title: Hexamerin-based regulation of juvenile hormone-dependent gene expression underlies phenotypic plasticity in a social insect.
abstract: Worker termites of the genus Reticulitermes are temporally-arrested juvenile forms that can terminally differentiate into adultsoldier- or reproductive-caste phenotypes. Soldier-caste differentiation is a developmental transition that is induced by high juvenile hormone (JH) titers. Recently, a status quo hexamerin mechanism was identified, which reduces JH efficacy and maximizes colony fitness via the maintenance of high worker-caste proportions. Our goal in these studies was to investigate more thoroughly the influences of the hexamerins on JH-dependent gene expression in termite workers. Our approach involved RNA interference (RNAi), bioassays and quantification of gene expression. We first investigated the expression of 17 morphogenesis-associated genes in response to RNAi-based hexamerin silencing. Hexamerin silencing resulted in significant downstream impacts on 15 out of the 17 genes, suggesting that these genes are members of a JH-responsive genomic network. Next, we compared gene-expression profiles in workers after RNAi-based hexamerin silencing to that of (i) untreated workers that were held away from the colony; and (ii) workers that were also held away from the colony, but with ectopic JH. Here, although there was no correlation between hexamerin silencing and colony-release effects, we observed a significant correlation between hexamerin silencing and JH-treatment effects. These findings provide further evidence supporting the hypothesis that the hexamerins modulate JH availability, thus limiting the impacts of JH on termite caste polyphenism. Results are discussed in a context relative to outstanding questions on termite developmental biology, particularly on regulatory gene networks that respond to JH-, colony- and environmental-cues.
authors.affiliation: Entomology and Nematology Department, University of Florida, Gainesville, FL 32611-0620, USA.
authors.forename: Xuguo
authors.initials: X
authors.lastname: Zhou
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Tarver
authors.forename: Michael E
authors.initials: ME
authors.lastname: Scharf
mesh_terms: D000818:Animals; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D017344:Genes, Insect; D019476:Insect Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism*; D020049:Isoptera / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D007605:Juvenile Hormones / Q000235:genetics* / Q000378:metabolism* / Q000494:pharmacology; D008297:Male; D008954:Models, Biological; D010641:Phenotype; D034622:RNA Interference; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D017931:DNA Primers; D019476:Insect Proteins; D007605:Juvenile Hormones; D014157:Transcription Factors; C041137:storage proteins, Insecta