Functional Multiplicity of an Insect Cytokine Family Assists Defense Against Environmental Stress.

Stephen B. Shears,Yoichi Hayakawa

doi:10.3389/fphys.2019.00222

Abstract

The widespread distribution of insects over many ecological niches owes much to evolution of multiple mechanisms to defend against environmental stress, especially because their ectothermic nature and small body size render them particularly susceptible to extremes in temperature and water availability. In this review, we will summarize the latest information describing a single, multifunctional cytokine family that is deployed by six orders of insect species to combat a diverse variety of environmental stresses. The originating member of this peptide family was identified in Mythimna (formerly called Pseudaletia) separata armyworm; the cytokine was named growth-blocking peptide (GBP), reflecting its actions in combating parasitic invasion. The peptide’s name has been retained, though the list of its regulatory activities has greatly expanded. All members of this family are small peptides, 19–25 amino acid residues, whose major source is fat body. They are now known to regulate embryonic morphogenesis, larval growth rates, feeding activities, immune responses, nutrition, and aging. In this review, we will describe recent developments in our understanding of the mechanisms of action of the GBP family, but we will also highlight remaining gaps in our knowledge.

Highlights

Growth-blocking peptide (GBP) was initially found as a peptidergic factor which blocks JH esterase activation in the hemolymph of early last instar larvae of host Mythimna separata armyworm upon infection by the parasitic wasp Cotesia kariyai (Hayakawa, 1990)
It was recently reported that DmGBP regulates the release of insulin-like peptides (ILPs) from the brain depending on nutrient levels in the hemolymph through target of rapamycin (TOR) in Drosophila (Koyama and Mirth, 2016)
Based on the prior results obtained by structural (Aizawa et al, 1999) and kinetic studies (Hayakawa and Ohnishi, 1998; Ohnishi et al, 2001), it is reasonable to expect that stimulation of cell growth by GBP requires another type of the receptor similar to the epidermal growth factor (EGF) family of receptor tyrosine kinases

Summary

Introduction

Growth-blocking peptide (GBP) was initially found as a peptidergic factor which blocks JH esterase activation in the hemolymph of early last instar larvae of host Mythimna (formerly called Pseudaletia) separata armyworm upon infection by the parasitic wasp Cotesia kariyai (Hayakawa, 1990). Subsequent studies established further functions of the GBP family such as cell growth activator, early morphogenetic mediator, and humoral immune mediator (Ohnishi et al, 2001; Tsuzuki et al, 2005, 2012). To identify their primary structures, hemolymph peptides that induce cell growth and plasmatocyte spreading activities were purified from Tenebrionid and bluebottle fly larvae (Matsumoto et al, 2012; Tsuzuki et al, 2012).

Results

Conclusion