ACTIVIN-A AND FOLLISTATIN REGULATE DEVELOPMENTAL COMPETENCE OF IN-VITRO-PRODUCED BOVINE EMBRYOS

The effects of activin A and/or follistatin on the development of bovi ne embryos were investigated. Presumptive zygotes matured and fertiliz ed in vitro were cultured in a chemically defined medium (modified syn thetic oviduct fluid medium; mSOF). Addition of 1-100 ng/ml of activin A to mSOF significantly increased the percentage of zygotes that deve loped to morulae and blastocysts (48-54% and 31-41%, respectively) com pared with no addition (41% and 25%, respectively). In contrast, addit ion of 1-100 ng/ml follistatin significantly reduced the percentage of zygotes developing to morulae and blastocysts (29-31% and 17-20%, res pectively) compared with no addition (41% and 28%, respectively). In a culture with 10 ng/ml of activin A, supplementation with the same con centration of follistatin neutralized the positive effect of activin A , while supplementation with 100 ng/ml of follistatin reduced the perc entage of zygotes that developed. The total cell numbers in morulae an d blastocysts were not affected by the addition of activin A and/or fo llistatin. The development-enhancing effects of activin A and the deve lopment-impeding effects of follistatin were observed when embryos wer e exposed to activin A or follistatin at a concentration of 10 ng/ml p rior to the 9- to 16-cell stage. These results suggest that activin A and follistatin may affect bovine embryos until the third cell cycle a nd may play important roles in regulation of the developmental compete nce of bovine embryos.