Developmental regulation of the larval hemolymph protein genes in Galleria mellonella.

Abstract

The role of juvenile hormone (JH) and 20-hydroxyecdysone (20-HE) in the stage-specific expression of the larval hemolymph protein (LHP) genes, Lhp82 and Lhp76, was investigated in the waxmoth, Galleria mellonella, larvae. Northern blot and dot hybridization analyses of total RNA in larvae that were undergoing an extralarval molt, induced either by cold shock or by application of JH to day-0 last instar larvae, showed that the last instar-specific Lhp82 transcripts were not present during this molt cycle. Lhp76 transcripts were, however, present transiently. During the course of an extralarval molt induced by JH in day-3 larvae both the transcripts were present but they were relatively less abundant than in the controls. JH had no effect on the relative abundance of the Lhp transcripts when applied to ligated day-3 or older larvae. By contrast, application of 20-HE either to intact or prothorax-ligated larvae of different developmental stages as well as to fat body in vitro resulted in a rapid decrease in the relative abundance of the Lhp transcripts. The natural decrease in the Lhp transcript levels that occurs in wandering and spinning last instar larvae was blocked in ligated larvae, probably due to deprivation of the source of the endogenous ecdysteroids. These observations suggest that ecdysteroids serve as the natural cue to turn off the Lhp genes at each molt and that JH blocks activation of only the last instar-specific Lhp82 gene.