Juvenile Hormone Molecular Actions and Interactions During Development of Drosophila melanogaster

This chapter summarizes the understanding of the molecular mechanism of juvenile hormone (JH) action in the fruit fly, Drosophila melanogaster. It details the growing evidence that JH acts primarily at the level of gene expression and does so in apparently two different ways—directly, as a transcriptional regulator of JH ‘‘target genes,’’ and indirectly, as a suppressor of 20‐hydroxyecdysone (20E)‐dependent transcriptional regulation. As Drosophila has emerged as a model genetic system for the analysis of insect hormone action, the chapter particularly emphasizes on the analysis of mutants that have proved useful for acquiring understanding of insect hormone action during development and reproduction. 20E and JH also have important functions in the adult, promoting both reproductive maturation and the stereotyped patterns of mating behavior. The chapter discusses the features of the three hormones that are relevant for understanding of JH function. The regulatory interplay between JH and 20E defines the outcome of each developmental transition in the insect life cycle. 20E initiates each transition from larva‐to-pupa‐to‐adult, and JH determines the nature of the transition. In Drosophila, at the end of the third instar, 20E acting in the absence of JH causes dramatic changes in the genetic programs leading to pupariation, and the BR‐C gene is known to play a key role in this process.