R S Thorn | PubMed Health

PubMed1992

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.

Animals↗

PubMed1989

Sex-specific neuronal respecification during the metamorphosis of the genital segments of the tobacco hornworm moth Manduca sexta.

At metamorphosis, the terminal abdominal segments of larvae of the moth Manduca sexta transform into either male or female genitalia. At the start of this transformation, the larval muscles degenerate but their remains may persist to form the scaffolding on which the new adult muscles differentiate. The survival and subsequent orientation of larval muscle remnants is determined by the sex of the individual and is independent of motor innervation at the start of metamorphosis. Many of the larval motoneurons persist through metamorphosis and innervate the skeletal muscle of the adult. The survival of particular motoneurons is also sex-dependent and correlated with the survival of its respective muscle remnant. No new skeletal motoneurons arise postembryonically, so all of the adult skeletal muscle motoneurons are derived from preexisting larval skeletal muscle motoneurons. The fates during metamorphosis are more complex for the visceral muscle motoneurons. Those innervating the adult hindgut of both sexes are identical and are derived from the larval hindgut motoneurons. Other hindgut motoneurons in the larva switch targets during metamorphosis and come to innervate the oviduct in adult females or perish in adult males. Other regions of the reproductive tract become innervated by adult-specific cells that differentiate during metamorphosis. These cells come from distinct lineages in males and females.

Animals↗