Hexamerin-based regulation of juvenile hormone-dependent gene expression underlies phenotypic plasticity in a social insect

• Published in: Development (Cambridge) Vol. 134; no. 3; pp. 601 - 610
• Main Authors: Zhou, Xuguo, Tarver, Matthew R, Scharf, Michael E
• Format: Journal Article
• Language: English
• Published: England The Company of Biologists Limited 01.02.2007
• Subjects: Animals; Base Sequence; DNA Primers - genetics; Female; Gene Expression Regulation, Developmental - drug effects; Genes, Insect; Insect Proteins - antagonists & inhibitors; Insect Proteins - genetics; Insect Proteins - metabolism; Isoptera - drug effects; Isoptera - genetics; Isoptera - growth & development; Isoptera - metabolism; Juvenile Hormones - genetics; Juvenile Hormones - metabolism; Juvenile Hormones - pharmacology; Male; Models, Biological; Phenotype; Reticulitermes; RNA Interference; Signal Transduction; Transcription Factors - genetics; Transcription Factors - metabolism
• ISSN: 0950-1991; 1477-9129
• DOI: 10.1242/dev.02755

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.