Age-dependent high-yield isolation of primordial, primary, and early secondary follicles from the bovine ovarian cortex.

In brief: Preantral follicles constitute the largest follicle reserve in the mammalian ovary. This study assesses a mechanical isolation method to maximize the number of follicles retrieved from a defined cortex volume. Abstract: Primordial, primary, and secondary follicles (collectively defined as preantral follicles) constitute the most abundant source of gametes inside the mammalian ovarian cortex. The massive isolation of preantral follicles and the refinement of stage-specific protocols for in vitro follicle growth would provide a powerful tool to boost the rescue and restoration of fertility in assisted reproduction interventions in human medicine, animal breeding, and vulnerable species preservation. Nevertheless, together with an efficient culture system, the most significant limitation to implementing in vitro follicle growth is the lack of an efficient method to isolate viable and homogeneous subpopulations of primordial, primary, and secondary follicles suitable for in vitro culture. Our study provides a strategy for high-yielding mechanical isolation of primordial, primary, and early secondary follicles from a limited portion of the ovarian cortex in the bovine animal model. In the first part of the study, we refined a mechanical isolation protocol of preantral follicles, adopting specific methodological strategies to separate viable and distinct subpopulations of primordial (oblate and prolate forms), primary, and early secondary follicles from 0.16 cm3 of the ovarian cortex. In the second part of the study, we tested the effectiveness of the isolation protocol, considering the individual's age as a critical factor, bearing in mind the progressive decrease in the ovarian reserve that naturally accompanies the reproductive life span. Our study provides a way for designing quantitative and conservative fertility preservation approaches to preserve organ function and minimize the invasiveness of the interventions, also considering age-related differences.

Meiotic maturation failure in primary ovarian insufficiency: insights from a bovine model.

PURPOSE: Oocytes from women presenting primary ovarian insufficiency (POI) generate viable embryos at a lower rate than non-POI women, but the mechanisms responsible for the lower oocyte quality remain elusive. Due to the scarcity of human oocytes for research, animal models provide a promising way forward. We aimed at investigating the molecular events characterizing final maturation in POI oocytes in a well-defined POI-like bovine model. METHODS: Single-cell RNA-sequencing of bovine control and POI-like, GV, and MII oocytes (n = 5 per group) was performed. DEseq2 was used to identify differentially expressed genes. Further, a Gene set enrichment analysis and a transcriptomic meta-analysis between bovine and human oocytes were performed. RESULTS: In control cows, we found 2223 differentially expressed genes between the GV and MII stages. Specifically, the affected genes were related to RNA processing and transport, protein synthesis, organelle remodeling and reorganization, and metabolism. The meta-analysis with a set of young human oocytes at different maturation stages revealed 315 conserved genes through the GV-MII transition in cows and humans, mostly related to meiotic progression and cell cycle. Gene expression analysis between GV and MII of POI-like oocytes showed no differences in terms of differentially expressed genes, pointing towards a substantial failure to properly remodel the transcriptome in the POI model, and with the clustering analysis indicating that the cow's genetic background had a higher impact than the oocyte's maturation stage. CONCLUSION: Overall, we have identified and characterized a valuable animal model of POI, paving the way to identifying new molecular mechanisms involved in POI.

A refined culture system of oocytes from early antral follicles promotes oocyte maturation and embryo development in cattle.

In brief: The proposed culture system improves the current state of in vitro culture of growing oocytes in the bovine species and allows access to the untapped gamete reserve, thus improving reproductive efficiency. Abstract: The present study aimed to improve the in vitro culture of bovine oocytes collected from early antral follicles (EAFs) to support the progressive acquisition of meiotic and developmental competence. The rationale that drove the development of such a culture system was to maintain as much as possible the physiological conditions that support the oocyte growth and differentiation in vivo. To this extent, oocytes were cultured for 5 days, which parallels the transition from early to medium antral follicles (MAFs) in the bovine, and supports promoting a 3D-like structure were provided. Additionally, the main hormones (follicle-stimulating hormone, estradiol, progesterone, and testosterone) were added in concentrations similar to the ones previously observed in bovine EAFs. The meiotic arrest was imposed using cilostamide. The cultured cumulus-oocyte complexes (COCs) reached a mean diameter of 113.4 ± 0.75 µm and showed a progressive condensation of the chromatin enclosed in the germinal vesicle (GV), together with a gradual decrease in the global transcriptional activity, measured by 5-ethynyl uridine incorporation. The described morpho-functional changes were accompanied by an increased ability to mature and develop to the blastocyst stage in vitro, although not matching the rates obtained by MAF-retrieved oocytes. The described system improves the current state of in vitro culture of growing oocytes in the bovine species, and it can be used to increase the number of gametes usable for in vitro embryo production in animals of high genetic merit or with specific desirable traits.

Roles of the cumulus-oocyte transzonal network and the Fragile X protein family in oocyte competence.

In brief: RNA granules travel through the cumulus cell network of transzonal projections which is associated with oocyte developmental competence, and RNA packaging involves RNA-binding proteins of the Fragile X protein family. Abstract: The determinants of oocyte developmental competence have puzzled scientists for decades. It is known that follicular conditions can nurture the production of a high-quality oocyte, but the underlying mechanisms remain unknown. Somatic cumulus cells most proximal to the oocyte are known to have cellular extensions that reach across the zona pellucida and contact with the oocyte plasma membrane. Herein, it was found that transzonal projections (TZPs) network quality is associated with developmental competence. Knowing that ribonucleoparticles are abundant within TZPs, the distribution of RNA-binding proteins was studied. The Fragile X-related proteins (FXR1P and FXR2P) and two partnering protein families, namely cytoplasmic FMRP-interacting protein and nuclear FMRP-interacting protein, exhibited distinctive patterns consistent with roles in regulating mRNA packaging, transport, and translation. The expression of green fluorescent protein (GFP)-FMRP fusion protein in cumulus cells showed active granule formation and their transport and transfer through filipodia connecting with neighboring cells. Near the projections' ends was found the cytoskeletal anchoring protein Filamin A and active protein synthesis sites. This study highlights key proteins involved in delivering mRNA to the oocyte. Thus, cumulus cells appear to indeed support the development of high-quality oocytes via the transzonal network.

Physiological parameters related to oocyte nuclear differentiation for the improvement of IVM/IVF outcomes in women and cattle.

In vitro maturation (IVM) has been applied in numerous different contexts and strategies in humans and animals, but in both cases it represents a challenge still far from being overcome. Despite the large dataset produced over the last two decades on the mechanisms that govern antral follicular development and oocyte metabolism and differentiation, IVM outcomes are still unsatisfactory. This review specifically focuses on data concerning the potential consequences of using supraphysiological levels of FSH during IVM, as well as on the regulation of oocyte chromatin dynamics and its utility as a potential marker of oocyte developmental competence. Taken together, the data revisited herein indicate that a significant improvement in IVM efficacy may be provided by the integration of pre-OPU patient-specific protocols preparing the oocyte population for IVM and more physiological culture systems mimicking more precisely the follicular environment that would be experienced by the recovered oocytes until completion of metaphase II.

Zinc supports transcription and improves meiotic competence of growing bovine oocytes.

In the last years, many studies focused on the understanding of the possible role of zinc in the control of mammalian oogenesis, mainly on oocyte maturation and fertilization. However, little is known about the role of zinc at earlier stages, when the growing oocyte is actively transcribing molecules that will regulate and sustain subsequent stages of oocyte and embryonic development. In this study, we used the bovine model to gain insights into the possible involvement of zinc in oocyte development. We first mined the EmbryoGENE transcriptomic dataset, which revealed that several zinc transporters and methallothionein are impacted by physiological conditions throughout the final phase of oocyte growth and differentiation. We then observed that zinc supplementation during in vitro culture of growing oocytes is beneficial to the acquisition of meiotic competence when subsequently subjected to standard in vitro maturation. Furthermore, we tested the hypothesis that zinc supplementation might support transcription in growing oocytes. This hypothesis was indirectly confirmed by the experimental evidence that the content of labile zinc in the oocyte decreases when a major drop in transcription occurs in vivo. Accordingly, we observed that zinc sequestration with a zinc chelator rapidly reduced global transcription in growing oocytes, which was reversed by zinc supplementation in the culture medium. Finally, zinc supplementation impacted the chromatin state by reducing the level of global DNA methylation, which is consistent with the increased transcription. In conclusion, our study suggests that altering zinc availability by culture-medium supplementation supports global transcription, ultimately enhancing meiotic competence.

A prematuration approach to equine IVM: considering cumulus morphology, seasonality, follicle of origin, gap junction coupling and large-scale chromatin configuration in the germinal vesicle.

Several studies report that a two-step culture where mammalian oocytes are first kept under meiosis-arresting conditions (prematuration) followed by IVM is beneficial to embryo development. The most promising results were obtained by stratifying the oocyte population using morphological criteria and allocating them to different culture conditions to best meet their metabolic needs. In this study, horse oocytes were characterised to identify subpopulations that may benefit from prematuration. We investigated gap-junction (GJ) coupling, large-scale chromatin configuration and meiotic competence in compact and expanded cumulus-oocyte complexes (COCs) according to follicle size (<1, 1-2, >2cm) and season. Then we tested the effect of cilostamide-based prematuration in compact COCs collected from follicles <1 and 1-2cm in diameter on embryo development. Meiotic competence was not affected by prematuration, whereas COCs from follicles 1-2cm in diameter yielded embryos with a higher number of cells per blastocyst than oocytes that underwent direct IVM (P<0.01, unpaired Mann-Whitney test), suggesting improved developmental competence. Oocytes collected from follicles <1cm in diameter were not affected by prematuration. This study represents an extensive characterisation of the functional properties of immature horse oocytes and is the first report of the effects of cilostamide-based prematuration in horse oocyte IVM on embryo development.

PGRMC1 localization and putative function in the nucleolus of bovine granulosa cells and oocytes.

Progesterone receptor membrane component-1 (PGRMC1) is a highly conserved multifunctional protein that is found in numerous systems, including reproductive system. Interestingly, PGRMC1 is expressed at several intracellular locations, including the nucleolus. The aim of this study is to investigate the functional relationship between PGRMC1 and nucleolus. Immunofluorescence experiments confirmed PGRMC1's nucleolar localization in cultured bovine granulosa cells (bGC) and oocytes. Additional experiments conducted on bGC revealed that PGRMC1 co-localizes with nucleolin (NCL), a major nucleolar protein. Furthermore, small interfering RNA (RNAi)-mediated gene silencing experiments showed that when PGRMC1 expression was depleted, NCL translocated from the nucleolus to the nucleoplasm. Similarly, oxidative stress induced by hydrogen peroxide (H2O2) treatment, reduced PGRMC1 immunofluorescent signal in the nucleolus and increased NCL nucleoplasmic signal, when compared to non-treated cells. Although PGRMC1 influenced NCL localization, a direct interaction between these two proteins was not detected using in situ proximity ligation assay. This suggests the involvement of additional molecules in mediating the co-localization of PGRMC1 and nucleolin. Since nucleolin translocates into the nucleoplasm in response to various cellular stressors, PGRMC1's ability to regulate its localization within the nucleolus is likely an important component of mechanism by which cells response to stress. This concept is consistent with PGRMC1's well-described ability to promote ovarian cell survival and provides a rationale for future studies on PGRMC1, NCL and the molecular mechanism by which these two proteins protect against the adverse effect of cellular stressors, including oxidative stress.

Oviductal microvesicles and their effect on in vitro maturation of canine oocytes.

The effect of conditioned medium (CM) or microvesicles (MVs), secreted by multicellular spheroids of oviductal cells, and the involvement of some microRNAs (miRNAs) were investigated in canine oocyte maturation. To generate CM, spheroids were cultured for 3 days. MVs were obtained by ultracentrifugation of CM at 100,000 g and measured for size and concentration by NanoSight instrument. Cumulus-oocyte complexes (COCs) were matured at 38.5°C with 5% CO2 and 5% of O2 in synthetic oviductal fluid (SOF) in biphasic systems: for 24 h, with 5.0 µg/mL of LH and for other 48 h with 10% oestrous bitch serum. SOF was used as control (CTR) or supplemented with 10% CM or 25-50-75-100-150 × 106 MVs/mL labeled with PKH-26. Results show that multicellular aggregates secreted shedding vesicles. By fluorescence microscopy, the incorporation of labeled MVs was visible only at 72 h in oocyte cytoplasm. These MVs had a positive effect (P < 0.05) on maturation rate (MII) at the concentration of 75 and 100 × 106 MVs/mL compared to CM and CTR (20.34% and 21.82% vs 9.09% and 8.66% respectively). The concentration of 150 × 106 MVs/mL provided only 9.26% of MII. The expression of three specific miRNAs (miR-30b, miR-375 and miR-503) was studied. The lower rate of MII with the higher concentration of MVs is possibly due to the high level of miR-375. In conclusion, the oviductal MVs could be involved in cellular trafficking during oocyte maturation and their possible use in vitro could facilitate the exploitment of canine reproductive biotechnologies.

Steroid hormones interact with natriuretic peptide C to delay nuclear maturation, to maintain oocyte-cumulus communication and to improve the quality of in vitro-produced embryos in cattle.

In vivo, oocyte maturation is triggered by the ovulatory LH surge, whereas in vitro it is precociously induced when the cumulus-oocyte complex is removed from the follicle. Natriuretic peptide C (NPPC) delays germinal vesicle breakdown (GVBD) while increasing oocyte-cumulus communication during in vitro maturation (IVM) in cattle. In the present study we first tested the hypothesis that steroids secreted by the follicle (17ß-oestradiol, progesterone and androstenedione) interact with NPPC to delay GVBD and to maintain oocyte-cumulus communication as assessed by transfer of a dye (Lucifer Yellow) from the oocyte to cumulus cells. Then, we assessed the effects of steroid hormones and NPPC, alone and in combination in a pre-IVM culture, on embryo production. The combination of NPPC with steroids delayed GVDB, increased natriuretic peptide receptor 2 (NPR2) mRNA abundance in cumulus cells during culture, and maintained oocyte-cumulus communication at levels not different from non-cultured controls. The addition of steroids and/or NPPC to a pre-IVM culture did not alter blastocyst rates after IVF, but supplementation with steroids increased blastocyst total cell number. The present study provides evidence, for the first time in cattle, that steroids interact with NPPC to regulate oocyte nuclear maturation and oocyte-cumulus communication, and improve oocyte developmental competence.

In vitro maturation affects chromosome segregation, spindle morphology and acetylation of lysine 16 on histone H4 in horse oocytes.

Implantation failure and genetic developmental disabilities in mammals are caused by errors in chromosome segregation originating mainly in the oocyte during meiosis I. Some conditions, like maternal ageing or in vitro maturation (IVM), increase the incidence of oocyte aneuploidy. Here oocytes from adult mares were used to investigate oocyte maturation in a monovulatory species. Experiments were conducted to compare: (1) the incidence of aneuploidy, (2) the morphology of the spindle, (3) the acetylation of lysine 16 on histone H4 (H4K16) and (4) the relative amount of histone acetyltransferase 1 (HAT1), K(lysine) acetyltransferase 8 (KAT8, also known as MYST1), histone deacetylase 1 (HDAC1) and NAD-dependent protein deacetylase sirtuin 1 (SIRT1) mRNA in metaphase II stage oocytes that were in vitro matured or collected from peri-ovulatory follicles. The frequency of aneuploidy and anomalies in spindle morphology was increased following IVM, along with a decrease in H4K16 acetylation that was in agreement with our previous observations. However, differences in the amount of the transcripts investigated were not detected. These results suggest that the degradation of transcripts encoding for histone deacetylases and acetyltransferases is not involved in the changes of H4K16 acetylation observed following IVM, while translational or post-translational mechanisms might have a role. Our study also suggests that epigenetic instabilities introduced by IVM may affect the oocyte and embryo genetic stability.

Differences in cumulus cell gene expression indicate the benefit of a pre-maturation step to improve in-vitro bovine embryo production.

STUDY QUESTION: Does the gene expression profile of cumulus cells (CC) accompanying oocytes with different degrees of chromatin compaction within the germinal vesicle (GV) reflect the oocyte's quality and response in culture during in-vitro embryo production (IVP). SUMMARY ANSWER: The transcriptomic profile of the CC is related to oocyte competence, setting the stage for the development of customized pre-maturation strategies to improve IVP. WHAT IS KNOWN ALREADY: Oocytes complete the acquisition of their competence during antral follicle development. During this period, the chromatin configuration within the GV changes dynamically and is indicative of oocyte's developmental potential. The interactions between somatic and germ cells modulate chromatin morphology and function and are critical for acquisition of oocyte competence. STUDY DESIGN, SIZE, DURATION: Bovine cumulus-oocyte complexes (COC) were isolated from 0.5 to 6 mm antral follicles. Surrounding CC were separated from the oocyte and classified as GV0, GV1, GV2 and GV3 according to the degree of the oocyte's chromatin compaction. PARTICIPANTS/MATERIALS, SETTING, METHOD: RNA extracted from CC of each group was amplified and hybridized on a bovine embryo-specific 44 K Agilent slide. The CC_GV1, CC_GV2 and CC_GV3 classes were each hybridized against the CC_GV0 class, representing an early oocyte differentiation stage with poor development competence. The data were normalized and fold changes of the differentially expressed genes were determined. Microarray data were validated using quantitative RT-PCR on selected targets. Microarray data were further analyzed through: (i) between-group analysis (BGA), which classifies the samples according to their transcriptomic profiles; (ii) cluster analysis according to the expression profile of each gene; and (iii) Ingenuity Pathway Analysis (IPA) to study gene regulation patterns and predicted functions. Furthermore, CC of each GV group were cultured and apoptotic cells were assessed after 3 h by caspase analysis. Finally, based on the analysis of CC transcriptomic profiles and the relationship between morphological features of the COC and the oocyte chromatin configuration, a customized, stage-dependent oocyte pre-maturation (pre-IVM) system was used to improve oocyte developmental potential before IVM. For this, the blastocyst rate and quality were assessed after in-vitro maturation and fertilization of pre-matured oocytes. MAIN RESULTS AND THE ROLE OF CHANCE: Overall, quantitative RT-PCR results of a subset of five selected genes were consistent with the microarray data. Clustering analysis generated 16 clusters representing the main profiles of transcription modulation. Of the 5571 significantly differentially expressed probes, the majority (25.49%) best fitted with cluster #6 (downregulation between CC_GV0 and CC_GV1 and stable low levels in successive groups). IPA identified the most relevant functions associated with each cluster. Genes included in cluster #1 were mostly related to biological processes such as 'cell cycle' and 'cell death and survival', whereas genes included in cluster #5 were mostly related to 'gene expression'. Interestingly, 'lipid metabolism' was the most significant function identified in clusters #6, #9 and #12. IPA of gene lists obtained from each contrast (i.e., CC_GV0 vs. CC_GV1; CC_GV0 vs. CC_GV2; CC_GV0 vs. CC_GV3) revealed that the main affected function in each contrast was 'cell death and survival'. Importantly, apoptosis was predicted to be inhibited in CC_GV1 and CC_GV2, but activated in CC_GV3. Caspase analysis indicated that a low percentage of CC_GV0 was prone to undergo apoptosis but apoptosis increased significantly in CC from oocytes with condensed chromatin, reaching a peak in CC_GV3 (P < 0.05). Finally, the tailored oocyte pre-maturation strategy, based on morphological features of the COC and the oocyte chromatin configuration, demonstrated that pre-IVM improved the developmental capability of oocytes at early stages of differentiation (GV1-enriched COC) but was detrimental for oocytes at more advanced stages of development (GV2 and GV3-enriched COC). LARGE SCALE DATA: The data are available through the GEO series accession number GSE79886. LIMITATIONS, REASONS FOR CAUTION: This study was conducted with bovine samples. Whether or not the results are applicable to human oocytes requests further elucidation. Embryo transfer experiments are required to determine whether the improvement in blastocyst rates in the tailored system leads to increased live birth rates. WIDER IMPLICATIONS OF THE FINDINGS: The identification of multiple non-invasive biomarkers predictive of oocyte quality can greatly strengthen the pre-IVM approach aimed to improve IVM outcomes. These results have potentially important implications in treating human infertility and in developing breeding schemes for domestic mammals. STUDY FUNDING/COMPETING INTERESTS: This work was supported in part by NSERC Strategic Network EmbryoGENE, Canada and in part by CIG-Marie Curie Actions-Reintegration Grants within the EU 7FP (n. 303640, 'Pro-Ovum'). The authors declare no potential conflict of interest.

Natriuretic peptide precursor C delays meiotic resumption and sustains gap junction-mediated communication in bovine cumulus-enclosed oocytes.

Oocyte in vitro maturation (IVM) has become a valuable technological tool for animal breeding and cloning and the treatment of human infertility because it does not require the administration of exogenous gonadotropin to obtain fertilizable oocytes. However, embryo development after IVM is lower compared to in vivo maturation, most likely because oocytes collected for IVM are heterogeneous with respect to their developmental competencies. Attempts to improve IVM outcome have relied upon either prematuration culture (PMC) or two-step maturation strategies in the hope of normalizing variations in developmental competence. Such culture systems invoke the pharmacological arrest of meiosis, in theory providing oocytes sufficient time to complete the acquisition of developmental competence after cumulus-enclosed oocytes isolation from the follicle. The present study was designed to test the efficiency of natriuretic peptide precursor C (NPPC) as a nonpharmacologic meiosis-arresting agent during IVM in a monoovulatory species. NPPC has been shown to maintain meiotic arrest in vivo and in vitro in mice and pigs; however, the use of this molecule for PMC has yet to have been explored. Toward this end, meiotic cell cycle reentry, gap-junction functionality, and chromatin configuration changes were investigated in bovine cumulus-enclosed oocytes cultured in the presence of NPPC. Moreover, oocyte developmental competence was investigated after IVM, in vitro fertilization, and embryo culture and compared to standard IVM-in vitro fertilization protocol without PMC. Our results suggest that NPPC can be used to delay meiotic resumption and increase the developmental competence of bovine oocytes when used in PMC protocols.

Reductions in the number of mid-sized antral follicles are associated with markers of premature ovarian senescence in dairy cows.

High-producing dairy cows are subfertile; however, the mechanisms responsible for the decreased fertility are unknown. The aim of the present study was to test the hypothesis that culled dairy cows (4-8 years old) characterised by 'Lo' ovaries (i.e. those with <10 mid-antral follicles) are affected by premature ovarian senescence. Cows in which both ovaries were 'Lo' ovaries represented 5% of the total population analysed, and exhibited reduced ovarian size (P<0.001) and increased perifollicular stroma (P<0.05) compared with age-matched controls (i.e. cows in which both ovaries had >10 mid-antral follicles; 'Hi' ovaries). The total number of follicles, including healthy and atretic primordial, primary, secondary and small antral follicles, was lower in Lo ovaries (P<0.01). Interestingly, the primordial follicle population in Lo ovaries was lower (P<0.05) than in the control. Finally, the follicular fluid of mid-antral follicles from Lo ovaries had reduced oestradiol and anti-Müllerian hormone levels (P<0.05), but increased progesterone concentrations (P<0.05). Together, these data account for the reduced fertility of cows with Lo ovaries and are in agreement with previous observations that oocytes isolated from Lo ovaries have reduced embryonic developmental competence. Cows with a specific Lo ovary condition may represent a suitable model to address the causes of low fertility in high-yielding dairy cows, as well as the condition of premature ovarian aging in single-ovulating species.

Method of Isolation and In Vitro Culture of Primordial Follicles in Bovine Animal Model.

The mammalian ovary is a substantial source of oocytes arranged into follicles at various stages of folliculogenesis, from the primordial to the ovulatory ones. Primordial follicles constitute the most abundant source of gametes inside the mammalian ovary at any given time.The isolation of a high number of primordial follicles, together with the development of protocols for in vitro follicle growth, would provide a powerful tool to fully exploit the female reproductive potential and boost the rescue and restoration of fertility in assisted reproduction technologies in human medicine, animal breeding, and preservation of threatened species. However, the most significant limitation is the lack of efficient methods for isolating a healthy and homogeneous population of viable primordial follicles suitable for in vitro culture. Here, we provide a fast and high-yield strategy for the mechanical isolation of primordial follicles from limited portions of the ovarian cortex in the bovine animal model.

Plasminogen activator inhibitor 1 RNA-binding protein interacts with progesterone receptor membrane component 1 to regulate progesterone's ability to maintain the viability of spontaneously immortalized granulosa cells and rat granulosa cells.

Progesterone receptor membrane component 1 (PGRMC1) mediates the antiapoptotic action of progesterone (P4). PGRMC1 interacts with plasminogen activator inhibitor 1 RNA-binding protein (PAIRBP1), but the functional significance of this interaction is unknown. To examine the function of PGRMC1-PAIRBP1 interaction, PAIRBP1 was depleted from spontaneously immortalized granulosa cells (SIGCs) and the effects on the expression and localization of PGRMC1 as well as P4's ability to bind to SIGCs and prevent apoptosis was assessed. Depleting PAIRBP1 enhanced cellular (3)H-P4 binding and did not alter the expression or cellular localization of PGRMC1 but attenuated P4's antiapoptotic action. Transfection of a PGRMC1-green fluorescent protein (GFP) peptide mimic, which binds PAIRBP1 as demonstrated by in situ proximity assay, doubled the rate at which SIGCs undergo apoptosis compared to cells transfected with either the empty GFP expression vector or Pairbp1 small interfering RNA. Moreover, P4 did not prevent these cells from undergoing apoptosis. Similar studies conducted with granulosa cells isolated from immature rats also showed that PGRMC1 interacts with PAIRBP1 and that transfection of PGRMC1-GFP peptide mimic accelerates the rate of granulosa cell apoptosis by 4-fold even in the presence of serum and P4. These studies support the concept that the interaction between PAIRBP1-PGRMC1 is an essential component of the mechanism through which P4 inhibits apoptosis. Surprisingly, PGRMC1-PAIRBP1 interaction is not required for P4 binding or the cellular localization of PGRMC1 but rather appears to couple PGRMC1 to downstream components of the P4-PGRMC1 signal transduction pathway.

Oocytes isolated from dairy cows with reduced ovarian reserve have a high frequency of aneuploidy and alterations in the localization of progesterone receptor membrane component 1 and aurora kinase B.

Oocytes isolated from cows of reproductive age with reduced antral follicle counts (AFC) have a diminished capacity of embryonic development, which may be related to alterations in the mechanism that directs the proper segregation of chromosomes. Because we demonstrated that progesterone receptor membrane component 1 (PGRMC1) is involved in chromosome congression and metaphase II (MII) plate formation, the present study was designed to determine 1) if the decrease in oocyte developmental competence observed in dairy cows with a reduced AFC is due to a higher incidence of aneuploidy and 2) whether alterations in PGRMC1 contributes to the incidence of aneuploidy. Oocytes from ovaries with reduced AFC and age-matched controls were matured in vitro and the occurrence of aneuploidy determined as well as the mRNA level and localization of PGRMC1. Although oocytes from ovaries with reduced AFC were capable of undergoing meiosis in vitro, these oocytes showed a 3-fold increase in aneuploidy compared to oocytes isolated from control ovaries (P < 0.05). Although Pgrmc1 mRNA levels were not altered, PGRMC1 and aurora kinase B (AURKB) failed to localize to precise focal points on MII chromosomes of oocytes from ovaries with reduced AFC. Furthermore, when oocytes of control ovaries were cultured with an inhibitor of AURKB activity, their MII plate was disrupted and PGRMC1 was not properly localized to the chromosomes. These results suggest that alterations in PGRMC1 and/or AURKB localization account in part for the increased aneuploidy and low development competence of oocytes from ovaries with reduced AFC.

The effect of cilostamide on gap junction communication dynamics, chromatin remodeling, and competence acquisition in pig oocytes following parthenogenetic activation and nuclear transfer.

In the pig, the efficiency of in vitro embryo production and somatic cell nuclear transfer (SCNT) procedures remains limited. It has been suggested that prematuration treatments (pre-IVM) based on the prolongation of a patent, bidirectional crosstalk between the oocyte and the cumulus cells through gap junction mediate communication (GJC), with the maintenance of a proper level of cAMP, could improve the developmental capability of oocytes. The aim of this study was to assess: 1) dose-dependent effects of cilostamide on nuclear maturation kinetics, 2) the relationship between treatments on GJC functionality and large-scale chromatin configuration changes, and 3) the impact of treatments on developmental competence acquisition after parthenogenetic activation (PA) and SCNT. Accordingly, cumulus-oocyte complexes were collected from 3- to 6-mm antral follicles and cultured for 24 h in defined culture medium with or without 1 µM cilostamide. GJC functionality was assessed by Lucifer yellow microinjection, while chromatin configuration was evaluated by fluorescence microscopy after nuclear staining. Cilostamide administration sustained functional coupling for up to 24 h of culture and delayed meiotic resumption, as only 25.6% of cilostamide-treated oocytes reached the pro-metaphase I stage compared to the control (69.7%; P < 0.05). Moreover, progressive chromatin condensation was delayed before meiotic resumption based upon G2/M biomarker phosphoprotein epitope acquisition using immunolocalization. Importantly, cilostamide treatment under these conditions improved oocyte developmental competence, as reflected in higher blastocyst quality after both parthenogenetic activation and SCNT.

Role of gap junction-mediated communications in regulating large-scale chromatin configuration remodeling and embryonic developmental competence acquisition in fully grown bovine oocyte.

PURPOSE: This study was aimed to test the hypothesis that gap junction mediated communications (GJC) are required to allow the progressive chromatin configuration remodeling (from GV1 to GV3) process to occur in fully grown oocytes in order to gain the final step of developmental competence acquisition, and that a premature disruption of GJC can alter this process. METHODS: Bovine cumulus-oocytes complexes collected from medium antral follicles were cultured for 2, 4, 6 and 8 h in the presence of 10(-4) IU/ml of r-hFSH and with 2 mM of the non-selective PDE inhibitor 3-isobutyl-1-methyl-xanthine (IBMX) to prevent meiotic resumption. GJC functionality and chromatin configuration were monitored during the culture period. After meiotic arrest, the developmental capability of oocytes was assessed after IVM and IVF. RESULTS: IBMX was effective in significantly sustaining GJC up to 6 h and maintaining meiotic arrest, when compared to control group. Moreover, the percentage of oocytes with less condensed chromatin (GV1) decreased within 4 h of culture, while the proportion of GV2 oocytes gradually increased up to 6 h. Interestingly, a decline in the proportion of GV2 oocytes and an increase in the proportion of GV3 oocytes were observed after 6 h of culture, when the major drop of GJC occurred. On the contrary, when GJC were uncoupled by adding 3 mM of 1-heptanol or through cumulus cells removal, chromatin condensation occurred rapidly throughout the culture period, more promptly in denuded oocytes. Moreover, the maintenance of GJC during meiotic arrest was accompanied by a significant increase of developmental competence compared to the control, as indicated by a higher percentage of hatched blastocysts and blastocyst cell number. CONCLUSIONS: Altogether, our data indicate that both paracrine and junctional mechanisms are involved in modulating large-scale chromatin structure during the final phase of oocyte differentiation.

Neuregulin 1 (NRG1) modulates oocyte nuclear maturation during IVM and improves post-IVF embryo development.

Oocyte in vitro maturation (IVM) is still a major challenge in human and animal assisted reproduction. Gradual instead of abrupt activation of the ovulatory cascade during IVM has been proposed to enhance nuclear-cytoplasmic synchrony and cumulus-oocyte communication, thus favoring oocyte developmental competence. Herein, we assessed the effects of neuregulin 1 (NRG1), an EGF-like factor that modulates EGFR signaling, on oocyte nuclear maturation dynamics, cumulus expansion and expression of mRNAs regulating these processes during IVM, as well as on post-IVF embryo development following AREG-stimulated IVM in cattle. In experiment 1, cumulus-oocyte complexes (COCs) were subjected to IVM with graded doses of NRG1 (1, 10 or 100 ng/mL) for 6, 9, 12, 20, and 24 h, after which oocyte nuclear status and cumulus mRNA expression were assessed. At 6 h of IVM, NRG1 at 1 ng/mL significantly decreased the percentage of GVBD (germinal vesicle breakdown) oocytes without altering later meiotic dynamics or the percentage of oocytes achieving meiosis II. In experiment 2, adding NRG1 (1 ng/mL) to the IVM medium did not affect cumulus expansion but increased the percentage of expanded and hatched blastocysts, and blastocyst total cell number following IVF/IVC. NRG1 decreased EGFR mRNA abundance while increasing NPR2 and PTX3 mRNA levels at 9 h, and TNFAIP6 mRNA abundance at 20 h of IVM. This is the first study that reports the modulatory effect of NGR1 during oocyte maturation in a mono-ovulatory species and demonstrates that this action may be applied during IVM to improve post-IVF embryo development.