Shaaya, E., Volcani Center, Institute of Technology, Bet-Dagan 50-250, Israel
Riddiford, L.M., Department of Zoology, University of Washington, Seattle, WA 98125, United States

Changes in RNA synthesis in the epidermis of last larval instar larvae of Ephestia cautella and Manduca sexta (Lepidoptera) were followed. For about 30 h just prior to wandering stage, total RNA synthesis was depressed. Analysis of RNA showed that the synthesis of all RNA species was decreased; in Ephestia this change caused a reduction of about 17% of the bulk RNA in the cells. Following this period, the wandering stage, pupally committed epidermal cells synthesize a new type of RNA termed hetero-disperse nuclear RNA (HnRNA), then as the prepupal period begins a marked increase in rRNA synthesis was observed. Ten micrograms methoprene, a juvenile hormone analogue, delayed the larval-pupal transformation and prevented these changes in RNA synthesis. In vitro 50 ng/ml 20-hydroxyecdysone was necessary and sufficient to cause the depression of RNA synthesis in day-1. Manduca epidermis. Moreover, the change to pupal commitment induced by 24 h exposure of day-2 epidermis to 500 ng/ml 20-hydroxyecdysone also caused a significant increase in total RNA synthesis. © 1988.