CHOLESTEROL SIDE-CHAIN CLEAVAGE CYTOCHROME-P450 GENE-EXPRESSION IN THE PRIMITIVE GUT OF THE MOUSE EMBRYO DOES NOT REQUIRE STEROIDOGENIC FACTOR-1

In situ hybridization studies reveal novel sites of expression of chol esterol side-chain cleavage cytochrome P450 (P450scc) during murine em bryonic development. In addition to fetal adrenals and testes, P450scc transcripts localize in situ to the primitive gut and to a subset of unidentified cells in the dermal mesenchyme of embryonic skin. In the gut, transcripts are most abundant in luminal epithelia of the hindgut , which will form the colon. P450scc transcript abundance at these nov el sites is a fraction of that in fetal adrenals or testes, suggesting a local rather than an endocrine function. Immunocytochemical analyse s localize P450scc protein to the fetal hindgut, indicating that the t ranscripts are translated in vivo. RNA isolated from microdissected em bryonic hindgut and skin was reverse transcribed and amplified by poly merase chain reaction. DNA sequence analyses of polymerase chain react ion products confirmed that specific hybridization in situ represents authentic P450scc gene (Cyp11A) transcripts and that 3P-hydroxysteroid dehydrogenase/Delta(5) --> Delta(4)-isomer ase transcripts are also p resent, demonstrating the potential of these fetal tissues to produce pregnenolone and progesterone. P450scc transcripts are also detectable by in situ hybridization in primitive gut and skin of Fushi tarazu fa ctor 1 null mice, which lack the nuclear receptor steroidogenic factor 1, proving that steroidogenic factor 1 is not required for steroid hy droxylase gene expression at these sites. The capacity for C21 steroid biosynthesis in primitive gut and skin during organogenesis raises th e question whether local production of steroid hormones may be require d for normal cellular growth and differentiation of these tissues duri ng embryogenesis.