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Steroidogenic factor 1 (SF-1) or Ad4BP is a member of the fushi tarazufactor 1 (FTZ-F1) family and an orphan nuclear receptor that plays an important role in the hypothalamus-pituitary-gonadal axis and the adrenal cortex. Although its critical role in the differentiation of adrenals, gonads, and pituitary gonadotropes has been well demonstrated, regulatory function of SF-1 during sexual maturation is yet to be examined. To investigate the potential role of SF-1 in sexual maturation, expression of two salmon FTZ-F1 homolog genes, sFF1-I and sFF1-II, was examined in the pituitaries of chum and sockeye salmons, using specific and sensitive RNase protection assays. Only sFF1-I mRNA was found in the pituitary and other organs, such as the ovary, spleen, liver, brain, and skeletal muscle. In chum salmon during upstream migration from the bay to the hatchery, the level of sFF1-I mRNA in the male fish was increased on the midway in the river, where the levels of gonadotropin α- and IIβ-subunit mRNAs were increased. In maturing sockeye salmon, the expression of the sFF1-I gene was elevated in the mature male fish, but the administration of GnRH analog did not further enhance the expression. These results indicate that sFF1-I gene expression in the pituitary is upregulated in maturing salmon, and this upregulation may not depend on GnRH.

Previous studies have shown that estrogen plays an important role in sex change of protogynous honeycomb grouper, and that the treatments with aromatase inhibitor (AI) cause estrogen depletion and complete sex inversion of pre-spawning females into functional males. In the present study, we examined whether AI causes sex inversion of sexually immature females. Female honeycomb groupers were implanted with various doses of Fadrozole (0, 100, 500 and 1000 µg/fish) in the non-breeding season, and resultant changes in the gonadal structures and the plasma levels of sex steroid hormones (estradiol-17 ß, E2; testosterone, T; 11-ketotestosterone, 11-KT) were examined three months after implantation. Vehicle-implanted groups did not change sex, while 100 and 500 µg AI-implanted groups had turned into transitionals with intersex gonad. In contrast, the highest dose receiving group exhibited both transitional and male phases. Transitional phase gonad had atretic oocytes and spermatogenic germ cells at the late stages of spermatogenesis, while male phase testis contained spermatozoa accumulated in the seminiferous tubules. All males released sperm upon slight pressure on the abdomen. In the AI-implanted fish, plasma levels of E2 decreased in a dose-dependent manner, while the levels of 11-KT were high in the highest dose receiving group. Present results suggest that estrogen plays an important role in sex change of protogynous honeycomb grouper, and that treatments with AI potentially inhibits endogenous E2 production in vivo, causing oocyte degeneration and subsequently the sex inversion from female to male. The Fadrozole could be an important tool for manipulating the sex of hermaphrodite fishes. [ABSTRACT FROM AUTHOR]