EGF-like peptides mediate FSH-induced maturation of cumulus cell-enclosed mouse oocytes

The growth factors amphiregulin and epiregulin are novel stimulators of feline ovarian granulosa cell functions

This study aimed to investigate the impact of the epidermal growth factor receptor ligands amphiregulin (AREG) and epiregulin (EREG) on the fundamental functions of feline ovarian granulosa cells. Granulosa cells isolated from feline ovaries were incubated with AREG and EREG (0, 0.1, 1 or 10 ng/mL). The effects of these growth factors on cell viability, proliferation (assessed through BrdU incorporation), nuclear apoptosis (evaluated through nuclear DNA fragmentation) and the release of progesterone and estradiol were determined using Cell Counting Kit-8 assays, BrdU analysis, TUNEL assays and ELISAs, respectively. Both AREG and EREG increased cell viability, proliferation and steroid hormone release and reduced apoptosis. The present findings suggest that these epidermal growth factor receptor ligands may serve as physiological stimulators of feline ovarian cell functions.

EGF-like growth factors upregulate pentraxin 3 expression in human granulosa-lutein cells

The epidermal growth factor (EGF)-like factors, comprising amphiregulin (AREG), betacellulin (BTC), and epiregulin (EREG), play a critical role in regulating the ovulatory process. Pentraxin 3 (PTX3), an essential ovulatory protein, is necessary for maintaining extracellular matrix (ECM) stability during cumulus expansion. The aim of this study was to investigate the impact of EGF-like factors, AREG, BTC, and EREG on the expression and production of PTX3 in human granulosa-lutein (hGL) cells and the molecular mechanisms involved. Our results demonstrated that AREG, BTC, and EREG could regulate follicular function by upregulating the expression and increasing the production of PTX3 in both primary (obtained from 20 consenting patients undergoing IVF treatment) and immortalized hGL cells. The upregulation of PTX3 expression was primarily facilitated by the activation of the extracellular signal-regulated kinase 1 and 2 (ERK1/2) signaling pathway, induced by these EGF-like factors. In addition, we found that the upregulation of PTX3 expression triggered by the EGF-like factors was completely reversed by either pretreatment with the epidermal growth factor receptor (EGFR) inhibitor, AG1478, or knockdown of EGFR, suggesting that EGFR is crucial for activating the ERK1/2 signaling pathway in hGL cells. Overall, our findings indicate that AREG, BTC, and EREG may modulate human cumulus expansion during the periovulatory stage through the upregulation of PTX3.

Oocyte secreted factors control genes regulating FSH signaling and the maturation cascade in cumulus cells: the oocyte is not in a hurry

PURPOSE

To assess the effects of the oocyte on mRNA abundance of FSHR, AMH and major genes of the maturation cascade (AREG, EREG, ADAM17, EGFR, PTGS2, TNFAIP6, PTX3, and HAS2) in bovine cumulus cells.

METHODS

(1) Intact cumulus-oocyte complexes, (2) microsurgically oocytectomized cumulus-oolema complexes (OOX), and (3) OOX + denuded oocytes (OOX+DO) were subjected to in vitro maturation (IVM) stimulated with FSH for 22 h or with AREG for 4 and 22 h. After IVM, cumulus cells were separated and relative mRNA abundance was measured by RT-qPCR.

RESULTS

After 22 h of FSH-stimulated IVM, oocytectomy increased FSHR mRNA levels (p=0.005) while decreasing those of AMH (p=0.0004). In parallel, oocytectomy increased mRNA abundance of AREG, EREG, ADAM17, PTGS2, TNFAIP6, and PTX3, while decreasing that of HAS2 (p<0.02). All these effects were abrogated in OOX+DO. Oocytectomy also reduced EGFR mRNA levels (p=0.009), which was not reverted in OOX+DO. The stimulatory effect of oocytectomy on AREG mRNA abundance (p=0.01) and its neutralization in OOX+DO was again observed after 4 h of AREG-stimulated IVM. After 22 h of AREG-stimulated IVM, oocytectomy and addition of DOs to OOX caused the same effects on gene expression observed after 22 h of FSH-stimulated IVM, except for ADAM17 (p<0.025).

CONCLUSION

These findings suggest that oocyte-secreted factors inhibit FSH signaling and the expression of major genes of the maturation cascade in cumulus cells. These may be important actions of the oocyte favoring its communication with cumulus cells and preventing premature activation of the maturation cascade.

Role of COX-2/PGE2 signaling pathway in the apoptosis of rat ovarian granulosa cells induced by MEHP

OBJECTIVE

MEHP, as the metabolite of DEHP, is a widely used environmental endocrine disruptor. Ovarian granulosa cells participate in maintaining the function of ovary and COX2/PGE2 pathway may regulate the function of granulosa cells. We aimed to explore how COX-2/PGE2 pathway affects cell apoptosis in ovarian granulosa cells caused by MEHP.

METHODS

Primary rat ovarian granulosa cells were treated with MEHP (0, 200, 250, 300 and 350 μM) for 48 h. Adenovirus was used for over-expression of COX-2 gene. The cell viability was tested with CCK8 kits. The apoptosis level was tested by flow cytometry. The levels of PGE2 were tested with ELISA kits. The expression levels of COX-2/PGE2 pathway related genes, ovulation-related genes and apoptosis-related genes, were measured with RT-qPCR and Western blot.

RESULTS

MEHP decreased the cell viability. After MEHP exposure, the cell apoptosis level increased. The level of PGE2 markedly decreased. The expression levels of COX-2/PGE2 pathway related genes, ovulation-related genes and anti-apoptotic genes decreased; the expression levels of pro-apoptotic genes increased. The apoptosis level was alleviated after over-expression of COX-2, and the level of PGE2 slightly increased. The expression levels of PTGER2 and PTGER4, and the levels of ovulation-related genes increased; the levels of pro-apoptotic genes decreased.

CONCLUSION

MEHP can cause cell apoptosis by down-regulating the levels of ovulation-related genes via COX-2/PGE2 pathway in rat ovarian granulosa cells.

A single-cell gene expression atlas of human follicular aspirates: Identification of leukocyte subpopulations and their paracrine factors

Leukocytes are in situ regulators critical for ovarian function. However, little is known about leukocyte subpopulations and their interaction with follicular cells in ovulatory follicles, especially in humans. Single-cell RNA sequencing (scRNA-seq) was performed using follicular aspirates obtained from four IVF patients and identified 13 cell groups: one granulosa cell group, one thecal cell group, 10 subsets of leukocytes, and one group of RBC/platelet. RNA velocity analyses on five granulosa cell populations predicted developmental dynamics denoting two projections of differentiation states. The cell type-specific transcriptomic profiling analyses revealed the presence of a diverse array of leukocyte-derived factors that can directly impact granulosa cell function by activating their receptors (e.g., cytokines and secretory ligands) and are involved in tissue remodeling (e.g., MMPs, ADAMs, ADAMTSs, and TIMPs) and angiogenesis (e.g., VEGFs, PGF, FGF, IGF, and THBS1) in ovulatory follicles. Consistent with the findings from the scRNA-seq data, the leukocyte-specific expression of CD68, IL1B, and MMP9 was verified in follicle tissues collected before and at defined hours after hCG administration from regularly cycling women. Collectively, this study demonstrates that this data can be used as an invaluable resource for identifying important leukocyte-derived factors that promote follicular cell function, thereby facilitating ovulation and luteinization in women.

Assessment of Epiregulin Effect and its Combination with Gonadotropins on Proliferation, Apoptosis, and Secretory Activity by Human Ovarian Cells

The release of epidermal growth factor ligand epiregulin (EREG) by human ovarian granulosa cells, its direct action on basic ovarian cell functions, and interrelationships with gonadotropins were investigated. We examined (1) the ovarian production of EREG (the time-dependent accumulation of EREG in the medium incubated with human ovarian granulosa cells, and (2) the effect of the addition of EREG (0, 1, 10, and 100 ng.ml^-1) given alone or in combination with FSH or LH (100 ng.ml^-1) on basic granulosa cells functions. Viability, proliferation (accumulation of PCNA and cyclin B1) and apoptosis (accumulation of bax and caspase 3), the release of steroid hormones (progesterone, testosterone, and estradiol), and prostaglandin E2 (PGE2) were analyzed by using the Trypan blue exclusion test, quantitative immunocytochemistry, and ELISA. A significant time-dependent accumulation of EREG in a medium cultured with human granulosa cells with a peak at 3 and 4 days was observed. The addition of EREG alone increased cell viability, proliferation, progesterone, testosterone, and estradiol release, decreased apoptosis, bud did not affect PGE2 release. The addition of either FSH or LH alone increased cell viability, proliferation, progesterone, testosterone, estradiol, and PGE2 release and decreased apoptosis. Furthermore, both FSH and LH mostly promoted the stimulatory action of EREG on granulosa cell functions. These results demonstrated, that EREG produced by ovarian cells can be an autocrine/paracrine stimulator of human ovarian cell functions. Furthermore, they demonstrate the functional interrelationship between EREG and gonadotropins in the control of ovarian functions.

The in-vitro effect of gonadotropins' type and combination on Granulosa cells gene expressions

OBJECTIVE

Nowadays, different modes and timing of GnRH-agonist combined with hCG trigger, for final follicular maturation, have been described. While LH + FSH are the naturally occurring final follicular maturation trigger, hCG is commonly use during stimulated cycle, and recently the introduction of the Dual/Double trigger combines LH + FSH + hCG. In the present study we aim to investigate the messenger RNA (mRNA) expression of reproduction-related genes in human granulosa cells (GCs) exposed to the aforementioned different types and combinations of gonadotropins.

MATERIAL AND METHODS

Mural GCs were obtained from follicular fluid aspirated during IVF protocol. GCs were seeded in culture for 4 days with daily medium exchange followed by administration of either hCG (1 U/ml); FSH (1 U/ml) and LH (8 U/ml); or hCG (1 U/ml) and FSH (1 U/ml) and LH (8 U/ml) for 16 h. mRNA was purified from harvested GCs and gene expression was quantitative by qPCR.

MAIN OUTCOME MEASURES

The expression of genes related to steroidogenesis (StAR/ CYP19) and oocyte maturation (COX2/Amphiregulin) in cultured GCs.

RESULTS

The Dual/Double trigger (LH + FSH + hCG) showed higher activation of steroidogenesis (StAR/CYP19) and maturation (COX2/Amphiregulin) as compared to the naturally occurring trigger (LH + FSH) and the hCG triggers. Moreover, while the naturally occurring trigger (LH + FSH) activated maturation significantly and more intensely than the hCG trigger, no in between group differences were observed with regards to steroidogenic related genes.

CONCLUSIONS

Our findings are in agreement with clinical experience, demonstrating the superiority of the double/dual (LH + FSH + hCG) trigger over the naturally occurring and the hCG triggers.

Positive effects of amphiregulin on human oocyte maturation and its molecular drivers in patients with polycystic ovary syndrome

STUDY QUESTION

Does use of medium containing amphiregulin improve meiotic maturation efficiency in oocytes of women with polycystic ovary syndrome (PCOS) undergoing in vitro maturation (IVM) preceded by a capacitation culture step capacitation IVM (CAPA-IVM)?

SUMMARY ANSWER

Use of medium containing amphiregulin significantly increased the maturation rate from oocytes retrieved from follicles with diameters <6 or ≥6 mm pre-cultured in capacitation medium.

WHAT IS KNOWN ALREADY

Amphiregulin concentration in follicular fluid is correlated with human oocyte developmental competence. Amphiregulin added to the meiotic trigger has been shown to improve outcomes of IVM in a range of mammalian species.

STUDY DESIGN, SIZE, DURATION

This prospective, randomized cohort study included 30 patients and was conducted at an academic infertility centre in Vietnam from April to December 2019. Patients with PCOS were included.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In the first stage, sibling oocytes from each patient (671 in total) were allocated in equal numbers to maturation in medium with (CAPA-AREG) or without (CAPA-Control) amphiregulin 100 ng/ml. After a maturation check and fertilization using intracytoplasmic sperm injection (ICSI), all good quality Day 3 embryos were vitrified. Cumulus cells (CCs) from both groups were collected at the moment of ICSI denudation and underwent a molecular analysis to quantify key transcripts of oocyte maturation and to relate these to early embryo development. On return for frozen embryo transfer (second stage), patients were randomized to have either CAPA-AREG or CAPA-Control embryo(s) implanted. Where no embryo(s) from the randomized group were available, embryo(s) from the other group were transferred. The primary endpoint of the study was meiotic maturation efficiency (proportion of metaphase II [MII] oocytes; maturation rate).

MAIN RESULTS AND THE ROLE OF CHANCE

In the per-patient analysis, the number of MII oocytes was significantly higher in the CAPA-AREG group versus the CAPA-Control group (median [interquartile range] 7.0 [5.3, 8.0] versus 6.0 [4.0, 7.0]; P = 0.01). When each oocyte was evaluated, the maturation rate was also significantly higher in the CAPA-AREG group versus the CAPA-Control group (67.6% versus 55.2%; relative risk [RR] 1.22 [95% confidence interval (CI) 1.08-1.38]; P = 0.001). No other IVM or embryology outcomes differed significantly between the two groups. Rates of clinical pregnancy (66.7% versus 42.9%; RR 1.56 [95% CI 0.77-3.14]), ongoing pregnancy (53.3% versus 28.6%; RR 1.87 [95% CI 0.72-4.85]) and live birth (46.7% versus 28.6%; RR 1.63 [95% CI 0.61-4.39]) were numerically higher in the patients who had CAPA-AREG versus CAPA-Control embryos implanted, but each fertility and obstetric outcome did not differ significantly between the groups. In the CAPA-AREG group, there were significant shifts in CC expression of genes involved in steroidogenesis (STAR, 3BHSD), the ovulatory cascade (DUSP16, EGFR, HAS2, PTGR2, PTGS2, RPS6KA2), redox and glucose metabolism (CAT, GPX1, SOD2, SLC2A1, LDHA) and transcription (NRF2). The expression of three genes (TRPM7, VCAN and JUN) in CCs showed a significant correlation with embryo quality.

LIMITATIONS, REASONS FOR CAUTION

This study included only Vietnamese women with PCOS, limiting the generalizability. Although 100 ng/ml amphiregulin addition to the maturation culture step significantly improved the MII rate, the sample size in this study was small, meaning that these findings should be considered as exploratory. Therefore, a larger patient cohort is needed to confirm whether the positive effects of amphiregulin translate into improved fertility outcomes in patients undergoing IVM.

WIDER IMPLICATIONS OF THE FINDINGS

Data from this study confirm the beneficial effects of amphiregulin during IVM with respect to the trigger of oocyte maturation. The gene expression findings in cumulus indicate that multiple pathways might contribute to these beneficial effects and confirm the key role of the epidermal growth factor system in the stepwise acquisition of human oocyte competence.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED; grant number FWO.106-YS.2017.02) and by the Fund for Research Flanders (FWO; grant number G.OD97.18N). L.N.V. has received speaker and conference fees from Merck, grants, speaker and conference fees from Merck Sharpe and Dohme, and speaker, conference and scientific board fees from Ferring. T.M.H. has received speaker fees from Merck, Merck Sharp and Dohme and Ferring. J.S. reports speaker fees from Ferring Pharmaceuticals and Biomérieux Diagnostics and grants from FWO Flanders, is co-inventor on granted patents on CAPA-IVM methodologies in USA (US10392601B2), Europe (EP3234112B1) and Japan (JP 6806683 registered 08-12-2020) and is a co-shareholder of Lavima Fertility Inc., a spin-off company of the Vrije Universiteit Brussel (VUB, Brussels, Belgium). NA, TDP, AHL, MNHN, SR, FS, EA and UDTH report no financial relationships with any organizations that might have an interest in the submitted work in the previous three years, and no other relationships or activities that could appear to have influenced the submitted work.

TRIAL REGISTRATION NUMBER

NCT03915054.

Approaches to oocyte meiotic arrest in vitro and impact on oocyte developmental competence

Oocytes are maintained in a state of meiotic arrest following the first meiotic division until ovulation is triggered. Within the antral follicle, meiotic arrest is actively suppressed in a process facilitated by the cyclic nucleotides cGMP and cAMP. If removed from this inhibitory follicular environment and cultured in vitro, mammalian oocytes undergo spontaneous meiotic resumption in the absence of the usual stimulatory follicular stimuli, leading to asynchronicity with oocyte cytoplasmic maturation and lower developmental competence. For more than 50 years, pharmacological agents have been used to attenuate oocyte germinal vesicle (GV) breakdown in vitro. Agents which increase intra-oocyte cAMP or prevent its degradation have been predominantly used, however agents such as kinase and protein synthesis inhibitors have also been trialled. Twenty years of research demonstrates that maintaining GV arrest for a period before in vitro maturation (IVM) improves oocyte developmental competence, and is likely attributed to maintenance of bidirectional communication with cumulus cells leading to improved oocyte metabolic function. However, outcomes are influenced by various factors including the mode of action of the modulators, dose, treatment duration, species, and the degree of hormonal priming of the oocyte donor. Cyclic GMP and/or cAMP modulation in a prematuration step (called pre-IVM) prior to IVM has shown the greatest consistency in improving oocyte developmental competence, whereas kinase and protein synthesis inhibitors have proven less effective at improving IVM outcomes. Such pre-IVM approaches have shown potential to alter current use of artificial reproductive technologies in medical and veterinary practice.

Improvement in early antral follicle development and gene expression modulation prior to follicle aspiration in bovine cumulus-oocyte complexes by equine chorionic gonadotropin

We aimed to evaluate the morphological ovarian response to equine chorionic gonadotropin (eCG) prior to ovum pick-up (OPU) and its effects on the molecular phenotype of immature cumulus-oocyte complexes (COCs) from Nelore cow (Bos indicus) donors. To this end, 20 Nelore cows were distributed randomly into the synchronized-OPU (Sync-OPU) and synchronized plus stimulated-OPU (Sync + eCG-OPU) groups using a cross-over experimental design, as each cow was used in both treatments. On a random day of the estrus cycle (Day 0), all cows received an intravaginal implant with 1.0 g of progesterone and 2 mg IM of estradiol benzoate. On the morning of Day 3, only the Sync + eCG-OPU group received 400 IU of eCG IM. On the morning of Day 5, the P4 device was removed and OPU was conducted in both groups. Before OPU management, ultrasonography was used to identify and measure the follicles. The aspirated COCs were morphologically classified based on their cumulus cells (CC) layers and the texture of the ooplasm. The COCs classified as Grade 1, Grade 2, and Grade 3 were considered viable and used for the assessment of quality markers. Oocytes and CC were mechanically separated from pools of 25 immature COCs of the Sync-OPU and Sync + eCG-OPU groups immediately after the follicular aspiration and stored at -80 °C until RNA extraction. Relative quantification of several markers for oocyte quality was assessed by RT-qPCR. The eCG treatment increased the number of follicles sized 3.0-5.0 mm and >5.0 mm compared to that in Sync-OPU group. Moreover, the protocol with eCG improved the total number of oocytes and the number of viable oocytes, which is related to a high number of oocytes in Grade 3. Regarding the impact on transcriptional regulation in immature oocytes, the mRNA encoding BMP15, SMAD1, SMAD2, SMAD3, ACACA, and CPT1A was upregulated in Sync + eCG-OPU compared with the Sync-OPU group. Moreover, the relative mRNA abundance of CTSZ, a member of the cathepsins family functionally related to reduced oocyte competence, was lower in the Sync + eCG-OPU group than in the Sync-OPU group. In addition, CC CTSB, CTSS, and CTSK mRNA abundances were lower in the Sync + eCG-OPU group than in the Sync-OPU group. However, the relative abundance of AREG and EREG mRNA was higher in CC recovered from cows stimulated with eCG. In conclusion, the eCG approach addressing follicular stimulation in Nelore cows had a positive impact on early antral follicle development, followed by a positive morphological and molecular phenotype in bovine COCs.

Mechanisms of Estradiol-induced EGF-like Factor Expression and Oocyte Maturation via G Protein-coupled Estrogen Receptor

Estrogen is an important modulator of reproductive activity through nuclear receptors and G protein-coupled estrogen receptor (GPER). Here, we observed that both estradiol and the GPER-specific agonist G1 rapidly induced cyclic adenosine monophosphate (cAMP) production in cumulus cells, leading to transient stimulation of phosphorylated cAMP response element binding protein (CREB), which was conducive to the transcription of epidermal growth factor (EGF)-like factors, amphiregulin, epiregulin, and betacellulin. Inhibition of GPER by G15 significantly reduced estradiol-induced CREB phosphorylation and EGF-like factor gene expression. Consistently, the silencing of GPER expression in cultured cumulus cells abrogated the estradiol-induced CREB phosphorylation and EGF-like factor transcription. In addition, the increase in EGF-like factor expression in the cumulus cells is associated with EGF receptor (EFGR) tyrosine kinase phosphorylation and extracellular signal-regulated kinase 1/2 (ERK1/2) activation. Furthermore, we demonstrated that GPER-mediated phosphorylation of EGFR and ERK1/2 was involved in reduced gap junction communication, cumulus expansion, increased oocyte mitochondrial activity and first polar body extrusion. Overall, our study identified a novel function for estrogen in regulating EGFR activation via GPER in cumulus cells during oocyte maturation.

The Phosphodiesterase Inhibitor, Isobutyl-1-Methylxanthine Prevents the Sudden Drop in Cyclic Adenosine Monophosphate Concentration and Modulates Glucose Metabolism of Equine Cumulus-Oocyte Complexes Matured in Vitro

Spontaneous nuclear maturation of mammalian oocytes can occur when physically removed from the ovarian follicle during in vitro oocyte maturation (IVM), largely because of a decrease in cyclic adenosine monophosphate (cAMP) concentration. Modulation of oocyte cAMP during IVM by using phosphodiesterase inhibitors has been shown to maintain elevated oocyte cAMP concentrations and control meiotic resumption of bovine and ovine oocytes. This study determined the effect of inclusion of isobutyl-1-methylxanthine (IBMX) during collection and the first 12 hours of incubation of equine oocytes on cAMP concentration and glucose metabolism of cumulus-oocyte complexes (COCs). Abattoir-derived COCs were collected in aspiration medium with (Asp-IBMX) or without (Asp) IBMX. Cumulus-oocyte complexes were then incubated for 12 hours in IVM medium with (Mat-IBMX) or without (Mat) IBMX, followed by additional 24 hours in Mat medium. The cAMP concentration, glucose consumption, lactate production, and metaphase II rates of the COCs were assessed. Cumulus-oocyte complexes aspirated into Asp-IBMX (62.2 ± 2.6 fmol per COC) medium had higher cAMP concentration than Asp (31.8 ± 2.8 fmol per COC) control group (P < .05). Likewise, at 12 hours of IVM, Mat-IBMX group (33.2 ± 2.1 fmol per COC) had higher cAMP concentration than the Mat group (7.68 ± 0.5 fmol per COC; P < .05). Glucose consumption and lactate production were lower during the first 12 hours of incubation in COCs cultured in Mat-IBMX (P < .05). Isobutyl-1-methylxanthine prevented the rapid drop in cAMP concentration and altered metabolism of glucose by the COC. Preventing the sudden drop in cAMP prevents the premature nuclear maturation of in vitro-matured oocytes causing poor developmental competence.

Does 'Dual Trigger' Increase Oocyte Maturation Rate?

The aim of this study was to evaluate the oocyte maturation rate when GnRH-a and hCG (dual trigger) are co-administered, compared to the standard hCG trigger within the same patient. Included in the study were GnRH antagonist ICSI cycles performed in 137 patients who had a standard hCG trigger cycle and a dual trigger cycle between 1/1/2013 and 31/12/2017. The mean patient age (35.9 ± 5.6 and 35.2 ± 5.9; <0.001), FSH dose (4140 ± 2065 and 3585 ± 1858; <0.01), number of retrieved oocytes (10.3 ± 6.2 and 8.9 ± 6.1; 0.011) were higher in the dual trigger group compared to the hCG trigger group, oocyte maturation rate was identical. Maturation rate following dual trigger was significantly higher among 34 patients who had a maturation rate of <70% following hCG triggering and among 16 patients with a maturation rate <50% rate following hCG trigger (54% vs. 74%, p < .001 and 44% vs. 73%, p = .006; respectively). In conclusion, co-administration of GnRH agonist and hCG for final oocyte maturation substantially increased the oocyte maturation rate in patients with low oocyte maturation rate in their hCG triggered cycle, but not in an unselected population of patients.IMPACT STATEMENTWhat is already known on this subject? The co-administration of GnRH agonist and hCG for final oocyte maturation prior to oocyte retrieval may improve IVF outcome in patients with a high proportion of immature oocytes. The few studies on dual trigger in patients with a high proportion of immature oocytes or in normal responders have shown conflicting results.What do the results of this study add? We found that co-administration of GnRH agonist and hCG for final oocyte maturation substantially increased the oocyte maturation rate in patients with low oocyte maturation rate in their hCG triggered cycle, but not in an unselected population of patients.What are the implications of these findings for clinical practice and/or further research? The results of this study implicate that in selected population with low oocyte maturation rate, there is an advantage in using dual trigger. However, larger prospective trials are warranted to better assess oocyte response in dual trigger.

EGFR promotes the proliferation of quail follicular granulosa cells through the MAPK/extracellular signal-regulated kinase (ERK) signaling pathway

Follicles develop into preovulatory follicles during folliculogenesis and the majority of small yellow follicles become atretic and gets reabsorbed. In this study, based the RNA-seq results of duck ovary, epidermal growth factor receptor (EGFR) was selected as a candidate gene in follicular development and the role was explored. The results demonstrated that EGFR-P8 was the quail EGFR core promoter. It had an E2F4 binding site within EGFR core promoter. E2F4 overexpression significantly increased EGFR expression in quail granulosa cells (GCs). However, the effect was abolished when the GCs were treated with corynoxeine, an inhibitor of the mitogen-activated protein kinase/extracellular regulated protein kinase (MAPK/ERK) signaling pathway. Moreover, luciferase reporter assay and chromatin immunoprecipitation experiments showed that E2F4 upregulated the expression of EGFR expression, which increased E2 and P4 production. In addition, EGFR regulated GCs proliferation and affected follicular development. Taken together, our findings suggested that EGFR, which was regulated by E2F4, enhanced the expression of MAPK/ERK pathway components and follicular development. These results provided an important basis for an improved understanding of the MAPK/ERK pathway and new insight into the development of quail follicles.

Involvement of PKCε in FSH-induced connexin43 phosphorylation and oocyte maturation in mouse

Gap junctions (GJs) are indispensable for communication between cumulus cells (CCs) and oocytes in coordinating the gonadotropin-induced meiotic maturation of oocytes. Of all proteins that constitute GJs, phosphorylated connexin43 (pCx43) is vital for mediating the actions of gonadotropins. In this study, the mechanism of Cx43 phosphorylation in response to follicle stimulating hormone (FSH) stimulation was examined using an in vitro model of mouse cumulus-oocyte complexes (COCs). The results confirmed that Cx43 phosphorylation occurred twice during FSH treatment. Importantly, the second Cx43 phosphorylation was closely related to cAMP level reduction within oocytes, which initiated oocyte maturation. Exploration of the underlying mechanism revealed that the CC-specific protein kinase C ε (PKCε) level was upregulated by FSH stimulation. PKCε was a kinase downstream from mitogen-activated protein kinase (MAPK) and was responsible for Cx43 phosphorylation. Interestingly, MAPK was involved in both Cx43 phosphorylation processes, while PKCε was only involved in the second. In conclusion, PKCε-mediated MAPK signals might contribute to Cx43 phosphorylation in CCs during FSH-induced oocyte meiotic resumption. Our findings contribute to a better understanding of the molecular regulation mechanism of oocyte maturation in response to FSH in vitro.

Summary: This research clarifies the important role of PKCε in mediating MAPK action on CX43 phosphorylation during FSH-induced oocyte maturation in vitro, and further explores the regulation mechanism of oocyte maturation.

The epidermal growth factor network: role in oocyte growth, maturation and developmental competence

BACKGROUND

The LH surge induces great physiological changes within the preovulatory follicle, which culminate in the ovulation of a mature oocyte that is capable of supporting embryo and foetal development. However, unlike mural granulosa cells, the oocyte and its surrounding cumulus cells are not directly responsive to LH, indicating that the LH signal is mediated by secondary factors produced by the granulosa cells. The mechanisms by which the oocyte senses the ovulatory LH signal and hence prepares for ovulation has been a subject of considerable controversy for the past four decades. Within the last 15 years several significant insights have been made into the molecular mechanisms orchestrating oocyte development, maturation and ovulation. These findings centre on the epidermal growth factor (EGF) pathway and the role it plays in the complex signalling network that finely regulates oocyte maturation and ovulation.

OBJECTIVE AND RATIONALE

This review outlines the role of the EGF network during oocyte development and regulation of the ovulatory cascade, and in particular focuses on the effect of the EGF network on oocyte developmental competence. Application of this new knowledge to advances in ART is examined.

SEARCH METHODS

The PubMed database was used to search for peer-reviewed original and review articles concerning the EGF network. Publications offering a comprehensive description of the role of the EGF network in follicle and oocyte development were used.

OUTCOMES

It is now clear that acute upregulation of the EGF network is an essential component of the ovulatory cascade as it transmits the LH signal from the periphery of the follicle to the cumulus-oocyte complex (COC). More recent findings have elucidated new roles for the EGF network in the regulation of oocyte development. EGF signalling downregulates the somatic signal 3'5'-cyclic guanine monophosphate that suppresses oocyte meiotic maturation and simultaneously provides meiotic inducing signals. The EGF network also controls translation of maternal transcripts in the quiescent oocyte, a process that is integral to oocyte competence. As a means of restricting the ovulatory signal to the Graffian follicle, most COCs in the ovary are unresponsive to EGF-ligands. Recent studies have revealed that development of a functional EGF signalling network in cumulus cells requires dual endocrine (FSH) and oocyte paracrine cues (growth differentiation factor 9 and bone morphogenetic protein 15), and this occurs progressively in COCs during the last stages of folliculogenesis. Hence, a new concept to emerge is that cumulus cell acquisition of EGF receptor responsiveness represents a developmental hallmark in folliculogenesis, analogous to FSH-induction of LH receptor signalling in mural granulosa cells. Likewise, this event represents a major milestone in the oocyte's developmental progression and acquisition of developmental competence. It is now clear that EGF signalling is perturbed in COCs matured in vitro. This has inspired novel concepts in IVM systems to ameliorate this perturbation, resulting in improved oocyte developmental competence.

WIDER IMPLICATIONS

An oocyte of high quality is imperative for fertility. Elucidating the fundamental molecular and cellular mechanims by which the EGF network regulates oocyte maturation and ovulation can be expected to open new opportunities in ART. This knowledge has already led to advances in oocyte IVM in animal models. Translation of such advances into a clinical setting should increase the efficacy of IVM, making it a viable treatment option for a wide range of patients, thereby simplifying fertility treatment and bringing substantial cost and health benefits.

LH prevents cisplatin-induced apoptosis in oocytes and preserves female fertility in mouse

Premature ovarian failure and female infertility are frequent side effects of anticancer therapies, owing to the extreme sensitivity of the ovarian reserve oocytes to the damaging effects of irradiation and chemotherapy on DNA. We report here a robust protective effect of luteinizing hormone (LH) on the primordial follicle pool of prepubertal ovaries against the cisplatin (Cs)-induced apoptosis. In vitro LH treatment of prepubertal ovarian fragments generated anti-apoptotic signals by a subset of ovarian somatic cells expressing LH receptor (LHR) through cAMP/PKA and Akt pathways. Such signals, reducing the oocyte level of pro-apoptotic TAp63 protein and favoring the repair of the Cs-damaged DNA in the oocytes, prevented their apoptosis. Noteworthy, in vivo administration to prepubertal female mice of a single dose of LH together with Cs inhibited the depletion of the primordial follicle reserve caused by the drug and preserved their fertility in reproductive age, preventing significant alteration in the number of pregnancy and of delivered pups. In conclusion, these findings establish a novel ovoprotective role for LH and further support the very attracting prospective to use physiological 'fertoprotective' approaches for preventing premature infertility and risks linked to precocious menopause in young patients who survived cancer after chemotherapy.

Oocyte maturation and quality: role of cyclic nucleotides

The cyclic nucleotides, cAMP and cGMP, are the key molecules controlling mammalian oocyte meiosis. Their roles in oocyte biology have been at the forefront of oocyte research for decades, and many of the long-standing controversies in relation to the regulation of oocyte meiotic maturation are now resolved. It is now clear that the follicle prevents meiotic resumption through the actions of natriuretic peptides and cGMP - inhibiting the hydrolysis of intra-oocyte cAMP - and that the pre-ovulatory gonadotrophin surge reverses these processes. The gonadotrophin surge also leads to a transient spike in cAMP in the somatic compartment of the follicle. Research over the past two decades has conclusively demonstrated that this surge in cAMP is important for the subsequent developmental capacity of the oocyte. This is important, as oocyte in vitro maturation (IVM) systems practised clinically do not recapitulate this cAMP surge in vitro, possibly accounting for the lower efficiency of IVM compared with clinical IVF. This review particularly focuses on this latter aspect - the role of cAMP/cGMP in the regulation of oocyte quality. We conclude that clinical practice of IVM should reflect this new understanding of the role of cyclic nucleotides, thereby creating a new generation of ART and fertility treatment options.

Embryonic Poly(A)-Binding Protein (EPAB) Is Required for Granulosa Cell EGF Signaling and Cumulus Expansion in Female Mice

Embryonic poly(A)-binding protein (EPAB) is the predominant poly(A)-binding protein in Xenopus, mouse, and human oocytes and early embryos before zygotic genome activation. EPAB is required for translational activation of maternally stored mRNAs in the oocyte and Epab(-/-) female mice are infertile due to impaired oocyte maturation, cumulus expansion, and ovulation. The aim of this study was to characterize the mechanism of follicular somatic cell dysfunction in Epab(-/-) mice. Using a coculture system of oocytectomized cumulus oophorus complexes (OOXs) with denuded oocytes, we found that when wild-type OOXs were cocultured with Epab(-/-) oocytes, or when Epab(-/-) OOXs were cocultured with WT oocytes, cumulus expansion failed to occur in response to epidermal growth factor (EGF). This finding suggests that oocytes and cumulus cells (CCs) from Epab(-/-) mice fail to send and receive the necessary signals required for cumulus expansion. The abnormalities in Epab(-/-) CCs are not due to lower expression of the oocyte-derived factors growth differentiation factor 9 or bone morphogenetic protein 15, because Epab(-/-) oocytes express these proteins at comparable levels with WT. Epab(-/-) granulosa cells (GCs) exhibit decreased levels of phosphorylated MEK1/2, ERK1/2, and p90 ribosomal S6 kinase in response to lutenizing hormone and EGF treatment, as well as decreased phosphorylation of the EGF receptor. In conclusion, EPAB, which is oocyte specific, is required for the ability of CCs and GCs to become responsive to LH and EGF signaling. These results emphasize the importance of oocyte-somatic communication for GC and CC function.

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.

Gene expression analysis of pig cumulus-oocyte complexes stimulated in vitro with follicle stimulating hormone or epidermal growth factor-like peptides

BACKGROUND

The gonadotropin-induced resumption of oocyte meiosis in preovulatory follicles is preceded by expression of epidermal growth factor (EGF)-like peptides, amphiregulin (AREG) and epiregulin (EREG), in mural granulosa and cumulus cells. Both the gonadotropins and the EGF-like peptides possess the capacity to stimulate resumption of oocyte meiosis in vitro via activation of a broad signaling network in cumulus cells. To better understand the rapid genomic actions of gonadotropins (FSH) and EGF-like peptides, we analyzed transcriptomes of cumulus cells at 3 h after their stimulation.

METHODS

We hybridized aRNA from cumulus cells to a pig oligonucleotide microarray and compared the transcriptomes of FSH- and AREG/EREG-stimulated cumulus cells with untreated control cells and vice versa. The identified over- and underexpressed genes were subjected to functional genomic analysis according to their molecular and cellular functions. The expression pattern of 50 selected genes with a known or potential function in ovarian development was verified by real-time qRT-PCR.

RESULTS

Both FSH and AREG/EREG increased the expression of genes associated with regulation of cell proliferation, cell migration, blood coagulation and extracellular matrix remodeling. FSH alone induced the expression of genes involved in inflammatory response and in the response to reactive oxygen species. Moreover, FSH stimulated the expression of genes closely related to some ovulatory events either exclusively or significantly more than AREG/EREG (AREG, ADAMTS1, HAS2, TNFAIP6, PLAUR, PLAT, and HSD17B7). In contrast to AREG/EREG, FSH also increased the expression of genes coding for key transcription factors (CEBPB, FOS, ID1/3, and NR5A2), which may contribute to the differing expression profiles of FSH- and AREG/EREG-treated cumulus cells.

CONCLUSIONS

The impact of FSH on cumulus cell gene transcription was higher than the impact of EGF-like factors in terms of the number of cell functions affected as well as the number of over- and underexpressed genes. Both FSH and EGF-like factors overexpressed genes involved in the post-ovulatory switch in steroidogenesis and tissue remodelling. However, FSH was remarkably more efficient in the up-regulation of several specific genes essential for ovulation of matured oocytes and also genes that been reported to play an important role in maturation of cumulus-enclosed oocytes in vitro.

Promotion of EGF receptor signaling improves the quality of low developmental competence oocytes

Oocytes acquire developmental competence with progressive folliculogenesis. Cumulus oocyte complexes (COCs) from small antral follicles have inherent low competence and are poorly responsive to amphiregulin (AREG) which normally mediates oocyte maturation and ovulation. Using low competence porcine COCs, in an in vitro AREG-induced oocyte maturation system, the combined exposure to N(6),2'-O-dibutyryladenosine 3':5' cyclic monophosphate (cAMP) and bone morphogenetic protein 15 (B15) and growth differentiation factor 9 (G9) was necessary to enhance the rate of oocyte meiotic maturation and blastocyst formation. Furthermore, the combination of cAMP+B15+G9 enabled AREG-stimulated cumulus expansion and increased expression of the matrix-related genes HAS2, TNFIPA6 and PTGS2. Additionally, the combination enhanced p-ERK1/2 which is downstream of the EGF receptor. The enhanced nuclear maturation and blastocyst formation rates with the combinational treatment were ablated by an EGF receptor phosphorylation inhibitor. These results indicate that cAMP and oocyte-secreted factors cooperate to promote EGF receptor functionality in developing COCs, representing a key component of the acquisition of oocyte developmental competence.

Cyclic guanosine monophosphate does not inhibit gonadotropin-induced activation of mitogen-activated protein kinase 3/1 in pig cumulus-oocyte complexes

BACKGROUND

Recent results indicate a key role for cyclic guanosine monophosphate (cGMP) in the regulation of oocyte meiotic arrest in preovulatory mammalian follicles. The aim of our study was to determine whether the resumption of oocyte meiosis and expansion of cumulus cells in isolated pig cumulus-oocyte complexes (COCs) can be blocked by a high intracellular concentration of cGMP, and whether this effect is mediated by a cGMP-dependent inhibition of mitogen-activated protein kinase 3/1 (MAPK3/1).

METHODS

The COCs were isolated from ovaries of slaughtered gilts and cultured in vitro in M199 supplemented with 5% fetal calf serum. The expression levels of the C-type natriuretic peptide (CNP) precursor (NPPC) and its receptor (NPR2) mRNAs during the culture of COCs were determined by real-time RT-PCR. To control the intracellular concentration of cGMP in the COCs, the culture medium was further supplemented with CNP or various concentrations of synthetic cGMP analogues; the concentration of cGMP in COCs was then assessed by ELISA. The effect of the drugs on oocyte maturation was assessed after 24 and 44 h of culture by determining nuclear maturation. The expansion of cumulus cells was assessed by light microscopy and the expression of cumulus expansion-related genes by real-time RT-PCR. A possible effect of cGMP on FSH-induced activation of MAPK3/1 was assessed by immunoblotting the COC proteins with phospho-specific and total anti-Erk1/2 antibodies.

RESULTS

The COCs expressed NPPC and NPR2, the key components of cGMP synthesis, and produced a large amount of cGMP upon stimulation with exogenous CNP, which lead to a significant (P < 0.05) delay in oocyte meiotic resumption. The COCs also responded to cGMP analogues by inhibiting the resumption of oocyte meiosis. The inhibitory effect of cGMP on meiotic resumption was reversed by stimulating the COCs with FSH. However, high concentration of intracellular cGMP was not able to suppress FSH-induced activation of MAPK3/1 in cumulus cells, cumulus expansion and expression of expansion-related genes (P > 0.05).

CONCLUSIONS

The findings of this study indicate that high cGMP concentrations inhibit the maturation of pig oocytes in vitro but the inhibitory mechanism does not involve the suppression of MAPK3/1 activation in cumulus cells.

Oocyte environment: follicular fluid and cumulus cells are critical for oocyte health

Bidirectional somatic cell-oocyte signaling is essential to create a changing intrafollicular microenvironment that controls primordial follicle growth into a cohort of growing follicles, from which one antral follicle is selected to ovulate a healthy oocyte. Such intercellular communications allow the oocyte to determine its own fate by influencing the intrafollicular microenvironment, which in turn provides the necessary cellular functions for oocyte developmental competence, which is defined as the ability of the oocyte to complete meiosis and undergo fertilization, embryogenesis, and term development. These coordinated somatic cell-oocyte interactions attempt to balance cellular metabolism with energy requirements during folliculogenesis, including changing energy utilization during meiotic resumption. If these cellular mechanisms are perturbed by metabolic disease and/or maternal aging, molecular damage of the oocyte can alter macromolecules, induce mitochondrial mutations, and reduce adenosine triphosphate production, all of which can harm the oocyte. Recent technologies are now exploring transcriptional, translational, and post-translational events within the human follicle with the goal of identifying biomarkers that reliably predict oocyte quality in the clinical setting.

Follicle-stimulating hormone regulates expression and activity of epidermal growth factor receptor in the murine ovarian follicle

Fertility depends on the precise coordination of multiple events within the ovarian follicle to ensure ovulation of a fertilizable egg. FSH promotes late follicular development, including expression of luteinizing hormone (LH) receptor by the granulosa cells. Expression of its receptor permits the subsequent LH surge to trigger the release of ligands that activate EGF receptors (EGFR) on the granulosa, thereby initiating the ovulatory events. Here we identify a previously unknown role for FSH in this signaling cascade. We show that follicles of Fshb(-/-) mice, which cannot produce FSH, have a severely impaired ability to support two essential EGFR-regulated events: expansion of the cumulus granulosa cell layer that encloses the oocyte and meiotic maturation of the oocyte. These defects are not caused by an inability of Fshb(-/-) oocytes to produce essential oocyte-secreted factors or of Fshb(-/-) cumulus cells to respond. In contrast, although expression of both Egfr and EGFR increases during late folliculogenesis in Fshb(+/-) females, these increases fail to occur in Fshb(-/-) females. Remarkably, supplying a single dose of exogenous FSH activity to Fshb(-/-) females is sufficient to increase Egfr and EGFR expression and to restore EGFR-dependent cumulus expansion and oocyte maturation. These studies show that FSH induces an increase in EGFR expression during late folliculogenesis and provide evidence that the FSH-dependent increase is necessary for EGFR physiological function. Our results demonstrate an unanticipated role for FSH in establishing the signaling axis that coordinates ovulatory events and may contribute to the diagnosis and treatment of some types of human infertility.

PKCδ and θ possibly mediate FSH-induced mouse oocyte maturation via NOX-ROS-TACE cascade signaling pathway

In mammals, gonadotropins stimulate oocyte maturation via the epidermal growth factor (EGF) network, and the protein kinase C (PKC) signaling pathway mediates this process. Tumor necrosis factor-α converting enzyme (TACE) is an important protein responding to PKC activation. However, the detailed signaling cascade between PKC and TACE in follicle-stimulating hormone (FSH)-induced oocyte maturation in vitro remains unclear. In this study, we found that rottlerin (mallotoxin, MTX), the inhibitor of PKC δ and θ, blocked FSH-induced maturation of mouse cumulus-oocyte complexes (COCs) in vitro. We further clarified the relationship between two molecules downstream of PKC δ and θ and TACE in COCs: nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) and its products, reactive oxygen species (ROS). We proved that the respective inhibitors of NOX, ROS and TACE could block FSH-stimulated oocyte maturation dose-dependently, but these inhibitory effects could be reversed partially by amphiregulin (Areg), an EGF family member. Notably, inhibition of PKC δ and θ prevented FSH-induced translocation of two cytosolic components of NOX, p47^phox and p67^phox, to the plasma membrane in cumulus cells. Moreover, FSH-induced TACE activity in cumulus cells was decreased markedly by inhibition of NOX and ROS. In conclusion, PKC δ and θ possibly mediate FSH-induced meiotic resumption in mouse COCs via NOX-ROS-TACE signaling pathway.

Effect of epidermal growth factor-like peptides on the metabolism of in vitro- matured mouse oocytes and cumulus cells

Oocyte in vitro maturation (IVM) is an assisted reproductive technology that involves the maturation of cumulus-oocyte complexes (COCs) that are then capable of normal development. We have shown that epidermal growth factor (EGF)-like peptide signaling is perturbed in mouse COCs undergoing IVM when matured with follicle-stimulating hormone (FSH) and/or EGF, but supplementation of IVM with EGF-like peptides amphiregulin or epiregulin improves oocyte developmental competence. Here we aimed to determine whether EGF-like peptides regulate COC metabolism. Immature 129/Sv mouse COCs underwent IVM with FSH, EGF, amphiregulin, epiregulin, betacellulin, or no treatment (control). Epiregulin significantly increased intraoocyte flavin adenine dinucleotide (FAD) and REDOX (reduction and oxidation) ratio compared to FSH and control. Amphiregulin and epiregulin significantly increased the proportion of J aggregates (from JC-1) in oocyte mitochondria compared to control, FSH, or EGF, and this coupled with FAD and REDOX measures indicates greater mitochondrial activity. There were no differences in glucose consumption, lactate production, or glycolysis between COCs matured with FSH, EGF, and EGF-like peptides. COCs matured with EGF or EGF-like peptides exhibited significantly higher mRNA expression of the hexosamine biosynthesis pathway (HBP) rate-limiting enzyme gene Gfpt2, Has2 expression, and global beta-O-linked glycosylation of proteins, compared to control or FSH, suggesting greater HBP activity. Our findings suggest that 1) EGF-like peptides, particularly epiregulin, induce more oocyte mitochondrial activity than EGF or FSH and 2) EGF-like peptides and EGF induce greater HBP activity, enabling more hyaluronic acid synthesis and protein beta-O-linked glycosylation. These metabolic alterations may be a mechanism by which EGF-like peptides increase oocyte developmental competence.

Protein kinase C (PKC) increases TACE/ADAM17 enzyme activity in porcine ovarian somatic cells, which is essential for granulosa cell luteinization and oocyte maturation

During in vitro maturation of porcine cumulus cell-oocyte complexes and in vitro luteinization of porcine granulosa cells, FSH induces the expression of the protease TNFα-converting enzyme/A disintegrin and metalloproteinase domain 17 (TACE/ADAM17) and the epidermal growth factor (EGF)-like factors, which activate the EGF receptor (EGFR)-MAPK3/1 pathway in both cumulus and granulosa cells. FSH is known to activate not only protein kinase A and p38MAPK pathways in both cell types but also activates protein kinase C (PKC). Because PKC-induced association of cellular-Sarcoma (c-Src) and TACE/ADAM17 is required for TACE/ADAM17 enzyme activation in some cancer cells, we hypothesized that PKC and c-Src impact TACE/ADAM17-mediated activation of EGFR signaling pathway in porcine granulosa and cumulus cells. When granulosa cells or cumulus cell-oocyte complexes were cultured with FSH, PKC activity and c-Src phosphorylation increased and were associated with increased TACE/ADAM17 enzyme activity. The PKC inhibitor calphostin C (CalC) and the c-Src inhibitor (4 amino 5 (4 chlorophenyl) 7 (t butyl)pyrazolo[3,4 d]pyrimidine [PP2]) suppressed TACE/ADAM17 enzyme activity, whereas these inhibitors did not affect Tace/Adam17 mRNA expression. Immunoprecipitation analysis showed that FSH mediated the association of c-Src with TACE/ADAM17 via a PKC-dependent mechanism. Either CalC or PP2 suppressed EGFR downstream signaling pathway (MAPK3/1) in these ovarian cell types and reduced cumulus expansion, meiotic maturation of oocytes, and progesterone production. The negative effects were overcome by the addition of amphiregulin. Collectively, these results indicate that activation of TACE/ADAM17 via a PKC-induced c-Src-dependent manner mediates proteolytic activation of the EGF-like factors that are involved in the induction of granulosa cell differentiation, cumulus expansion, and meiotic maturation of porcine oocytes in vitro.

Pre-maturation with cAMP modulators in conjunction with EGF-like peptides during in vitro maturation enhances mouse oocyte developmental competence

Recent studies have independently shown that cyclic adenosine 3'5'-monophosphate (cAMP) modulation prior to in vitro maturation (IVM) and epidermal growth factor (EGF)-like peptide supplementation during IVM improve subsequent oocyte developmental outcomes. This study investigated the effects of an IVM system that incorporates these two concepts. Cumulus-oocyte complexes (COCs) were collected from pre-pubertal mice either 46 hr post-equine chorionic gonadotropin (eCG) (IVM) or post-eCG + post-human chorionic gonadotropin (hCG) stimulation (in vivo maturation; IVV). IVM COCs were treated with the cAMP modulators forskolin and IBMX for 1, 2, or 4 hr (pre-IVM phase) prior to IVM. COCs then underwent IVM with the EGF-like peptides amphiregulin or epiregulin, or with the common IVM stimulants follicle-stimulating hormone (FSH) or EGF. A pre-IVM phase increased the size of the subsequent blastocysts' inner-cell-mass compared to standard IVM, regardless of IVM treatment (P < 0.05). Unlike FSH or EGF, amphiregulin or epiregulin significantly increased blastocyst quality (trophectoderm and total cell numbers) and/or yield (P < 0.01) compared to standard IVM, and were the only treatments that produced blastocysts comparable to IVV-derived blastocysts. Forskolin acutely up-regulated EGF-like peptide mRNA expression after a 2-hr pre-IVM phase (P < 0.001), although EGF receptor and ERK1/2 activities were not significantly different than control. IVV-like levels of EGF-like peptide mRNA expression during IVM were maintained only by supplementing with EGF-like peptides and EGF, since expression levels induced by FSH were significantly lower in vitro than during IVV. However, EGF receptor and ERK1/2 phosphorylation levels were not significantly different across treatment groups. In conclusion, a pre-IVM phase in conjunction with IVM in the presence of EGF-like peptides endows high oocyte developmental competence, as evidenced by increased embryo yield and/or quality relative to FSH and EGF.

Lysophosphatidic acid stimulates hyaluronan production by mouse cumulus-oocyte complexes

Purpose

In mammals, cumulus expansion due to increased synthesis of hyaluronan was suggested to correlate with modification of the gap junction between cumulus cells and the oocyte, leading to cumulus expansion. We examined whether lysophosphatidic acid, a lipid mediator detected in mammalian body fluids, stimulates significant production of hyaluronan and thus affects mouse cumulus expansion in vitro.

Methods

Cumulus-oocyte complexes isolated from the gonadotropin-treated ovaries of B6C3F1 mice were exposed to lysophosphatidic acid in the presence and absence of 0.3 % fetal bovine serum for measurement of cumulus expansion and released hyaluronan, respectively.

Results

Exogenously added lysophosphatidic acid concentration-dependently stimulated production of hyaluronan in the cumulus cell-oocyte complex, and the stimulatory effect of lysophosphatidic acid on hyaluronan production was mediated through the signal pathways, including LPA receptor-Gi coupling, EGF receptor transactivation, and activations of phosphatidylinositol-specific phospholipase C, protein kinase C and mitogen-activated protein kinases. LPA increased mRNA expression of tumor necrosis α-induced protein 6, a hyaluronan-binding protein, and expansion of cumulus cell-oocyte complex.

Conclusions

Lysophosphatidic acid in follicular fluids may participate in physiological cumulus expansion before ovulation by stimulating production of hyaluronan and proteins that enable the association of hyaluronan with cumulus cells and oocytes.

FSH in vitro versus LH in vivo: similar genomic effects on the cumulus

The use of gonadotropins to trigger oocyte maturation both in vivo and in vitro has provided precious and powerful knowledge that has significantly increased our understanding of the ovarian function. Moreover, the efficacy of most assisted reproductive technologies (ART) used in both humans and livestock species relies on gonadotropin input, mainly FSH and LH. Despite the significant progress achieved and the huge impact of gonadotropins, the exact molecular pathways of the two pituitary hormones, FSH and LH, still remain poorly understood. Moreover, these pathways may not be the same when moving from the in vivo to the in vitro context. This misunderstanding of the intricate synergy between these two hormones leads to a lack of consensus about their use mainly in vitro or in ovulation induction schedules in vivo. In order to optimize their use, additional work is thus required with a special focus on comparing the in vitro versus the in vivo effects. In this context, this overview will briefly summarize the downstream gene expression pathways induced by both FSH in vitro and LH in vivo in the cumulus compartment. Based on recent microarray comparative analysis, we are reporting that in vitro FSH stimulation on cumulus cells appears to achieve at least part of the gene expression activity after in vivo LH stimulation. We are then proposing that the in vitro FSH-response of cumulus cells have similitudes with the in vivo LH-response.

A requirement for fatty acid oxidation in the hormone-induced meiotic maturation of mouse oocytes

We have previously shown that fatty acid oxidation (FAO) is required for AMP-activated protein kinase (PRKA)-induced maturation in vitro. In the present study, we have further investigated the role of this metabolic pathway in hormone-induced meiotic maturation. Incorporating an assay with (3)H-palmitic acid as the substrate, we first examined the effect of PRKA activators on FAO levels. There was a significant stimulation of FAO in cumulus cell-enclosed oocytes (CEO) treated with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) and RSVA405. In denuded oocytes (DO), AICAR stimulated FAO only in the presence of carnitine, the molecule that facilitates fatty acyl CoA entry into the mitochondria. The carnitine palmitoyltransferase 1 activator C75 successfully stimulated FAO in CEO. All three of these activators trigger germinal vesicle breakdown. Meiotic resumption induced by follicle-stimulating hormone (FSH) or amphiregulin was completely inhibited by the FAO inhibitors etomoxir, mercaptoacetate, and malonyl CoA. Importantly, FAO was increased in CEO stimulated by FSH and epidermal growth factor, and this increase was blocked by FAO inhibitors. Moreover, compound C, a PRKA inhibitor, prevented the FSH-induced increase in FAO. Both carnitine and palmitic acid augmented hormonal induction of maturation. In a more physiological setting, etomoxir eliminated human chorionic gonadotropin (hCG)-induced maturation in follicle-enclosed oocytes. In addition, CEO and DO from hCG-treated mice displayed an etomoxir-sensitive increase in FAO, indicating that this pathway was stimulated during in vivo meiotic resumption. Taken together, our data indicate that hormone-induced maturation in mice requires a PRKA-dependent increase in FAO.

Bone morphogenetic protein 15 and fibroblast growth factor 10 enhance cumulus expansion, glucose uptake, and expression of genes in the ovulatory cascade during in vitro maturation of bovine cumulus-oocyte complexes

Oocyte-secreted factors (OSFs) regulate differentiation of cumulus cells and are of pivotal relevance for fertility. Bone morphogenetic protein 15 (BMP15) and fibroblast growth factor 10 (FGF10) are OSFs and enhance oocyte competence by unknown mechanisms. We tested the hypothesis that BMP15 and FGF10, alone or combined in the maturation medium, enhance cumulus expansion and expression of genes in the preovulatory cascade and regulate glucose metabolism favouring hyaluronic acid production in bovine cumulus-oocyte complexes (COCs). BMP15 or FGF10 increased the percentage of fully expanded COCs, but the combination did not further stimulate it. BMP15 increased cumulus cell levels of mRNA encoding a disintegrin and metalloprotease 10 (ADAM10), ADAM17, amphiregulin (AREG), and epiregulin (EREG) at 12 h of culture and of prostaglandin (PG)-endoperoxide synthase 2 (PTGS2), pentraxin 3 (PTX3) and tumor necrosis factor alpha-induced protein 6 (TNFAIP6 (TSG6)) at 22 h of culture. FGF10 did not alter the expression of epidermal growth factor-like factors but enhanced the mRNA expression of PTGS2 at 4 h, PTX3 at 12 h, and TNFAIP6 at 22 h. FGF10 and BMP15 stimulated glucose consumption by cumulus cells but did not affect lactate production or levels of mRNA encoding glycolytic enzymes phosphofructokinase and lactate dehydrogenase A. Each growth factor increased mRNA encoding glucosamine:fructose-6-PO4 transaminases, key enzymes in the hexosamine pathway leading to hyaluronic acid production, and BMP15 also stimulated hyaluronan synthase 2 (HAS2) mRNA expression. This study provides evidence that BMP15 and FGF10 stimulate expansion of in vitro-matured bovine COCs by driving glucose metabolism toward hyaluronic acid production and controlling the expression of genes in the ovulatory cascade, the first acting upon ADAM10, ADAM17, AREG, and EREG and the second on downstream genes, particularly PTGS2.

Recombinant human follicle-stimulating hormone and transforming growth factor-alpha enhance in vitro maturation of porcine oocytes

The biological functions of recombinant human follicle-stimulating hormone (FSH) and transforming growth factor-α (TGF-α) on in vitro maturation of porcine oocytes were investigated. Cumulus-oocyte complexes were matured in defined porcine oocyte medium containing 0-0.1 IU/ml FSH in the presence or absence of 10 ng/ml TGF-α. The percentage of oocytes reaching metaphase II was significantly higher with the addition of 0.01-0.1 IU/ml FSH compared with no addition, and was further enhanced in the presence of TGF-α. The rates of sperm penetration and blastocyst formation were significantly higher with the addition of 0.05-0.1 IU/ml FSH compared with no addition after in vitro fertilization and embryo culture. There was no beneficial effect of FSH and TGF-α on nuclear maturation of denuded oocytes. The specific EGF receptor inhibitor, AG1478, completely inhibited TGF-α-induced meiotic resumption, but did not completely prevent the stimulatory effect of FSH. Addition of both FSH and TGF-α significantly enhanced cumulus expansion compared with no addition. When cumulus expansion-related genes (HAS2, HAPLN1, and VCAN) mRNA expression in COCs was measured during in vitro maturaiton, addition of both of FSH and TGF-α upregulated the expression of HAS2 mRNA after 20 hr culture and HAPLN1 mRNA after 44 hr culture compared with no addition. Expression of VCAN mRNA was significantly higher in the presence of FSH compared with addition of TGF-α alone. These results suggest that FSH and TGF-α synergistically enhance porcine oocyte maturation via cumulus cells, and act through different signaling pathways.

Effects of FSH on the expression of receptors for oocyte-secreted factors and members of the EGF-like family during in vitro maturation in cattle

FSH induces expansion of bovine cumulus–oocyte complexes (COCs) in cattle, which can be enhanced by oocyte-secreted factors (OSFs). In this study it was hypothesised that FSH stimulates COC expansion in part from direct stimulation of the epidermal growth factor (EGF)-like ligands amphiregulin (AREG), epiregulin (EREG) and betacellulin (BTC), but also in part through regulation of OSFs or their receptors in cumulus cells. Bovine COCs were cultured in defined medium with graded doses of FSH. In the absence of FSH, COCs did not expand. FSH caused cumulus expansion, and increased the abundance of AREG and EREG mRNA in a time- and dose-dependent manner, but decreased BTC mRNA levels. FSH had modest stimulatory effects on the levels of mRNA encoding the bone morphogenetic protein 15 (BMP15) receptor, BMPR1B, in cumulus cells, but did not alter mRNA expression of the growth and differentiation factor 9 (GDF9) receptor, TGFBR1. More interestingly, FSH dramatically stimulated levels of mRNA encoding two receptors for fibroblast growth factors (FGF), FGFR2C and FGFR3C, in cumulus cells. FSH also stimulated mRNA expression of FGFR1B, but not of FGFR2B in cumulus cells. Based on dose-response studies, FGFR3C was the receptor most sensitive to the influence of FSH. This study demonstrates that FSH stimulates the expression of EGF-like factors in bovine cumulus cells, and provides evidence that FSH differently regulates the expression of distinct receptors for OSFs in cumulus cells.

Agonist-activated Ca2+ influx and Ca2+ -dependent Cl- channels in Xenopus ovarian follicular cells: functional heterogeneity within the cell monolayer

Xenopus follicles are endowed with specific receptors for ATP, ACh, and AII, transmitters proposed as follicular modulators of gamete growth and maturation in several species. Here, we studied ion-current responses elicited by stimulation of these receptors and their activation mechanisms using the voltage-clamp technique. All agonists elicited Cl(-) currents that depended on coupling between oocyte and follicular cells and on an increase in intracellular Ca(2+) concentration ([Ca(2+) ](i)), but they differed in their activation mechanisms and in the localization of the molecules involved. Both ATP and ACh generated fast Cl(-) (F(Cl)) currents, while AII activated an oscillatory response; a robust Ca(2+) influx linked specifically to F(Cl) activation elicited an inward current (I(iw,Ca)) which was carried mainly by Cl(-) ions, through channels with a sequence of permeability of SCN(-)  > I(-)  > Br(-)  > Cl(-). Like F(Cl), I(iw,Ca) was not dependent on oocyte [Ca(2+) ](i) ; instead both were eliminated by preventing [Ca(2+) ](i) increase in the follicular cells, and also by U73122 and 2-APB, drugs that inhibit the phospolipase C (PLC) pathway. The results indicated that F(Cl) and I(iw,Ca) were produced by the expected, PLC-stimulated Ca(2+) -release and Ca(2+) -influx, respectively, and by the opening of I(Cl(Ca)) channels located in the follicular cells. Given their pharmacological characteristics and behavior in conditions of divalent cation deprivation, Ca(2+) -influx appeared to be driven through store-operated, calcium-like channels. The AII response, which is also known to require PLC activation, did not activate I(iw,Ca) and was strictly dependent on oocyte [Ca(2+) ](i) increase; thus, ATP and ACh receptors seem to be expressed in a population of follicular cells different from that expressing AII receptors, which were coupled to the oocyte through distinct gap-junction channels.

Specific protein kinase C isoforms α and βI are involved in follicle-stimulating hormone-induced mouse follicle-enclosed oocytes meiotic resumption

Protein kinase C (PKC) is involved in gonadotrophin-induced oocyte maturation. In the present study, we investigated the role of specific PKC isoforms in the process of follicle-stimulating hormone (FSH)-induced oocyte meiotic resumption. Small antral follicles (200–300 µm in diameter) were isolated from immature mice and cultured in vitro. FSH significantly induced follicle-enclosed oocytes (FEOs) meiotic resumption after 8 hr culture. However, the induced effect of FSH was dose-dependently inhibited by the specific PKC α and βI inhibitor Gö6976, and 100 nM Gö6976 completely blocked FSH function in oocyte meiotic resumption. Furthermore, FSH dramatically induced the expression of transcripts encoding epidermal growth factor (EGF)-like growth factors Areg, Btc, and Ereg mRNA levels, and up-regulated tyrosine phosphorylation level of EGF receptor (EGFR) in granulosa cells. Blocking the function of EGFR by AG1478 eliminated the effect of FSH-induced FEOs meiotic resumption, suggesting that FSH induced oocyte maturation through the activation of EGFR. FSH-induced phosphorylation of EGFR could also be inhibited by Gö6976. Next, we examined the effect of FSH on the expression and phosphorylation PKC α and βI. FSH induced the expression of PKC α at mRNA and protein level, and also up-regulated its phosphorylation level in granulosa cells after 8 hr culture. However, FSH had no effect on the expression of PKC βI but down-regulated its phosphorylation level. In conclusion, FSH-induced activation of PKC α alone, or together with the inactivation of PKC βI in granulosa cells, participates in mouse oocyte meiotic resumption, possibly by the activation of EGFR signaling pathway.

FSH modulates PKAI and GPR3 activities in mouse oocyte of COC in a gap junctional communication (GJC)-dependent manner to initiate meiotic resumption

Many studies have shown that cyclic adenosine-5′-monophosphate (cAMP)-dependent protein kinase A (PKA) and G-protein-coupled receptor 3 (GPR3) are crucial for controlling meiotic arrest in oocytes. However, it is unclear how gonadotropins modulate these factors to regulate oocyte maturation, especially by gap junctional communication (GJC). Using an in vitro meiosis-arrested mouse cumulus-oocyte complex (COC) culture model, we showed that there is a close relationship between follicle-stimulating hormone (FSH) and the PKA type I (PKAI) and GPR3. The effect of FSH on oocyte maturation was biphasic, initially inhibitory and then stimulatory. During FSH-induced maturation, rapid cAMP surges were observed in both cumulus cells and oocyte. Most GJC between cumulus cells and oocyte ceased immediately after FSH stimulation and recommenced after the cAMP surge. FSH-induced maturation was blocked by PKAI activator 8-AHA-cAMP. Levels of PKAI regulatory subunits and GPR3 decreased and increased, respectively, after FSH stimulation. In the presence of the GJC inhibitor carbenoxolone (CBX), FSH failed to induce the meiotic resumption and the changes in PKAI, GPR3 and cAMP surge in oocyte were no longer detected. Furthermore, GPR3 was upregulated by high cAMP levels, but not by PKAI activation. When applied after FSH stimulation, the specific phosphodiesterase 3A (PDE3A) inhibitor cilostamide immediately blocked meiotic induction, regardless of when it was administered. PKAI activation inhibited mitogen-activated protein kinase (MAPK) phosphorylation in the oocytes of COCs, which participated in the initiation of FSH-induced meiotic maturation in vitro. Just before FSH-induced meiotic maturation, cAMP, PKAI, and GPR3 returned to basal levels, and PDE3A activity and MAPK phosphorylation increased markedly. These experiments show that FSH induces a transient increase in cAMP levels and regulates GJC to control PKAI and GPR3 activities, thereby creating an inhibitory phase. After PDE3A and MAPK activities increase, meiosis resumes.

Signaling pathways regulating FSH- and amphiregulin-induced meiotic resumption and cumulus cell expansion in the pig

To define signaling pathways that drive FSH- and epidermal growth factor (EGF)-like peptide-induced cumulus expansion and oocyte meiotic resumption, in vitro cultured pig cumulus-oocyte complexes were treated with specific protein kinase inhibitors. We found that FSH-induced maturation of oocytes was blocked in germinal vesicle (GV) stage by protein kinase A (PKA), MAPK14, MAPK3/1, and EGF receptor (EGFR) tyrosine kinase inhibitors (H89, SB203580, U0126, and AG1478 respectively) whereas phosphoinositide-3-kinase/v-akt murine thymoma viral oncogene homolog (PI3K/AKT) inhibitor (LY294002) blocked maturation of oocytes in metaphase I (MI). Amphiregulin (AREG)-induced maturation of oocytes was efficiently blocked in GV by U0126, AG1478, and low concentrations of LY294002; H89, SB203580, and high concentrations of LY294002 allowed the oocytes to undergo breakdown of GV and blocked maturation in MI. Both FSH- and AREG-induced cumulus expansion was incompletely inhibited by H89 and completely inhibited by SB203580, U0126, AG1478, and LY294002. The inhibitors partially or completely inhibited expression of expansion-related genes (HAS2, PTGS2, and TNFAIP6) with two exceptions: H89 inhibited only TNFAIP6 expression and LY294002 increased expression of PTGS2. The results of this study are consistent with the idea that PKA and MAPK14 pathways are essential for FSH-induced transactivation of the EGFR, and synthesis of EGF-like peptides in cumulus cells and MAPK3/1 is involved in regulation of transcriptional and posttranscriptional events in cumulus cells required for meiotic resumption and cumulus expansion. PI3K/AKT signaling is important for regulation of cumulus expansion, AREG-induced meiotic resumption, and oocyte MI/MII transition. The present data also indicate the existence of an FSH-activated and PKA-independent pathway involved in regulation of HAS2 and PTGS2 expression in cumulus cells.

Regulation of gap-junctional communication between cumulus cells during in vitro maturation in swine, a gap-FRAP study

Intercellular gap-junctional communication (GJC) plays an important role in ovarian cell physiology. Closure of GJC has been proposed to be involved in oocyte maturation, particularly in the resumption of meiosis, both in vivo and in vitro, by controlling the flow of meiosis inhibitors, such as cAMP and cGMP. Understanding how GJC dynamics are regulated during in vitro maturation (IVM) could provide a powerful tool for controlling meiotic resumption and oocyte maturation in vitro. Since little is known about the GJC dynamic regulation between cumulus cells, we have developed an assay based on recovery of calcein fluorescence in photobleached cumulus cells, a gap-FRAP assay. The GJC profile has been characterized during the first hours of porcine IVM. We showed that equine chorionic gonadotropin (eCG) and epidermal growth factor (EGF) down-regulated GJC effectiveness between cumulus cells. However, human chorionic gonadotropin was not down-regulating GJC effectiveness. We also showed that the GJC network expanded during this period and that this effect was not regulated by gonadotropins. Porcine follicular fluid present in the maturation medium also had an impact on GJC regulation, increasing GJC network establishment and the effectiveness of calcein transfer rate between cumulus cells. These results show that both eCG and EGF are regulating the decrease in GJC effectiveness after 4.5 h of IVM, while the network extension is gonadotropin independent. Regulation of GJC between cumulus cells would then be specifically regulated during in vitro IVM.

EGF-like factors induce expansion of the cumulus cell-oocyte complexes by activating calpain-mediated cell movement

Cumulus cell-oocyte complex (COC) expansion is obligatory for LH-induced ovulation and is initiated by LH induction of the epidermal growth factor (EGF)-like factors that mediate the synthesis of the hyaluronan-rich matrix and hyaluronan-stabilizing factors. COC expansion also involves the movement of cumulus cells within the matrix by mechanisms that have not been characterized. We document herein that two proteases, calpain 2 and to a lesser extent calpain 1, are expressed in cumulus cells and that the proteolytic activity of these enzymes is rapidly and significantly increased in COC isolated from human chorionic gonadotropin-induced ovulatory follicles in vivo. Stimulation of calpain activity was associated with proteolytic degradation of paxillin and talin (two components of focal adhesion complexes), cell detachment, and the formation of cell surface bleb-like protrusions. Injection of a calpain inhibitor in vivo reduced 1) human chorionic gonadotropin-stimulated calpain enzyme activity, 2) cell detachment, 3) membrane protrusion formation, and 4) COC expansion by mechanisms that did not alter Has2 expression. During EGF-like factor induction of COC expansion in culture, calpain activity was increased by ERK1/2 and intracellular Ca(2+) signaling pathways. Inhibition of calpain activity in cultured COC blocked cumulus cell detachment, protrusion formation, and the vigorous movement of cumulus cells. As a consequence, COC expansion was impaired. Collectively, these results show that two highly coordinated processes control COC expansion. One process involves the synthesis of the hyaluronan matrix, and the other mediates cumulus cell detachment and movement. The latter are controlled by calpain activation downstream of the EGF receptor activation of the Ca(2+) pathway and ERK1/2 pathways.

Regulation of oocyte mitochondrial DNA copy number by follicular fluid, EGF, and neuregulin 1 during in vitro maturation affects embryo development in pigs

Little is known about mitochondrial DNA (mtDNA) replication during oocyte maturation and its regulation by extracellular factors. The present study determined the effects of supplementation of maturation medium with porcine follicular fluid (pFF; 0, 10%, 20%, and 30%) on mtDNA copy number and oocyte maturation in experiment 1; the effects on epidermal growth factor (EGF; 10 ng/mL), neuregulin 1 (NRG1; 20 ng/mL), and NRG1 + insulin-like growth factor 1 (IGF1; 100 ng/mL + NRG1 20 ng/mL), on mtDNA copy number, oocyte maturation, and embryo development after parthenogenic activation in experiment 2; and effects on embryo development after in vitro fertilization in experiment 3. Overall, mtDNA copy number increased from germinal vesicle (GV) to metaphase II (MII) stage oocytes after in vitro maturation (GV: 167 634.6 ± 20 740.4 vs. MII: 275 131.9 ± 9 758.4 in experiment 1; P < 0.05; GV: 185 004.7 ± 20 089.3 vs. MII: 239 392.8 ± 10 345.3 in experiment 2; P < 0.05; Least Squares Means ± SEM). Supplementation of IVM medium with pFF inhibited mtDNA replication (266 789.9 ± 11 790.4 vs. 318 510.1 ± 20 377.4; P < 0.05) and oocyte meiotic maturation (67.3 ± 0.7% vs. 73.2 ± 1.2%, for the pFF supplemented and zero pFF control, respectively; P < 0.01). Compared with the control, addition of growth factors enhanced oocyte maturation. Furthermore, supplementation of NRG1 stimulated mitochondrial replication, increased mtDNA copies in MII oocytes than in GV oocytes, and increased percentage of blastocysts in both parthenogenetic and in vitro fertilized embryos. In this study, mitochondrial biogenesis in oocytes was stimulated during in vitro maturation. Oocyte mtDNA copy number was associated with developmental competence. Supplementation of maturation medium with NRG1 increased mtDNA copy number, and thus provides a means to improve oocyte quality and developmental competence in pigs.

Effect of epidermal growth factor on follicle-stimulating hormone-induced proliferation of granulosa cells from chicken prehierarchical follicles

The development of ovarian follicular cells is controlled by multiple circulating and local hormones and factors, including follicle-stimulating hormone (FSH) and epidermal growth factor (EGF). In this study, the stage-specific effect of EGF on FSH-induced proliferation of granulosa cells was evaluated in the ovarian follicles of egg-laying chickens. Results showed that EGF and its receptor (EGFR) mRNAs displayed a high expression in granulosa cells from the prehierarchical follicles, including the large white follicle (LWF) and small yellow follicle (SYF), and thereafter the expression decreased markedly to the stage of the largest preovulatory follicle. SYF represents a turning point of EGF/EGFR mRNA expression during follicle selection. Subsequently the granulosa cells from SYF were cultured to reveal the mediation of EGF in FSH action. Cell proliferation was remarkably increased by treatment with either EGF or FSH (0.1-100 ng/ml). This result was confirmed by elevated proliferating cell nuclear antigen (PCNA) expression and decreased cell apoptosis. Furthermore, EGF-induced cell proliferation was accompanied by increased mRNA expressions of EGFR, FSH receptor, and the cell cycle-regulating genes (cyclins D1 and E1, cyclin-dependent kinases 2 and 6) as well as decreased expression of luteinizing hormone receptor mRNA. However, the EGF or FSH-elicited effect was reversed by simultaneous treatment with an EGFR inhibitor AG1478. In conclusion, EGF and EGFR expressions manifested stage-specific changes during follicular development and EGF mediated FSH-induced cell proliferation and retarded cell differentiation in the prehierarchical follicles. These expressions thus stimulated follicular growth before selection in the egg-laying chicken.