Oocyte secreted factors improve embryo developmental competence of COCs from small follicles in prepubertal goats

Effects of cumulus cells on the in vitro cytoplasmic maturation of immature oocytes in pigs

The exposure of cumulus cells to nuclear matured oocytes can be regulated through the forced delay of nuclear maturation or the alteration of in vitro maturation (IVM) time in cumulus-oocyte complexes (COCs). However, to date, no evidence has been presented for the enhancement of cytoplasmic maturation by them, indicating irrelevance of cumulus cells in cytoplasmic maturation. Therefore, in order to identify the requirement of cumulus cells in achieving the cytoplasmic maturation of immature oocytes, this study investigated the effects of cumulus cells on the in vitro cytoplasmic maturation of oocytes within COCs derived from porcine medium antral follicles (MAFs) post-the completion of nuclear maturation. For these, with IVM of COCs for 44 h (control), cumulus cell-free oocytes with completed nuclear maturation were in-vitro-matured additionally for 0, 6, or 12 h, and then a variety of factors representing the cytoplasmic maturation of oocytes were analyzed and compared. As the results, the IVM of COCs for 32 h showed complete nuclear maturation and incomplete cytoplasmic maturation. Moreover, after the removal of cumulus cells from COCs with the completion of nuclear maturation, IVM for an additional 6 or 12 h resulted in significant increases in the size of the perivitelline space, the proportion of oocytes with a normal intracellular mitochondrial distribution and a normal round first polar body, and the preimplantation development into the 2-cell and blastocyst stages after parthenogenetic activation. Simultaneously, they showed significant reduction in the level of intracellular reactive oxygen species and no significant differences in the total number of blastocysts. Furthermore, oocytes obtained by this approach did not significantly differ from control oocytes produced by IVM of COCs for 44 h. Our results demonstrate that the cumulus cells enclosing COCs derived from porcine MAFs are not essential for the completion of cytoplasmic maturation after complete nuclear maturation by COCs.

Paracrine regulation of granulosa cell development in the antral follicles in mammals

Background

Development of ovarian follicles is regulated by a complex interaction of intra- and extra-follicular signals. Oocyte-derived paracrine factors (ODPFs) play a central role in this process in cooperation with other signals.

Methods

This review provides an overview of the recent advances in our understanding of the paracrine regulation of antral follicle development in mammals. It specifically focuses on the regulation of granulosa cell development by ODPFs, along with other intrafollicular signals.

Main Findings

Bi-directional communication between oocytes and surrounding cumulus cells is a fundamental mechanism that determines cumulus cell differentiation. Along with estrogen, ODPFs promote the expression of forkhead box L2, a critical transcription factor required for mural granulosa cells. Follicle-stimulating hormone (FSH) facilitates these processes by stimulating estrogen production in mural granulosa cells.

Conclusion

Cooperative interactions among ODPFs, FSH, and estrogen are critical in determining the fate of cumulus and mural granulosa cells, as well as the development of oocytes.

Maternal age affects oocyte developmental potential at both ends of the age spectrum

Maternal age has a significant effect on oocyte developmental competence. Overall, evidence suggests that oocytes from both prepubertal females and reproductively aged females are inherently less competent. Reduced oocyte quality in both age groups is problematic for human medicine and agriculture. Some of the cellular mechanisms implicated in poor oocyte quality associated with maternal age are mitochondrial function and location, reduction of oxygen radicals, balance of metabolic pathways, regulation of maternal mRNAs and appropriate communication between the oocyte and cumulus cells. However, additional knowledge must be gained about the deficiencies present in prepubertal and reproductively aged oocytes that result in poor developmental potential before significant improvement can be achieved. This review discusses the evidence currently available regarding oocyte quality at both ends of the maternal age spectrum, what we know, or hypothesise, about the mechanisms involved and current thoughts regarding potential treatment for improvement.

Buffalo oocyte-secreted factors promote cumulus cells apoptosis and the rate of cGMP production but not steroidogenesis

The objectives of this study were to investigate the effect of buffalo oocyte-secreted factors (OSFs) on cumulus cells (CCs) functions, apoptosis and cGMP generation, and whether the direct contact between oocyte and CCs is essential for oocyte-mediated regulation of CCs functions. Buffalo CCs were cultured during IVM within three groups: (a) intact cumulus-oocyte complexes (COCs), (b) CCs cocultured with denuded oocytes (DOs) (CCs + DOs) and (c) CCs monolayer cultured alone (CCsM). After 24 hr of IVM, CCs were harvested for evaluation of the relative mRNA abundance of the genes encoding gap junction (GJA1), glycolysis (PFKP and LDHA), apoptosis (CASPASE-3 and BCL-2) and steroidogenesis (ER-β and PGR) by QRT-PCR, and CASPASE-3 proteins, using western blot. Intracellular cGMP content was also assessed by ELISA. Results showed that the relative abundance of LDHA, PFKP and BCL-2 significantly increased (p < 0.05) in COCs, whereas GJA1 and CASPASE-3 exhibited lower expression (p < 0.05) compared to CCs + DOs and CCsM groups. However, the expression levels of CASPASE-3, both mRNA and protein, were significantly (p < 0.05) downregulated in CCs + DOs compared to CCsM. There was no significant difference in the expression level of PGR and ER-β between the groups. The intracellular content of cGMP was notably (p < 0.05) higher in COCs compared to CCs + DOs and CCsM groups. In conclusion, this study demonstrated, for the first time, that buffalo OSFs protect CCs against apoptosis and stimulate their cGMP production; however, the regulation of cumulus glycolysis and gap junction is confined to those in close contact with the oocyte. Neither OSFs from COCs nor those from DOs have any effect on CCs steroidogenesis.

GDF-9 and BMP-15 direct the follicle symphony. J Assist Reprod Genet. 2018;35:1741-1750. [PMID: 30039232 DOI: 10.1007/s10815-018-1268-4]

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

Presence of vascular endothelial growth factor during the first half of IVM improves the meiotic and developmental competence of porcine oocytes from small follicles

The aim of the present study was to investigate the effect of vascular endothelial growth factor (VEGF) on the meiotic and developmental competence of porcine oocytes from small follicles (SF; 0.5-3mm diameter). When cumulus-oocyte complexes (COCs) from medium-sized follicles (MF; 3-6mm diameter) and SF were cultured for IVM, the maturation rates were significantly higher for oocytes from MF than SF. Concentrations of VEGF in the medium were significantly higher for COCs cultured from MF than SF. When COCs from SF were exposed to 200ngmL^-1 VEGF during the first 20h of IVM, the maturation rate improved significantly and was similar to that of oocytes derived from MF. The fertilisability of oocytes was also significantly higher than that of VEGF-free SF controls. Following parthenogenetic activation, the blastocyst formation rate improved significantly when SF COC culture was supplemented with 200ngmL^-1 VEGF, with the rate similar to that of oocytes from MF. The results of the present study indicate that VEGF markedly improves the meiotic and developmental competence of oocytes derived from SF, especially at a concentration of 200ngmL^-1 during the first 20h of IVM.

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.

Impact of oocyte-secreted factors on its developmental competence in buffalo

Oocyte-secreted factors (OSFs) play an important role in the acquisition of oocyte developmental competence through bidirectional cross-talk between oocyte and cumulus cells via gap junctions. Thus, the present study was designed to investigate the effect of two OSFs, growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15), on the developmental competence of buffalo oocytes derived from two different follicle sizes. Cumulus–oocyte complexes (COCs) from large follicles (LF, >6 mm) or small follicles (SF, <6 mm) were collected and matured in vitro either in the presence of GDF9 or BMP15, or both, or with the denuded oocytes (DOs) as a source of native OSFs. Cleavage and blastocyst rates were significantly (P < 0.05) higher in LF-derived than SF-derived oocytes. Cleavage and blastocyst rates were significantly higher (P < 0.05) in the DOs and the combination groups compared with the control, GDF9 alone and BMP15 alone groups, both in LF-derived and SF-derived oocytes, although the cleavage and blastocyst rates did not differ significantly (P > 0.05) between DOs and combination groups. Relative mRNA analysis revealed significantly higher (P > 0.05) expression of the cumulus cell marker genes EGFR, HAS2, and CD44 in LF-derived than SF-derived oocyte; the expression of these markers was significantly higher (P > 0.05) in DOs and combination groups, irrespective of the follicle size. These results suggested that LF-derived oocytes have a higher developmental competence than SF-derived oocytes and that supplementation of GDF9 and BMP15 modulates the developmental competence of buffalo oocytes by increasing the relative abundance of cumulus-enabling factors and thereby increasing cleavage and the quality of blastocyst production.

Embryo splitting affects the transcriptome during elongation stage of in vitro-produced bovine blastocysts

Embryo splitting has been used for the production of identical twins and to increase the pregnancy rate per available embryo. Split blastocysts can develop to term; however, little is known about the impact on gene expression of split embryos, especially at the whole transcriptome level. This work was aimed to evaluate the effect of blastocyst splitting on global gene expression profile at the elongation stage. For that, split and time-matched nonsplit (control group) bovine blastocysts were transferred to a bovine recipient and recovered at Day 17 of development. The number of collected embryos, their size, and global gene expression was compared between both groups. From 16 transferred split embryos, six (37.5%) were collected, whereas nine elongated were recovered from 17 nonsplit (52.9%). Neither the recovery rate nor the average length of the elongated embryos was significantly different between both groups. However more than 50% of embryos from the control group had a length surpassing 100 mm, whereas only 33% of the split embryos reached that size. Global gene expression was performed in individual elongated embryos from both groups using Two-Color Microarray-Based Gene Expression Analysis. From detected genes, 383 (1.31%) were differentially expressed between both groups, among them, 185 (0.63%) were downregulated and 198 (0.67%) genes were upregulated in split embryos. Bioinformatic analysis of differentially expressed genes revealed that embryo splitting affects transcriptomes of resulting elongated embryos, mainly downregulating genes involved in matrix remodelation, control of growth, detoxification, and transport of metabolites. These in turns might have a detrimental impact on the developmental potential of produced embryos.

Porcine oocyte maturation in vitro: role of cAMP and oocyte-secreted factors - A practical approach

Polyspermy or the penetration of more than one sperm cell remains a problem during porcine in vitro fertilization (IVF). After in vitro culture of porcine zygotes, only a low percentage of blastocysts develop and their quality is inferior to that of in vivo derived blastocysts. It is unknown whether the cytoplasmic maturation of the oocyte is sufficiently sustained in current in vitro maturation (IVM) procedures. The complex interplay between oocyte and cumulus cells during IVM is a key factor in this process. By focusing on this bidirectional communication, it is possible to control the coordination of cumulus expansion, and nuclear and cytoplasmic maturation during IVM to some extent. Therefore, this review focuses on the regulatory mechanisms between oocytes and cumulus cells to further the development of new in vitro embryo production (IVP) procedures, resulting in less polyspermy and improved oocyte developmental potential. Specifically, we focused on the involvement of cAMP in maturation regulation and function of oocyte-secreted factors (OSFs) in the bidirectional regulatory loop between oocyte and cumulus cells. Our studies suggest that maintaining high cAMP levels in the oocyte during the first half of IVM sustained improved oocyte maturation, resulting in an enhanced response after IVF and cumulus matrix disassembly. Recent research indicated that the addition of OSFs during IVM enhanced the developmental competence of small follicle-derived oocytes, which was stimulated by epidermal growth factor (EGF) via developing EGF-receptor signaling.

Modifications of human growth differentiation factor 9 to improve the generation of embryos from low competence oocytes

Growth differentiation factor 9 (GDF9) is an oocyte-derived growth factor that plays a critical role in ovarian folliculogenesis and oocyte developmental competence and belongs to the TGF-β family of proteins. Recombinant human GDF9 (hGDF9) is secreted in a latent form, which in the case of the fully processed protein, has the proregion noncovalently associated with the mature region. In this study, we investigated a number of amino acid residues in the mature region of hGDF9 that are different from the corresponding residues in the mouse protein, which is not latent. We designed, expressed, and purified 4 forms of chimeric hGDF9 (M1-M4) that we found to be active in a granulosa cell bioassay. Using a porcine in vitro maturation model with inherent low developmental competence (yielding 10%-20% blastocysts), we tested the ability of the chimeric hGDF9 proteins to improve oocyte maturation and developmental competence. Interestingly, one of the chimeric proteins, M3, was able to significantly increase the level of embryo production using such low competence oocytes. Our molecular modeling studies suggest that in the case of hGDF9 the Gly(391)Arg mutation probably increases receptor binding affinity, thereby creating an active protein for granulosa cells in vitro. However, for an improvement in oocyte developmental competence, a second mutation (Ser(412)Pro), which potentially decreases the affinity of the mature region for the proregion, is also required.

Current status of in vitro embryo production in sheep and goats

Sheep and goat production is an important economic activity in Spain with an increasing interest in milk production. Multiovulation and Embryo Transfer (MOET) and In vitro Embryo Production (IVEP) are assisted reproductive technologies aimed at increasing the genetic diffusion of females. In vitro embryo production is a multi-step methodology comprising the following procedures: (i) In vitro Maturation (IVM) of oocytes recovered directly from the follicles, (ii) In vitro Fertilization (IVF) or co-incubation of capacitated spermatozoa with in vitro matured oocytes and (iii) In vitro culture (IVC) of zygotes up to the blastocyst stage. In vitro embryo production from oocytes recovered from prepubertal females is called JIVET (Juvenile in vitro Embryo Transfer) and allows shortened generation intervals and increased genetic gain. Embryo production together with embryo cryoconservation would allow large-scale embryo marketing, a pathogen-free genetic movement and easier and cheaper germplasm commercial transactions. Commercial Embryo activity in small ruminants is low compared to cows in the European Union (data from the European Embryo Transfer Association) and in the world (data from the International Embryo Transfer Association). There is less IVEP research in small ruminants compared to other livestock species. The aim of this review was to provide an overview of the current status of IVEP of small ruminant with an emphasis on (i) description of the main methodologies currently used for IVM, IVF and IVC of embryos (ii) comparing procedures and outputs from JIVET and IVEP of adult females and (iii) the future research perspectives of this technology.

Influence of co-culture with denuded oocytes during in vitro maturation on fertilization and developmental competence of cumulus-enclosed porcine oocytes in a defined system

Co-culture of cumulus-oocyte complexes (COCs) with denuded oocytes (DOs) during in vitro maturation (IVM) was reported to improve the developmental competence of oocytes via oocyte-secreted factors in cattle. The aim of the present study was to investigate if addition of DOs during IVM can improve in vitro fertilization (IVF) and in vitro culture (IVC) results for oocytes in a defined in vitro production system in pigs. The maturation medium was porcine oocyte medium supplemented with gonadotropins, dbcAMP and β-mercaptoethanol. Cumulus-oocyte complexes were matured without DOs or with DOs in different ratios (9 COC, 9 COC+16 DO and 9 COC+36 DO). Consequently; oocytes were subjected to IVF as intact COCs or after denudation to examine if DO addition during IVM would affect cumulus or oocyte properties. After fertilization, penetration and normal fertilization rates of zygotes were not different between all tested groups irrespective of denudation before IVF. When zygotes were cultured for 6 days, no difference could be observed between all treatment groups in cleavage rate, blastocyst rate and cell number per blastocyst. In conclusion, irrespective of the ratio, co-culture with DOs during IVM did not improve fertilization parameters and embryo development of cumulus-enclosed porcine oocytes in a defined system.

Oocyte induction of EGF responsiveness in somatic cells is associated with the acquisition of porcine oocyte developmental competence

Oocytes progressively acquire the competence to support embryo development as oogenesis proceeds with ovarian folliculogenesis. The objectives of this study were to investigate oocyte-secreted factor (OSF) participation in the development of somatic cell epidermal growth factor (EGF) responsiveness associated with oocyte developmental competence. A well-established porcine model was employed using oocytes from small (<4 mm) vs medium sized (>4 mm) antral follicles, representing low vs moderate developmental competence, respectively. Cumulus-oocyte complexes (COCs) were treated in vitro with inducers of oocyte maturation, and cumulus cell functions and oocyte developmental competence were assessed. COCs from small follicles responded to FSH but, unlike COCs from larger follicles, were incapable of responding to EGF family growth factors known to mediate oocyte maturation in vivo, exhibiting perturbed cumulus expansion and expression of associated transcripts (HAS2 and TNFAIP6). Low and moderate competence COCs expressed equivalent levels of EGF receptor (EGFR) mRNA; however, the former had less total EGFR protein leading to failed activation of phospho-EGFR and phospho-ERK1/2, despite equivalent total ERK1/2 protein levels. Native OSFs from moderate, but not from low, competence oocytes established EGF responsiveness in low competence COCs. Four candidate recombinant OSFs failed to mimic the actions of native OSFs in regulating cumulus expansion. Treatment with OSFs and EGF enhanced oocyte competence but only of the low competence COCs. These data suggest that developmental acquisition by the oocyte of capacity to regulate EGF responsiveness in the oocyte's somatic cells is a major milestone in the oocyte's developmental program and contributes to coordinated oocyte and somatic cell development.

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.

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.

Oocyte-secreted factors in oocyte maturation media enhance subsequent development of bovine cloned embryos

Successful in vitro maturation (IVM) and oocyte quality both affect the subsequent development of cloned embryos derived from somatic-cell nuclear transfer (SCNT). Developmental competence is usually lower in oocytes matured in vitro compared with those that matured in vivo, possibly due to insufficient levels of oocyte-secreted factors (OSFs) and disrupted oocyte-cumulus communication. This study investigated the effects of OSFs secreted by denuded oocytes (DOs) during IVM on the subsequent developmental competence of cloned bovine embryos. Cumulus-oocyte complexes (COCs) from antral follicles of slaughtered-cow ovaries collected from an abattoir were divided into four groups: COCs co-cultured with and without DOs in maturation media used for SCNT, as well as COCs co-cultured with and without DOs in maturation media used for in vitro fertilization (IVF). Based on the developmental competence and embryo quality of bovine embryos generated from these four groups, we found that co-culturing the COCs with DOs enhanced the in vitro development of IVF and cloned bovine embryos, and potentially generated more high-quality cloned blastocysts that possessed locus-specific histone modifications at levels similar to in vitro-fertilized embryos. These results strongly suggest that co-culturing COCs with DOs enhances subsequent developmental competence of cloned bovine embryo.

In vitro production of small ruminant embryos: late improvements and further research

Beyond the potential use of in vitro production of embryos (IVP) in breeding schemes, embryos are also required for the establishment of new biotechnologies such as cloning and transgenesis. Additionally, the knowledge of oocyte and embryo physiology acquired through IVP techniques may stimulate the further development of other techniques such as marker assisted and genomic selection of preimplantation embryos, and also benefit assisted procreation in human beings. Efficient in vitro embryo production is currently a major objective for livestock industries, including small ruminants. The heterogeneity of oocytes collected from growing follicles by laparoscopic ovum pick up or in ovaries of slaughtered females, remains an enormous challenge for IVM success, and still limits the rate of embryo development. In addition, the lower quality of the IVP embryos, compared with their in vivo-derived counterparts, translates into poor cryosurvival, which restricts the wider use of this promising technology. Therefore, many studies have been reported in an attempt to determine the most suitable conditions for IVM, IVF, and in vitro development to maximize embryo production rate and quality. This review aims to present the current panorama of IVP production in small ruminants, describing important steps for its success, reporting the recent advances and also the main obstacles identified for its improvement and dissemination.

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.

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

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

Differential expression of GDF9, TGFB1, TGFB2 and TGFB3 in porcine oocytes isolated from follicles of different size before and after culture in vitro

The TGFB superfamily genes are involved in several important cell functions, including proliferation and differentiation, and the role of the expression of these genes in growth and development of theca and granulosa cells is well recognised. However, the dependence between the stage of oocyte maturation or follicular size and the expression of these genes in pigs is still not entirely known. This study was aimed at investigating the expression pattern of GDF9, TGFB1, TGFB2 and TGFB3 in porcine oocytes before and after in vitro maturation (IVM) as well as in oocytes collected from follicles of different sizes. RQ-PCR was performed to analyse the expression of GDF9, TGFB1, TGFB2 and TGFB3 in oocytes before and after IVM (oocytes cultured for 44 h in TCM-199), isolated from large (> 5 mm), medium (3-5 mm) and small (< 3 mm) follicles collected from ovaries of 28 puberal crossbred Landrace gilts after slaughter. We found an increased expression of both TGFB1 and TGFB2 in oocytes before IVM collected from large as compared to medium and small follicles (P < 0.05, P < 0.001, P < 0.01, P < 0.05, respectively). In these groups of oocytes we did not observe differences in GDF9 and TGFB3 mRNA levels. However, after IVM, GDF9 protein distribution in oocytes was significantly higher in large and medium follicles as compared to small ones (P < 0.01, P < 0.001, respectively). Moreover, an increased TGFB1, TGFB2 and TGFB3 proteins pattern was observed in oocytes of large compared to small follicles. The highest GDF9 and TGFB1 mRNA levels were found in oocytes after IVM compared to those before IVM. Based on our study we can suppose that the distribution pattern of TGFB superfamily genes is associated with the stage of maturation of porcine oocytes and the follicle size. Furthermore, GDF9 and TGFB1 may serve as molecular markers of the develop-mental potential of porcine oocytes. The confocal microscopic observation revealed that TGFB1 and TGFB3 were translocated between the zona and the cytoplasm of oocytes, depending on the stage of maturation and follicle size.

Recent insights into oocyte-follicle cell interactions provide opportunities for the development of new approaches to in vitro maturation

The last 5-10 years of research in ovarian and oocyte biology has delivered some major new advances in knowledge of the molecular and cellular processes regulating oocyte maturation and oocyte developmental competence. These new insights include, among others: (1) the knowledge that oocytes regulate granulosa and cumulus cell differentiation, ovulation rate and fertility via the secretion of soluble paracrine growth factors; (2) new perspectives on the participation of cyclic nucleotides, phosphodiesterases and gap junctions in the regulation of oocyte meiotic arrest and resumption; and (3) the new appreciation of the mechanisms of LH-induced oocyte maturation and ovulation mediated by the follicular cascade of epidermal growth factor (EGF)-like peptides, the EGF receptor and their intracellular second messengers. These recent insights into oocyte-follicle cell interactions provide opportunities for the development of new approaches to oocyte in vitro maturation (IVM). Laboratory IVM methodologies have changed little over the past 20-30 years and IVM remains notably less efficient than hormone-stimulated IVF, limiting its wider application in reproductive medicine and animal breeding. The challenge for oocyte biologists and clinicians practicing IVM is to modernise clinical IVM systems to benefit from these new insights into oocyte-follicle cell interactions in vivo.

Temporal effects of exogenous oocyte-secreted factors on bovine oocyte developmental competence during IVM

We investigated whether paracrine signalling between the bovine oocyte and cumulus cells is altered during the course of in vitro maturation (IVM). Bovine COCs were cocultured with denuded oocytes or treated with specific oocyte-secreted factors, namely recombinant bone morphogenetic protein (BMP)-15 or growth differentiation factor (GDF)-9, beginning from 0 or 9 h IVM. To generate a 9-h denuded oocyte (DO) group, COCs were cultured intact for the first 9 h of IVM and then denuded. Coculturing intact COCs with DOs denuded immediately after collection or following 9 h of maturation did not affect cleavage rate, but improved blastocyst yield (P < 0.05) on Day 8 (51 and 61%, respectively; P < 0.05) and cell number compared with COCs cultured alone (41%). Significantly, we observed higher levels of endogenous GDF-9 and BMP-15 protein in oocytes of COCs matured for 9 h compared with no incubation. The addition of 175 ng mL–1 GDF-9 or 10% v/v BMP-15 from partially purified transfected 293H cell supernatant for 24 h IVM significantly enhanced development to the blastocyst stage from 40% (control) to 51 and 47%, respectively (P < 0.05). However, treatment of COCs with GDF-9 or BMP-15 between 9 and 24 h of IVM did not increase blastocyst yield. These results provide evidence of quantitative and possibly qualitative temporal changes in oocyte paracrine factor production during IVM.