In animals, sensing nutrient status is an important input in controlling growth via regulation of insulin signalling. Drosophila gustatory receptors (Gr), which are expressed in sensory neurons known as gustatory receptor neurons (GRNs), detect nutritional and environmental cues, but the role of GRNs in larval development and insulin-like peptide (ILP) production was unknown. Now, Yuya Ohhara and Naoki Yamanaka discover that Gr28a-expressing peripheral internal sensory neurons, known as v’td neurons, are important for larval development. The authors screen 66 Gr-Gal4 lines using UAS-Kir2.1, a neural silencer, and find that larvae with suppressed Gr28a-expressing v’td neurons display delayed pupariation and retarded growth. They observe that Gr28-positive v’td neurons project to the central nervous system where they physically interact with insulin-producing cells (IPCs). Upon silencing of Gr28a-expressing v’td neurons in the mid larval period, ILP2 accumulates in IPCs due to impaired secretion. Furthermore, the authors detect increased transcript levels of insulin-like receptor and eIF-4E binding protein along with decreased levels of phosphorylated Akt, which are all indicative of deficient insulin signalling. Together, these data show the GRNs regulate ILP release from IPCs, controlling insulin signalling and growth rate in Drosophila larvae.
