Sterol Regulation of Development and 20-Hydroxyecdysone Biosynthetic and Signaling Genes in Drosophila melanogaster

Ecdysteroids are crucial in regulating the growth and development of insects. In the fruit fly Drosophila melanogaster, both C(27) and C(28) ecdysteroids have been identified. While the biosynthetic pathway of the C(27) ecdysteroid 20-hydroxyecdysone (20E) from cholesterol is relatively well understood, the biosynthetic pathway of C(28) ecdysteroids from C(28) or C(29) dietary sterols remains unknown. In this study, we found that different dietary sterols (including the C(27) sterols cholesterol and 7-dehydrocholesterol, the C(28) sterols brassicasterol, campesterol, and ergosterol, and the C(29) sterols β-sitosterol, α-spinasterol, and stigmasterol) differentially affected the expression of 20E biosynthetic genes to varying degrees, but similarly activated 20E primary response gene expression in D. melanogaster Kc cells. We also found that a single dietary sterol was sufficient to support D. melanogaster growth and development. Furthermore, the expression levels of some 20E biosynthetic genes were significantly altered, whereas the expression of 20E signaling primary response genes remained unaffected when flies were reared on lipid-depleted diets supplemented with single sterol types. Overall, our study provided preliminary clues to suggest that the same enzymatic system responsible for the classical C(27) ecdysteroid 20E biosynthetic pathway also participated in the conversion of C(28) and C(29) dietary sterols into C(28) ecdysteroids.