Ontogeny of steroidogenesis in the fetal sheep gonad

The aim of this study was to determine 1) the time of onset and cellular lo calization of gene expression for steroidogenic factor-1 (SF-1), steroidoge nic acute regulatory protein, 3 beta -hydroxysteroid dehydrogenase Delta (5 ),Delta (4) isomerase (3 beta -HSD), and the cytochrome P450 enzymes for ch olesterol side-chain cleavage (P450(scc)), 17 alpha -hydroxylase (P450(17 a lpha OH)), and aromatase (P450(arom)) during gonadal development; and 2) th e amount of progesterone, androstenedione, testosterone, and 17 beta -estra diol present in the fetal sheep gonad. Fetuses were collected on Days 24, 2 6, 28, 30, 32, 35, 40, 55, and 75 of gestation, and gene expression was det ermined by in situ hybridization. The steroid content of gonads collected o n Days 30, 35, 55, and 75 of gestation was determined by RIA. Developing go nads collected from both male and female fetuses were steroidogenically act ive around the time of morphological sexual differentiation. In the female, the steroidogenic cells were initially located at the boundary of the cort ex and medulla but become increasingly restricted to the mesonephric-derive d cell streams. In the male, once tubules were identifiable, steroidogenesi s was restricted to the interstitial regions. Interestingly, expression of both SF-1 and 3 beta -HSD was observed prior to morphological sexual differ entiation. In addition, expression of both of these genes was more widespre ad than the other genes in both males and females.