Catecholamine metabolism and in vitro induction of premature cuticle melanization in wild type and pigmentation mutants of Drosophila melanogaster.

The major pathway leading to adult cuticle melanization in Drosophila melanogaster has been investigated by a combination of biochemical and genetic approaches. By comparing catecholamine pools in newly emerged flies and in frass (excreta) collected 1 to 4 days after eclosion from wild type with those obtained from several pigmentation mutants, the major flow of catecholamines through the pathway to an unidentified final catabolite was determined. We also demonstrate that incubation with dopamine in vitro induces premature melanization in wild type unpigmented pharate adults several hours before the developmentally programmed onset of melanization, supporting the hypothesis that the availability of catecholamines may be the limiting factor determining the onset of melanization and that the major enzymatic activities that act downstream of dopa decarboxylase in the pathway are deposited into the cuticle before pigmentation begins. In vitro melanization studies with various pigmentation mutants that are associated with critical enzymatic steps in Drosophila catecholamine metabolism are consistent with their proposed function and suggest a central role of N-beta-alanyldopamine in adult cuticle pigmentation.