Glutamate receptor composition at Drosophila neuromuscular junctions depends on developmental stage and muscle identity

The neuromuscular junction (NMJ) of larval Drosophila is widely used for studying synaptic transmission. Larval body wall muscles express five ionotropic glutamate receptor (iGluR) subunits that assemble into two tetrameric complexes, with subunit composition determining the strength and plasticity of synaptic transmission. Because NMJ function has been extensively characterized in larvae, it is often assumed that adult fly NMJs have similar molecular composition, despite substantial differences between life stages. Here, we systematically compare glutamate receptor expression across larval and adult Drosophila muscles. We find that adult leg and flight muscles exhibit different iGluR expression than larvae, lacking several receptors previously considered essential for viability and NMJ function. Adjacent muscles within the adult femur express distinct iGluRs, suggesting specialization of flexor and extensor muscles. Finally, the glutamate-gated chloride channel (GluCl) is expressed extrasynaptically in adult but not larval muscle fibers. Our results reveal unexpected heterogeneity in glutamate receptor expression across muscles and developmental stages, challenging assumptions about the uniformity of neuromuscular function and demonstrating the need for muscle-specific analyses in flies and other animals.