Neural birth time and somatosensory circuit assembly are linked by Robo3 regulation of dendrite morphology

Neural circuit wiring requires a remarkable level of precision, as thousands of neurons generate millions of synapses in distinct configurations. While neural circuits are known to be shaped by both neural birth timing and multiple classes of guidance molecules, the relationship between the two and how they coordinate circuit assembly has yet to be evaluated. Leveraging the well-defined stem cell lineages of the Drosophila embryonic nerve cord, we investigate how Roundabout (Robo) guidance receptors are regulated by neural birth timing to establish neural morphology and function for circuit assembly. Our data reveal that Robo receptor expression in neurons is tightly linked to neural birth timing and controlled by temporal transcription factors. Notably, we identify a Robo3 guidance receptor code that is pivotal for assembly of somatosensory circuits, distinguishing stretch-detecting PNS neurons and late-born EL interneurons (lacking Robo3) from vibration detecting PNS neurons and early-born EL interneurons (expressing Robo3). These insights propose a shared guidance receptor code connecting neural birth timing to circuit assembly, providing a molecular foundation for developmental wiring specificity.