Programmed neuronal death in insect development.

Programmed death in the developing nervous system of insects serves to remove obsolete neurons, generate segmental specializations and sexual dimorphism, as well as adjust neuronal number. This diversity is also reflected in the mechanisms which control the death of these neurons. In general, but not without exception, these deaths occur independent of target fate, while endocrine cues, segmental identity, and neural signalling often play critical roles. In addition, the programmed death of at least some neurons can be delayed by behavioral feedback. The study of neuronal death in Drosophila and the cloning of an ecdysteroid receptor bring the promise of understanding the genetic factors and molecular events that regulate this phenomenon.