Alicia Hidalgo (Cambridge University, Cambridge, UK) and colleagues determined the effects of the protein Vein on survival of glial cells in the developing ventral nerve cord of Drosophila. The protein is made in the pioneer neurons that lay down the scaffolding for the nerve cord. Blocking Vein production or blocking its receptors kills the glia near the pioneer neurons, the authors found. They also showed that Vein acts by activating the Ras/MAP-kinase pathway in those glia.

Whereas most neurons require glia for survival, pioneer neurons depend on glia to guide their growth, not for survival. As the nervous system develops, glia help to establish the trajectories of the pioneers' axons by stationing themselves at key points where the axons “decide” which direction to steer or to which partner axon to adhere, Hidalgo says. Normal flies produce far too many glia, many of which eventually...

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