Tissue distribution and levels of gene expression of three steroid hydroxylases in ovine fetal adrenal glands.

Northern blotting and hybridization histochemistry were used to evaluate the ontogeny and cellular distribution of the mRNAs of the cytochrome P-450 enzymes: cholesterol side-chain cleavage (P-450scc), 17 alpha-hydroxylase (P-450(17 alpha] and 21-hydroxylase (P-450c21) in 40 ovine fetal adrenals from 42 days of gestation until term (151 days). The genes for P-450(17 alpha) and P-450scc were expressed strongly in tissue from young (40-60 days) and old fetuses (120 days to term), but to a very minor degree in 90-120 day fetuses. P-450c21 showed a steady increase throughout gestation. In the morphologically immature an unzoned adrenal of the 40-50 day fetus there was some differentiation in gene expression, all cells containing P-450scc and P-450c21 but a few lacking P-450(17 alpha). Once morphological zonation had occurred (80 days), P-450(17 alpha) was confined to the fasciculata. After 120 days there was a radial maturation pattern of the fasciculata cells morphologically, adult-type cells first appearing at the medullary border. However, P-450(17 alpha) and P-450scc mRNAs were equally well expressed in all sections of the fasciculata. The conclusions were: 1) the previously demonstrated triphasic cortisol biosynthetic capacity of ovine fetal adrenals was correlated with the presence, absence, and reappearance of mRNAs P-450(17 alpha) and P-450scc; 2) morphological appearance of fetal adrenocortical cells and expression of three major steroidogenic enzyme genes were not correlated.