Down-regulation of expression of a pupal cuticle protein gene by transcriptional and posttranscriptional control mechanisms during metamorphosis in Galleria

Down-regulation of expression of a pupal cuticle protein gene (GmPCP52) was investigated during metamorphosis in Galleria during normal development and in response to 20-hydroxyecdysone (20 E) and a juvenile hormone analogue (epofenonane). The developmental profile of GmPCP52 transcription was traced by nuclear run-on transcription assays. Transcription of the GmPCP52 gene is highest shortly after pupal ecdysis. There is a rapid decline between a pupal age of 12 and 18 h. Transcription becomes undetectable at 24 h. 20 E accelerates cessation of transcription, but induces a short second period of GmPCP52 transcriptional activity. Epofenonane prolongs transcription and induces a second round of transcriptional activity in relation to the synthesis of a second pupal cuticle. Analysis of changes in poly(A) tail length of GmPCP52 mRNA demonstrated control of expression at the level of mRNA translatability and stability. At 6 to 9 h poly(A) tails of GmPCP52 mRNA have lengths of 70 to 170 A-residues. From 9 h on mRNA with about 50 As accumulates. This material is regarded as translationally inactive. From 18 h on, further poly(A) shortening and degradation of the transcript occurs. Again, 20 E has an accelerating effect. In accordance with the results of the run-on experiments, there is a second increase in GmPCP52 mRNA with poly(A) tail lengths greater than 50 A. Epofenonane causes delay but does not prevent the changes observed in untreated animals. The results demonstrate, that expression of the GmPCP52 gene is regulated at the level of transcription, translation, as well as transcript accumulation and degradation. Targets of hormonal action are discussed.