Quantitative analysis of fushi tarazu factor 1 homolog messenger ribonucleic acids in the pituitary of salmon at different prespawning stages

Steroidogenic factor 1 (SF-1) or Ad4BP is a member of the fushi tarazu fact or 1 (FTZ-F1) family and an orphan nuclear receptor that plays an important role in the hypothalamus-pituitary-gonadal axis and the adrenal cortex. Al though its critical role in the differentiation of adrenals, gonads, and pi tuitary gonadotropes has been well demonstrated, regulatory function of SF- 1 during sexual maturation is yet to be examined. To investigate the potent ial role of SF-1 in sexual maturation, expression of two salmon FTZ-F1 homo log 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 ma le fish was increased on the midway in the river, where the levels of gonad otropin alpha- and II beta -subunit mRNAs were increased. In maturing socke ye salmon, the expression of the sFF1-I gene was elevated in the mature mal e fish, but the administration of CnRH analog did not further enhance the e xpression. These results indicate that sFF1-I gene expression in the pituit ary is upregulated in maturing salmon, and this upregulation may not depend on GnRH.