Characterization of hexamerin proteins and their mRNAs in the adult lubber grasshopper: The effects of nutrition and juvenile hormone on their levels

Abstract

The lubber grasshopper ( Romalea microptera) has three major hemolymph proteins with apparent sizes on native PAGE of 90, 270, and 500 kDa and subunit sizes (79, 81 and 82 kDa respectively) determined by SDS-PAGE . Trypsin fragments from each protein band were sequenced, used to design degenerate primers to amplify core cDNA fragments, which were extended by 5′ and 3′ RACE. All three cDNAs were closely related to insect hexamerins, had an N-terminal signal sequence, and their transcripts were found solely in the fat body. Adult females fed an ad libitum diet had their highest hexamerin levels on day 18 when oocytes begin rapid growth. Hexamerin levels fell as oocytes reached their maximum length on day 30. Animals fed a restricted diet had their highest hexamerin levels on day 30 which then fell as oocytes reached their maximum length on day 36. Hexamerin mRNA levels were only modestly different for animals on the two diets, indicating that nutrition affected translation of the hexamerin mRNA. Allatectomized animals treated with juvenile hormone III (JH) or methoprene caused the appearance of vitellogenin in the hemolymph, but had no effect on hexamerin levels. Thus, JH does not appear to directly regulate hexamerin production.