Temporal control of urate oxidase activity during development of the third‐instar larva of Drosophila: The role of 20‐hydroxyecdysone

Abstract

AbstractThe tissue‐specific enzyme urate oxidase is confined exclusively to the Malpighian tubules of Drosophila melanogaster and expressed only in the third‐instar larva and the adult. Shortly before pupariation urate oxidase activity declines precipitously and is not detectable 24 hours later. That 20‐hydroxyecdysone is the factor that triggers the disappearance of urate oxidase activity in late third‐instar larvae is demonstrated using the temperature sensitive mutant ecd1 which at the nonpermissive temperature of 29°C fails to accumulate a sufficient concentration of 20‐hydroxyecdysone necessary for puparium formation and thus remains a third‐instar larva for 1 to 2 weeks before death. Both the life cycle and the temporal profile of urate oxidase activity in ecd1 larvae at 19°C is identical to that of the wild type. However, at 29°C ecd1 third‐instar larvae retain high urate oxidase activity. A precipitous decline in urate oxidase activity is observed when ecd1 larvae at 29°C are fed 20‐hydroxyecdysone. These data implicate 20‐hydroxyecdysone in the process that controls the rapid decline of urate oxidase activity at the time of puparium formation. In whole homogenates of Malpighian tubules, the urate oxidase polypeptide was identified in SDS‐polyacrylamide gels by its Rf with respect to homogeneously pure Drosophila urate oxidase and also by immunoprecipitation with rabbit anti‐Drosophila urate oxidase IgG. Throughout development the amount of the urate oxidase polypeptide is correlated with the magnitude of urate oxidase activity.