Drosophila egg production depends upon the nutritional available to females. When food is in short supply, oogenesis is arrested and apoptosis of the nurse cells is induced at mid-oogenesis via a mechanism that is probably controlled by
ecdysteroid hormone. We have shown that expression of some
ecdysone-response genes is correlated with apoptosis of egg chambers. Moreover,
ecdysteroid injection and application of
juvenile hormone induces and suppresses the apoptosis, respectively. In this study, we investigated which tissues show increases in the concentration of
ecdysteroids under nutritional shortage to begin to link together nutrient intake,
hormone regulation and the choice between egg development or apoptosis made within egg chambers. We measured
ecdysteroid levels in the whole body, ovaries and haemolymph samples by RIA and found that the concentration of
ecdysteroid increased in all samples. This contributes to the idea that nutritional shortage leads to a rapid high
ecdysteroid concentration within the fly and that the high concentration induces apoptosis. Low concentrations of
ecdysteroid are essential for normal oogenesis. We suggest there is threshold concentration in the egg chambers and that apoptosis at mid-oogenesis is induced when the
ecdysteroid levels exceed the threshold.
Starvation causes the ovary to retain the
ecdysteroid it produces, thus enabling individual egg chambers to undergo apoptosis and thus control the number of eggs produced in relation to food intake.