title: Soldier morphogenesis in the damp-wood termite is regulated by the insulin signaling pathway.
abstract: Eusocial insects exhibit various morphological castes associated with the division of labor within a colony. Termite soldiers possess defensive traits including mandibles that are greatly exaggerated and enlarged, as compared to termite reproductives and workers. The enlarged mandibles of soldiers are known to result from dynamic morphogenesis during soldier differentiation that can be induced by juvenile hormone and its analogs. However, the detailed developmental mechanisms still remain unresolved. Because the insulin/insulin-like growth factor signaling (IIS) pathway has been shown to regulate the relative sizes of organs (i.e., allometry) in other insects, we examined the expression profiles of major IIS factors in the damp-wood termite Hodotermopsis sjostedti, during soldier differentiation. The relative expression patterns of orthologs for termite InR (HsjInR), PKB/Akt (HsjPKB/Akt), and FOXO (HsjFOXO) suggest that HsjInR and HsjPKB/Akt were up-regulated in the period of elongation of mandibles during soldier development. In situ hybridization showed that HsjInR was strongly expressed in the mandibular epithelial tissues, and RNA interference (RNAi) for HsjInR disrupted soldier-specific morphogenesis including mandibular elongation. These results suggest that signaling through the IIS pathway is required for soldier-specific morphogenesis. In addition, up-regulation of the IIS pathway in other body tissues occurred at earlier stages of development, indicating that there is tissue-specific IIS regulation. Because the IIS pathway is generally thought to act upstream of JH in insects, our results suggest the damp-wood termite may have evolved a novel feedback loop between JH and IIS that enables social interactions, rather than nutrition, to regulate caste determination.
authors.affiliation: Graduate School of Environmental Science, Hokkaido University, Sapporo, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Hattori
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Sugime
authors.forename: Chifune
authors.initials: C
authors.lastname: Sasa
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Miyakawa
authors.forename: Yuki
authors.initials: Y
authors.lastname: Ishikawa
authors.forename: Satoshi
authors.initials: S
authors.lastname: Miyazaki
authors.forename: Yasukazu
authors.initials: Y
authors.lastname: Okada
authors.forename: Richard
authors.initials: R
authors.lastname: Cornette
authors.forename: Laura Corley
authors.initials: LC
authors.lastname: Lavine
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Emlen
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Koshikawa
authors.forename: Toru
authors.initials: T
authors.lastname: Miura
mesh_terms: D000818:Animals; D017403:In Situ Hybridization; D007328:Insulin / Q000378:metabolism*; D020049:Isoptera / Q000254:growth & development*; D007605:Juvenile Hormones / Q000378:metabolism; D009024:Morphogenesis; D015398:Signal Transduction; D014934:Wood / Q000737:chemistry
chemical_list: D007328:Insulin; D007605:Juvenile Hormones