Dpp and Hedgehog mediate neuron–glia interactions in Drosophila eye development by promoting the proliferation and motility of subretinal glia

Neuron-glia interactions are crucial for the establishment of normal connectivity in the nervous system during development, but the molecular signals involved in these interactions are largely unknown. Here we show that differentiating photoreceptors in the developing Drosophila eye influence the proliferative and migratory behavior of the subretinal glia through the diffusible factors Decapentaplegic (Dpp) and Hedgehog (Hh). We demonstrate that proliferation and migration of the glia are separable processes, and that Dpp promotes both the proliferation and motility of the glia, whereas Hh appears to promote only their motility; neither specifies the direction of migration. We present evidence that Dpp and Hh act on the glia in parallel and through the regulation of transcription. Finally, we show that ectopic migration of subretinal glia can result in the ectopic projection of photoreceptor axons. Our study suggests a novel function for Hh in regulating migratory behavior and provides further evidence for a complex mutual dependence between glial and neuronal cells during development.