The presence of regenerating tissue in a larval insect inhibits the endocrine system from initiating molting or metamorphosis until the regeneration is complete, but the nature of the inhibitory signal is unknown. A similar effect of growing peripheral tissues on the endocrine system is thought to be responsible for the dramatically prolonged larval life which is associated with continuously growing imaginal discs in lethal imaginal-disc overgrowth mutants of Drosophila. Dr. Bryant proposes to test the latter idea by investigating the endocrinology of these mutants. He will complete his measurements of ecdysteroid titers in mutant larvae and on wild type larvae containing regenerating imaginal disc, and he will determine whether there are changes in the ratio between C-27 and C-28 ecdysteroids. Using in vitro culture of imaginal discs and ring glands, he will investigate whether the reduced ecdysteroid titer that he has documented in the mutants is due to increased utilization or degradation of ecdysteroids by the imaginal discs or to inhibition of ecdysteroid release by the ring gland. The preliminary results already show a reduction of ring gland output in tow of the mutants. Dr. Bryant will investigate whether such effects are ring gland autonomous or are indirect effects due to the presence of growing imaginal discs. The effect on the endocrine system will be investigated by measuring the production of prothoracicotropic hormone by mutant nervous systems. %%% This study will provide new evidence on an important but little understood link in the chain of events that control developmental timing in insects.
