ONTOGENY OF EXPRESSION OF THE GENES FOR STEROIDOGENIC ENZYMES P450 SIDE-CHAIN CLEAVAGE, 3-BETA-HYDROXYSTEROID DEHYDROGENASE, P450 17-ALPHA-HYDROXYLASE C-17-20 LYASE, AND P450 AROMATASE IN FETAL MOUSE GONADS

It is well known that fetal androgens are required for male sexual dif ferentiation, and it is thought that fetal ovaries are not steroidogen ically active. However, molecular details, such as which steroidogenic enzymes are present in fetal testes and which enzymes are absent in f etal ovaries, have not been established. The pattern of expression of the genes that encode four of the steroidogenic enzymes necessary for androgen and estrogen production was examined during fetal development in mouse gonads. Messenger RNA (mRNA) expression for cholesterol side -chain cleavage (P450scc), 3 beta P-hydroxysteroid dehydrogenaselase/D elta(5)-Delta(4)-isomerase (3 beta HSD), P450 17 alpha-hydroxylase/C-1 7-20 lyase (P450c17), and P450 aromatase (P450arom) was determined bef ore ovaries and testes were distinguishable (13 days postconception) a nd during sexual differentiation (15, 17, and 20 days postconception) using reverse transcriptase-polymerase chain reactions (RT-PCR). A PCR assay for Sry was used to determine gender on day 13. P450scc, 3 beta HSD, and P450c17 transcripts were detected at all ages in fetal teste s, indicating that mRNAs for the steroidogenic enzymes that are requir ed to convert cholesterol to androgens are present in the male gonad e ven before sexual differentiation. P450arom mRNA was detected in sever al fetal testes on day 17, but consistently observed on day 20. The ex pression of P450arom suggests the potential of fetal and neonatal test es to convert androgens to estrogens, In contrast, although B beta HSD mRNA was detected in several of the ovaries examined, the detection o f P450scc, P450c17, and P450arom transcripts was rare. These data sugg est that the absence of fetal ovarian steroid hormone production is th e result of lack of expression of at least three of the steroidogenic enzymes, P450scc, P450c17, and P450arom.