No abstract

An arthropod-specific peptidergic system, the neuropeptide designated here as natalisin and its receptor, was identified and investigated in three holometabolous insect species: Drosophila melanogaster, Tribolium castaneum, and Bombyx mori. In all three species, natalisin expression was observed in 3-4 pairs of the brain neurons: the anterior dorso-lateral interneurons, inferior contralateral interneurons, and small pars intercerebralis neurons. In B. mori, natalisin also was expressed in two additional pairs of contralateral interneurons in the subesophageal ganglion. Natalisin-RNAi and the activation or silencing of the neural activities in the natalisin-specific cells in D. melanogaster induced significant defects in the mating behaviors of both males and females. Knockdown of natalisin expression in T. castaneum resulted in significant reduction in the fecundity. The similarity of the natalisin C-terminal motifs to those of vertebrate tachykinins and of tachykinin-related peptides in arthropods led us to identify the natalisin receptor. A G protein-coupled receptor, previously known as tachykinin receptor 86C (also known as the neurokinin K receptor of D. melanogaster), now has been recognized as a bona fide natalisin receptor. Taken together, the taxonomic distribution pattern of the natalisin gene and the phylogeny of the receptor suggest that natalisin is an ancestral sibling of tachykinin that evolved only in the arthropod lineage.N europeptides are ancestral signaling molecules that function as cell-cell communication mediators in multicellular organisms. Large numbers of diverse neuropeptides are involved in the control of animal behavior, development, and physiology. Recent genomic approaches have revealed diverse groups of neuropeptides in different taxa, based on similarities in the amino acid sequences to neuropeptides discovered in earlier physiological and anatomical studies (1-4). Sequenced genomes of many insect species (5) provide an opportunity to explore the evolutionary processes of neuropeptides and their receptors. Furthermore, the tools available in biotechnology that are readily applicable in suitable insect model species have advanced our understanding of the functions of neuropeptides. Drosophila melanogaster has been the best model system, allowing functional studies of neuropeptides and their receptors by the use of highly advanced molecular genetic tools and various publicly available resources (6). A number of other insect species, especially those with sequenced genomes, such as Bombyx mori and Tribolium castaneum, also have been used for investigations into the functions of neuropeptide signals, using piggyBac transformation (7) and RNAi (8,9).Previous studies on insect neuropeptides and their G proteincoupled receptors (GPCRs) have described tachykinin-related peptides (TRPs) and two GPCRs as the receptors for the TRPs in D. melanogaster and other insect species (10-14). In vertebrates tachykinin and the TRPs form a group of ancestral neuropeptides that are found in a wide rang...