 9 and bone morphogenetic protein 15, which activate signaling pathways in CCs to regulate key genes and cellular processes required for CC differentiation and for CCs to maintain their distinctive phenotype. Hence, oocytes appear to tightly control their neighboring somatic cells, directing them to perform functions required for appropriate development of the oocyte. This oocyte-CC regulatory loop and the capacity of oocytes to regulate their own microenvironment by OSFs may constitute important components of oocyte quality. In support of this notion, it has recently been demonstrated that supplementing oocyte in vitro maturation (IVM) media with exogenous OSFs improves oocyte developmental potential, as evidenced by enhanced pre- and post-implantation embryo development. This new perspective on oocyte-CC interactions is improving our knowledge of the processes regulating oocyte quality, which is likely to have a number of applications, including improving the efficiency of clinical IVM and thereby providing new options for the treatment of infertility.

Exogenous growth differentiation factor 9 in oocyte maturation media enhances subsequent embryo development and fetal viability in mice

BACKGROUND

Successful oocyte in vitro maturation (IVM) would eliminate the need for hormonal stimulation used in assisted reproduction techniques. Unfortunately, oocytes matured in vitro have compromised developmental competence possibly due to disrupted oocyte-cumulus communication resulting from inappropriate levels of oocyte-secreted factors such as growth differentiation factor 9 (GDF9). Hence, the aim of this study was to investigate the effects of exogenous GDF9 during IVM of mouse oocytes on development and subsequent fetal viability.

METHODS

Cumulus-oocyte complexes from pregnant mare's serum gonadotrophin primed mice were cultured with or without 200 ng/ml exogenous recombinant GDF9, 50 mIU/ml FSH and 10 ng/ml epidermal growth factor (EGF). After 18 h, cumulus expansion was scored and oocytes were fertilized in vitro. Cleavage, blastocyst development, blastocyst total, inner cell mass (ICM) and trophectoderm cell numbers were assessed. Viability of embryos was assessed by transfer to recipient females and pregnancy outcome determined at day 15.

RESULTS

Oocytes matured with exogenous GDF9 in the presence of FSH and EGF had higher rates of development, percentage of hatching blastocyst and blastocyst total and ICM cell numbers (all P < 0.05). Although implantation rate and fetal and placental weights were not affected, the number of viable fetuses at day 15 was increased with exogenous GDF9.

CONCLUSIONS

Exogenous GDF9 during IVM improved embryo development and fetal viability and provides a promising approach for human IVM.

Effects of ovarian stimulation, with and without human chorionic gonadotrophin, on oocyte meiotic and developmental competence in the marmoset monkey (Callithrix jacchus)

A reliable ovarian stimulation protocol for marmosets is needed to enhance their use as a model for studying human and non-human primate oocyte biology. In this species, a standard dose of hCG did not effectively induce oocyte maturation in vivo. The objectives of this study were to characterize ovarian response to an FSH priming regimen in marmosets, given without or with a high dose of hCG, and to determine the meiotic and developmental competence of the oocytes isolated. Ovaries were removed from synchronized marmosets treated with FSH alone (50 IU/d for 6 d) or the same FSH treatment combined with a single injection of hCG (500 IU). Cumulus-oocyte complexes (COCs) were isolated from large (>1.5mm) and small (0.7-1.5mm) antral follicles. In vivo-matured oocytes were subsequently activated parthenogenetically or fertilized in vitro. Immature oocytes were subjected to in vitro maturation and then activated parthenogenetically. Treatment with FSH and hCG combined increased the number of expanded COCs from large antral follicles compared with FSH alone (23.5 +/- 9.3 versus 6.4 +/- 2.7, mean +/- S.E.M.). Approximately 90% of oocytes surrounded by expanded cumulus cells at the time of isolation were meiotically mature. A blastocyst formation rate of 47% was achieved following fertilization of in vivo-matured oocytes, whereas parthenogenetic activation failed to induce development to the blastocyst stage. The capacity of oocytes to complete meiosis in vitro and cleave was positively correlated with follicle diameter. A dramatic effect of follicle size on spindle formation was observed in oocytes that failed to complete meiosis in vitro. Using the combined FSH and hCG regimen described in this study, large numbers of in vivo matured marmoset oocytes could be reliably collected in a single cycle, making the marmoset a valuable model for studying oocyte maturation in human and non-human primates.

The common marmoset as a novel preclinical transplant model: identification of new MHC class II DRB alleles and prediction ofin vitroalloreactivity

The difficulties with using nonhuman primate species such as rhesus macaques and baboons have led us to investigate the common marmoset (Callithrix jacchus) as an alternative preclinical model for transplantation research. This requires reliable methods of detecting alloreactivity between donor and recipient pairs, particularly if colonies are inbred and share just a few common alleles for leucocyte antigens. We firstly identified marmoset major histocompatibility complex (MHC) Class II DRB genes (Caja-DRB*W1201, Caja-DRB1*03, Caja-DRB*W16) using sequence-based typing techniques. Genomic DNA (n= 49) was extracted from whole blood or spleen tissue. Exon 2 of target genes was amplified by PCR using primers specific for known marmoset alleles, and then sequenced using ABI PRISM((R)) Big Dye Terminator technology and Assign sequence analysis software. DRB*W1201 was universally present. Eight DRB*W16 alleles and five DRB1*03 alleles were identified in this colony. We also identified two previously unreported DRB*W16 alleles, and confirmed inheritance of these alleles within several sibling groups. Subsequently, we investigated whether matching at MHC Class II DRB loci alone could predict alloreactivity, as assessed in vitro by two-way mixed lymphocyte reactions (MLRs). Fully DRB-matched, partially mismatched and fully mismatched animal pairs were prospectively chosen. MLR was performed using mononuclear cells (MNC) isolated from whole blood by density gradient separation. T-cell proliferation after 5-day culture was measured by (3)H-thymidine incorporation. Combined MNC from fully mismatched and partially mismatched animal pairs exhibited significant in vitro T-cell proliferation above single cell controls (P < 0.01). MNC from fully DRB-matched (but unrelated) animal pairs exhibited no proliferation compared with controls (P= 0.3). Using DRB genotyping, suitably alloreactive donor-recipient pairs may therefore be rapidly and accurately identified for use in further studies of cellular and solid organ transplantation.

Metabolism of the bovine cumulus-oocyte complex and influence on subsequent developmental competence

The two types of cells that make up the cumulus-oocyte complex (i.e. the oocyte and cumulus cells) have very different metabolic demands, with glucose occupying a central role in metabolic activity. Cumulus cells have a significant requirement for and utilise high levels of glucose, yet appear to have little need for oxidative metabolism. In contrast, oocytes have a requirement for oxidative metabolism, although limited glucose metabolism may also be an important aspect of meiotic and developmental competence. Nevertheless, because of the metabolic and communication link between the cumulus and the oocyte, glucose availability and metabolism within the cumulus can have a significant impact on oocyte meiotic and developmental competence. In particular, the role of the hexosamine biosynthesis pathway within cumulus cells appears critical for the supply of substrate from glucose for extracellular matrix production, yet if overstimulated can significantly decrease developmental competence of the oocyte. Current static systems for in vitro maturation are clearly incompatible with meeting substrate demands, especially glucose. In the future, in vitro maturation will include a more dynamic approach, which will adjust nutrient components to meet the changing functional requirements of cumulus-oocyte complexes during the final process of maturation.

Oocyte maturation: Emerging concepts and technologies to improve developmental potential in vitro

Oocyte in vitro maturation (IVM) is an important reproductive technology that generates mature oocytes that are capable of supporting preimplantation embryo development and full development to term. There is great clinical and commercial incentive to improve the efficiency of the technology, however, progress has been slow over the past decade. A critical challenge is to understand what constitutes oocyte developmental competence and the mechanisms governing it. We have taken the approach of studying in detail oocyte-somatic cell interactions; including, oocyte-cumulus cell (CC) gap-junctional communication, and bidirectional paracrine signalling between the two cell types. It is becoming clear that, compared to oocytes matured in vivo, IVM oocytes undergo maturation prematurely as they are still in the process of acquiring developmental competence in vivo, and the molecular cascade reinitiating meiosis differs entirely to that in vivo. Attempts to enhance oocyte developmental competence by attenuating the spontaneous meiotic resumption of oocytes in vitro have been met with mixed success. Kinase inhibitors that prevent maturation-promoting factor activity have, in general, been ineffectual on promoting oocyte developmental potential post-IVM. In contrast, agents that modulate oocyte cAMP during IVM show greater potential, possibly as these compounds extend oocyte-CC gap-junctional communication. An important concept that is now emerging is that the oocyte secretes potent growth factors that regulate fundamental aspects of CC function and thereby determine the distinctive phenotype of the cumulus-oocyte complex. The capacity of an oocyte to regulate its own microenvironment by oocyte-secreted factors (OSFs) may constitute an important component of oocyte developmental competence. In support of this notion, we have recently demonstrated that supplementing IVM media with exogenous OSFs improves oocyte developmental potential, as evidenced by enhanced pre- and post-implantation embryo development.

Anti-Müllerian hormone as a predictor of IVF outcome

Serum anti-Müllerian hormone (AMH) concentration and antral follicle count (AFC) are two increasingly popular static measures used to predict ovarian reserve prior to IVF treatment. While they have been shown to be good predictors of oocyte yield during ovarian stimulation, their status as indicators of oocyte quality and pregnancy rates is currently uncertain. The present study measured baseline concentrations of serum AMH and FSH, and AFC from 126 women undergoing IVF treatment. These data were then related to IVF outcomes. As expected, patients with lower serum AMH and AFC produced a significantly (P < 0.001) lower number of oocytes compared with patients with higher serum AMH/AFC. Fertilization rates in patients with lower serum AMH were significantly inferior compared with patients with higher serum AMH, irrespective of whether IVF (P = 0.043) or intracytoplasmic sperm injection (P = 0.006) was used to achieve fertilization. These low AMH patients yielded fewer oocytes, had lower fertilization rates, generated fewer embryos, and had a higher incidence of miscarriage during fresh transfers, ultimately culminating in a halving of the pregnancy rate per IVF cycle compared with the high AMH group.

Oocyte-secreted factor activation of SMAD 2/3 signaling enables initiation of mouse cumulus cell expansion

Expansion of the mouse cumulus-oocyte complex (COC) is dependent on oocyte-secreted paracrine factors. Transforming growth factor beta (TGFB) superfamily molecules are prime candidates for the cumulus expansion-enabling factors (CEEFs), and we have recently determined that growth differentiation factor 9 (GDF9) alone is not the CEEF. The aim of this study was to examine oocyte paracrine factors and their signaling pathways that regulate mouse cumulus expansion. Using RT-PCR, oocytes were found to express the two activin subunits, Inhba and Inhbb, and activin A and activin B both enabled FSH-induced cumulus expansion of oocytectomized (OOX) complexes. Follistatin, an activin-binding protein, neutralized activin-induced expansion but had no effect on oocyte-induced expansion. The type I receptors for GDF9 and activin are activin receptor-like kinase 5 (ALK5) and ALK4, respectively, both of which activate the same SMAD 2/3 signaling pathway. We examined the requirement for this signaling system using an ALK 4/5/7 inhibitor, SB-431542. SB-431542 completely ablated FSH-stimulated GDF9-, activin A-, activin B-, and oocyte-induced cumulus expansion. Moreover, SB-431542 also antagonized epidermal growth factor-stimulated, oocyte-induced cumulus expansion. Using real-time RT-PCR, SB-431542 also attenuated GDF9-, activin A-, and oocyte-induced OOX expression of hyaluronan synthase 2, tumor necrosis factor alpha-induced protein 6, prostaglandin synthase 2, and pentraxin 3. This study provides evidence that the CEEF is composed of TGFB superfamily molecules that signal through SMAD 2/3 to enable the initiation of mouse cumulus expansion.

Adenosine 5'-monophosphate kinase-activated protein kinase (PRKA) activators delay meiotic resumption in porcine oocytes

Adenosine monophosphate-activated kinase (PRKA) is a serine/threonine kinase that functions as a metabolic switch in a number of physiological functions. The present study was undertaken to assess the role of this kinase in nuclear maturation of porcine oocytes. RT-PCR and immunoblotting revealed the expression of the PRKAA1 subunit in granulosa cells, cumulus-oocyte complexes (COC), and denuded oocytes (DO). Porcine COC and DO contained transcripts that corresponded to the expected sizes of the designed primers for PRKAB1 and PRKAG1. The PRKAA2 subunit was detected in granulosa cells and COC, whereas the PRKAG3 subunit was not detected in granulosa cells, COC or DO, whereas it was detected in the heart. The PRKAA1 protein was detected in granulosa cells, COC, DO, and zona pellucida (ZP). In the presence of the pharmacological activator of PRKA 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranosyl 5'-monophosphate (ZMP), COC were transiently maintained in meiotic arrest in a fully reversible manner. This inhibitory effect was not observed in DO. Other known PRKA activators, 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) and metformin, also blocked meiotic resumption in COC. In contrast to mouse oocytes, in which PRKA activators reverse the inhibitory effect of PDE3 inhibitors, this combination still blocked meiotic resumption in porcine COC. These results demonstrate that the meiotic resumption of porcine COC is transiently blocked by PRKA activators in a dose-dependent manner, and that this effect is dependent on PRKA activity in cumulus cells. The present study describes a new role for PRKA in regulating meiotic resumption in COC and strongly suggests that cumulus cells play an essential role in the control of porcine oocyte maturation through the PRKA metabolic switch.

Molecular basis of oocyte-paracrine signalling that promotes granulosa cell proliferation

Oocytes regulate follicle growth by secreting paracrine growth factors that act on neighbouring granulosa cells (GCs). Those factors identified to date are mainly members of the transforming growth factor-beta (TGFbeta) superfamily, but little is known about which specific receptor/signalling system(s) they employ. This study was conducted to determine the requisite pathways utilised by oocytes to promote GC proliferation. We used an established oocyte-secreted mitogen bioassay, where denuded mouse oocytes are co-cultured with mural GCs. Oocytes, growth differentiation factor-9 (GDF9), TGFbeta1 and activin-A all promoted GC DNA synthesis, but bone-morphogenetic protein 6 (BMP6) did not. Subsequently, we tested the capacity of various TGFbeta superfamily receptor ectodomains (ECD) to neutralise oocyte- or specific growth factor-stimulated GC proliferation. The BMP type-II receptor (BMPR-II) ECD antagonised oocyte and GDF9 bioactivity dose-dependently, but had no or minimal effect on TGFbeta1 and activin-A bioactivity, demonstrating its specificity. The TGFbetaR-II, activinR-IIA and activinR-IIB ECDs all failed to neutralise oocyte- or GDF9-stimulated GC DNA synthesis, whereas they did antagonise the activity of their respective native ligands. An activin receptor-like kinase (ALK) 4/5/7 inhibitor, SB431542, also antagonised both oocyte and GDF9 bioactivity in a dose-dependent manner. Consistent with these findings, oocytes, GDF9 and TGFbeta1 all activated SMAD2/3 reporter constructs in transfected GC, and led to phosphorylation of SMAD2 proteins in treated cells. Surprisingly, oocytes did not activate the SMAD1/5/8 pathway in transfected GCs although exogenous BMP6 did. This study indicates that oocyte paracrine factors primarily utilise a similar signalling pathway first identified for GDF9 that employs an unusual combination of TGFbeta superfamily receptors, the BMPR-II and a SMAD2/3 stimulatory ALK (4, 5 or 7), for transmitting their mitogenic actions in GC. This cell-signalling pathway may also have relevance in the hypothalamic-pituitary axis and in germ-somatic cell interactions in the testis.

Oocyte-secreted factors enhance oocyte developmental competence

The capacity of fully grown oocytes to regulate their own microenvironment by paracrine factors secreted by the oocyte (oocyte-secreted factors, OSFs) may in turn contribute to oocyte developmental competence. Here, we investigated if OSFs have a direct influence on oocyte developmental competence during in vitro maturation (IVM). Bovine cumulus-oocyte complexes (COCs) were aspirated from abattoir-derived ovaries and matured in serum-free medium. COCs were either co-cultured with denuded oocytes (DOs) or treated with specific OSFs: recombinant bone morphogenetic protein 15 (BMP15) and/or growth differentiation factor 9 (GDF9). Following maturation, embryos were fertilized and cultured in vitro and blastocyst development and cell number were assessed on day 8. Co-culturing intact COCs with DOs did not affect cleavage rate, but increased (P<0.001) the proportion of cleaved embryos that reached the blastocyst stage post-insemination from 39% to 51%. OSFs also altered blastocyst cell allocation as co-culture of COCs with DOs significantly increased total and trophectoderm cell numbers, compared to control COCs. BMP15 alone, GDF9 alone or the two combined all (P<0.05) increased the proportion of oocytes that reached the blastocyst stage post-insemination from 41% (controls) to 58%, 50% and 55%, respectively. These results were further verified in neutralization experiments of the exogenous growth factors and of the native OSFs. Follistatin and the kinase inhibitor SB-431542, which antagonize BMP15 and GDF9, respectively, neutralized the stimulatory effects of the exogenous growth factors and impaired the developmental competence of control COCs. These results demonstrate that OSFs, and particularly BMP15 and GDF9, enhance oocyte developmental competence and provide evidence that OSF regulation of the COC microenvironment is an important determinant of oocyte developmental programming.

Glucosamine Supplementation During In Vitro Maturation Inhibits Subsequent Embryo Development: Possible Role of the Hexosamine Pathway as a Regulator of Developmental Competence1

Glucose concentration during cumulus-oocyte complex (COC) maturation influences several functions, including progression of oocyte meiosis, oocyte developmental competence, and cumulus mucification. Glucosamine (GlcN) is an alternative hexose substrate, specifically metabolized through the hexosamine biosynthesis pathway, which provides the intermediates for extracellular matrix formation during cumulus cell mucification. The aim of this study was to determine the influence of GlcN on meiotic progression and oocyte developmental competence following in vitro maturation (IVM). The presence of GlcN during bovine IVM did not affect the completion of nuclear maturation and early cleavage, but severely perturbed blastocyst development. This effect was subsequently shown to be dose-dependent and was also observed for porcine oocytes matured in vitro. Hexosamine biosynthesis upregulation using GlcN supplementation is well known to increase O-linked glycosylation of many intracellular signaling molecules, the best-characterized being the phosphoinositol-3-kinase (PI3K) signaling pathway. We observed extensive O-linked glycosylation in bovine cumulus cells, but not oocytes, following IVM in either the presence or the absence of GlcN. Inhibition of O-linked glycosylation significantly reversed the effect of GlcN-induced reduction in developmental competence, but inhibition of PI3K signaling had no effect. Our data are the first to link hexosamine biosynthesis, involved in cumulus cell mucification, to oocyte developmental competence during in vitro maturation.

Oocytes prevent cumulus cell apoptosis by maintaining a morphogenic paracrine gradient of bone morphogenetic proteins

Paracrine factors secreted by the oocyte regulate a broad range of cumulus cell functions. Characteristically, cumulus cells have a low incidence of apoptosis and we proposed that this is due to oocyte-secreted factors acting in an anti-apoptotic manner. Bovine cumulus-oocyte complexes (COC) were aspirated from abattoir-derived ovaries and oocytectomized (OOX) by microsurgical removal of the oocyte. OOX were treated with doses of either denuded oocytes (DO) or various growth factors for 24 hours (+/- rFSH; 0.1 IU/ml). Proportions of apoptotic cumulus cells were assessed using TUNEL and laser confocal scanning microscopy followed by image analysis. Quantification of Bcl-2 and Bax proteins in OOX was undertaken by western analysis. Oocyte removal led to a significant increase in cumulus cell apoptosis compared with COC controls (35% versus 9% TUNEL positive, respectively; P<0.001). Levels of OOX apoptosis were significantly reversed (P<0.001) in a dose-dependent manner when co-cultured with oocytes. Furthermore, the anti-apoptotic effect of oocyte-secreted factors followed a gradient from the site of the oocyte(s). Growth differentiation factor 9 (GDF9) had no significant effect on cumulus cell apoptosis. By contrast, cumulus cell apoptosis was significantly (P<0.001) reduced by bone morphogenetic proteins (BMP) 15, 6 or 7. Accordingly, levels of anti-apoptotic Bcl-2 were high in OOX+DO and OOX+BMP15 and low with OOX+GDF9 or OOX alone, whereas the reverse was observed for pro-apoptotic Bax. DO, BMP15 and BMP6 were also able to protect cumulus cells from undergoing apoptosis induced by staurosporine. FSH partially prevented apoptosis in all treatment groups (P<0.001). Follistatin and a BMP6 neutralizing antibody, which antagonized the anti-apoptotic effects of BMP15 and BMP6, respectively, whether alone or combined, blocked approximately 50% of the anti-apoptotic actions of oocytes. These results are the first to demonstrate that oocyte-secreted factors, and particularly BMP15 and BMP6, maintain the low incidence of cumulus cell apoptosis by establishing a localized gradient of bone morphogenetic proteins.

Androgens Augment the Mitogenic Effects of Oocyte-Secreted Factors and Growth Differentiation Factor 9 on Porcine Granulosa Cells1

In this study, we test the hypothesis that the growth-promoting action of androgens on granulosa cells requires paracrine signaling from the oocyte. Mural granulosa cells (MGCs) from small antral (1-3 mm) prepubertal pig follicles were cultured in the presence or absence of denuded oocytes (DO) from the same follicles to determine whether mitogenic and/or steroidogenic responses, to combinations of FSH, insulin-like growth factor 1 (IGF1), and dihydrotestosterone (DHT) were influenced by oocyte-secreted factors (OSFs). To further explore the identity of such factors we performed the same experiments, substituting growth differentiation factor 9 (GDF9), a known OSF, for the DO. OSFs and GDF9 both potently enhanced IGF1-stimulated proliferation, and inhibited FSH-stimulated progesterone secretion. Alone, DHT had little effect on DNA synthesis, but significantly enhanced the mitogenic effects of OSFs or GDF9 in the presence of IGF1. Denuded oocytes, GDF9, and DHT independently inhibited FSH-stimulated progesterone secretion, and androgen, together with DO or GDF9, caused the most potent steroidogenic inhibition. Focusing on mitogenic effects, we demonstrate that both natural androgen receptor (AR) agonists, testosterone and DHT, dose-dependently augmented the mitogenic activity of DO or GDF9. Antiandrogen (hydroxyflutamide) treatment, which is used to block androgen receptor activity, opposed the interaction between androgen and GDF9. In conclusion, androgens stimulate porcine MGC proliferation in vitro by potentiating the growth-promoting effects of oocytes or GDF9, via a mechanism that involves the AR. These signaling pathways are likely to be important regulators of folliculogenesis in vivo, and may contribute to the excess follicle growth that is observed in androgen-treated female animals.