Insulin-like and IGF-like peptides in the silkmoth Bombyx mori: discovery, structure, secretion, and function.

Akira Mizoguchi,Naoki Okamoto

doi:10.3389/fphys.2013.00217

Abstract

A quarter of a century has passed since bombyxin, the first insulin-like peptide identified in insects, was discovered in the silkmoth Bombyx mori. During these years, bombyxin has been studied for its structure, genes, distribution, hemolymph titers, secretion control, as well as physiological functions, thereby stimulating a wide range of studies on insulin-like peptides in other insects. Moreover, recent studies have identified a new class of insulin family peptides, IGF-like peptides, in B. mori and Drosophila melanogaster, broadening the base of the research area of the insulin-related peptides in insects. In this review, we describe the achievements of the studies on insulin-like and IGF-like peptides mainly in B. mori with short histories of their discovery. Our emphasis is that bombyxins, secreted by the brain neurosecretory cells, regulate nutrient-dependent growth and metabolism, whereas the IGF-like peptides, secreted by the fat body and other peripheral tissues, regulate stage-dependent growth of tissues.

Highlights

THE AIM OF THIS REVIEW Since 1984, when bombyxin was identified as the first insulinlike peptide in invertebrates (Nagasawa et al, 1984b), this brain neurosecretory hormone of the silkmoth Bombyx mori has been extensively characterized for its chemical nature, gene structure, distribution, secretion control, as well as physiological functions
CONCLUDING REMARKS Two classes of insulin-related peptides were discovered and characterized in B. mori; one is bombyxin, which is a functional counterpart of vertebrate insulin, and the other is Bombyx IGF-Like Peptide (BIGFLP), which is more similar to insulin-like growth factors (IGFs) rather than to insulin in the structural and biological traits
The hair density analysis demonstrated that dilp6 mutants have normal cell size but reduced cell number, which likely accounts for the reduction in body size (Okamoto et al, 2009b)

Summary

INTRODUCTION

THE AIM OF THIS REVIEW Since 1984, when bombyxin was identified as the first insulinlike peptide in invertebrates (Nagasawa et al, 1984b), this brain neurosecretory hormone of the silkmoth Bombyx mori has been extensively characterized for its chemical nature, gene structure, distribution, secretion control, as well as physiological functions. Even before the discovery of bombyxin, the existence of hypoglycemic hormones had been demonstrated in the honeybee Apis mellifera (Kramer et al., 1977, 1982; Bounias et al, 1986), the blowfly Calliphora vomitoria (Duve et al, 1979), the tobacco hornworm Manduca sexta (Tager et al, 1976; Kramer et al, 1982), the cockroach Periplaneta americana (Barrett and Loughton, 1987) and others (for a review, see Kramer, 1985) These hypoglycemic hormones were presumed to be insulin-related peptides, because insulin-immunoreactive substances had been detected in many insects including abovementioned species as well as the locust Locusta migratoria and the silkmoth B. mori by radioimmunoassay (RIA) (Ishay et al, 1976; Tager et al, 1976; Kramer et al, 1977; Duve et al, 1979; Orchard and Loughton, 1980; Kramer, 1985) and/or immunocytochemistry (Duve and Thorpe, 1979; Yui et al, 1980). The adult heads of B. mori were used as the starting material for purification and the debrained dormant pupae of the heterologous moth Samia cynthia ricini were used for the bioassay of the hormone, because PTTH was believed www.frontiersin.org

Mizoguchi and Okamoto

BOMBYXIN BIOSYNTHESIS AND RELEASE

BOMBYXIN ACTIONS