Ecdysone has an effect on the regeneration of midgut epithelial cells thatis distinct from 20-hydroxyecdysone in the silkworm Bombyx mori

We investigated the effects of two ecdysteroids, ecdysone (E) and 20-hydrox yecdysone (20E), on silkworm larval development. Silkworm larvae, Bombyx mo ri, were fed an artificial diet supplemented with 20E during the fourth ins tar to promote premature molting. At the onset of the fifth instar, these p recocious fifth-instar larvae were fed diets supplemented with either E or 20E to determine the effects of the two ecdysteroids on the morphology of m idgut epithelial cells. Regeneration of midgut epithelial cells normally oc curs only during the molting period. However, in larvae fed E, complete rep lacement of midgut epithelial cells was observed 24 h be-fore the larvae en tered apolysis. In larvae fed 20E, the morphology of midgut epithelial cell s was disrupted, leading to death of the larvae during the fifth instar. We also observed similar differences in the effects of the two ecdysteroids i n an in vitro experiment. These results suggest that E has a specific effec t on the morphological change of midgut epithelial cells in precocious fift h-instar lan ae that is distinct from 20E, (C) 1999 Academic Press.