Dt. Champlin et Jw. Truman, ECDYSTEROID CONTROL OF CELL-PROLIFERATION DURING OPTIC LOBE NEUROGENESIS IN THE MOTH MANDUCA-SEXTA, Development, 125(2), 1998, pp. 269-277
Cell proliferation within the optic lobe anlagen is dependent on ecdys
teroids during metamorphosis of the moth Manduca serta. We use culture
d tissues to show that ecdysteroids must be maintained above a sharp t
hreshold concentration to sustain proliferation. Proliferation can be
turned on and off repeatedly simply by shifting the ecdysteroid concen
tration to above or below this threshold. In subthreshold hormone, cel
ls arrest in the G(2) phase of the cell cycle. Ecdysteroid control of
proliferation is distinguished from differentiative and maturational r
esponses to ecdysteroids by requiring tonic exposure to the hormone an
d lower levels of 20-hydroxyecdysone, and by being sensitive to either
20-hydroxyecdysone or its precursor, ecdysone. These characteristics
allow optic lobe development to be divided into two ecdysteroid-depend
ent phases. Initially, moderate levels of ecdysteroid stimulate prolif
eration. Later, high levels of 20-hydroxyecdysone trigger a wave of ap
optosis within the anlage that marks completion of its proliferative p
hase.