Expression of Steroidogenic Enzyme Genes in the Equine Feto-Placental Unit

The expression of equine cytochrome P450 aromatase gene (CYP19) in various tissues include placenta and fetal gonads were examined by reverse-transcription polymerase chain reaction (RT-PCR), in addition to northern blot analysis of cytochrome P450 steroid 17α-hydroxylase/C17-20 lyase gene (CYP17) and 3β-hydroxysteroid dehydrogenase Δ5-Δ4 isomerase gene (HSD3B). Prior to this, testicular expression of CYP19 mRNA in adolescence was confirmed by RT-PCR and successive sequencing. The successful amplification of RT-PCR and nucleotide sequence of the PCR products meant the equine testis expresses CYP19 mRNA. In the RT-PCR of the pregnancy samples, CYP19 was expressed only in the placenta and not in the fetal gonads. The equine fetal gonads, which express CYP17, should convert progestins into androgens to supply substrates for aromatization in placenta expressing CYP19. It is suggested that the fetal gonads are the major androgen source in equine gestations, and this function will not be affected by the fetal gender.