Hormonal regulation and properties of a new group of basic hemolymph proteins expressed during insect metamorphosis

Two abundant basic proteins, and arylphorin, that are expressed during metamorphosis of Trichoplusia ni were isolated, their cDNAs cloned, and regulation of their expression assessed. According to the criteria of encoded protein sequence, positions of sequence coinitiation and cotermination, amino acid compositions, nonsex-specificity, and immunological analyses, the related yet distinct basic proteins do not correspond to any previously established group of insect proteins, each of which can be distinguished on the basis of such criteria, although they appear to be within the arthropod hemocyanin superfamily. The basic proteins can be separated under native isoelectric focusing conditions, indicating that they do not preferentially form heteromeric complexes under such conditions. While the transcripts for both basic proteins and a coexpressed acidic protein (Jones, G., Brown, N., Manczak, M., Hiremath, S., and Kafatos, F. (1990) J. Biol. Chem. 265, 8596-8602) appeared in both sexes on the day prior to ecdysteroid-driven metamorphic commitment, and persisted at high abundance for the next 24 h, the arylphorin mRNA appeared 1 day earlier and declined immediately after metamorphic commitment. The dynamics of suppression of the appearance and abundance of transcripts in response to maintenance of a high juvenile hormone titer was different for the acidic versus the two basic proteins. Another regulatory difference in response to juvenile hormone was shown by a decreased translatability of the mRNAs for the two basic proteins, but not for the acidic protein. In contrast, the abundance and translatability of arylphorin mRNA was insensitive to a high juvenile hormone level. A further difference in regulation was shown by the maintenance of a high level of both arylphorin and the acidic protein in the hemolymph after disappearance of their transcripts, while the basic proteins instead disappeared from the hemolymph and persisted in the fat body. These results establish at least three qualitatively different effects of juvenile hormone on the abundance of transcripts for these representatives of three groups in the hemocyanin superfamily, and also establish mRNA translatability as another differential level of regulation among them. Given these differences in mechanisms of regulation of evolutionarily related proteins, this system of metamorphosis-associated proteins in T. ni should prove to be a valuable tool in studies of mechanisms of hormonal regulation of gene expression during the metamorphic transformation of larval tissues.