Developmental profiles of the mRNAs for Manduca arylphorin and two other storage proteins during the final larval instar of Manduca sexta

Abstract

When fat body mRNA from the tobacco hornworm larva, Manduca sexta, was translated in a rabbit reticulocyte lysate system, three major polypeptides were found, each having a different developmental profile. One mRNA coded for a 74 kilodalton (K) polypeptide doublet precipitated by an antibody to the arylphorin (manducin). This mRNA was present only during the intermolt feeding phase of the penultimate and the final larval instars. Its appearance 16–24 hr after larval ecdysis was dependent upon the incoming nutrient supply and independent of the juvenile hormone (JH) level. Immunoblots of proteins of the fat body, epidermis, and cuticle revealed the presence of arylphorin in all three tissues. Additionally, several small polypeptides that cross-reacted with the arylphorin antibody were found in the fat body during and up to 24 hr after the last larval molt and in the tanning pupal cuticle. The larval epidermis was also found to contain a small amount of arylphorin mRNA. At the time of the JH decline prior to the onset of metamorphosis, a female-specific mRNA coding for a 79 K translation product appeared. In allatectomized larvae this mRNA was detectable earlier, and its appearance in intact larvae was prevented by application of methoprene, indicating that JH regulates its appearance. At wandering a new mRNA that also codes for a 79 K polypeptide appeared in both sexes and was the major messenger present during the prepupal stage. Neither it nor the female-specific mRNA were translatable after pupal ecdysis.