PRECURSOR POLYPROTEIN FOR MULTIPLE NEUROPEPTIDES SECRETED FROM THE SUBESOPHAGEAL GANGLION OF THE SILKWORM BOMBYX-MORI - CHARACTERIZATION OFTHE CDNA-ENCODING THE DIAPAUSE HORMONE PRECURSOR AND IDENTIFICATION OF ADDITIONAL PEPTIDES

Peptidergic neurons, which serve as source of various endocrine neurop eptides, were identified in the suboesophageal ganglion (SG) and brain of insects. In the silkworm Bombyx mori, SG is known to secrete two n europeptides, diapause hormone (DH) responsible for induction of embry onic diapause and pheromone biosynthesis-activating neuropeptide, whic h share a pentapeptide amide, Phe-Xaa-Pro-Arg-Leu-NH2 (Xaa = Gly or Se r), at the C terminus. We have isolated cDNA clones for DH from the cD NA library of SG by using oligonucleotide probes. The molecular charac terization of the cDNA reveals that the mRNA encodes an open reading f rame consisting of 192 aa residues in which the 24-aa DH peptide is lo calized at the N-terminal region just after the signal peptide. A homo logy search proposed that the cDNA encodes pheromone biosynthesis-acti vating neuropeptide and three other neuropeptides [alpha-, beta-, and gamma-SG neuropeptide (SGNP)] in the region following DH, all of which are flanked by possible tryptic cleavage sites and share the Phe-Xaa- Pro-Arg-Leu-Gly sequence at the C terminus. Northern hybridization ana lysis clearly showed that the gene expression was limited to SG. We ch emically synthesized alpha-, beta-, and gamma-SGNP and used them to id entify components in extracts of SG and to examine biological function s. Alpha- and gamma-SGNP were identified in extracts of SG, and the sy nthetic beta- and gamma-SGNP expressed weak DH activity. These results indicate that DH, along with four other neuropeptides, is generated f rom a common precursor polyprotein that is encoded by a single mRNA tr anscribed in neurosecretory cells of SG.