Action cascade of an insect gonadotropin, testis ecdysiotropin, in male Lepidoptera

Summary Testis sheaths from late last instar larvae and mid-developing pupae of Heliothis virescens and Lymantria dispar synthesize ecdysteroid in vitro. Gonadal ecdysteroid can stimulate the production of growth factors from the sheaths which, in turn, promote the growth and development of the genital tract. Ongoing basal synthesis is controlled by positive feedback to exogenous ecdysteroid; titers of this hormone approaching those of molting last instar larvae and developing pupae effect maximum synthesis. These findings suggest that circulating titers of ecdysteroid hormone promote gonadal ecdysteroidogenesis, and thus coordinate the actions of the gonads with metamorphic events in the whole animal. Synthesis of ecdysteroid by testes is initiated, however, by a brain neuropeptide, testis ecdysiotropin (TE). TE is a 21 amino acid peptide of molecular weight 2472 Da. TE boosts basal steroid synthesis by pupal testis sheaths as well. It acts primarily via Gi protein and second messengers diacyl glycerol a...