The role of ecdysone in DNA-puff formation and DNA synthesis in the polytene chromosomes of Sciara coprophila.

Abstract

The so-called "DNA-puffs" are a characteristic and exclusive feature of sciarid polytene chromosomes.A number of descriptive and comparative studies on these structures have been carried out over the last two decades both in Rhynchosciara angelae and in Sciara coprophila.They have revealed the fact that concurrent with puffing at these sites an excessive and disproportionate syn- thesis of DNA occurs.1 2 It has also been suggested that these events are some- how related to development,3 a conclusion which has been recently contested.4Much of the confusion that exists in the literature with respect to the significance and nature of the DNA-puffs is simply due to a lack of precise data at the morphological and biological level.Recent studies in our laboratory demonstrate that, contrary to a widely held conviction, the DNA-puffs are not just illdefined, chance manifestations of some kind of cellular "senility" preceding histol- ysis.To the contrary, a number of facts attest to the general significance of the DNA-puffs: (1) They always arise from specific points in the salivary gland chromosome, usually a pair of light-staining bands or the space between the two.