Nicotinamide mononucleotide supplementation improves the quality of porcine oocytes under heat stress

Background:Elevated ambient temperature-caused heat stress is a major concern for livestock production due to its negative impact on animal feed intake,growth,reproduction,and health.Particularly,the germ cells are extremely sensitive to the heat stress.However,the effective approach and strategy regarding how to protect mammalian oocytes from heat stress-induced defects have not been determined.Methods:Germinal vesicle(GV)porcine oocytes were cultured at 41.5℃ for 24 h to induce heat stress,and then cultured at 38.5℃ to the specific developmental stage for subsequent analysis.Nicotinamide mononucleotide(NMN)was dissolved in water to 1 mol/L for a stock solution and further diluted with the maturation medium to the final concentrations of 10μmol/L,20μmol/L,50μmol/L or 100μmol/L,respectively,during heat stress.Immunostaining and fluorescence intensity quantification were applied to assess the effects of heat stress and NMN supplementation on the key processes during the oocyte meiotic maturation.Results:Here,we report that NMN supplementation improves the quality of porcine oocytes under heat stress.Specifically,we found that heat stress resulted in oocyte maturation failure by disturbing the dynamics of meiotic organelles,including the cytoskeleton assembly,cortical granule distribution and mitochondrial function.In addition,heat stress induced the production of excessive reactive oxygen species(ROS)and DNA damage,leading to the occurrence of apoptosis in oocytes and subsequent embryonic development arrest.More importantly,we validated that supplementation of NMN during heat stress restored the meiotic defects during porcine oocyte maturation.Conclusions:Taken together,our study documents that NMN supplementation is an effective approach to improve the quality of oocytes under heat stress by promoting both nuclear and cytoplasmic maturation.

Phosphorylation of histone H3 on Ser10 by auto-phosphorylated PAK1 is not essential for chromatin condensation and meiotic progression in porcine oocytes

Background： The p21-activated kinase 1 （PAK1）is essential of microtubule assembly during oocyte meiotic maturation porcine oocytes. for mitosis and plays an important role in the regulatio in mice; however, little is known about its role in Result： Total p21-activated kinase 1 （PAK1） and phosphorylated PAK1 at Thr423 （PAK1^Thr423） were consistently expressed in porcine oocytes from the germinal vesicle （GV） to the second metaphase （MII） stages, but phosphorylation of histone H3 at Serr10 （H3^ser10） was only expressed after the GV stage. Immunofiuorescence analysis revealed that PAK1Thr423 and H3^ser10 colocalized on chromosomes after the GV stage. Blocking of endogenous PAK1^Thr423 by injecting a specific antibody decreased the phosphorylation level of H3^ser10; however, it had no impact on chromatin condensation, meiotic progression, cleavage rate of blastomeres or the rate of blastocyst formation. Conclusion： Phosphorylation of PAK1^Thr423 is a spontaneous activation process and the activated PAK1^Thr423 can promote the phosphorylation of H3^ser10; however, this pathway is not required for meiotic maturation of porcine oocytes or early embryonic development.

Casein kinase 2 modulates the spindle assembly checkpoint to orchestrate porcine oocyte meiotic progression

Background:CK2(casein kinase 2)is a serine/threonine-selective protein kinase that has been involved in a variety of cellular processes such as DNA repair,cell cycle control and circadian rhythm regulation.However,its functional roles in oocyte meiosis have not been fully determined.Results:We report that CK2 is essential for porcine oocyte meiotic maturation by regulating spindle assembly checkpoint(SAC).Immunostaining and immunoblotting analysis showed that CK2 was constantly expressed and located on the chromosomes during the entire oocyte meiotic maturation.Inhibition of CK2 activity by its selective inhibitor CX-4945 impaired the first polar body extrusion and arrested oocytes at M I stage,accompanied by the presence of BubR1 at kinetochores,indicative of activated SAC.In addition,we found that spindle/chromosome structure was disrupted in CK2-inhibited oocytes due to the weakened microtubule stability,which is a major cause resulting in the activation of SAC.Last,we found that the level DNA damage as assessed byγH2A.X staining was considerably elevated when CK2 was inhibited,suggesting that DNA damage might be another critical factor leading to the SAC activation and meiotic failure of oocytes.Conclusions:Our findings demonstrate that CK2 promotes the porcine oocyte maturation by ensuring normal spindle assembly and DNA damage repair.

Screening high-quality fetal bovine serum for porcine oocyte maturation in vitro

Fetal bovine serum(FBS) is widely used in cell cultures due to its high stability and easy access. It was also used as a substitute for porcine follicular fluid(PFF) in previous studies. However, FBS components are unclear, and the presence of FBS in culture media may introduce a variation from batch to batch. This study aimed to establish an effective method to screen FBS in place of PFF in the culture media for porcine oocytes in vitro. We screened FBS from different sources by using porcine fetal fibroblast cells. The effects of six FBS samples on porcine fetal fibroblast cell growth were tested via frozen cell survival assay, cell clone formation assay, cell growth curve, and cell passage activity assay. The best serum that we called GFBS(heat-inactivated FBS, cat. no. 10500-64;Gibco) showed a similar effect on the maturation and development of porcine oocytes to that of PFF and can be used as a good substitute for PFF. These results suggested that the porcine fetal fibroblast cell culture test can be used as a valuable method to screen FBS for porcine oocyte maturation and embryonic development in vitro.

Effect of GPAG Supplement on Porcine Oocyte Maturation and Its Following Embryonic Development by Parthenogenetic Activated

The aim of this study was to compare the effect of GPAG and commonly used FCS on porcine oocyte maturation and subsequent embryonic development after the fertilization. COCs were aspirated from follicles and cultured for 16, 24, 32, 40 and 48 h in TCM-199 medium either with GPAG or FCS. After 24 h with GPAG, 89.4% of oocytes reached M Ⅰ stage while in the medium supplemented with FCS, only 27.7% of oocytes reached the same stage （P〈0.05）. Prolonged incubation for up to 32 h clearly demonstrated that some of oocytes cultured in GPAG medium were at M Ⅱ stage （35.7%）, few of oocytes from FCS medium were at M Ⅱ stage （7.5%） （P〈0.05）. Both groups of oocytes reached the same stage of maturation within 48 h. After 48 h of culture, the oocytes with extruded polar bodies were inseminated. Fertilized oocytes were cultured in PZM3 medium supplemented with 3 mg.mL of BSA. After 7 days, the development and the quality of embryos were evaluated. The results showed that the maturation of oocytes in the presence of GPAG significantly increased their subsequent developmental ability when compared with FCS supplementation （29.2% ： 18.9% of blastocysts, P〈0.05）. However, differential staining revealed that once blastocysts were formed in either group, they had the same total cell number （39 ： 38） and the ICM/total cell ratio （0.26 ： 0.28）

Resveratrol compares with melatonin in improving in vitro porcine oocyte maturation under heat stress

Background： Resveratrol, an important phyto-antioxidant commonly found in grapes, mulberry, and other plants,has a variety of functions including anti-aging, anti-cancer and anti-inflammatory activities. In the current study, we investigated the beneficial effects of resveratrol on in vitro porcine oocyte maturation under heat stress（HS）. The effect of resveratrol, melatonin and their combination on alleviating HS was compared according to the maturation rate of oocytes and the development competence of embryos after parthenogenetic activation（PA）.Results： Supplementation with resveratrol（2.0 μmol/L） not only improved the nuclear maturation but also raised the blastocyst rate of porcine embryos＇ PA from oocytes that underwent HS by increasing their glutathione（GSH）level, reducing reactive oxygen species（ROS） and up-regulating the expression of Sirtuin 1（SIRT1）. It was also found that melatonin（10^-7mol/L） and the combination of resveratrol（2.0 μmol/L） plus melatonin（10^-7mol/L） exhibited more potent effects than resveratrol alone regarding their protective activities on oocyte maturation under HS.Conclusions： This study compared the efficiencies of resveratrol, melatonin and their combination for protecting porcine oocytes from heat stress. The mechanisms are attributed to the fact that each treatment may have different ability to regulate the synthesis of steroid hormones and the expression of mature related genes.

Effective generation of maternal genome point mutated porcine embryos by injection of cytosine base editor into germinal vesicle oocytes

Cytosine and adenine base editors are promising new tools for introducing precise genetic modifications that are required to generate disease models and to improve traits in pigs. Base editors can catalyze the conversion of C→T(C>T) or A→G(A>G) in the target site through a single guide RNA. Injection of base editors into the zygote cytoplasm can result in the production of offspring with precise point mutations, but most F0 are mosaic, and breeding of F1 heterozygous pigs is time-intensive. Here, we developed a method called germinal vesicle oocyte base editing(GVBE) to produce point mutant F0 porcine embryos by editing the maternal alleles during the GV to MⅡ transition. Injection of cytosine base editor 3(BE3) mRNA and X-linked Dmdspecific guide RNAs into GVoocytes efficiently edited maternal Dmd during in vitro maturation and did not affect the maturation potential of the oocytes. The edited MⅡ oocytes developed into blastocysts after parthenogenetic activation(PA) or in vitro fertilization(IVF). However, BE3 may reduce the developmental potential of IVF blastocysts from 31.5%±0.8% to 20.4%±2.1%. There 40%–78.3% diploid PA blastocysts had no more than two different alleles, including up to 10% embryos that had only C>T mutation alleles. Genotyping of IVF blastocysts indicated that over 70% of the edited embryos had one allele or two different alleles of Dmd. Since the male embryos had only a copy of Dmd allele, all five(5/19) F0 male embryos are homozygous and three of them were Dmd precise C>T mutation. Nine(9/19) female IVF embryos had two different alleles including a WT and a C>T mutation. DNA sequencing showed that some of them might be heterozygous embryos. In conclusion, the GVBE method is a valuable method for generating F0 embryos with maternal point mutated alleles in a single step.