Molecular Aspects of Juvenile Hormone Reception and Action

Abstract

Molting and metamorphosis in insects are governed by two hormones, ecdysone which initiates and coordinates the molting process, and juvenile hormone (JH) which allows molting but prevents metamorphosis. In this morphogenetic action JH does not act by itself but rather directs the action of ecdysone. At the molecular level ecdysone can activate or inactivate genes either directly or via the induction of trans-acting regulatory factors (Lepesant and Richards, 1989). During a molt it causes the suppression of ongoing intermolt gene expression and “selects”, in a sequential manner, genes necessary for formation of the next stage; the activation of these genes occurs as the ecdysteroid titer falls (Riddiford et al., 1986, 1990). The presence of JH allows the inactivation of the intermolt genes but ensures that they may be re-expressed when the ecdysteroid titer falls. Its presence also prevents the activation of new genes and therefore metamorphosis.