In vitro production (IVP) of porcine embryos facilitates research related to biotechnology and biomedicine. Even though many attempts have been made to optimize the IVP of porcine embryos, the outcome is still unsatisfactory compared to other species, such as mouse and cattle. The high incidence of polyspermic fertilization is one of the major causes lowering the overall efficiency of porcine IVF. The common procedure for fertilization in vitro involves the co-culture of both gametes in the medium drop, which increases sperm concentration and incidence of polyspermy. Therefore, the present study was carried out to increase the efficiency of porcine IVF by reducing polyspermy using a modified swim-up method. This method modifies conventional swim-up washing by placing oocytes directly at the time of washing. Porcine oocytes were aspirated from ovaries and matured. Sperm pellet was prepared in the tube and mature oocytes were placed on a cell strainer with 70-μm pore size (Falcon 2350) at the top of the tube. After fertilization, the oocytes were fixed and stained for examination. Also, the developmental potential of fertilized embryos was measured to evaluate for the feasibility of this method. While penetration rates were similar in both methods (86.67±2.36% to 83.33±1.36%), there was a significant reduction of polyspermy in the modified swim-up method (17.50±1.60%) compared to the control (44.1±3.70%) (P<0.05). Subsequent culture showed higher rate of blastocyst formation in the modified swim-up method (20.44±0.99%) than in the control (15.73±3.26%) (P<0.05), even though the difference was not significant. These results suggest that, by controlling the number of spermatozoa reaching the oocytes, porcine oocytes might be protected from polyspermy in vitro. Also, the developmental potential of the fertilized embryos using this method could be improved by increasing the pool of spermatozoa with better quality. Further optimization of the procedure is required to impliment this method in routine porcine IVF.
In somatic cell nuclear transfer, serum starvation is a widely used method to synchronize donor cells at the quiescent stage (Go) of the cell cycle. However, it has been shown that serum starvation during culture of mammalian cells could induce cell death via apoptosis by removing growth factors and increasing intracellular stress. Therefore, apoptosis caused by serum starvation in somatic cells could induce damages to nuclear DNA contributing to a lower efficiency of nuclear transfer. This study was performed to characterize apoptosis during serum starvation of bovine embryonic fibroblasts (BEFs) and to determine the effects of BEFs treated with apoptosis inhibitors on the development of bovine embryos after nuclear transfer. BEFs, collected from a fetus with a 3–4-cm crown-rump length, were cultured for 7 days in starvation medium consisting of Dulbecco's modified Eagle's medium containing 0.5% fetal bovine serum to induce quiescence. Cells were also placed in starvation medium containing the apoptosis inhibitors, β2-macroglobulin (broad-range protease inhibitor: MAC; 1.4 pM) and glutathione (GSH: reactive oxygen species scavenger; 2.0 mM). Apoptosis of serum starved BEFs with or without apoptosis inhibitors were analyzed morphologically with light and electron microscope, and biochemically using a TUNEL assay. Somatic cell nuclear transfer was performed by our standard procedure as follows. Bovine oocytes were matured in vitro and enucleated after 22 h. Nuclear donor cells were collected randomly before injection. The reconstructed embryos were placed into the fusion chamber in a solution containing 0.28 M mannitol and aligned manually. A double pulse of 1.8 kV/cm for 15 μs was used to fuse the cells and activate the embryos simultaneously. The fused embryos were cultured for 4 min in 5 μÂM ionomycin and 4 h in 2 mM 6-DMAP. Then, embryos were moved to culture media and cultured in 5% CO2 and 39°C in 100% humidity. Development of NT embryos was recorded at 120 h post NT (morulae) and 168 h (blastocysts) with experiments being repeated three times. Serum starved BEFs showed typical morphology of apoptotic cells such as chromatin condensation and membrane blebbing. Also, when stained for DNA fragmentation by TUNEL assay, 22.6% ofBEFs showed apoptosis, in contrast to 0.1% in actively growing cells. However, when BEFs were cultured with MAC and GSH, the proportions of apoptotic BEFs were greatly reduced, 6.0% and 2.1%, respectively. After nuclear transfer with BEFs, embryos reconstructed with BEF treated with apoptosis inhibitors showed significant improvement in in vitro development compared to the controls (Table 1). In conclusion, while there are a number of factors affecting the nuclear transfer procedure, damage to the donor nuclei by serum starvation is likely to reduce the efficiency of the procedure; the addition of apoptosis inhibitors could reduce this unnecessary damage to donor nuclei and result in improvement in the development of nuclear transferred embryos. Further experiments are needed to assess the effect of apoptosis inhibitors on improvement of overall nuclear transfer efficiency. Table 1. Development of bovine embryos nuclear transferred with embryonic fibroblasts treated with or without apoptosis inhibitors
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