Embryos at the 2- to 4-cell stage did not develop in medium with cytochalasin D, indicating that actin filaments play an important role in embryo development.
The present study is the first detailed examination of morphology of pig embryos produced by IVM/IVF/IVD. Although 58.3% of cleaved embryos developed to the blastocyst stage under present conditions, the nuclear number in blastocysts was still low (less than one third of in vivo-derived blastocysts). We found that fragmentation was a major defect in these embryos. Fragmentation has also been frequently found in human embryos produced in vitro. Studies in the human suggest that the best possible reason for embryonic fragmentation is an inadequate culture environment in vitro. One in vitro culture condition differing from in vivo conditions is that the oxygen concentration is higher and, under such conditions, a higher concentration of reactive oxygen species (ROS) is produced in culture. Yang et al. found that fragmented blastomeres in human embryos had higher ROS than did normal embryos. proventil inhaler
High ROS is thought to increase membrane permeability and cause cell damage and DNA fragmentation. It may also inhibit or delay polymerization and depolymerization of actin filaments, inducing the cytoplasm and nucleus to divide asynchronously, which results in fragmentation or binucleation. Reduced oxygen strength has been used for IVM, IVF, and IVD in some mammals, and it seems superior to the concentration (20%) commonly used. However, Ma-chaty et al. cultured in vivo pig embryos for 4 days under two levels (5% vs. 20%) of oxygen and did not find beneficial effects on blastocyst development with a 5% oxygen concentration. It is possible that in vivo embryos collected from oviducts have already developed the ability to reduce ROS while in the oviducts, thus masking the effects of oxygen level on embryo development.