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.
Highlights
The insect brain regulates the activity of the prothoracic glands to secrete ecdysteroids, which affect growth, molting, and metamorphosis
The prothoracicostatic activity of a sample was expressed as an inhibition/activation index calculated with the formula: inhibition/activation index ϭ
Purification of the Prothoracicostatic Factor—As a bioassay system to evaluate the prothoracicostatic activity of the brain extracts, we developed a cAMP assay combining in vitro prothoracic glands (PGs) incubation and subsequent cAMP quantification because cAMP is a prerequisite second messenger for ecdysteroidogenesis [4]
Summary
The insect brain regulates the activity of the prothoracic glands to secrete ecdysteroids, which affect growth, molting, and metamorphosis. The prothoracicostatic peptide (PTSP) isolated from larval brains of Bombyx mori is the only cerebral factor elucidated so far to inhibit ecdysteroid synthesis in the PG [9, 10] This peptide inhibits both the basal and the PTTH-stimulated ecdysteroidogenesis in vitro in a dose-dependent manner, but its physiological role has yet to be demonstrated. Its low EC50 value, storage in neurohemal organs, and high expression of its functional receptor in the PG all indicate that BMS plays a role as a prothoracicostatic hormone To our knowledge, this is the first report on the prothoracicostatic activity of FaRPs, proposing these extensively studied peptides as important candidates for the regulator of insect growth, molting, and metamorphosis. The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EBI Data Bank with accession number(s) AB188256 and AB188257
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