P1 gene expression in Drosophila larval fat body: induction by various ecdysteroids

Using the developmental mutant ecd1, the biological activity of 20-hydroxyecdysone (20E) and 20E metabolites 3-dehydro-20-hydroxyecdysone (3D20E), 3-epi-20-hydroxyecdysone (3D20E), 3-epi-20-hydroxyecdysone-3-phosphate (20E'3P), 20,26-dihydroxyecdysone (20,26E), and 20-hydroxyecdysonoic acid (20Eoic) was tested for their ability to induce the transcription of the steroid-inducible gene P1 in the Drosophila larval fat body. 3D20E was the most efficient ecdysteroid in the initiation of P1 gene transcription therefore the formation of 3D20E and the 3-epimer could not be regarded as an inactivation pathway in Drosophila larvae. Formation of 20,26E and 20Eoic may be an inactivation pathway in this biological model.