MRNA changes during imaginal determination of the epidermal cells in the pupa ofGalleria mellonella L

Abstract

Changes in the mRNA population of the mesonotal epidermal cells were investigated inGalleria mellonella during the first 48 h after pupation. Total RNA was extracted and assayed by in vitro translation. The translational products were separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and visualized by autoradiography. The changing banding pattern of the in vitro synthesized proteins indicates changes in the cellular pattern of mRNAs, most of which occur between 6 h and 18 h after pupal ecdysis. These changes mostly consist in the decrease or disappearance of bands. The injection of juvenile hormone (JH) immediately after pupal ecdysis does not qualitatively influence mRNA changes, but does alter their time course, for they are postponed for 6–12 h. After the injection of 20-hydroxyecdysone (20HE) the same changes can again be seen, but they are greatly accelerated. A comparison of these results with known data on the time course of reprogramming and ecdysteroid titre leads to the conclusion that the mRNA changes in the epidermal cells are a prerequisite for the renewed expression of a developmental programme. This is independent of whether, in the absence of JH, a new programme is determined or whether, under the influence of JH, the previous programme is restored. 20HE does not have any effect on the change in the developmental programme. The change seems to occur as an active and autonomous process in the epidermal cells, in accordance with a genetically fixed developmental programme.