Glia maintain follower neuron survival during Drosophila CNS development.

While survival of CNS neurons appears to depend on multiple neuronal and non-neuronal factors, it remains largely unknown how neuronal survival is controlled during development. Here we show that glia regulate neuronal survival during formation of the Drosophila embryonic CNS. When glial function is impaired either by mutation of the glial cells missing gene, which transforms glia toward a neuronal fate, or by targeted genetic glial ablation, neuronal death is induced non-autonomously. Pioneer neurons, which establish the first longitudinal axon fascicles, are insensitive to glial depletion whereas the later extending follower neurons die. This differential requirement of neurons for glia is instructive in patterning and links control of cell number with axon guidance during CNS development.