Involvement of calcium/calmodulin-dependent protein kinase kinase in meiotic maturation of pig oocytes

Plasma membrane lipid composition and metabolomics analysis of Yorkshire boar sperms with high and low resistance to cryopreservation

The resistance of sperm to freezing varies widely among boars. The semen ejaculate of different boars can be grouped into poor freezability ejaculate (PFE) and good freezability ejaculate (GFE). In this study, five Yorkshire boars each of the GFE and PFE were selected by comparing the changes in sperm motility before and after cryopreservation. Firstly, we found that the sperm plasma membrane of the PFE group showed weak integrity after PI and 6-CFDA staining. Then the electron microscopy results verified that the plasma membrane condition of all segments of GFE was better than that of PFE segments. Furthermore, the lipid composition of sperm plasma membranes in GPE and PFE sperm was analyzed by using mass spectrometry, and 15 lipids showed differences between the two groups. Among those lipids, only phosphatidylcholine (PC) (14:0/20:4) and phosphatidylethanolamine (PE) (14:0/20:4) were higher in PFE. The remaining lipid contents, including those of dihydroceramide (18:0/18:0), four hexosylceramides (18:1/20:1, 18:0/22:1, 18:1/16:0, 18:1/18:0), lactosylceramide (18:1/16:0), two hemolyzed phosphatidylethanolamines (18:2, 20:2), five phosphatidylcholines (16:1/18:2, 18:2/16:1, 14:0/20:4, 16:0/18:3, 18:1/20:2), and two phosphatidylethanolamines (14:0/20:4, 18:1/18:3), were all positively correlated with resistance to cryopreservation (p < 0.05, r > 0.6). Moreover, we analyzed the metabolic profile of sperm using untarget metabolomic. KEGG annotation analysis revealed that the altered metabolites were mainly involved in fatty acid biosynthesis. Finally, we determined that the contents of oleic acid, oleamideetc, N8-acetylspermidine etc., were different between GFE and PFE sperm. In summary, the different lipid metabolism levels and long-chain polyunsaturated fatty acids (PUFAs) in plasma membrane may be key factors contributing to differences in sperm resistance to cryopreservation among boars.

Cdx2 represses Oct4 function via inducing its proteasome-dependent degradation in early porcine embryos

Reciprocal repression of inner cell mass specific factor OCT4 and trophectoderm specific factor CDX2 promotes mouse first lineage segregation. Studies in mouse embryonic stem (ES) cells revealed that they bind to each other's regulatory regions to reciprocally suppress transcription, additionally they form protein complex for mutual antagonism. However, so far the molecular interaction of Oct4 and Cdx2 in other mammal's early embryo is not yet investigated. Here, over-expression of Cdx2 in early porcine embryo showed CDX2 represses Oct4 through neither the transcriptional repression nor forming repressive complex, but promoting OCT4 nuclear export and proteasomal degradation. The results showed novel molecular regulation of CDX2 on Oct4, and provided important clues for clarifying the mechanism of interaction between CDX2 and Oct4 in embryo of mammals other than mouse.

The Extracellular Calcium-Sensing Receptor (CASR) Regulates Gonadotropins-Induced Meiotic Maturation of Porcine Oocytes

Gonadotropins and epidermal growth factor (EGF) play crucial roles in promoting oocyte maturation. The regulatory network downstream of these key factors is not well understood. The present study was designed to investigate the role of the calcium-sensing receptor (CASR) in porcine oocyte in vitro maturation. CASR expression was up-regulated in oocytes matured in gonadotropin-containing medium. Cortical distribution of CASR was enhanced with gonadotropins but not EGF. Supplementation of a CASR agonist (NPS R-568) in the gonadotropin (FSH and/or LH)-containing maturation medium significantly enhanced oocyte nuclear maturation. Addition of NPS2390, a CASR antagonist, compromised oocyte nuclear maturation. Furthermore, increased cortical distribution and decreased expression of CASR was observed after the NPS R-568 treatment. Oocytes treated with NPS R-568 had higher concentration of CYCLIN B1, decreased reactive oxygen species, and increased glutathione levels, indicative of advanced cytoplasmic maturation. In contrast, NPS2390 treatment compromised oocyte cytoplasmic maturation. A higher blastocyst formation rate after parthenogenetic activation was observed when oocytes were matured in the presence of the CASR agonist, NPS R-568. MAPK3/1 phosphorylation was increased during in vitro maturation and after NPS R-568 treatment, and decreased following CASR antagonist supplementation. Taken together, our data showed that the CASR is a gonadotropin-regulated factor that promotes porcine oocyte maturation in a MAPK-dependent manner.

Characterization of the effects of metformin on porcine oocyte meiosis and on AMP-activated protein kinase activation in oocytes and cumulus cells

The adenosine monophosphate-activated protein kinase (AMPK) activators 5-aminoimidazole-4-carboxamide 1-β-d-ribofuranoside (AICAR) and metformin (MET) inhibit resumption of meiosis in porcine cumulus-enclosed oocytes. The objective of this study was to characterize the inhibitory effect of MET on porcine oocyte meiosis by: (1) determining the effects of an AMPK inhibitor and of inhibitors of signalling pathways involved in MET-induced AMPK activation in other cell types on MET-mediated meiotic arrest in porcine cumulus-enclosed oocytes; (2) determining whether MET and AICAR treatments lead to increased activation of porcine oocyte and/or cumulus cell AMPK as measured by phosphorylation of its substrate acetyl-CoA carboxylase; and (3) determining the effects of inhibition of the AMPK kinase, Ca2+/calmodulin-dependent protein kinase kinase (CaMKK), and Ca2+ chelation on oocyte meiotic maturation and AMPK activation in porcine oocytes and cumulus cells. The AMPK inhibitor compound C (CC; 1 μM) did not reverse the inhibitory effect of AICAR (1 mM) and MET (2 mM) on porcine oocyte meiosis. Additionally, CC had a significant inhibitory effect on its own. eNOS, c-Src and PI-3 kinase pathway inhibitors did not reverse the effect of metformin on porcine oocyte meiosis. The level of acetyl-CoA carboxylase (ACC) phosphorylation in oocytes and cumulus cells did not change in response to culture in the presence of MET, AICAR, CC, the CaMKK inhibitor STO-609 or the Ca2+ chelator BAPTA-AM for 3 h, but STO-609 increased the percentage of porcine cumulus-enclosed oocytes (CEO) that remained at the germinal vesicle (GV) stage after 24 h of culture. These results indicate that the inhibitory effect of MET and AICAR on porcine oocyte meiosis was probably not mediated through activation of AMPK.

The G protein coupled receptor 3 is involved in cAMP and cGMP signaling and maintenance of meiotic arrest in porcine oocytes

The arrest of meiotic prophase in mammalian oocytes within fully grown follicles is dependent on cyclic adenosine monophosphate (cAMP) regulation. A large part of cAMP is produced by the Gs-linked G-protein-coupled receptor (GPR) pathway. In the present study, we examined whether GPR3 is involved in the maintenance of meiotic arrest in porcine oocytes. Expression and distribution of GPR3 were examined by western blot and immunofluorescence microscopy, respectively. The results showed that GPR3 was expressed at various stages during porcine oocyte maturation. At the germinal vesicle (GV) stage, GPR3 displayed a maximal expression level, and its expression remained stable from pro-metaphase I (MI) to metaphase II (MII). Immunofluorescence staining showed that GPR3 was mainly distributed at the nuclear envelope during the GV stage and localized to the plasma membrane at pro-MI, MI and MII stages. RNA interference (RNAi) was used to knock down the GPR3 expression within oocytes. Injection of small interfering double-stranded RNA (siRNA) targeting GPR3 stimulated meiotic resumption of oocytes. On the other hand, overexpression of GPR3 inhibited meiotic maturation of porcine oocytes, which was caused by increase of cGMP and cAMP levels and inhibition of cyclin B accumulation. Furthermore, incubation of porcine oocytes with the GPR3 ligand sphingosylphosphorylcholine (SPC) inhibited oocyte maturation. We propose that GPR3 is required for maintenance of meiotic arrest in porcine oocytes through pathways involved in the regulation of cAMP and cGMP.

Short-term preservation of porcine oocytes in ambient temperature: novel approaches

The objective of this study was to evaluate the feasibility of preserving porcine oocytes without freezing. To optimize preservation conditions, porcine cumulus-oocyte complexes (COCs) were preserved in TCM-199, porcine follicular fluid (pFF) and FCS at different temperatures (4°C, 20°C, 25°C, 27.5°C, 30°C and 38.5°C) for 1 day, 2 days or 3 days. After preservation, oocyte morphology, germinal vesicle (GV) rate, actin cytoskeleton organization, cortical granule distribution, mitochondrial translocation and intracellular glutathione level were evaluated. Oocyte maturation was indicated by first polar body emission and spindle morphology after in vitro culture. Strikingly, when COCs were stored at 27.5°C for 3 days in pFF or FCS, more than 60% oocytes were still arrested at the GV stage and more than 50% oocytes matured into MII stages after culture. Almost 80% oocytes showed normal actin organization and cortical granule relocation to the cortex, and approximately 50% oocytes showed diffused mitochondria distribution patterns and normal spindle configurations. While stored in TCM-199, all these criteria decreased significantly. Glutathione (GSH) level in the pFF or FCS group was higher than in the TCM-199 group, but lower than in the non-preserved control group. The preserved oocytes could be fertilized and developed to blastocysts (about 10%) with normal cell number, which is clear evidence for their retaining the developmental potentiality after 3d preservation. Thus, we have developed a simple method for preserving immature pig oocytes at an ambient temperature for several days without evident damage of cytoplasm and keeping oocyte developmental competence.