Regulation of Sciarid DNA Puffs by Ecdysone: Mechanisms and Perspectives

DNA puffs, formed in the salivary gland polytene chromosomes at the end of the larval stage, are characteristic of Sciaridae. Cytological demonstrations coupled to the molecular characterization of DNA puffs revealed that they are sites of disproportional DNA synthesis and abundant transcription. The biologi- cal purpose of DNA amplification at these loci is to enable the synthesis of large amounts of proteins in short periods of time. Here, the role of ecdysone in DNA puffs formation and DNA puff genes amplification and expression is reviewed and a new model for ecdysone action on DNA puffs is proposed. Studies in transgenic Drosophila that contributed to the understanding of the mechanisms that regulate Sciaridae DNA puff gene amplification and transcription are described. Finally, the availability of antibodies raised against the EcR, will further extend the knowledge about the roles exerted by ecdysone in this unique model system.