A step-by-step guide to visual circuit assembly in Drosophila

The ability of vertebrates and insects to perceive and process information about the visual world is mediated by neural circuits, which share a strikingly conserved architecture of reiterated columnar and layered synaptic units. Recent genetic approaches conferring single-cell resolution have enabled major advances in our understanding of the cellular and molecular strategies that orchestrate visual circuit assembly in Drosophila. Photoreceptor axon targeting relies on a sequence of interdependent developmental steps to achieve temporal coordination with the formation and maturation of partner neurons. Distinct targeting events depend on anterograde and autocrine signaling, neuron–glia interactions, axon tiling and the timely expression of homophilic cell surface molecules. These mediate local adhesive or repulsive interactions of photoreceptor axons with each other and with target neurons.