Expression of the P450 side-chain cleavage and adrenodoxin genes begins during early stages of adrenal cortex development.

The steroid hormone products of the fetal adrenal cortex play an essential role in normal maturation of several organ systems during fetal development. In addition, adrenal steroids appear to play a local role in the establishment and maintenance of the chromaffin cells of the adrenal cortex. Despite these developmental roles of cortical steroids, little is known about when the cells of the fetal rat adrenal cortex begin to undergo biochemical differentiation into cells capable of producing steroid hormones and whether the timing of developmental changes in cortical properties is related to chromaffin cell differentiation. To investigate these problems, in situ hybridization and immunocytochemistry were used to examine the ontogeny of expression of both the P450 side-chain cleavage (P450scc) and adrenodoxin genes during rat development. Transcripts from both genes (but not P450c17) and the respective proteins encoded by them were detected specifically in the cells of the presumptive cortex as early as embryonic day 12 (e12), which is several days before the layered architecture of the adrenal cortex is established and the earliest age at which biochemical differentiation of these cells has been detected. The spatial and temporal expression patterns for both genes were similar over the period examined (e12-e16.5), and no heterogeneity of expression was observed among cortical cells. In addition, significant increases in the accumulation of P450scc and adrenodoxin mRNA transcripts occurred during the midgestational period, when the synthesis and secretion of ACTH from the fetal pituitary are increasing.(ABSTRACT TRUNCATED AT 250 WORDS)