Apoptosis helps to control cell numbers throughout development. In the developing nervous system of vertebrate embryos, neurons apoptose after differentiating and extending their axons; in invertebrate embryos, apoptosis typically occurs immediately after neuron generation. On p. 6093, Miguel-Aliaga and Thor provide the first example of the apoptosis of differentiated neurons in the Drosophila embryo. They show that Drosophila dMP2 and MP1 pioneer neurons undergo apoptosis in anterior segments at late embryonic stages, after they have fulfilled their duties as pioneer neurons. Apoptosis in posterior segments is prevented by the Hox gene Abdominal B, which represses the death activators reaper and grim in a cell-autonomous manner. These results reveal a new mechanism – selective elimination of mature neurons – by which Hox positional information controls neuronal architecture along the anteroposterior axis. A similar mechanism could act in vertebrate embryos, suggest the researchers.

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