Hierarchical axon targeting of Drosophila olfactory receptor neurons specified by the proneural transcription factors Atonal and Amos

Sensory information is spatially represented in the brain to form a neural map. It has been suggested that axon–axon interactions are important for neural map formation; however, the underlying mechanisms are not fully understood. We used the Drosophila antennal lobe, the first olfactory center in the brain, as a model for studying neural map formation. Olfactory receptor neurons ( ORN s) expressing the same odorant receptor target their axons to a single glomerulus out of approximately 50 glomeruli in the antennal lobe. Previous studies have showed that the axons of Atonal ORN s, specified by Atonal, a basic helix‐loop‐helix ( bHLH ) transcription factor, pioneer antennal lobe formation; however, the details remain to be elucidated. Here, we show that genetic ablation of Atonal ORN s affects antennal lobe structure and axon targeting of Amos ORN s, another type of ORN specified by the bHLH transcription factor Amos. During development, Atonal ORN s reach the antennal lobe and form the axon commissure before Amos ORN s. We also found that N‐cadherin knockdown specifically in Atonal ORN s disrupts the glomerular boundary in the whole antennal lobe. Our results suggest that Atonal ORN s function as pioneer axons. Thus, correct axon targeting of Atonal ORN s is essential for formation of the whole antennal lobe.