title: Insect neuropeptide bursicon homodimers induce innate immune and stress genes during molting by activating the NF-κB transcription factor Relish.
abstract: BACKGROUND
  Bursicon is a heterodimer neuropeptide composed of two cystine knot proteins, bursicon α (burs α) and bursicon β (burs β), that elicits cuticle tanning (melanization and sclerotization) through the Drosophila leucine-rich repeats-containing G protein-coupled receptor 2 (DLGR2). Recent studies show that both bursicon subunits also form homodimers. However, biological functions of the homodimers have remained unknown until now.
  
  
  RESULTS
  In this report, we show in Drosophila melanogaster that both bursicon homodimers induced expression of genes encoding antimicrobial peptides (AMPs) in neck-ligated adults following recombinant homodimer injection and in larvae fat body after incubation with recombinant homodimers. These AMP genes were also up-regulated in 24 h old unligated flies (when the endogenous bursicon level is low) after injection of recombinant homodimers. Up-regulation of AMP genes by the homodimers was accompanied by reduced bacterial populations in fly assay preparations. The induction of AMP expression is via activation of the NF-κB transcription factor Relish in the immune deficiency (Imd) pathway. The influence of bursicon homodimers on immune function does not appear to act through the heterodimer receptor DLGR2, i.e. novel receptors exist for the homodimers.
  
  
  CONCLUSIONS
  Our results reveal a mechanism of CNS-regulated prophylactic innate immunity during molting via induced expression of genes encoding AMPs and genes of the Turandot family. Turandot genes are also up-regulated by a broader range of extreme insults. From these data we infer that CNS-generated bursicon homodimers mediate innate prophylactic immunity to both stress and infection during the vulnerable molting cycle.
authors.affiliation: Division of Plant Sciences, University of Missouri, Columbia, Missouri, United States of America.
authors.forename: Shiheng
authors.initials: S
authors.lastname: An
authors.forename: Shengzhang
authors.initials: S
authors.lastname: Dong
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.forename: Sheng
authors.initials: S
authors.lastname: Li
authors.forename: Lawrence I
authors.initials: LI
authors.lastname: Gilbert
authors.forename: David
authors.initials: D
authors.lastname: Stanley
authors.forename: Qisheng
authors.initials: Q
authors.lastname: Song
mesh_terms: D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000378:metabolism; D019281:Dimerization; D029721:Drosophila Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000254:growth & development / Q000276:immunology*; D005786:Gene Expression Regulation; D007113:Immunity, Innate; D007447:Invertebrate Hormones / Q000276:immunology / Q000378:metabolism*; D007814:Larva; D018978:Molting / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D023181:Antimicrobial Cationic Peptides; D029721:Drosophila Proteins; D007447:Invertebrate Hormones; C101626:Rel protein, Drosophila; D014157:Transcription Factors; C002295:bursicon