Steroid induction of a peptide hormone gene leads to orchestration of a defined behavioral sequence

At the end of each molt, insects shed the old cuticle by performing preecdy sis and ecdysis behaviors. Regulation of these centrally patterned movement s involves peptide signaling between endocrine Inka cells and the CNS. In I nka cells, we have identified the cDNA and gene encoding preecdysis-trigger ing hormone (PETH) and ecdysis-triggering hormone (ETH), which activate the se behaviors. Prior to behavioral onset, rising ecdysteroid levels induce e xpression of the ecdysone receptor (EcR) and ETH gene in Inka cells and evo ke CNS sensitivity to PETH and ETH. Subsequent ecdysteroid decline is requi red for peptide release, which initiates three motor patterns in specific o rder: PETH triggers preecdysis I, while ETH activates preecdysis II and ecd ysis. The Inka cell provides a model for linking steroid regulation of pept ide hormone expression and release with activation of a defined behavioral sequence.