Activin, inhibin, and follistatin in zebrafish ovary: Expression and role in oocyte maturation

Activins, inhibins, and follistatins are important regulators of mammalian reproduction. However, their roles in lower vertebrates are poorly understo od. In this study, we examined the expression of activin A, inhihin A, and follistatins in the zebrafish ovary and determined their role in final oocy te maturation. Using reverse transcription-polymerase chain reaction with p rimers specific for activin/inhibin beta(A) subunit and for follistatins, w e detected DNA fragments of the expected size, which, upon sequencing, conf ormed to activin/inhibin beta(A) and follistatin, Western blot analysis usi ng an antibody against activin/inhibin beta(A) subunit revealed two bands w ith sizes similar to those of activin A and inhibin A. The expression of fo llistatins was also confirmed by Western blot analysis. These results Sugge st that activin A, an inhibin A-like molecule, and follistatins are express ed in the zebrafish ovary. In cultured zebrafish follicles, activin A and i nhibin A both induced final oocyte maturation in a dose-dependent manner. T he effects of activin A and inhibin A were blocked by their binding protein , follistatin-288. Interestingly, follistatin-288 also inhibited final oocy te maturation induced by gonadotropin and by maturation-inducing hormone (M IH), suggesting that activin A and/or inhibin A may be local regulators med iating gonadotropin- and MIH-induced final oocyte maturation. Taken togethe r, these findings suggest that activin A and inhibin A are paracrine regula tors of ovarian functions in fish.