Developmental Expression of Genes for the Stereoidogenic Enzymes P450scc (20,22-Desmolase), P450cl7 (17αHydroxylase/17,20-Lyase), and P450c21 (21-Hydroxylase) in the Human Fetus*

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Abstract
Fetal adrenal steroidogenesis is required for the production of placental estrogen, and fetal testicular steroidogenesis is required for the development of male external genitalia. We studied the ontogeny and tissue specificity of expression of the genes for three steroidogenic enzymes: P450scc (the cholesterol side-chain cleavage enzyme), P450cl7 (17αhydroxylase/17,20lyase), and P450c21 (21-hydroxylase) in the human fetus. RNA from fetal tissues was probed with homologous human P450scc, P450cl7, and P450c21 cDNAs cloned in our laboratory. At 20–21 weeksgestation, P450scc mRNA was most abundant in the adrenal, followed by testis, placenta, and ovary.P450cl7 mRNA was also most abundant in the adrenal, followed by testis and ovary, but was undetectable in the placenta. P450c21 mRNA was detected only in the adrenal. None of these mRNAs was detected in kidney, liver, spleen, intestine, or muscle Twenty—two fetal testis samples (13–25.8 weeks gestation) were studied. P450scc and P450cl7 mRNAs were most abundant at 14 –16 weeks and diminished to 35 and 19/ of their peak values, respectively, by 20–25.8 weeks. Ovarian P450scc and P450cl7 mRNAs were present, respectively, in only 6.2/ and 1.8/ of the maximum amount in the testis and did not vary detectably from 14.9 to 21.5 weeks gestation.The testicular and ovarian steroidogenic enzyme mRNA data correlate well with previously reported changes in gonadal steroidogenesis with gestational age. The presence of P450scc mRNA, but not P450cl7 mRNA, in the placenta indicates that the placenta is able to initiate the synthesis of some steroid hormones, but is not able to synthesize estrogen de novo. Since P450c21 was found only in the adrenal, the extraadrenal 21-hydroxylation of progesteroneto deoxycorticosterone, a common event in the fetus, is probably mediated by an erizyme(s) other than P450c21.

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