Journal of Neuroscience, Vol 7, 4107-4114, Copyright © 1987 by Society for Neuroscience
Postembryonic neurogenesis in the CNS of the tobacco hornworm, Manduca sexta. II. Hormonal control of imaginal nest cell degeneration and differentiation during metamorphosis
R Booker and JW Truman
Department of Zoology, University of Washington, Seattle 98195.
The nervous system of an adult moth is comprised of retained larval neurons
that are remodeled during metamorphosis and a set of new adult specific
neurons. The new neurons arise from a stereotyped array of stem cells
(neuroblasts) that divide during larval life to generate nests of up to 100
arrested postmitotic immature neurons, the imaginal nest (IN) cells. At the
onset of metamorphosis, some of the IN cells die while the remainder
differentiate into mature functional neurons. Metamorphosis in insects is
regulated by 2 classes of hormones, the ecdysteroids and the juvenile
hormones. The transition from larva to pupa requires the disappearance of
juvenile hormones followed by 2 releases of ecdysteroids: a small
"commitment peak" and a larger "prepupal peak." Through a series of
endocrine manipulations, we demonstrate that the death and differentiation
observed among the abdominal IN cells at metamorphosis are both influenced
by these hormonal cues. If the abdomen was isolated from the hormonal
sources in the anterior half of the larva before the onset of
metamorphosis, death and differentiation of the IN cells were prevented.
Infusion of ecdysteroids into such abdomens, to mimic the prepupal peak,
resulted in the IN cells showing the same fate as seen in control animals
during the early phases of metamorphosis. The response of the IN cells to
the small commitment peak of ecdysteroids was heterogeneous. Exposure to
this small peak of steroids caused some cells to become committed to resume
their development, making them resistant to juvenile hormone
application.(ABSTRACT TRUNCATED AT 250 WORDS)