Identification of a cis-regulatory element that directs prothoracicotropic hormone gene expression in the silkworm Bombyx mori

Abstract

In the silkworm Bombyx mori and other insects, prothoracicotropic hormone (PTTH) plays a central role in controlling molting and metamorphosis by stimulating the prothoracic glands to synthesize and release the molting hormone ecdysone. Using an AcNPV (Autographa californica nucleopolyhedrovirus)-mediated transient gene transfer system, we identified a cis-regulatory element that participates in the decision to switch expression of PTTH on or off in PTTH-producing neurosecretory cells (PTPCs). The nucleotide sequence of this cis-regulatory element is similar to a cis-regulatory element that participates in direction of expression of diapause hormone-pheromone biosynthesis activating neuropeptide gene (DH-PBAN) (Shiomi et al., 2007). Furthermore, we found that B. mori Pitx (BmPitx), a bicoid-like homeobox transcription factor, binds the element and activates PTTH expression. Therefore, we propose that the cell-specific expression of two neuropeptide hormone genes, PTTH and DH-PBAN, is activated by the Pitx transcription factor, which may act as a pan-activator in the insect neuroendocrine system and in vertebrate pituitary cells.