ABSTRACT
The discovery of Dna sequence amplification in sciarid flies and investigations into its control and biological significance are reviewed. Results thus far show that amplification of specific salivary gland polytene chromosome bands is a general phenomenon in sciarids. It brought about as part of a final endoreplication cycle by the rising titer of ecdysterone that occurs as the Larvae approach the prepupal period. Amplification and transcription of these bands is a late, multistep effect of this hormone.The Dna puffs which form in amplified region produce mRNAs which are translated into polypeptides that appear to be involved in coccon formation. Application of molecular cloning techniques to the study of Dna amplification has allowed precise quantitation of amplification for several Dna puffs and is yielding maps of their transcription units.These techniques will ultimately help to define the origins of Dna puff replication and contribute to an understanding of the mechanism and control of the amplification phenomenon in sciaridae. Projections for future experimental approaches are presented
Subject(s)
Animals , Female , Diptera/genetics , DNA Replication/genetics , Gene Amplification/genetics , Base Sequence , Chromosomes/physiology , Cloning, Molecular , DNA Replication/physiology , DNA/drug effects , DNA/genetics , DNA/physiology , Ecdysterone/pharmacology , Gene Amplification/physiology , Larva , Molecular Sequence Data , Salivary Glands , Transcription, Genetic/genetics , Transcription, Genetic/physiologyABSTRACT
1. Fourth-instar larvae of Rhynchosciara americana were injected with the insect molting hormone, ecdysterone, giving final hemolymph concentrations from 4.46 to 223µM. 2. Induction of the DNA puff, B2b, in the proximal (S1) region of the salivary glands of Rhynchosciara americana by 22.6 µM ecdyesterone, was accompanied by the production of an mRNA and a polypeptide with the same characteristics as B2b products produced during normal development. This mRNA and polypeptide were restricted to the proximal region of the gland, as is the B2b puff. 3. Synthesis of other poly (A) +RNAs was also stimulated in S1 by ecdysterone, and other puffs that appear during normal development were induced. However, rRNA production in S1 goes through a pattern of inhibition, followed by recovery when B2b is puffed, and subsequent inhibition. 4. Low molecular weight RNA, with a peak in the region of 4S, is stimulated after ecdysterone administration