Identification of a Novel Prothoracicostatic Hormone and Its Receptor in the Silkworm Bombyx mori

Abstract

The insect brain regulates the activity of the prothoracic glands to secrete ecdysteroids, which affect growth, molting, and metamorphosis. Here we report the identification of a novel prothoracicostatic factor and its receptor in the silkworm Bombyx mori. The prothoracicostatic factor purified from pupal brains of B. mori is a decapeptide with the conserved structure of an insect myosuppressin and thus named Bommo-myosuppressin. Bommo-myosuppressin dose dependently suppressed the cAMP level and inhibited ecdysteroidogenesis in the larval prothoracic glands at much lower concentrations than the prothoracicostatic peptide, the other prothoracicostatic factor reported previously. In vitro analyses using a prothoracic gland incubation method revealed that Bommo-myosuppressin and prothoracicostatic peptide regulate the prothoracic gland activity via different receptors. In situ hybridization and immunohistochemistry revealed the existence of Bommo-myosuppressin in the brain neurosecretory cells projecting to neurohemal organs in which it is stored. We also identified and functionally characterized a specific receptor for Bommo-myosuppressin and showed its high expression in the prothoracic glands. All these results suggest that Bommo-myosuppressin functions as a prothoracicostatic hormone and plays an important role in controlling insect development.

Regulation of insect steroid hormone biosynthesis by innervating peptidergic neurons

“…To elucidate the prothoracicostatic activity of BRFa, cAMP and ecdysteroid assays were performed by using PGs of the fifth larval instar on day 4, as described for BMS in ref. 12. As shown in Fig.…”

“…We developed an ELISA system to purify endogenous FaRPs in Bombyx, in addition to BMS. Competitive ELISA revealed that some HPLC fractions, originally prepared from Bombyx pupal brains for the purification of BMS (12), show FMRFamide-like immunoreactivity (Fig. 1A).…”

“…BRFa peptides were shown to regulate ecdysteroidogenesis by means of BMSR, the receptor previously reported to mediate the prothoracicostatic effect of BMS (12). Although effective concentrations of BRFa were much higher than BMS, this difference reflects their different modes of action on the PGs.…”

“…We previously identified Bommo-myosuppressin (BMS), which is an FMRFamide-related peptide (FaRP), as a previously unidentified prothoracicostatic factor in the silkworm Bombyx mori (12). BMS was shown to suppress ecdysteroidogenesis in the PG, where the BMS receptor (BMSR) is highly expressed.…”

Characterization of kinesin-like proteins in silkworm posterior silkgland cells

“…Prehybridization solution was prepared as reported previously [58]. After 2 h of prehybridization at 50 °C, DIG-labelled RNA probe, produced by in vitro transcription system (Promega) and DIG RNA Mix (Roche), were added into the same buffer.…”