Digitonin Activates Different Sets of Puff Loci Depending on Developmental Stages in Drosophila melanogaster Salivary Glands: (salivary gland chromosomes/detergent/gene regulation/ecdysone-inducible puffs/Drosophila melanogaster).

We showed previously that treatment of Drosophila melanogaster salivary glands with a mild detergent, digitonin, induces heat shock puffs and many developmentally regulated puffs. To find if the mechanism underlying the puff induction by digitonin is related to the temporal control of gene expression in salivary glands, we examined effects of digitonin on salivary glands at various puff stages from late third instar larva to white prepupa. The results indicate that (a) all the heat shock puffs are induced by digitonin irrespective of the developmental stage of the treated glands, (b) intermolt and early puff loci are always irresponsive to digitonin, and (c) late puff loci respond to digitonin to form puffs only before the stage of their developmentally programmed puffing. Based on the stage at which the locus becomes digitonin responsive, the digitonin-responsive late puff loci were divided into two groups: group A loci, responsive to digitonin continuously from PS1 until programmed puffing begins, and group B loci, responsive to digitonin only in a short period of time immediately before the programmed puffing. The results suggest that a digitonin-sensitive suppression mechanism(s) is involved in the temporal control of gene expression in Drosophila salivary glands.