AN E-BOX ELEMENT IS REQUIRED FOR THE EXPRESSION OF THE AD4BP GENE, A MAMMALIAN HOMOLOG OF FTZ-F1 GENE, WHICH IS ESSENTIAL FOR ADRENAL AND GONADAL DEVELOPMENT

Ad4BP, also known as SF-1, is a cell type-specific transcription facto r regulating all the steroidogenic P-450 genes, Recently, the targeted disruption of the mouse ftz-f1 gene encoding Ad4BP/SF-1 has establish ed its essential function in both adrenal and gonadal development and sexual differentiation. As an initial step toward understanding its ro le in the cascade of gene activations necessary for the differentiatio n of the steroidogenic tissues and the sex differentiation of the gona ds, we isolated and characterized the rat ad4bp gene. A sequence analy sis of the ad4bp gene revealed that another nuclear factor ELF was als o transcribed from the same gene by alternative promoter usage and spl icing. The promoter of the ad4bp gene showed activities in the steroid ogenic cells such as Y-1 adrenocortical cells and I-10 testicular Leyd ig cells when examined by transient transfection assays. Using deletio n analysis and site-directed mutagenesis, we identified a cis-element at the position from -82 bp to -77 bp in the 5'-upstream region, The c is-element was identical to the consensus E box element, which is the binding site for the basic-helix-loop-helix proteins, Gel mobility shi ft analyses revealed the amount of a binding factor to this E box in t he nuclear extract prepared from the rat testes attained a maximal lev el 1 week after birth and then decreased dramatically thereafter, and only trace amounts were detected in adult rats. In contrast, the bindi ng factor in the ovaries attained a maximal level just after birth and kept its level thereafter. These dimorphic expressions of the binding factor to the E box correlated well with those of Ad4BP, and thus sug gested that the expression of Ad4BP is transcriptionally regulated thr ough this E box element.