The use of an inhibitor of protein synthesis to investigate the roles of ecdysteroids and sex-determination genes on the expression of the genes encoding the Drosophila yolk proteins.

The three yolk-protein genes of Drosophila are normally expressed only in adult female fat bodies and ovaries. 20-hydroxyecdysone can affect the transcription of these genes in males and females, as can mutations in the sex-determining genes tra, tra-2, ix and dsx. We have asked a number of basic questions about how these genes are regulated, using an inhibitor of protein synthesis (cycloheximide), labelling RNA in vivo, a temperature-sensitive sex-determination mutant (tra-2ts1), and 20-hydroxyecdysone. We have found that the yolk-protein genes are continuously transcribed in the fat bodies of adult females and that maintenance of this transcription requires protein synthesis. Hormone induction in males is also inhibited by cycloheximide, suggesting that the products of other genes are essential both for 20-hydroxyecdysone to be able to switch on the genes, and for their continuous transcription in the female fat body. The products of the tra-2 gene are also required for continuous transcription of the yolk-protein genes, suggesting that the pathway inhibited by the cycloheximide is that of the sex-determination hierarchy. 20-hydroxyecdysone can override the sex-determination system and induce yolk protein synthesis in normal males and tra-2ts reared and maintained at the restrictive temperature.