Hormonal control of gene amplification and transcription in the salivary gland chromosomes of Trichosia pubescens

Abstract

Trichosia pubescens larvae were ligated at different prepupal developmental stages in order to investigate whether ecdysterone acts just as a trigger or whether its presence in the hemolymph is constantly necessary for the induction of the late puffs, in particular the DNA puffs. The larvae were ligated in the middle of the body being sure that the salivary glands were divided in two halves. Some of the ligated larvae had the anterior portion of the body dissected immediately in order to determine the puff pattern at the time of ligature. These patterns were compared with those from the posterior half which were dissected at different times after ligature. The results obtained in these experiments can be summarized as follow: (1) the absence of ecdysterone source prevents the induction of late puffs even when ligature is carried out after the induction of the early ecdysterone-responsive puffs; (2) the lack of an ecdysterone source blocks the process of gene amplification when the ligature is carried out at the beginning of this process (L 3 stage); (3) the gene amplification process would not seem to be blocked but DNA puffs do not expand if the larvae are ligated some hours later (early L 4 stage); (4) both gene amplification and DNA puffs expansion occur normally when larvae are ligated at a more advanced stage (at late L 4 stage or thereafter). These results show that the presence of ecdysterone source is necessary for the induction of the late puffs up to a critical period at L 4 stage. They also show that gene amplification and transcription of amplified sequences at the DNA puffs are two independently controlled phenomena.