Reverse physiology in Drosophila: identification of a novel allatostatin-like neuropeptide and its cognate receptor structurally related to the mammalian somatostatin/galanin/opioid receptor family

By using degenerate oligonucleotide primers deduced from the conserved regi ons of the mammalian somatostatin receptors, a novel G-protein-coupled rece ptor from Drosophila melanogaster has been isolated exhibiting structural s imilarities to mammalian somatostatin/ galanin/opioid receptors. To identif y the bioactive ligand, a 'reverse physiology' strategy was used whereby or phan Drosophila receptor-expressing frog oocytes were screened against pote ntial ligands. Agonistic activity was electrophysiologically recorded as in ward potassium currents mediated through co-expressed G-protein-gated inwar dly rectifying potassium channels (GIRK). Using this approach a novel pepti de was purified from Drosophila head extracts. Mass spectrometry revealed a n octapeptide of 925 Da with a sequence Ser-Arg-Pro-Tyr-Ser-Phe-Gly-Leu-NH2 reminiscent of insect allatostatin peptides known to control diverse funct ions such as juvenile hormone synthesis during metamorphosis or visceral mu scle contractions. Picomolar concentrations of the synthesized octapeptide activated the cognate receptor response mediated through GIRK1, indicating that we have isolated the 394-amino-acid Drosophila allatostatin receptor w hich is coupled to the Gi/Go class of G proteins.