The results of the present study clearly demonstrate that activin A enhanced the developmental competence of bovine embryos to the morula and blastocyst stages when embryos were cultured under a gas atmosphere of 5% CO2: 5% 02:90% N2. In contrast, follistatin not only neutralized the development-enhancing effect of activin A added to medium but also impeded the developmental competence of embryos by itself. The development-enhancing effect of activin A and the development-impeding effect of follistatin were observed when embryos were exposed to these cytokines up to the third cell cycle of the embryos. ampicillin antibiotic
In our previous study, we found that activin A increased dose-dependently the percentages of zygotes that developed to blastocysts by 6-17% under a gas atmosphere of 5% CO2 in air. However, mSOF is optimized in the culture of bovine embryos under a low oxygen condition (5% O2) rather than under a gas atmosphere of 5% CO2 in air (20% 02) . When the oxygen tension was reduced to 5% in the present study, activin A increased dose-depen-dently the percentages of zygotes that developed to blastocysts by 25-41%. Although the mechanism by which oxygen concentration affects embryo development in vitro is not fully understood, in part, low oxygen tension may suppress the production of reactive oxygen species such as O2~ and H2O2 that cause lipid peroxidation and enzyme inactivation, resulting in cell damage in embryos. The mechanism by which activin A enhances embryo development is not clear. However, the action of activin A may differ from that of low oxygen tension, since activin A enhanced embryo development at oxygen tensions of both of 20% and 5%.