marmite defines a novel conserved neuropeptide family mediating nutritional homeostasis
Neuropeptides play a key role in regulating physiology and behavior, including feeding. While animals modify their food choices to respond to the lack of specific nutrients, the mechanisms mediating nutrient-specific appetites remain unclear. Here, we identified marmite (mmt), a previously uncharacterized Drosophila melanogaster gene encoding a secreted peptide that controls feeding decisions. We show that both mmt mutants and neuronal knockdown of mmt specifically increased the intake of proteinaceous food, whereas neuronal mmt overexpression reduced protein appetite. mmt expression is also higher in animals maintained on amino acid rich food, suggesting that mmt encodes a protein-specific satiety signal. Mmt is expressed in a small number of neurons in the adult nervous system, with a single pair of neurons modulating protein appetite. Finally, sequence and phylogenetic analysis showed that mmt is part of an ancient and conserved family of neuropeptides, including the poorly understood vertebrate neuropeptides B and W genes. Functional experiments showed that mmt and vertebrate NPB and NPW modulate food intake in both flies and mice. Therefore, we discovered an ancient family of neuropeptides involved in controlling feeding across phyla.