Axon-secreted chemokine-like Orion is a signal for astrocyte infiltration during neuronal remodeling

The remodeling of neurons is a conserved fundamental mechanism underlying nervous system maturation and function. Glial cells are known to clear neuronal debris but also to have an active role in the remodeling process. Developmental axon pruning of Drosophila memory center neurons occurs by a degenerative process mediated by infiltrating astrocytes. However, how these glial processes are recruited by the axons is unknown. In an unbiased screen, we identified a new gene ( orion ) which is necessary for both the pruning of some axons and removal of the resulting debris. Orion is secreted from the neurons and bears some features common to the chemokines, a family of chemoattractant cytokines. Thus, chemokine involvement in neuron/glial cell interaction is an evolutionarily ancient mechanism. We propose that Orion is the neuronal signal that elicits astrocyte infiltration required for developmental neuronal remodeling.