c-fos activity in Rana esculenta testis: Seasonal and estradiol-induced changes

Estradiol-17 beta (E-2) is suspected to exert a role in the regulation of t esticular activity. Using a nonmammalian vertebrate model (the frog, Rana e sculenta), we have investigated whether c-fos activity is detectable in the testis during the annual sexual cycle and whether E-2 exerts a regulatory role on spermatogenesis through fos activity. FOS protein is available in t esticular nuclear extracts (about 60 kDa) and, surprisingly, also in cytoso lic extracts (about 60, 80, and 100 kDa). Estradiol induces primary spermat ogonia (ISPG) proliferation [this effect is counteracted by antiestrogens ( Tamoxifen and ICI 182-780)] and FOS appearance in testicular cytosolic extr acts as well as c-fos transcription. Also, this effect is counteracted by I CI 182-780. Interestingly, the number of FOS immunopositive nuclei of ISPG strongly increases after E-2 treatment, whereas a great increase of immunop ositivity in the cytoplasm of ISPG is observed with the contemporaneous tre atment with antiestrogens. In conclusion, our results demonstrate that E-2 induces ISPG multiplication in the frog, R, esculenta, and, for the first time in a vertebrate species , that it triggers c-fos activity in the testis. Moreover, E-2 may be invol ved in mechanisms related to FOS transport in the nucleus of ISPG to induce the mitotic activity.