MICE DEFICIENT IN THE ORPHAN RECEPTOR STEROIDOGENIC FACTOR-I LACK ADRENAL-GLANDS AND GONADS BUT EXPRESS P450 SIDE-CHAIN-CLEAVAGE ENZYME IN THE PLACENTA AND HAVE NORMAL EMBRYONIC SERUM LEVELS OF CORTICOSTEROIDS

The orphan nuclear receptor steroidogenic factor 1 (SF-1) is expressed in the adrenal cortex and gonads and regulates the expression of several P450 steroid hydroxylases in vitro. We examined the role of SF-1 in the adrenal glands and gonads in vivo by a targeted disruption of the mouse SF-1 gene. All SF-1-deficient mice died shortly after delivery. Their adrenal glands and gonads were absent, and persistent Mullerian structures were found in all genotypic males. While serum levels of corticosterone in SF-1-deficient mice were diminished, levels of adrenocorticotropic hormone (ACTH) were elevated, consistent with intact pituitary corticotrophs. Intrauterine survival of SF-1 deficient mice appeared normal, and they had normal serum level of corticosterone and ACTK, probably reflecting transplacental passage of maternal steroids. We tested whether SF-1 is required for P450 side-chain-cleavage enzyme (P450scc) expression in the placenta, which expresses both SF-1 and P450scc, and found that in contrast to its strong activation of the P450scc gene promoter in vitro, the absence of SF-1 had no effect on P450scc mRNA levels in vivo. Although the region targeted by our disruption is shared by SF-1 and by embryonal long terminal repeat-binding protein (ELF), a hypothesized alternatively spliced product, we believe that the observed phenotype reflects absent SF-1 alone, as PCR analysis failed to detect ELF transcripts in any mouse tissue, and sequences corresponding to ELF are not conserved across species. These results confirm that SF-1 is an important regulator of adrenal and gonadal development, but its regulation of steroid hydroxylase expression in vivo remains to be established.