Steroidogenic factor 1 and Dax-1 colocalize in multiple cell lineages: Potential links in endocrine development

Mutations of the orphan nuclear receptors, steroidogenic factor 1 (SF- 1) and DAX-1, cause complex endocrine phenotypes that include impaired adrenal development and hypogonadotrophic hypogonadism. These similar phenotypes suggest that SF-1 and DAX-1 act in the same pathway(s) of endocrine development. To explore this model, we now compare directly their sites of expression. In mouse embryos, SF-1 expression in the urogenital ridge and brain either preceded or coincided with Dax-1 expression, with coordinate expression thereafter in the adrenal cortex, testis, ovary, hypothalamus, and anterior pituitary. The striking colocalization of SF-1 and Dax-1 supports the model that they are intimately linked in a common pathway of endocrine development. The slightly earlier onset of SF-1 expression and its ability to bind specifically to a conserved sequence in the Dax-1 5'- flanking region suggested that SF-1 may activate Dax-1 expression. However, promoter activity of Dax-15'-flanking sequences did not require this potential SF-1-responsive element, and Dax-1 expression was unimpaired in knockout mice lacking SF-1, establishing that SF-1 is not required for Dax-1 gene expression in these settings. Although the precise mechanisms remain to be established and may be multifactorial, our results strongly suggest that these two orphan nuclear receptors interact in a common pathway of endocrine development.