The drosulfakinin 0 (DSK 0) peptide encoded in the conserved Dsk gene affects adult Drosophila melanogaster crop contractions.

We report that the drosulfakinin 0 (DSK 0; NQKTMSFNH2) structure and genomic organization are conserved. The DSK 0 C-terminus, SFNH2, is widely distributed in the animal kingdom suggesting it defines a novel peptide family. We also report the first description of DSK 0 activity. DSK 0, I (DSK I, FDDYGHMRFNH2), and II (DSK II, GGDDQFDDYGHMRFNH2) are encoded in sulfakinin (Dsk). Drosophila erecta, Drosophila sechellia, Drosophila simulans, and Drosophila yakuba shared 62.5-87.5% identity to Drosophila melanogaster DSK 0; Drosophila pseudoobscura shared 37.5% identity; numerous amino acids were one nucleotide different from a corresponding residue in D. melanogaster. DSK I and II were identical among the drosopholids. DSK 0 proteolytic processing sites were RR except D. yakuba contained KR and D. pseudoobscura contained HR, one nucleotide different from RR. DSK I and II processing sites were identical among the drosopholids. We established DSK 0 decreased adult (EC50=237nM and R(2)=0.941), but not larval gut contractions. DSK 0 exists in the central nervous system including the subesophageal ganglion and an abdominal ganglion. Peptide and genomic conservation, activity, and spatial and temporal distribution support the conclusion that DSK 0 plays diverse biological roles in drosopholids including regulating gut muscle contraction.

The structure of the FMRFamide receptor and activity of the cardioexcitatory neuropeptide are conserved in mosquito.

Numerous peptides are structurally related to the cardioexcitatory tetrapeptide FMRFamide. One subgroup of FMRFamide-related peptides (FaRPs) contains an FMRFamide C terminus. Searches of the Drosophila melanogaster genome database identified the first invertebrate FMRFamide G-protein coupled receptor (GPCR), DrmFMRFa-R (Cazzamali and Grimmelikhuijzen, Meeusen et al., 2002). In order to explore molecular mechanisms involved in FMRFamide signal transduction we identified a receptor from the malaria mosquito Anopheles gambiae genome (Holt et al., 2002), AngFMRFa-R, and compared its structure to DrmFMRFa-R. The cytoplasmic loops, extracellular loops, and transmembrane regions are highly conserved between these two FMRFamide receptors. Another subgroup of FaRPs is the sulfakinins which are represented by the consensus structure -XDYGHMRFamide, where X is D or E (Nichols, 2003). We compared AngFMRFa-R and DrmFMRFa-R to the A. gambiae sulfakinin receptors, ASK-R1 and ASK-R2 ( Duttlinger et al., 2003), and the D. melanogaster sulfakinin receptors, DSK-R1 and DSK-R2 Brody and Cravchik, 2000; Hewes and Taghert, 2001 ). The cytoplasmic loops, extracellular loops, and the transmembrane regions are not highly conserved between the FMRFamide and sulfakinin receptors. In order to explore the role of FMRFamide in mosquito biology we measured the effect of the tetrapeptide on in vivo heart rate. The tetrapeptide increased the frequency of spontaneous contractions of the larval mosquito heart and, thus, increased heart rate. These data support the conclusion that the structure of the FMRFamide receptor and activity of the cardioexcitatory FMRFamide neuropeptide are conserved in mosquito.

The different effects of three Drosophila melanogaster dFMRFamide-containing peptides on crop contractions suggest these structurally related peptides do not play redundant functions in gut.

A Drosophila melanogaster dFMRFamide gene product, TPAEDFMRFamide, decreased crop contractions. However, DPKQDFMRFamide and SDNFMRFamide, also encoded in dFMRFamide, did not affect crop motility, which suggests these peptides are not functionally redundant in the crop and their unique N-terminal structures are important for activity. TPAEDFMRFamide-specific antisera did not stain the crop, which suggests it acts as a hormone. TDVDHVFLRFamide (DMS), encoded in D. melanogaster myosuppressin, stops crop contractions. TPAEDFMRFamide and DMS each contains a RFamide C-terminus; however, their effects on crop contractions differ, which suggests that unique receptors or different ligand:receptor binding requirements exist for these structurally related peptides.