ACTION CASCADE OF AN INSECT GONADOTROPIN, TESTIS ECDYSIOTROPIN, IN MALE LEPIDOPTERA

Testis sheaths from late last instar larvae and mid-developing pupae o f Heliothis virescens and Lymantria dispar synthesize ecdysteroid in v itro. Gonadal ecdysteroid can stimulate the production of growth facto rs from the sheaths which, in turn, promote the growth and development of the genital tract. Ongoing basal synthesis is controlled by positi ve feedback to exogenous ecdysteroid; titers of this hormone approachi ng those of molting last instar larvae and developing pupae effect max imum synthesis. These findings suggest that circulating titers of ecdy steroid hormone promote gonadal ecdysteroidogenesis, and thus coordina te the actions of the gonads with metamorphic events in the whole anim al. Synthesis of ecdysteroid by testes is initiated, however, by a bra in neuropeptide, testis ecdysiotropin (TE). TE is a 21 amino acid pept ide of molecular weight 2472 Da. TE boosts basal steroid synthesis by pupal testis sheaths as well. It acts primarily via G(i) protein and s econd messengers diacyl glycerol and low calcium influx, resulting in stimulation of phosphokinase C. G(s) protein and its resultant messeng er, cyclic AMP, also play roles in activation and inhibition of ecdyst eroidogenesis. The interplay of controlling systems probably serves to fine tune a system essential to gonadal development and function.