The effects of 20-hydroxyecdysone on the metabolic labeling of membrane proteins in Drosophila imaginal discs.

20-Hydroxyecdysone induces evagination of imaginal discs of Drosophila melanogaster cultured in vitro. The possible involvement of cell-surface proteins in this process has prompted us to study the synthesis of membrane proteins in imaginal discs. A procedure is reported for the isolation of membrane vesicle fractions from discs that are enriched for the plasma membrane enzyme, Na+/K+-ATPase, and that label with the surface-labeling reagent [125I]iodosulfanilic acid. 20-Hydroxyecdysone alters the pattern of [35S]methionine incorporation into polypeptides in these membrane vesicle fractions. Increased and decreased incorporation as well as changes in migration on two-dimensional gels of specific polypeptides are caused by the hormone. These changes parallel in time the onset and the continuation of evagination.