Cloning and identification of an oxytocin/vasopressin-like receptor and its ligand from insects

Abstract

However, no similar peptide could be identified in other insects, nor could its prohormone be cloned, or its physiological actions be established. Here, we report that the recently sequenced genome from the red flour beetle Tribolium castaneum contains a gene coding for an oxytocin/vasopressin-like peptide, identical to the locust peptide, which we named inotocin (for insect oxytocin/vasopressin-like peptide) and a gene coding for an inotocin G protein-coupled receptor (GPCR). We cloned the Tribolium inotocin preprohormone and the inotocin GPCR and expressed the GPCR in CHO cells. This GPCR is strongly activated by low concentrations of inotocin (EC50, 5 ؋ 10 ؊9 M), demonstrating that it is the inotocin receptor. Quantitative RT-PCR (qPCR) showed that in adult Tribolium, the receptor is mainly expressed in the head and much less in the hindgut and Malpighian tubules, suggesting that the inotocin/receptor couple does not play a role in water homeostasis. Surprisingly, qPCR also showed that the receptor is 30؋ more expressed in the first larval stages than in adult animals. The inotocin/receptor couple can also be found in the recently sequenced genome from the parasitic wasp Nasonia vitripennis but not in any other holometabolous insect with a completely sequenced genome (12 Drosophila species, the malaria mosquito Anopheles gambiae, the yellow fever mosquito Aedes aegypti, the silk worm Bombyx mori, and the honey bee Apis mellifera), suggesting that this neuropeptide system is confined to basal holometabolous insects. Furthermore, we identified an oxytocin/ vasopressin-like peptide and receptor in the recently sequenced genome from the water flea Daphnia pulex (Crustacea). To our knowledge, this is the first report on the molecular cloning of an oxytocin/vasopressin-like receptor and its ligand from arthropods.inotocin ͉ neuropeptide ͉ GPCR ͉ evolution ͉ reproduction

Discovery of a Novel Insect Neuropeptide Signaling System Closely Related to the Insect Adipokinetic Hormone and Corazonin Hormonal Systems

“…11) and confirms earlier observations that insects easily can duplicate or abandon hormonal systems (5,8,9,16). We have seen this phenomenon, for example, for the corazonin hormonal system that is widespread, but does not occur in Coleoptera (9), and for the recently discovered inotocin system that does occur in Coleoptera but is absent in Diptera, Lepidoptera, and some Hymenoptera (16). Fig.…”

“…All vertebrates, for example, have an oxytocin-and a vasopressin-like peptide. In mammals, there are one oxytocin and three vasopressin (V1a, V1b, and V2) receptors, and these GPCRs are structurally closely related (16). Also, the oxytocin and vasopressin peptides are structurally very similar, as are their preprohormones each of which contains a similar neurophysin part characterized by seven cystine bridges (16).…”

“…8 illustrates in more detail how common neurohormone receptor gene duplications and losses are in holometabolous insects. This figure shows five receptor types, the AKH, ACP, corazonin, inotocin, and crustacean cardioactive peptide (CCAP) receptors (2,6,7,16,31). These five receptor types form a distinct branch in phylogenetic tree analyses of insect neuropeptide receptors (8,9), suggesting that they have a common evolutionary origin.…”

“…In mammals, there are one oxytocin and three vasopressin (V1a, V1b, and V2) receptors, and these GPCRs are structurally closely related (16). Also, the oxytocin and vasopressin peptides are structurally very similar, as are their preprohormones each of which contains a similar neurophysin part characterized by seven cystine bridges (16). Within its range of physiological concentrations, oxytocin does not activate the vasopressin receptors, and vice versa vasopressin does not activate the oxytocin receptor (25,26), so they are, like the insect ACP, AKH, and corazonin systems, independent hormonal systems that can co-exist without direct interference.…”

“…being small cyclic neuropeptides with no sequence homologies to the AKHs, ACPs, and corazonins (1,16,17). Some insects such as the 12 Drosophila species with a sequenced genome and the honeybee have only one AKH, one corazonin, and one CCAP receptor, whereas they have lost the ACP and inotocin systems ( Fig.…”