Identification of a proctolin preprohormone gene (Proct) of Drosophila melanogaster: expression and predicted prohormone processing.

Proctolin was the first insect neuropeptide to be sequenced and has been the subject of many physiological and pharmacological studies in insects and crustaceans. We have identified a Drosophila gene (CG7105, Proct) encoding a precursor protein containing the neuropeptide proctolin (RYLPT). In situ hybridization with a riboprobe to the Proct gene revealed a distribution of transcript in neurons of the larval central nervous system (CNS) matching that seen with antiserum to proctolin. An antiserum raised to a sequence in the precursor downstream of proctolin labeled the same neurons as those seen with the antiproctolin antisera. The predicted protein encoded by Proct has a single copy of the RYLPT sequence that directly follows the predicted signal peptidase cleavage point and precedes a consensus recognition site for a furinlike processing endoprotease. Ectopic expression of Proct in the CNS and midgut via the GAL4-UAS system, using an Actin5C-GAL4 driver, confirmed that the predicted preproproctolin can be processed to generate immunoreactive proctolin peptide. Pupae over-expressing Proct displayed a 14% increase in heart rate, providing evidence in support of a cardioacceleratory endocrine function for proctolin in Drosophila. The distribution of proctolin suggests roles as a neuromodulator in motoneurons and interneurons, and as a neurohormone that could be released from brain neurosecretory cells with terminations in the ring gland. Copyright 2003 Wiley Periodicals, Inc. J Neurobiol 58: 379-391, 2004