Immunocytochemical Evidence for the Presence of Inhibin and Activin-like Proteins and Their Localization in Goldfish Gonads

Abstract

In previous studies, we have demonstrated that inhibin and activin are stimulatory to goldfish gonadotropin release. In the present study, the distribution of immunoreactive inhibin and activin subunits (α, β A, and β B) in goldfish gonads was examined with domain-specific antibodies against mammalian inhibin and activin subunits, using the avidin-biotin-peroxidase complex method. In the ovary, follicle cells surrounding the oocyte were heavily stained with anti-porcine β A and human β B subunits. The cytoplasm of previtellogenic oocytes, at all stages of the ovarian cycle, also showed strong reactions with anti-β A and β B. As ovarian recrudescence progressed, oocytes that started to accumulate cortical vesicles gradually lost their immunoreactivity, with the reaction intensity inversely proportional to the amount of cortical vesicles in the oocyte; when oocytes became full of cortical vesicles, the oocytoplasm was no longer immunoreactive to anti-β A and β B. The staining with antiporcine α subunit was similar to that with anti-β A and β B but the reaction intensity was weaker than that with anti-β A and β B. In the testis, the mature sperm in the tubular lumen exhibited a strong immunoreaction to anti-α antibody, while the interstitial tissue was completely negative. However, the immunoreactivities with anti-β A and β B in the testis were exclusively restricted to the interstitial tissues. These results provide evidence for the presence of inhibin and activin-like molecules in the goldfish and reveal the distribution of these molecules in the goldfish gonads.