Morphogenetic Action of Insect Hormones

Two classes of hormones-ecdysones and juvenile hormones (JH)-regulate the morphogenetic changes of insect metamorphosis. Recent advances in structural analysis and synthesis have resulted in the ready availability of synthetic forms, analogues, and mimics of these hormones; and there has already been considerable speculation on their molecular modes of action (4, 26, 27, 68, 87.92, 102). However, the morphogenetic responses of the various experimental systems to these hormones must be more rigorously established and understood before final judgement can be passed on their molecular bases of action. The following questions summarize the key areas of active research which are amenable to morphological analysis: 1. Does JH exert an all-or-none action on an individual cell? 2. Does JH reprogram embryonic cells? 3. Does JH regulate changes in larval structure? 4. Can JH cause a reversal of metamorphosis? 5: What is the nature of the interaction of JH and ecdysone: synergism, antago­ nism, mimicry, or mutual interdependence? 6. Is regulation of DNA synthesis the key step in the action of ecdysone or JH? 7. Is ecdysone capable of initiating all of the steps needed for the completion of a new cuticle? Although these will comprise the main topics to be covered in this review;because of broad areas of overlap between some of these topics, I have found it more logical to organize the following discussion somewhat differently. Further, recent compre­ hensive reviews of insect endocrinology (12, 67, 70, 76, 98, 106) and morphogenesis (89) make a survey of all the pertinent literature unnecessary and I have selected