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 factor regulating all the steroidogenic P-450 genes, Recently, the targeted disruption of the mouse ftz-f1 gene encoding Ad4BP/SF-1 has established its essential function in both adrenal and gonadal development and sexual differentiation. As an initial step toward understanding its role in the cascade of gene activations necessary for the differentiation of the steroidogenic tissues and the sex differentiation of the gonads, we isolated and characterized the rat ad4bp gene. A sequence analysis of the ad4bp gene revealed that another nuclear factor ELF was also transcribed from the same gene by alternative promoter usage and splicing. The promoter of the ad4bp gene showed activities in the steroidogenic cells such as Y-1 adrenocortical cells and I-10 testicular Leydig cells when examined by transient transfection assays. Using deletion 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 cis-element was identical to the consensus E box element, which is the binding site for the basic-helix-loop-helix proteins, Gel mobility shift analyses revealed the amount of a binding factor to this E box in the nuclear extract prepared from the rat testes attained a maximal level 1 week after birth and then decreased dramatically thereafter, and only trace amounts were detected in adult rats. In contrast, the binding 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 suggested that the expression of Ad4BP is transcriptionally regulated through this E box element.