Sex- and age-related variation in neurosteroidogenic enzyme mRNA levels during quail embryonic development

Brain can synthesize steroids de novo from cholesterol and this biochemical feature is a conserved property of vertebrates. There is growing evidence indicating that neurosteroids might participate in sexual differentiation of the brain. Therefore, in this study we investigated the presence, the sex differences, and the development-dependent variation of mRNAs coding for key neurosteroidogenic enzymes, namely cytochrome P450 side-chain cleavage enzyme (P450scc), 3β-hydroxysteroid-dehydrogenase/Δ5-Δ4-isomerase (3β-HSD), cytochrome P450 17α-hydroxylase/c17, 20-lyase (P450c17), and aromatase in embryonic prosencephali. Our results indicated that 3β-HSD mRNA levels were sexually dimorphic and developmental age-dependent. In particular, 3β-HSD mRNA levels were higher in females than in males at E7, whereas, this dimorphism was reversed at E9 and E15. In females, the relative levels of 3β-HSD mRNA were highest at E7, whereas, in males they were significantly higher at E9 and E15 than at E7 and at E11. This sexual dimorphism was a peculiar feature of the prosencephalon, it could not be observed before gonadal sexual differentiation and it was not paralleled by a dimorphism in the brain content of progesterone. The level of mRNA coding for P450scc and for P450c17 did not show obvious developmental- or sex-related variation. Aromatase mRNA varied as a function of the embryonic age but not of the sex. These results, taken together, are suggestive of a potential role of some neurosteroidogenic enzymes in the development of quail brain and suggest that sexual differences in the hormonal environment may occur during brain development.