Glia maintain follower neuron survival during Drosophila CNS development

While survival of CNS neurons appears to depend on multiple neuronal and no n-neuronal factors, it remains largely unknown how neuronal survival is con trolled during development. Here we show that glia regulate neuronal surviv al during formation of the Drosophila embryonic CNS. When glial function is impaired either by mutation of the glial cells missing gene, which transfo rms glia toward a neuronal fate, or by targeted genetic glial ablation, neu ronal death is induced non-autonomously. Pioneer neurons, which establish t he first longitudinal axon fascicles, are insensitive to glial depletion wh ereas the later extending follower neurons die. This differential requireme nt of neurons for glia is instructive in patterning and links control of ce ll number with axon guidance during CNS development.