UP-REGULATION OF AN ADULT CUTICULAR GENE BY 20-HYDROXYECDYSONE IN INSECT METAMORPHOSING EPIDERMIS CULTURED IN-VITRO

Pupal forewing epidermis of the Coleoptera, Tenebrio molitor, was used to develop an in vitro system to study the hormonal control of metamo rphosis al the cellular and molecular levels, Exposure to 1 mu M 20-hy droxyecdysone for 48 h caused the formation of a typical adult cuticle . Under these conditions the expression of ACP-20, an adult-specific c uticular gene, was fivefold higher than in absence of exogenous hormon e. This stimulation was also observed when a higher level of 20-hydrox yecdysone was maintained, and prevented by protein inhibitors, indicat ing that 20-hydroxyecdysone does not act directly on this gene. Exposu re to 20-hydroxyecdysone followed by exposure in hormone-free medium c aused the cessation of this stimulation, showing the requirement of th e 20-hydroxyecdysone continuous presence for stimulating ACP-20 gene e xpression. Thus, unlike the other cuticular protein genes so far studi ed, its expression is not repressed by 20-hydroxyecdysone, and does no t need the decline in ecdysteroids titer.