Juvenile hormone signaling-a mini review

Since it was first postulated by Wigglesworth in 1934, juvenile hormone (JH) is considered a status quo hormone in insects because it prevents metamorphosis that is initiated by the molting hormone 20-hydroxyecdysone (20E). During the last decade, significant advances have been made regarding JH signaling. First, the bHLH-PAS transcription factor Met/Gce was identified as the JH intracellular receptor. In the presence of JH, with the assistance of Hsp83, and through physical association with a bHLH?PAS transcriptional co-activator, Met/Gce enters the nucleus and binds to E-box-like motifs in promoter regions of JH primary?response genes for inducing gene expression. Second, the zinc finger transcription factor Kr-hl was identified as the anti-metamorphic factor which transduces JH signaling. Via Kr-hl binding sites, Kr-hl represses expression of 20E primary?response genes (i.e. Bi\ E93 and E5) to prevent 20E-induced metamorphosis. Third, through the intracellular signaling, JH promotes differ ent aspects of female reproduction. Nevertheless, this action varies greatly from species to species. Last, a hypothetical JH membrane receptor has been predicted to be either a GPCR or a tyrosine kinase receptor. In future, it will be a great challenge to understand how the JH intracellular receptor Met/Gce and the yet unidentified JH membrane receptor coordinate to regulate metamorphosis and reproduction in insects.