A neural progenitor mitotic wave is required for asynchronous axon outgrowth and morphology

Spatiotemporal mechanisms generating neural diversity are fundamental for understanding neural processes. Here, we investigated how neural diversity arises from neurons coming from identical progenitors. In the dorsal thorax ofDrosophila, rows of mechanosensory organs originate from the division of sensory organ progenitor (SOPs). We show that in each row of the notum, a central SOP divides first, then neighboring SOPs divide, and so on. This centrifugal wave of mitoses depends on cell-cell inhibitory interactions mediated by SOP cytoplasmic protrusions and Scabrous, a secreted protein interacting with the Delta/Notch complex. Furthermore, when the mitotic wave was abolished, axonal growth was more synchronous, axonal terminals had a complex branching pattern and fly behavior was impaired. We show that the temporal order of progenitor divisions influences the birth order of sensory neurons, axon branching and impact on grooming behavior. These data support the idea that developmental timing controls axon wiring neural diversity.