Ontogeny of adrenal steroid hydroxylases: evidence for cAMP-independent gene expression

Abstract

Total RNA from normal and anencephalic human fetal adrenals was examined by blot analysis for transcripts encoding P-450 scc, P-450 11β P-450 17α P-450 c21 and adrenodoxin using bovine cDNA clones specific for these different enzymes. The specific contents of RNA encoding these components of the adrenocortical steroidogenic pathway were found to be similar in both types of adrenal tissue. Likewise, immunoblot analysis showed comparable concentrations of P-450 scc, P-450 17α and adrenodoxin protein to be present in adrenal tissues from normal and anencephalic human fetuses. Immunoblot analysis of homogenates of fetal sheep adrenals of increasing gestational age (85–145 days) showed constant levels of P-450 scc and P-450 11α, but increasing P-450 17α content, especially near term. Both sheep fetuses prior to 136 days gestational age and human anencephalic fetuses are known to have extremely low circulating levels of immunoreactive ACTH as well as very low adrenal adenylate cyclase activity. Thus, it is concluded that factors other than pituitary ACTH which operate independent of adenylate cyclase activation are required for the initial expression (imprinting) of steroid hydroxylase genes.