Oocyte-secreted factor TGFB2 enables mouse cumulus cell expansion in vitro.

Cumulus expansion is necessary for the release of a fertilizable oocyte from the ovary, which is critical for the normal fertilization of mammals. Cumulus expansion requires cooperation between epidermal growth factor (EGF)-like growth factors and oocyte paracrine factors. Growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) are well-known paracrine factors secreted by oocytes. In addition, transforming growth factor-ß2 (TGFB2) was primarily expressed in oocytes and its membrane receptors type 1 receptor (TGFBR1) and type 2 receptor (TGFBR2) were located in cumulus cells. In our present study, TGFB2 induced expansion of oocytectomized (OOX) complexes and increased the expression of expansion-related genes in the presence of EGF, suggesting that TGFB2 enables cumulus expansion. Inhibition of TGF-ß signaling with SD208 blocked TGFB2-promoted cumulus expansion. Furthermore, in the culture of OOX complexes from mice of Tgfbr2-specific depletion in granulosa cells, TGFB2-promoted cumulus expansion and the expression of expansion-related genes were impaired. These results suggest that TGFB2 could induce cumulus expansion through TGFBR-SMAD2/3 signaling. Tgfb2-specific depletion in oocytes using Zp3-Cre mice had no effect on cumulus expansion in vivo, possibly due to the compensatory effect of other cumulus expansion-enabling factors. Taken together, TGFB2 is involved in expansion-related gene expression and consequent cumulus expansion.

[Advances in molecular mechanisms of meiotic arrest and luteinizing hormone-induced meiotic resumption in oocytes].

Mammalian oocytes within Graafian follicles are arrested at prophase I of meiosis. C-type natriuretic peptide (NPPC), secreted by mural granulosa cells (MGCs), maintains oocyte meiotic arrest via binding to its cognate receptor natriuretic peptide receptor 2 (NPR2) and producing cyclic guanosine monophosphate (cGMP). NPR2 is most concentrated in the cumulus cells. In addition, cAMP, gap junction, inosine monophosphate dehydrogenase (IMPDH) and other important regulatory factors are also involved in meiotic arrest. Luteinizing hormone (LH) then rapidly decreases cGMP and induces oocyte meiotic resumption. In this paper, advances in the molecular mechanisms of meiotic arrest and LH-induced meiotic resumption were reviewed. This paper may provide new ideas for the prevention, diagnosis and treatment of related reproductive diseases.

Epidermal Growth Factor-Mobilized Intracellular Calcium of Cumulus Cells Decreases Natriuretic Peptide Receptor 2 Affinity for Natriuretic Peptide Type C and Induces Oocyte Meiotic Resumption in the Mouse.

Natriuretic peptide type C (NPPC) activation of the guanylyl cyclase-linked natriuretic peptide receptor (NPR) 2 maintains oocyte meiotic arrest. Luteinizing hormone (LH)-dependent epidermal growth factor (EGF) receptor signaling elevates calcium of cumulus cells to inactivate NPR2, resulting in meiotic resumption. This study investigated the regulatory mechanism of calcium on NPR2 inactivation. In mouse ovarian follicles, LH, through the activation of EGF receptor, significantly elevated calcium levels in cumulus cells, but decreased the binding affinity of NPR2 for NPPC. In cultured cumulus-oocyte complexes, the activation of EGF receptor by EGF mobilized intracellular calcium of cumulus cells to decrease NPR2 affinity and cGMP levels, resulting in meiotic resumption. However, hormone treatments had not changed NPR2 protein levels. In addition, the removal of magnesium ions from the medium decreased the binding affinity of NPR2 for NPPC, resulting in a decrease in cGMP levels and meiotic resumption. It is concluded that magnesium ions are required to maintain functional NPR2, and that LH-dependent EGF receptor signaling mobilizes intracellular calcium of cumulus cells to reduce NPPC-NPR2 interaction that is required for meiotic resumption.

CREB activity is required for luteinizing hormone-induced the expression of EGF-like factors.

A surge of luteinizing hormone (LH) from the pituitary gland induces the expression of the epidermal growth factor (EGF)-like factors, which triggers oocyte maturation, cumulus expansion, and ovulation. How LH induces EGF-like factor expression is unclear. In the present study, a rapid increase of phosphorylated cAMP response element binding protein (CREB) was observed after the activation of LH receptor by human chorionic gonadotropin. Large antral follicles from equine chorionic gonadotropin-primed mice were cultured in medium with LH to stimulate the expression of EGF-like factors. CREB phosphorylation was increased in granulosa cells; conversely KG-501, a CREB functional inhibitor, significantly reduced LH-induced gene expression of EGF-like factors, oocyte meiotic resumption, and cumulus cell expansion. Reduction of CREB expression by Creb siRNA also repressed LH-induced expression of EGF-like factors in cultured granulosa cells. Inactivation of mitogen-activated protein kinase (MAPK3/1) by U0126 inhibited LH-induced CREB phosphorylation and EGF-like factors gene expression, whereas the activation of LH receptor increased Akt/protein kinase B phosphorylation, which is involved in LH-induced CREB phosphorylation and the expression of EGF-like factors. Thus, LH induces MAPK3/1 and Akt activation, both of which are required for the CREB-promoted expression of EGF-like factors in granulosa cells. Mol. Reprod. Dev. 83: 1116-1127, 2016. © 2016 Wiley Periodicals, Inc.

Conductivity and phase morphology of carbon black-filled immiscible polymer blends under creep: an experimental and theoretical study.

Blends of carbon black (CB)-filled co-continuous immiscible polystyrene/poly(methyl-methacrylate) (PS/PMMA) with a PS/PMMA ratio of 50/50 and CB selectively located in the PS phase have been prepared by melt blending. The simultaneous evolution of conductivity and phase morphology of blend composites was investigated under shear and in the quiescent state at 200 °C. It was found that shear deformation had a significant influence on the conductivity of the unfilled PS/PMMA blend and its composites, which was attributed to the change of phase morphology during shear. After the shear stress of 10 kPa, the conductivity of PS/PMMA blends filled with 2 vol% of CB decreased by about two orders of magnitude and the phase morphology transformed from a fine co-continuous structure into a highly elongated lamellar structure. The deformation of phase morphology and the decrease of conductivity were weakened upon decreasing the shear stress or increasing the CB concentration. During subsequent recovery, pronounced phase structure coarsening was observed in the mixture and the conductivity increased as well. A simple model describing the behavior of conductivity under shear deformation was derived and utilized for the description of the experimental data. For the first time, the Burgers model was used to describe the conductivity, and the viscoelastic and viscoplastic parameters were deduced by fitting the conductivity under shear. The results obtained in this study provide a deeper insight into the evolution of phase structure in the conductive polymer blend composite induced by shear deformation.

Porcine natriuretic peptide type B (pNPPB) maintains mouse oocyte meiotic arrest via natriuretic peptide receptor 2 (NPR2) in cumulus cells.

In mouse ovarian follicles, the oocyte is maintained in meiotic prophase arrest by natriuretic peptide type C (NPPC) acting via its cognate receptor, natriuretic peptide receptor 2 (NPR2). As there is a marked species difference in the receptor selectivity of the natriuretic peptide family, this study examined the functional effect of other natriuretic peptides, type A (NPPA) and type B (NPPB), acting via NPR2 on mouse-oocyte meiotic arrest. The results by quantitative, reverse-transcriptase PCR showed that Npr2 was the predominant natriuretic peptide receptor transcript, and that Npr1 and Npr3 mRNA levels were negligible in cumulus cells isolated from equine chorionic gonadotropin (eCG)-primed, immature female mice. While NPPA and NPPB from human and rat had no effect on oocyte maturation, porcine NPPB (pNPPB) maintained oocyte meiotic arrest in a dose-dependent manner. Furthermore, pNPPB-mediated meiotic arrest and cGMP production could be completely blocked by the NPR2 inhibitor sphingosine-1-phosphate (S1P). Neither the NPR1 antagonist anantin or Npr1 knockout had an effect on pNPPB-mediated meiotic arrest. Thus, pNPPB can functionally maintain mouse-oocyte meiotic arrest by the receptor NPR2 of cumulus cells. These findings demonstrate that pNPPB may be used as a probe to identify the essential amino acid sequences for activation of NPR2.

Fluoride promotes the secretion of inflammatory factors in microglia through NLRP3/Caspase-1/GSDMD pathway.

It is widespread of endemic fluorosis in China, and the exposure of excessive fluoride will cause nervous system disease and activate microglia. However, the mechanism of the damage is not clear. It is well-known that NLRP3/Caspase-1/GSDMD pathway, a classic pyroptosis pathway, is widely involved in the occurrence and development of nervous system-related diseases, infectious diseases, and atherosclerotic diseases. This research aimed to explore the molecular mechanism of sodium fluoride on inflammation and pyroptosis in BV2 microglia based on the NLRP3/Caspase-1/GSDMD signaling pathway. BV2 microglia was treated with sodium fluoride at the dose of 0.25, 1, and 2 mmol/L for 24, 48, and 72 h, respectively. Cell viability, cell morphology, lactate dehydrogenase content, and related proteins and genes were examined to investigate if sodium fluoride caused damage to BV2 microglia through the pyroptosis pathway. Dithiolam (5 µmol/L), a pyroptosis inhibitor, was added for further verification. NaF could induced BV2 cells injury in a dose-dependent fashion through disrupting the integrity of cell membranes and increasing IL-1ß via upregulating NLRP3, Caspase-1, and its downstream protein GSDMD. Disulfiram could improve these changes caused by NaF. In conclusion, our results suggested that NLRP3/Caspase-1/GSDMD-mediated classical pyroptosis pathway was involved in fluoride-induced BV2 microglia damage.

Oocyte-specific deletion of eukaryotic translation initiation factor 5 causes apoptosis of mouse oocytes within the early-growing follicles by mitochondrial fission defect-reactive oxygen species-DNA damage.

BACKGROUND: Mutations in several translation initiation factors are closely associated with premature ovarian insufficiency (POI), but the underlying pathogenesis remains largely unknown. METHODS AND RESULTS: We generated eukaryotic translation initiation factor 5 (Eif5) conditional knockout mice aiming to investigate the function of eIF5 during oocyte growth and follicle development. Here, we demonstrated that Eif5 deletion in mouse primordial and growing oocytes both resulted in the apoptosis of oocytes within the early-growing follicles. Further studies revealed that Eif5 deletion in oocytes downregulated the levels of mitochondrial fission-related proteins (p-DRP1, FIS1, MFF and MTFR) and upregulated the levels of the integrated stress response-related proteins (AARS1, SHMT2 and SLC7A1) and genes (Atf4, Ddit3 and Fgf21). Consistent with this, Eif5 deletion in oocytes resulted in mitochondrial dysfunction characterized by elongated form, aggregated distribution beneath the oocyte membrane, decreased adenosine triphosphate content and mtDNA copy numbers, and excessive accumulation of reactive oxygen species (ROS) and mitochondrial superoxide. Meanwhile, Eif5 deletion in oocytes led to a significant increase in the levels of DNA damage response proteins (γH2AX, p-CHK2 and p-p53) and proapoptotic proteins (PUMA and BAX), as well as a significant decrease in the levels of anti-apoptotic protein BCL-xL. CONCLUSION: These findings indicate that Eif5 deletion in mouse oocytes results in the apoptosis of oocytes within the early-growing follicles via mitochondrial fission defects, excessive ROS accumulation and DNA damage. This study provides new insights into pathogenesis, genetic diagnosis and potential therapeutic targets for POI. KEY POINTS: Eif5 deletion in oocytes leads to arrest in oocyte growth and follicle development. Eif5 deletion in oocytes impairs the translation of mitochondrial fission-related proteins, followed by mitochondrial dysfunction. Depletion of Eif5 causes oocyte apoptosis via ROS accumulation and DNA damage response pathway.

Trifunctional phosphorus-doped cobalt molybdate catalyst in self-driven coupling systems for synchronized sulfur recovery and hydrogen evolution.

This study introduces a self-driven system that effectively achieves synchronized sulfur recovery and hydrogen production using a Zn-air battery. The system ingeniously integrates the sulfur oxidation reaction (SOR) and the hydrogen evolution reaction (HER) into a single, efficient process. Central to this system is the trifunctional phosphorus-doped cobalt molybdate catalyst (P-CoMoO4/NF), which exhibits superior performance in both HER (ηj = 100 = 0.13 V) and SOR (ηj = 100 = 0.30 V) with remarkable stability (∼360 h), reaching 0.64 V at 100 mA cm-2 for simultaneous sulfur ion degradation and hydrogen production. Through density functional theory simulations and extensive characterizations, it has been shown that phosphorus doping in the cobalt molybdate catalyst facilitates electron redistribution, enhancing the catalyst's conductivity, generating more oxygen vacancies, and promoting improved mass and electron transfer. This modification also lowers the energy barrier for adsorbing reaction intermediates, thus increasing the hydrogen production rate and sulfur oxide conversion in this self-powered system. In summary, this research marks a substantial advancement in the development of trifunctional catalysts and proposes an eco-friendly, cost-effective strategy for integrated reaction systems, paving the way for sustainable energy solutions.

Synthesis of tetraphenylethylene-based small molecular sensor for the selective "turn-on" detection of pyrophosphoric acid in the aqueous solution.

Pyrophosphoric acid (PPi) is a crucial indicator for monitoring adenosine triphosphate hydrolysis processes, and abnormal PPi levels in the human body seriously threaten human health. Thus the efficient detection of the concentration of PPi in the aqueous solution is important and urgent. This paper described the successful synthesis of a tetraphenylethylene (TPE) derivative, named as TPE-4B, which contained four chelate pyridinium groups exhibiting aggregation-induced emission characteristics. TPE-4B was explicitly developed for the selective and sensitive fluorescence detection of PPi in aqueous solutions, showing a fluorescence "turn-on" response, and the detection limit was 65 nM. The four chelate pyridinium moieties of TPE-4B exhibited robust electrostatic interactions and binding capacity towards PPi, leading to the formation of aggregations, which was confirmed by zeta potential, dynamic light scattering, and scanning electron microscopy. Compared with free TPE-4B in the aqueous solution, the zeta potential of aggregations decreased from 20.7 to 4.2 mV, the average diameter increased from 155 to 403 nm, and the morphology transformed from porous nanostructures into a block-like format. Leveraging these properties, TPE-4B is a promising candidate for a "turn-on" fluorescence sensor designed to detect PPi in the aqueous solution.

Removal of high concentration of chloride ions by electrocoagulation using aluminium electrode.

Wastewater containing a high concentration of chloride ions (Cl- ions) generated in industrial production will corrode equipment and pipelines and cause environmental problems. At present, systematic research on Cl- removal by electrocoagulation is scarce. To study the Cl- removal mechanism, process parameters (current density and plate spacing), and the influence of coexisting ions on the removal of Cl- in electrocoagulation, we use aluminum (Al) as the sacrificial anode, combined with physical characterization and density functional theory (DFT) to study Cl- removal by electrocoagulation. The result showed that the use of electrocoagulation technology to remove Cl- can reduce the concentration of Cl- in an aqueous solution below 250 ppm, meeting the Cl- emission standard. The mechanism of Cl- removal is mainly co-precipitation and electrostatic adsorption by forming chlorine-containing metal hydroxyl complexes. The current density and plate spacing affect the Cl- removal effect and operation cost. As a coexisting cation, magnesium ion (Mg2+) promotes the removal of Cl-, while calcium ion (Ca2+) inhibits it. Fluoride ion (F-), sulfate (SO42-), and nitrate (NO3-) as coexisting anions affect the removal of Cl- ions through competitive reaction. This work provides a theoretical basis for the industrialization of Cl- removal by electrocoagulation.

Post-cationic modification of a porphyrin-based conjugated microporous polymer for enhanced removal performance of bisphenol A.

A porphyrin-based conjugated microporous polymer photocatalyst named LDPO-2 was synthesized by a post-modification approach, which improved its hydrophilicity and visible light absorption ability. LDPO-2 achieved >99.5% removal efficiency for bisphenol A (BPA, 10 ppm) within 12 min of exposure to visible light, and the photocatalytic mechanism and potential degradation pathways were well investigated. LDPO-2 also exhibited impressive removal efficiency against BPA analogues, proving its practical applications in real-water treatment scenarios.

Specific separation and recovery of phosphate anions by a novel NiFe-LDH/rGO hybrid film based on electroactivity-variable valence.

Phosphorus is anon-renewable resource. Supplies are limited and muchphosphorusis currently wasted during the production and utilization process, causing concerns about future supplies and widespread environmental problems. To solve these problems, a new type of NiFe-LDH/rGO electrically switched ion-selective (ESIX) film is designed, based on the dominant mechanism of inner-sphere complexation. An ESIX process allows the NiFe-LDH/rGO hybrid film to achieve a controllably selective uptake and release of the phosphate anions. This route involves tuning potential steps to regulate the redox states of the composite film and the variable metal (e.g., Ni, Fe (II)/(III)) in coordination centers, as the inner-sphere complexation of the metals to phosphate anions is combined with the assistance of the outer electric field. A high absorption capacity (270 mg·g-1) and regeneration rate (>85%) were achieved, together with good cycle stability.

SphK-produced S1P in somatic cells is indispensable for LH-EGFR signaling-induced mouse oocyte maturation.

Germ cell division and differentiation require intimate contact and interaction with the surrounding somatic cells. Luteinizing hormone (LH) triggers epidermal growth factor (EGF)-like growth factors to promote oocyte maturation and developmental competence by activating EGF receptor (EGFR) in somatic cells. Here, we showed that LH-EGFR signaling-activated sphingosine kinases (SphK) in somatic cells. The activation of EGFR by EGF increased S1P and calcium levels in cumulus-oocyte complexes (COCs), and decreased the binding affinity of natriuretic peptide receptor 2 (NPR2) for natriuretic peptide type C (NPPC) to release the cGMP-mediated meiotic arrest. These functions of EGF were blocked by the SphK inhibitor SKI-II, which could be reversed by the addition of S1P. S1P also activated the Akt/mTOR cascade reaction in oocytes and promoted targeting protein for Xklp2 (TPX2) accumulation and oocyte developmental competence. Specifically depleting Sphk1/2 in somatic cells reduced S1P levels and impaired oocyte meiotic maturation and developmental competence, resulting in complete female infertility. Collectively, SphK-produced S1P in somatic cells serves as a functional transmitter of LH-EGFR signaling from somatic cells to oocytes: acting on somatic cells to induce oocyte meiotic maturation, and acting on oocytes to improve oocyte developmental competence.

Biomass-Derived N-Doped Carbon for Efficient Electrocatalytic CO2 Reduction to CO and Zn-CO2 Batteries.

Conversion of CO2 into valuable chemicals via electrochemical CO2 reduction reaction (CO2RR) is a promising technology to alleviate the energy crisis and the greenhouse effect. Herein, low-cost wood biomass was applied as the carbon source to prepare nitrogen (N)-doped carbon electrocatalysts for the conversion of CO2 to CO and further as the cathode material for Zn-CO2 batteries. By virtue of N-doping and assistance of FeCl3, a cedar biomass-derived three-dimensional (3D) N-doped graphitized carbon with a high N-doping content (5.38%), an ultrahigh specific surface area (1673.6 m2 g-1), rich nanopores, and sufficient active N sites was successfully obtained, which exhibited super CO2RR activity with a high faradaic efficiency of 91% at a low applied potential of 0.56 V (vs RHE) and a long-term stability for at least 20 h. Furthermore, a Zn-CO2 battery with it as the cathode material delivered a stable open circuit voltage of 0.79 V, a peak power density of 0.51 mW cm-2 at 2.14 mA cm-2, and a maximum faradaic efficiency to CO of 80.4% at 2.56 mA cm-2, indicating that it could be applied in a practical process by using CO2 to generate power with the production of CO. Density functional theory calculations revealed that pyridinic N could more effectively decrease the free energy barriers for CO2RR and boost the reaction. This work not only revealed a facile approach to convert waste biomass into N-doped-graphitization carbon as valuable CO2RR electrocatalysts but also provided a new strategy to achieve "carbon solving carbon's problem".

N-Doped Carbon Nanotubes Derived from Graphene Oxide with Embedment of FeCo Nanoparticles as Bifunctional Air Electrode for Rechargeable Liquid and Flexible All-Solid-State Zinc-Air Batteries.

This work reports a novel approach for the synthesis of FeCo alloy nanoparticles (NPs) embedded in the N,P-codoped carbon coated nitrogen-doped carbon nanotubes (NPC/FeCo@NCNTs). Specifically, the synthesis of NCNT is achieved by the calcination of graphene oxide-coated polystyrene spheres with Fe3+, Co2+ and melamine adsorbed, during which graphene oxide is transformed into carbon nanotubes and simultaneously nitrogen is doped into the graphitic structure. The NPC/FeCo@NCNT is demonstrated to be an efficient and durable bifunctional catalyst for oxygen evolution (OER) and oxygen reduction reaction (ORR). It only needs an overpotential of 339.5 mV to deliver 10 mA cm-2 for OER and an onset potential of 0.92 V to drive ORR. Its bifunctional catalytic activities outperform those of the composite catalyst Pt/C + RuO2 and most bifunctional catalysts reported. The experimental results and density functional theory calculations have demonstrated that the interplay between FeCo NPs and NCNT and the presence of N,P-codoped carbon structure play important roles in increasing the catalytic activities of the NPC/FeCo@NCNT. More impressively, the NPC/FeCo@NCNT can be used as the air-electrode catalyst, improving the performance of rechargeable liquid and flexible all-solid-state zinc-air batteries.

Fabrication of a High-Energy Flexible All-Solid-State Supercapacitor Using Pseudocapacitive 2D-Ti3C2Tx-MXene and Battery-Type Reduced Graphene Oxide/Nickel-Cobalt Bimetal Oxide Electrode Materials.

Owing to excellent metallic conductivity, hydrophilic surfaces, and surface redox properties, a two-dimensional (2D) metal carbide of Ti3C2Tx-MXene could serve as a promising pseudocapacitive electrode material for energy storage devices. Meanwhile, the 2D reduced graphene oxide (rGO) combining with the hierarchical cubic spinel nickel-cobalt bimetal oxide (NiCo2O4) nanospikes could control ion diffusion for charge storage, thereby facilitating the improvement of the energy density of a supercapacitor. As per the strategy, the pseudocapacitive 2D Ti3C2Tx was loaded on a flexible acid-treated carbon fiber (ACF) backbone to prepare a Ti3C2Tx/ACF negative electrode by a convenient drop-casting method. Meanwhile, 2D rGO was deposited on ACF by a simple dip-dry process, which was further decorated by the spinel NiCo2O4 nanospikes using a hydrothermal method to obtain a NiCo2O4@rGO/ACF positive electrode. The fabricated Ti3C2Tx/ACF electrode exhibited an excellent specific capacitance of 246.9 F/g (197.5 mF/cm2) at 4 mA/cm2 along with 96.7% capacity retention over 5000 charge/discharge cycles, whereas the NiCo2O4@rGO/ACF electrode showed a specific capacitance of 1487 F/g (458.3 mA h/g) at 3 mA/cm2 with a cycling stability of 88.2% over 10 000 charge/discharge cycles. As a result, a flexible all-solid-state hybrid supercapacitor (FHSC) device using the pseudocapacitive Ti3C2Tx/ACF on the negative side with a widespread voltage window and the battery-type NiCo2O4@rGO/ACF on the positive side with high electrochemical activity delivered an excellent volumetric capacitance of 2.32 F/cm3 (141.9 F/g) at a current density of 5 mA/cm2 with a high-energy density of 44.36 Wh/kg (0.72 mWh/cm3) at a power density of 985 W/kg (16.13 mW/cm3) along with a cycling stability of 90.48% over 4500 charge/discharge cycles. Therefore, the pseudocapacitive 2D Ti3C2Tx/ACF negative electrode could replace carbon-based electrodes and a combination of it with the battery-type NiCo2O4@rGO/ACF positive electrode should be a promising way to step up the energy density of a supercapacitor.

Natriuretic peptide type C induces sperm attraction for fertilization in mouse.

Mammalian spermatozoa undergo selective movement along the isthmus of the oviduct to the ampulla during ovulation, which is a prerequisite for fertilization. The factor(s) that involves in selective spermatozoa movement is still unknown. In this study, we found that the oviductal epithelium in mouse ampulla expressed high levels of natriuretic peptide type C (NPPC) in the presence of ovulated oocyte-cumulus complexes (OCCs). Spermatozoa expressed NPPC receptor natriuretic peptide receptor 2 (NPR2, a guanylyl cyclase) on the midpiece of flagellum. NPPC increased intracellular levels of cGMP and Ca2+ of spermatozoa, and induced sperm accumulation in the capillary by attraction. Importantly, spermatozoa from Npr2 mutant mice were not attracted by NPPC, preventing fertilization in vivo. Oocyte-derived paracrine factors promoted the expression of Nppc mRNA in the ampulla. Therefore, NPPC secreted by oviductal ampulla attracts spermatozoa towards oocytes, which is essential for fertilization.

Epidermal growth factor receptor signaling-dependent calcium elevation in cumulus cells is required for NPR2 inhibition and meiotic resumption in mouse oocytes.

In preovulatory ovarian follicles, the oocyte is maintained in meiotic prophase arrest by natriuretic peptide precursor C (NPPC) and its receptor natriuretic peptide receptor 2 (NPR2). LH treatment results in the decrease of NPR2 guanylyl cyclase activity that promotes resumption of meiosis. We investigated the regulatory mechanism of LH-activated epidermal growth factor (EGF) receptor signaling on NPR2 function. Cumulus cell-oocyte complex is cultured in the medium with 30 nM NPPC to prevent oocyte spontaneous maturation. In this system, EGF could stimulate oocyte meiotic resumption after 4 hours of incubation. Further study showed that EGF elevated intracellular calcium concentrations of cumulus cells and decreased cGMP levels in cumulus cells and oocytes, and calcium-elevating reagents ionomycin and sphingosine-1-phosphate mimicked the effects of EGF on oocyte maturation and cGMP levels. EGF-mediated cGMP levels and meiotic resumption could be reversed by EGF receptor inhibitor AG1478 and the calcium chelator bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, tetra(acetoxymethyl)-ester. EGF also decreased the expression of Npr2 mRNA in cumulus cells, which may not be involved in meiotic resumption, because the block of NPR2 protein de novo synthesis by cycloheximide had no effect on NPPC and EGF-mediated oocyte maturation. However, EGF had no effect on oocyte maturation when meiotic arrest was maintained in the present of cGMP analog 8-bromoadenosine-cGMP. These results suggest that EGF receptor signaling induces meiotic resumption by elevating calcium concentrations of cumulus cells to decrease NPR2 guanylyl cyclase activity.