Arguments for two distinct gonadotropic activities triggered by different domains of the ovary maturating parsin of Locusta migratoria

To complete previous results concerning the role of the ovary maturating pa rsin of Locusta migratoria (Lom OMP), we determined, by an enzyme immunoass ay, the liters of circulating ecdysteroids and analyzed circulating vitello genin (Vg) and oocyte growth following (1) suppression of 20 hydroxyecdyson e (20E) and (2) injection of the Lom OMP, either as an entire molecule in a llatectomized adults or as smaller peptides in allatectomized fifth-instar larvae females. Titers of ecdysteroids appeared unrelated to che presence o f circulating Vg but increased during the first phase of vitellogenesis and injection of OMP accelerated the occurrence of circulating 20E. Neverthele ss, immunoneutralization of 20E at the beginning of adult life delayed bur: did not prevent rapid oocyte growth contrary to immunoneutralization of Lo m OMP suggesting an additive gonadotropic effect of the neurohormone. disti nct from that of 20E. Of two synthetic peptides corresponding to the C- and N-terminal gonadotropic domains of the OMP. respectively, only the C-termi nal peptide was able to induce Vg in allatectomized larvae. After metamorph osis, injection of OMP did not induce Vg in adults allatectomized at the be ginning of imaginal life but improved the maintenance of circulating Vg in adults allatectomized after Vg appeared in the haemolymph. This result sugg ests that OMP either delays the Vg mRNA decay or increases the translation of Vg mRNA. Thus, Lom OMP appears to have two distinct roles: an ecdysteroi dogenic effect triggered by its C-terminal domain with the ovary as the tar get tissue and a protecting effect an Vg mRNA probably triggered by its oth er gonadotropic domain, the N-terminal, with the fat body as the target tis sue. (C) 1998 Elsevier Science Ltd. All rights reserved.