Although the production of activins, inhibins, and FS by the ovary has been well documented in mammals, very little has been done in fish. The present study is the first one in fish to detect the intact molecules of activin, inhibin, and FS. RT-PCR experiments and subsequent sequencing demonstrated that activin/inhibin pA subunit mRNA and FS mRNA are expressed in the zebrafish ovary. Since PCR products were obtained only from the cDNA sample, but not from the corresponding RNA or the control without added cDNA, the possibility of genomic DNA or cross contamination can be ruled out. Western blot analysis with an antibody directed against rh-activin/inhibin pA revealed several bands with molecular sizes similar to those of activin and inhibin from the zebrafish ovary. The 26-kDa band may represent activin A or activin A/B, while the 32-kDa band may be the fish homologue of inhibin A. The expression of pA mRNA and the detection of a 26-kDa pA immunoreactive molecule strongly suggest that ac-tivin A is produced by the zebrafish ovary. However, since the expression of a subunit has not been examined, the true identity of the 32-kDa inhibin A-like molecule requires further investigation. The detection of activin A and an inhibin A-like molecule in the zebrafish ovary is in agreement with previous studies in the goldfish. Using immunocytochem-istry, Ge et al. showed the expression of a, (3A, and pB subunits in goldfish follicular cells and oocytes, suggesting that activin- and inhibin-like molecules may be produced by the ovary.
In mammals, several molecular forms of FS have been characterized, which are derived from alternative splicing of the FS gene, proteolytic cleavage, and variable gly-cosylations. In the present study, we observed several FS-immunoreactive molecules with molecular sizes ranging from 30 to 50 kDa. Although only the truncated form of FS has been cloned, Northern blot analysis revealed two transcripts. These results, together with the detection of multiple bands from proteins extracted from ze-brafish ovary, suggest that, similar to the case in mammals, multiple forms of FS are present in fish.