GENE-REGULATION OF STEROIDOGENESIS

The biosynthesis of various steroid hormones in animal tissues are cat alyzed by six forms of cytochrome P450 and two hydroxysteroid dehydrog enases. The tissue-specific expression of these enzymes, which are und er the control of the pituitary gland and mainly regulated at the tran scriptional level, determines the steroidogenesis of animal tissues. A nalysis of the promoter regions of the steroidogenic P450 genes reveal ed various cis-acting elements, including cAMP-responsive sequences (C RS), Ad4, and CC-rich sequences, which were needed for the tissue-spec ific and cAMP-dependent expression of the genes. Some of the nuclear p rotein factors binding to the cis-acting elements were isolated and ch aracterized. A zinc-finger protein binding to Ad4, which was termed Ad 4BP or SF-1, seems to be of particular importance in steroidogenesis. Ad4BP was expressed in the cells of the steroidogenic tissues, adrenal gland and gonadal tissues, in the rat fetus prior to the expression o f steroidogenic P450s, and remained expressed only in steroidogenic ce lls in adult animals. Close investigation of the temporal and spacial expression of Ad4BP in the fetal tissues suggested its role in the dif ferentiation of the steroidogenic tissues and the sex determination of the gonadal tissues.