Ecdysteroids regulate yolk protein uptake by Drosophila
melanogaster oocytes.
David S. Richard, Noel L. Watkins, Robert B. Serafin, and Lawrence I. Gilbert
Abstract:
Juvenile hormones (JHs) are thought to drive the regulation of yolk
protein uptake by ovaries in Drosophila melanogaster. However, the
level of JH production in a mutant stock (ap56f)
is depressed yet the flies are normally vitellogenic. The production of
ecdysteroids by these ap56f ovaries in vitro
is elevated above that of wild-type ovaries. The incubation of wild-type
ovaries in the presence of 0.1mM JHB3 increased ecdysteroid
biosynthesis only during the first 18 h following eclosion. Female Drosophila
melanogaster undergo a pre-vitellogenic reproductive diapause when exposed
to low temperature (11oC) and a short-day photoperiod
(L12:D12). The rate of ecdysteroid synthesis by the ovaries, but not JH
production, increased within 12 h of a temperature upshift to 25oC
from a basal level of 20+/-1pg/10 pair of ovaries/ 5 h to a sustained level
of 150+/-20 pg/10 pair/5 h. Vitellogenic oocytes were noted in all
females within 12 h of this temperature upshift. Diapause was also terminated
by the injection of 1ug of 20-hydroxyecdysone into the abdomens of diapausing
females as determined by an increase in ovary size, and the appearance of
vitellogenic oocytes as compared to controls. These results are consistent
with a revised model for the regulation of yolk protein uptake by ovaries
in which ecdysteroids, and not JHs, play the prominent role.