Targeting expression to projection neurons that innervate specific mushroom body calyx and antennal lobe glomeruli in larval Drosophila.

The first and secondary olfactory centers in the olfactory pathway in Drosophila are organized into neuropil structures called glomeruli. The antennal lobe (AL), the first olfactory center in larval Drosophila, is organized in 21 glomeruli. Each AL glomerulus receives innervation from a specific olfactory sensory neuron (OSN), and is therefore identifiable anatomically by the position of the OSN terminal. Olfactory projection neurons (PNs) send a dendrite to a single AL glomerulus and an axon that usually terminates in a single glomerulus in the mushroom body (MB) calyx, a secondary olfactory center, and in the lateral horn. By random labeling of single PNs that express GH146-GAL4, it was previously shown that PNs stereotypically innervate specific AL and calyx glomeruli, and most of these connections have been mapped. Here we report the pattern of innervation of GAL4 lines that drive expression of reporter genes in single or a few PNs, including PNs not identified by the widely used GH146-GAL4 driver. We have mapped the AL and calyx glomeruli innervated by these labeled PNs. This study provides a collection of GAL4 lines to molecularly mark the connections between specific AL and calyx glomeruli. It thus confirms and extends the previous map of AL-calyx connectivity that was based only on randomly labeled single PNs, and provides tools for targeted manipulation of specific PNs for developmental and functional studies.