Reproductive stage-related effects of salmon GnRH and sex steroid hormones on expression of genes encoding fushi tarazu factor 1 homolog and estrogen receptor α in masu salmon pituitary cells in vitro

Expression of genes encoding gonadotropin (GTH) subunits in the salmon pituitary was regulated by salmon gonadotropin-releasing hormone (sGnRH) and sex steroid hormones in a reproductive stage-dependent manner, probably through DNA-binding transcription factors. Direct effects of these hormones on expression of genes encoding salmon fushi tarazu factor 1 homolog (sFF1-I) and estrogen receptor α (ERα) were therefore examined by use of primary pituitary cell cultures of masu salmon at different reproductive stages. Pituitaries were collected in March (before initiation of gonadal maturation), in May (early maturing), in July (late maturing), and in September (spawning period). Amounts of sFF1-I and ERα mRNAs in the pituitary cells were determined by real-time polymerase chain reactions after a treatment with sGnRH, estradiol-17β (E2), testosterone (T) or 11-ketotestosterone (11KT). The amounts of sFF1-I mRNA were elevated by E2 in the males, and by sGnRH and T in the females before initiation of gonadal maturation and at the early maturing stage. The amounts of ERα mRNA in the early maturing females were elevated by sGnRH. Effects of sGnRH were not significant at the late maturing and spawning stages. The amounts of ERα mRNA in the spawning males were halved by 11KT and E2, and those of sFF1-I and ERα mRNAs in the late maturing females were decreased by T and 11KT. These results indicated that responsiveness of sFF1-I and ERα genes to sGnRH and sex steroid hormones is seasonally variable in relation to reproductive stages. Expression of sFF1 and ERα genes should be stimulated at the early stages of gonadal maturation prior to increases in the amounts of GTH subunit mRNAs, while attenuated after the late maturing period when stored amounts of GTH subunit mRNAs reached near the maximum.