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

Age-related changes in the cytoplasmic ultrastructure of feline oocytes

This study elucidates the impact of aging on the cellular architecture of feline oocytes, with a particular emphasis on organelles essential for fertilization and embryo development. Using transmission electron microscopy (TEM), the research compares oocytes from prepubescent, cycling adult, and aged cats, revealing notable differences in the arrangement of key structures, particularly mitochondria, lipid droplets, and vacuoles. Oocytes from adult donors are at their metabolic peak, demonstrating a higher concentration of mitochondria near lipid droplets, supporting efficient energy metabolism. In contrast, younger and older oocytes exhibit larger lipid droplets and reduced mitochondrial density, indicative of diminished metabolic activity. These findings not only underscore the necessity of selecting an optimal donor age for in vitro fertilization but also suggest potential biomarkers for oocyte quality assessment. This novel insight offers promising strategies to enhance reproductive success, improve assisted reproduction outcomes, and support feline conservation efforts.

Effects of Exogenous Regulation of PPARγ on Ovine Oocyte Maturation and Embryonic Development In Vitro

Lactating oocytes consume a lot of energy during maturation, a large part of which comes from lipid metabolism. PPARγ is a key regulator of lipid metabolism. In this study, rosiglitazone (RSG), an activator of PPARγ, was added to a mature medium to investigate its effects on the levels of spindle and the chromosome arrangement, lipid deposition, reactive oxygen species (ROS), and glutathione (GSH) levels, oocyte secretion factors, apoptosis and lipid metabolism-related gene expression, and subsequent embryonic development during the maturation of sheep oocytes. The oocyte secretion factor affects gene expression related to apoptosis and lipid metabolism and subsequent embryonic development. The results showed that the proportion of spindle and normal chromosome arrangements increased in the 5 μM RSG treatment group, the lipid content increased after cell maturation, the ROS level decreased, and the GSH level increased. The expressions of oocyte secretion factor (GDF9 and BMP15), anti-apoptosis gene (BCL2), and lipid metabolism-related genes (ACAA1, CPT1A, PLIN2) were increased in the 5 μM treatment group. Finally, the development of blastocysts was examined. After the oocytes were treated with 5 μM RSG, the blastocyst rate and the gene expression of the totipotency gene (OCT4) were increased. It was concluded that increasing PPARγ activity during ovine oocyte maturation could promote lipid metabolism, reduce oxidative stress, and improve the ovine oocyte maturation rate and subsequent embryo development.

Exposure to chlorpyrifos interferes with intercellular communication in cumulus-oocyte complexes during porcine oocyte maturation

Chlorpyrifos (CPF), a widely used organophosphorus pesticide (OP) to control pests has been verified reproductive toxicity on mammalian oocytes. However, limited information exists on its correlation with the dysfunction of the intercellular communication in cumulus-oocyte complexes (COCs). Herein, our study utilized porcine COCs as models to directly address the latent impact of CPF on the communication between cumulus cells (CCs) and oocytes during in vitro maturation. The results demonstrated that CPF exposure decreased the rate of the first polar body (PB1) extrusion and blocked meiosis progression. Notably, the cumulus expansion of CPF-exposed COCs was suppressed significantly, accompanied by the down-regulated mRNA levels of cumulus expansion-related genes. Furthermore, the early apoptotic level was raised and the expression of BAX/BCL2 and cleaved caspase 3 was up-regulated in the CCs of CPF-exposed COCs (p < 0.05). Moreover, CPF exposure impaired mRNA levels of antioxidant enzyme-related genes, induced higher levels of reactive oxygen species (ROS) and reduced the levels of mitochondrial membrane potential (MMP) in CCs (p < 0.05). Additionally, the integrated optical density (IOD) rate (cumulus/oocyte) of calcein and the expression of connexin 43 (CX43) was increased in CPF treatment groups (p < 0.05). As well, CPF exposure reduced the expression levels of FSCN1, DAAM1 and MYO10, which resulted in a significant decrease in the number and fluorescence intensity of transzonal projections (TZPs). In conclusion, CPF inhibited the expansion of cumulus and caused oxidative stress and apoptosis as well as disturbed the function of gap junctions (GJs) and TZPs, which eventually resulted in the failure of oocyte maturation.

Growth differentiation factor 9 regulates the expression of estrogen receptors via Smad2/3 signaling in goat cumulus cells

Both oocyte secretory factors (OSFs) and estrogen are essential for the development and function of mammalian ovarian follicles, playing synergistic role in regulating oocyte growth. OSFs can significantly affect the biological processes regulated by estrogen in cumulus cells (CCs). It is a scientific question worth investigating whether oocyte secretory factors can influence the expression of estrogen receptors in CCs. In our study, we observed a significant increase in the mRNA and protein expressions of estrogen receptor β (Esr2/ERβ) and G-protein-coupled estrogen receptor (GPER) in cumulus cells of goat cumulus-oocyte complexes (COCs) cultured in vitro for 6 h. Furthermore, the addition of 10 ng/mL growth-differentiation factor 9 (GDF9) and 5 ng/mL bone morphogenetic protein 15 (BMP15) to the culture medium of goat COCs resulted in a significant increase in the expressions of ERβ and GPER in cumulus cells. To explore the mechanism further, we performed micromanipulation to remove oocyte contents and co-cultured the oocytectomized complexes (OOXs) with denuded oocytes (DOs) or GDF9/BMP15. The expressions of ERβ and GPER in the co-culture groups were significantly higher than those in the OOXs group, but there was no difference compared to the COCs group. Mechanistically, we found that SB431542 (inhibitor of GDF9 bioactivity), but not LDN193189 (inhibitor of BMP15 bioactivity), abolished the upregulation of ERβ and GPER in cumulus cells and the activation of Smad2/3 signaling. In conclusion, our results demonstrate that the oocyte secretory factor GDF9 promotes the activation of Smad2/3 signaling in cumulus cells during goat COCs culture in vitro, and the phosphorylation of Smad2/3 induces the expression of estrogen receptors ERβ and GPER in cumulus cells.

Compromised Cumulus-Oocyte Complex Matrix Organization and Expansion in Women with PCOS

The cumulus-oocyte complex (COC) matrix plays a critical role in the ovulation and fertilization process and a major predictor of oocyte quality. Proteomics studies of follicular fluid showed differential expression of COC matrix proteins in women with polycystic ovary syndrome (PCOS), indicating altered COC matrix in these women. In the present study, we aimed to understand COC matrix gene induction in humans and its probable dysfunction in women with PCOS. Animal studies have shown that amphiregulin (AREG) and growth differentiation factor-9 (GDF-9) are important in the induction of COC matrix genes which are involved in cumulus expansion. The effects of AREG and GDF-9 on expression of tumor necrosis factor alpha induced protein 6 (TNFAIP6) and hyaluronan synthase 2 (HAS2) on human cumulus granulosa cells (CGCs) and murine COC expansion were evaluated. Further time-dependent effects of growth factor supplementation on these gene expressions in CGCs from PCOS and control women were compared. Follicular fluid from PCOS showed reduced COC matrix expansion capacity, using murine COCs. Expression of COC matrix genes TNFAIP6 and HAS2 were significantly reduced in CGCs of PCOS. Treatment of CGCs with AREG and GDF-9 together induced expression of both these genes in controls and could only restore HAS2 but not TNFAIP6 expression in PCOS. Our results suggest that the reduced potential of follicular fluid to support COC expansion, altered expression of structural constituents, and intrinsic defects in granulosa cells of women with PCOS may contribute to the aberrant COC organization and expansion in PCOS, thus affecting fertilization.

The Molecular Regulation in the Pathophysiology in Ovarian Aging

The female reproductive system is of great significance to women’s health. Aging of the female reproductive system occurs approximately 10 years prior to the natural age-associated functional decline of other organ systems. With an increase in life expectancy worldwide, reproductive aging has gradually become a key health issue among women. Therefore, an adequate understanding of the causes and molecular mechanisms of ovarian aging is essential towards the inhibition of age-related diseases and the promotion of health and longevity in women. In general, women begin to experience a decline in ovarian function around the age of 35 years, which is mainly manifested as a decrease in the number of ovarian follicles and the quality of oocytes. Studies have revealed the occurrence of mitochondrial dysfunction, reduced DNA repair, epigenetic changes, and metabolic alterations in the cells within the ovaries as age increases. In the present work, we reviewed the possible factors of aging-induced ovarian insufficiency based on its clinical diagnosis and performed an in-depth investigation of the relevant molecular mechanisms and potential targets to provide novel approaches for the effective improvement of ovarian function in older women.

Growth differentiation factor 9 (gdf9) and bone morphogenetic protein 15 (bmp15) are potential intraovarian regulators of steroidogenesis in Japanese flounder (Paralichthys olivaceus)

Members of transforming growth factor-β (TGF-β) superfamily are vital regulators during the development of fish ovary. However, its intraovarian functions in teleost are still unclear. As members of the TGF-β superfamily, gdf9 and bmp15 are necessary for follicle formation and granulosa cell proliferation. Here in Japanese flounder, quantitative real-time polymerase chain reaction (qRT-PCR) and in situ hybridization (ISH) analysis showed that gdf9 and bmp15 were mainly expressed in oogonia and oocytes, whereas weakly expressed in non-ovarian tissues. Overexpression of single gdf9 and the co-overexpression with bmp15 could up-regulate the expression of most steroidogenic genes, while the overexpression of single bmp15 could down-regulate the expression of most steroidogenic genes. These findings demonstrate that single gdf9 and the combination with bmp15 may act as "activator", while single bmp15 may act as "inhibitor" in the process of steroidogenesis in flounder. This was also verified in negative feedback regulation of gdf9 and bmp15 during hormone treatment. High concentration of human chorionic gonadotropin (hCG) could down-regulate gdf9 and up-regulate bmp15, which were beneficial for the homeostasis of hCG hormone. Besides, knockdown of either gdf9 or bmp15 could significantly down-regulate most steroidogenic genes. This indicated that heterodimer of GDF9:BMP15 might be the most bioactive ligand in gonad development of flounder. Taken together, our study provided a novel recognition that gdf9 and bmp15 could regulate steroidogenesis in teleost through mechanism different from that in mammals.

Granulosa secreted factors improve the developmental competence of cumulus oocyte complexes from small antral follicles in sheep

Oocyte in vitro maturation can be improved by mimicking the intra-follicular environment. Oocyte, cumulus cells, granulosa cells, and circulating factors act as meiotic regulators in follicles and maintain oocyte in the meiotic phase until oocyte becomes competent and ready to be ovulated. In a randomized experimental design, an ovine model was used to optimize the standard in vitro maturation media by Granulosa secreted factors. At first, the development capacity of oocyte derived from medium (>4 to 6 mm) and small (2 to ≤4 mm) size follicles was determined. Differential gene expression of granulosa secreted factors and their receptors were compared between the cumulus cells of the two groups. Then, the best time and concentration for arresting oocytes at the germinal vesicle stage by natriuretic peptide type C (CNP) were determined by nuclear staining in both groups. Oocyte quality was further confirmed by calcein uptake and gene expression. The developmental competence of cumulus oocyte complexes derived from small size follicles that were cultured in the presence of CNP in combination with amphiregulin (AREG) and prostaglandin E2 (PGE2) for 24 h was determined. Finally, embryo quality was specified by assessing expressions of NANOG, SOX2, CDX2, OCT4, and TET1. The cumulus oocyte complexes derived from small size follicles had a lower capacity to form blastocyst in comparison with cumulus oocyte complexes derived from medium size follicles. Prostaglandin E receptor 2 and prostaglandin-endoperoxide synthase 2 had significantly lower expression in cumulus cells derived from small size follicles in comparison with cumulus cells derived from medium size follicles. Natriuretic peptide type C increased the percentage of cumulus oocyte complexes arresting at the germinal vesicle stage in both oocytes derived from medium and small follicles. Gap junction communication was also improved in the presence of natriuretic peptide type C. In oocytes derived from small size follicles; best blastocyst rates were achieved by sequential exposure of cumulus oocyte complexes in [TCM+CNP (6 h), then cultured in TCM+AREG+PGE2 (18h)] and [TCM+CNP (6 h), then cultured in conventional IVM supplements+AREG+PGE2 (18h)]. Increased SOX2 expression was observed in [TCM+CNP (6 h), then cultured in TCM+AREG+PGE2 (18h)], while decreased OCT4 expression was observed in [TCM+CNP (6 h), then cultured in conventional IVM supplements+AREG+PGE2 (18h)]. It seems that the natriuretic peptide type C modulates meiotic progression, and oocyte development is probably mediated by amphiregulin and prostaglandin E2. These results may provide an alternative IVM method to optimize in vitro embryo production in sheep and subsequently for humans.

A 5-Methylcytosine Site of Growth Differentiation Factor 9 (GDF9) Gene Affects Its Tissue-Specific Expression in Sheep

Simple Summary

Growth differentiation factor 9 (GDF9) is an important gene for ovine fertility. GDF9 is highly expressed in the ovary as opposed to other tissues, but the reason for this is unknown. Our study found this can be caused by the methylation level of the promoter CpG island mC-4 site. This finding contributes to the understanding of the regulatory mechanism of GDF9 gene in reproduction.

Abstract

Growth differentiation factor 9 (GDF9) plays an important role in the early folliculogenesis of sheep. This study investigated the mRNA expression of ovine GDF9 in different tissues by real-time PCR. GDF9 exhibits significantly higher levels of expression (p < 0.01) in the ovary, relative to other tissues, indicating that its expression is tissue specific. To explore the regulatory mechanism of this tissue-specific expression, the methylation level of one CpG island (−1453 to −1854) of GDF9 promoter in ovary and heart was determined. In this region (−1987 to −1750), only the mC-4 site was present in the Sp4 binding site showed differential methylation between the heart and ovary; with increased (p < 0.01) methylation being observed in the heart. Additionally, the methylation level was negatively correlated with GDF9 mRNA expression (R = −0.75, p = 0.012), indicating that the methylation of this site plays an important role in transcriptional regulation of GDF9. The methylation effect of the mC-4 site was confirmed by using dual-luciferase. Site-directed mutation (methylation) of mC-4 site significantly reduced (p < 0.05) basal transcriptional activity of GDF9 promoter in oocytes. These results imply that methylation of GDF9 promoter CpG island mC-4 site may affect the binding of the Sp4 transcription factor to the GDF9 promoter region in sheep, thereby regulating GDF9 expression and resulting in a tissue-specific expression.

Supplementation with CTGF, SDF1, NGF, and HGF promotes ovine in vitro oocyte maturation and early embryo development

The strategies for improving the in vitro maturation (IVM) of domestic animal oocytes focus on promoting nuclear and cytoplasmic maturation. The identification of paracrine factors and their supplementation in the culture medium represent effective approaches for oocyte maturation and embryo development. This study investigated the effects of paracrine factor supplementation including connective tissue growth factor (CTGF), nerve growth factor (NGF), hepatocyte growth factor (HGF), and stromal derived factor 1 (SDF1) on ovine oocytes and early parthenogenetic embryos using an in vitro culture system. First, we identified the optimal concentrations of CTGF (30 ng/mL), SDF1 (10 ng/mL), NGF (3 ng/mL), and HGF (100 ng/mL) for promoting oocyte maturation, which combined, induced nuclear maturation in 94.19% of oocytes. This combination also promoted cumulus cell expansion and inhibited oocyte/cumulus apoptosis, while enabling a larger proportion (33.04%) of embryos to develop into blastocysts than in the controls and prevented embryo apoptosis. These novel findings demonstrate that the paracrine factors CTGF, SDF1, NGF, and HGF facilitate ovine oocyte and early parthenogenetic embryo development in vitro. Thus, supplementation with these factors may help optimize the IVM of ovine oocytes and early parthenogenetic embryo development strategies.

Functional characterization of NANOG in goat pre-implantation embryonic development

Nanog as a novel pluripotent cell-specific gene plays important roles in regulation of signaling pathways for maintenance and induction of pluripotency in inner cell mass (ICM) and embryonic stem cells (ESC) in mouse. The molecular features and transcription regulation of NANOG gene in domestic animals are not well defined. In this study, we performed knockdown of NANOG mRNA in goat embryos and examined its effect on early embryonic development. Presumptive zygotes were injected with a volume of 8-10 pl NANOG or scrambled (SCR) siRNA, and subsequently cleavage and blastocyst formation rate were assessed. Furthermore, gene expression analysis was carried out in 6-8 cell and blastocyst derived embryos from non-injected controls, SCR - and siRNA-injected presumptive zygotes. Cleavage and blastocyst rates in siRNA groups were insignificantly lower than the control and SCR groups. Embryos with reduced expression of NANOG showed decrease in number of trophectoderm (TE) and total cells in blastocysts. Analysis of expression of developmentally important genes (SOX2, OCT4 and NANOG), which work as a network, showed that NANOG knockdown results in significant increase in expression of SOX2 and OCT4 and among the possible target genes (CDX2, REX1 and GATA4) of this network, only GATA4 showed increased expression. Our results suggest that NANOG is likely to be required for proliferation of trophoblastic cells.

Expression of genes for enzymes synthesizing lysophosphatidic acid, its receptors and follicle developmental factors derived from the cumulus-oocyte complex is dependent on the ovarian follicle type in cows

Cumulus-oocyte complexes (COCs) release factors potentially involved in follicular growth and development, such as growth and differentiation factor 9 (GDF9), bone-morphogenetic protein 15 (BMP15), follistatin (FST) and cathepsins (CTSs). Moreover, the quality of the oocytes and follicles may be related to both the lipid composition of the follicle cells and follicular fluid. One of the lipids, locally regulating the reproductive functions in ovaries of cattle, is lysophosphatidic acid (LPA). In this study, the expression was investigated of the genes for LPA and other factors in COCs of follicles at different stages of development and regression. The relative abundances of mRNA were determined by real-time PCR for receptors for LPA (LPARs), enzymes synthesizing LPA (autotaxin (AX) and phospholipase A2 (PLA2)), BMP15, GDF9, CTSZ, CTSB and FST in COCs isolated from healthy, transitional and atretic follicles. The expression of genes for the LPARs, AX, PLA2 and the factors involved in follicular development in cattle COCs is follicle-type dependent. Greater expression of LPAR1-3 and AX genes were detected in the healthy follicles compared to the atretic and transitional follicles (P < 0.05). The relative abundance of GDF9, BMP15, CTSZ and CTSB was also greater in COCs from healthy follicles than from transitional and atretic follicles (P < 0.05). It is postulated that the greater expression of LPARs and AX genes in healthy follicles compared with atretic follicles indicates an enhanced role of LPA in follicular development. Results of the present study also suggest the regulatory role of factors derived from the COCs in the growth and development of follicles.

The effects of activated omental extract on nuclear and cytoplasmic in vitro maturation of rat oocytes

Objective:

The role of growth factors, including vascular endothelial growth factor of activated omentum on mitosis is clearly known, though not on all the aspects of in vitro oocyte maturation. This study was designed to assess the effect of activated-omental extract (AOE) on in vitro maturation (IVM) of rat cumulus-oocyte complexes (COCs).

Materials and Methods:

In this experimental study, the COCs were incubated in Ham’s F-10 supplemented with either 20% AOE, 20% fetal bovine serum (FBS) or serum-free media. Post-culture COCs were studied according to the cumulus cells (CCs) expansion, nuclear maturation and cytoplasmic maturation. Cumuli expansion was evaluated by inverted microscope without staining; nuclear maturation was assessed by aceto-orcein staining (light microscope) and cytoplasmic maturation was also observed by TEM.

Results:

Expansion of CCs and nuclear maturation of the oocytes in in vitro for 24 hr was significantly higher in AOE- and FBS-supplemented groups (P=0.000 and 0.013) and (P=0.004 and 0.014), respectively, compared to serum-free group. At ultra-structural level, after 24 hr, both FBS and AOE-supplemented media showed uniformly wide perivitelline space (PVS). After 12 hr, the cortical granules were found in the oocytes cultured in FBS and AOE-supplemented media. Within 24 hr, both granules and mitochondria were large without any detectable topographic tendency across the ooplasm. In AOE and FBS-supplemented oocytes, the number and size of microvilli were more than those in serum-free one.

Conclusion:

Although AOE supplementation induced a higher rate of the CCs expansion, and resuming meiosis, it was not as potent as FBS to provide cytoplasmic maturation of rat oocytes.

Differential gene-expression profiles from canine cumulus cells of ovulated versus in vitro-matured oocytes

We compared the nuclear maturation status and gene-expression profiles of canine cumulus cells (CCs) derived from cumulus-oocyte complexes (COCs) that were spontaneously ovulated versus those that were matured in vitro. Cumulus-oocyte complexes were retrieved from uteri by surgical flushing (after spontaneous ovulation) or by ovariectomy follicle aspiration and in vitro maturation. The objective of Experiment 1 was to investigate the nuclear maturation status of in vivo- versus in vitro-matured oocytes. The objective of Experiment 2 was to compare gene-expression profiles of CCs derived from in vivo- versus in vitro-matured COCs. Genes analysed are related to cell maturation, development and apoptosis, including GDF9, MAPK1, PTX3, CX43, Bcl2 and BAX; mRNA expression for all of these genes, except for GDF9, differed (P<0.05) between in vivo- and in vitro-matured CCs. In conclusion, we found that gene-expression profiles are related to the quality of CCs and therefore posit that monitoring gene expression could be a useful strategy to guide attempts to improve in vitro culture systems.

Differential activation of noncanonical SMAD2/SMAD3 signaling by bone morphogenetic proteins causes disproportionate induction of hyaluronan production in immortalized human granulosa cells

Successful fertilization depends upon proper cumulus-oocyte complex (COC) expansion. Synthesized by hyaluronan synthases (HASs), hyaluronan forms the backbone of the COC matrix and plays a critical role in COC expansion. This study investigated the effects and mechanisms of ovarian BMPs on HAS expression and hyaluronan production in human granulosa cells. Treatment with BMP4, BMP6, BMP7 or BMP15 induced differing levels of noncanonical SMAD2/3, but equal levels of canonical SMAD1/5/8, phosphorylation which were mirrored by differing levels of HAS2 up-regulation and hyaluronan production. The effects of BMP4 and BMP15 on HAS2 mRNA were partially reversed by knockdown of SMAD3, and blocked by knockdown of SMAD2+SMAD3 or SMAD4. BMP4-induced SMAD2/3 phosphorylation and HAS2 mRNA up-regulation were mediated by both BMP and activin/transforming growth factor-β type I receptors. Our results suggest differential activation of noncanonical SMAD2/SMAD3 signaling by BMPs causes disproportionate induction of HAS2 expression and hyaluronan production in immortalized human granulosa cells.

Molecular analysis of the cumulus matrix: insights from mice with O-glycan-deficient oocytes

During follicle development, oocytes secrete factors that influence the development of granulosa and cumulus cells (CCs). In response to oocyte and somatic cell signals, CCs produce extracellular matrix (ECM) molecules resulting in cumulus expansion, which is essential for ovulation, fertilisation, and is predictive of oocyte quality. The cumulus ECM is largely made up of hyaluronan (HA), TNF-stimulated gene-6 (TSG-6, also known as TNFAIP6), pentraxin-3 (PTX3), and the heavy chains (HCs) of serum-derived inter-α-inhibitor proteins. In contrast to other in vivo models where modified expansion impairs fertility, the cumulus mass of C1galt1 Mutants, which have oocyte-specific deletion of core 1-derived O-glycans, is modified without impairing fertility. In this report, we used C1galt1 Mutant (C1galt1^FF:ZP3Cre) and Control (C1galt1^FF) mice to investigate how cumulus expansion is affected by oocyte-specific deletion of core 1-derived O-glycans without adversely affecting oocyte quality. Mutant cumulus–oocyte complexes (COCs) are smaller than Controls, with fewer CCs. Interestingly, the CCs in Mutant mice are functionally normal as each cell produced normal levels of the ECM molecules HA, TSG-6, and PTX3. However, HC levels were elevated in Mutant COCs. These data reveal that oocyte glycoproteins carrying core 1-derived O-glycans have a regulatory role in COC development. In addition, our study of Controls indicates that a functional COC can form provided all essential components are present above a minimum threshold level, and thus some variation in ECM composition does not adversely affect oocyte development, ovulation or fertilisation. These data have important implications for IVF and the use of cumulus expansion as a criterion for oocyte assessment.

Control of Oocyte Growth and Development by Intercellular Communication Within the Follicular Niche

In the mammalian ovary, each oocyte grows and develops within its own structural and developmental niche-the follicle. Together with the female germ cell in the follicle are somatic granulosa cells, specialized companion cells that surround the oocyte and provide support to it, and an outer layer of thecal cells that serve crucial roles including steroid synthesis. These follicular compartments function as a single physiological unit whose purpose is to produce a healthy egg, which upon ovulation can be fertilized and give rise to a healthy embryo, thus enabling the female germ cell to fulfill its reproductive potential. Beginning from the initial stage of follicle formation and until terminal differentiation at ovulation, oocyte and follicle growth depend absolutely on cooperation between the different cellular compartments. This cooperation synchronizes the initiation of oocyte growth with follicle activation. During growth, it enables metabolic support for the follicle-enclosed oocyte and allows the follicle to fulfill its steroidogenic potential. Near the end of the growth period, intra-follicular interactions prevent the precocious meiotic resumption of the oocyte and ensure its nuclear differentiation. Finally, cooperation enables the events of ovulation, including meiotic maturation of the oocyte and expansion of the cumulus granulosa cells. In this chapter, we discuss the cellular interactions that enable the growing follicle to produce a healthy oocyte, focusing on the communication between the germ cell and the surrounding granulosa cells.

Genomic expression profiles in cumulus cells derived from germinal vesicle and MII mouse oocytes

Cumulus cells (CCs) are distinct from other granulosa cells and the mutual communication between CCs and oocytes is essential for the establishment of oocyte competence. In the present study we assessed genomic expression profiles in mouse CCs before and after oocyte maturation in vitro. Microarray analysis revealed significant changes in gene expression in CCs between the germinal vesicle (GV) and metaphase II (MII) stages, with 2615 upregulated and 2808 downregulated genes. Genes related to epidermal growth factor, extracellular matrix (Ptgs2, Ereg, Tnfaip6 and Efemp1), mitochondrial metabolism (Fdx1 and Aifm2), gap junctions and the cell cycle (Gja1, Gja4, Ccnd2, Ccna2 and Ccnb2) were highlighted as being differentially expressed between the two development stages. Real-time polymerase chain reaction confirmed the validity and reproducibility of the results for the selected differentially expressed genes. Similar expression patterns were identified by western blot analysis for some functional proteins, including EFEMP1, FDX1, GJA1 and CCND2, followed by immunofluorescence localisation. These genes may be potential biomarkers for oocyte developmental competence following fertilisation and will be investigated further in future studies.

Recombinant human growth differentiation factor-9 improves oocyte reprogramming competence and subsequent development of bovine cloned embryos

Previously, we found that oocyte-secreted factors (OSFs) secreted by denuded oocytes during in vitro maturation (IVM) enhance subsequent development of bovine somatic cell nuclear transfer (SCNT) embryos. This treatment requires many oocytes during IVM. Hence, the aim of this study was to investigate whether supplementing with recombinant growth differentiation factor-9 (GDF9), one of crucial OFSs, in oocyte maturation medium could improve developmental competence of bovine oocytes and subsequent development of cloned embryos. Cumulus-oocyte complexes (COCs) from antral follicles of bovine ovaries collected from an abattoir were cultured with (SCNT+GDF9 group) or without (SCNT group) 200 ng/mL recombinant human GDF9 in oocyte maturation medium. After 22 h, metaphase II (MII) oocytes were used for SCNT. The presence of 200 ng/mL GDF9 significantly increased oocyte maturation rates, the cleavage rate, and blastocyst formation rates of bovine cloned embryos. The blastocyst total, inner cell mass (ICM) cell numbers, and ratio of ICM:TE were higher, whereas the rate of apoptosis in bovine cloned blastocysts was lower in the SCNT+GDF9 group than in the SCNT group. The histone modifications at various sites were also different between each group. These results suggest that COCs cultured with recombinant GDF9 in oocyte maturation medium improve oocyte developmental competence and subsequent developmental competence of cloned embryo in cattle.