Characterization in relation to development of an ecdysteroid agonist-responsive cytochrome P450, CYP18A1, in Lepidoptera

Cytochrome P450 enzymes are involved in a number of steps in ecdysteroid (moulting hormone) homeostasis in insects. We report the cloning and characterization of an ecdysteroid agonist-responsive cytochrome P450, CYP18A1, from the cotton leafworm, Spodoptera littoralis. Northern blot analysis showed that the mRNA transcript was expressed at times of increasing ecdysteroid titre in final instar S. littoralis larvae and was induced by the ecdysteroid receptor agonist, RH-5992, in midgut and fat body. In addition, transcript expression was also detected in the prothoracic glands, a major ecdysteroid biosynthetic tissue, in both S. littoralis and the tobacco hornworm, Manduca sexta, at a time of increasing ecdysteroid titre. The exact significance of the temporal and spatial expression of CYP18A1 is unclear. The characterization of a P450 that is ecdysteroid agonist-responsive may provide a future target for exploitation in the development of novel insect control strategies.