Hox Gene Deformed is likely involved in mandibular regression during presoldier differentiation in the nasute termite Nasutitermes takasagoensis

Abstract

Division of labor is a distinguishing characteristic of eusocial insects. To understand the proximate factors underlying caste determination, it is essential to clarify the developmental mechanisms during the differentiation of each caste. Termite soldiers have species-specific and diverse morphologies that are specialized for colony defense. Soldiers of the subfamily Nasutitermitinae (Termitidae), one of the most derived termite groups, possess a long, horn-like frontal projection (nasus), an invaginated glandular structure in the head (frontal gland), and regressed mandibles. These morphological changes occur prior to the molt into presoldiers (the preceding stage of soldiers). In Drosophila and other insects, Hox genes determine segment identities; thus they might be involved in such body-part-specific modifications during soldier differentiation. Deformed (Dfd) functions not only in the formation of the mandible and maxilla but also in other head parts (e.g., eye-antennal disc) in other insects. In this study, we examined Dfd functions in nasus/frontal gland formation and mandibular regression in Nasutitermes takasagoensis. Relative expression analyses showed that Dfd expression levels in the mouthparts were significantly higher than those in any other body parts of workers before presoldier molt. Dfd RNA interference resulted in the inhibition of mandibular regression during presoldier differentiation, but nasus and frontal gland formation were not affected. These results suggest that Dfd is involved in the determination of mandibular positional information and specific modification during presoldier differentiation in N. takasagoensis. This is the first work to show the effects of Hox genes on caste-specific morphogenesis in social insects.

Social interactions affecting caste development through physiological actions in termites

“…In these cases, JH titers in workers might be suppressed to lower levels by the presence of soldiers (Figure 5D). Since the social interactions are suggested to affect the expression patterns of genes that were shown to regulate the soldier-specific morphogenesis (Koshikawa et al, 2002, 2003, 2005, 2010; Hattori et al, 2013; Toga et al, 2012, 2013), the relationships between those gene expression patterns and social interactions will be clarified sooner or later.…”

Expressions of juvenile hormone biosynthetic genes during presoldier differentiation in the incipient colony of Zootermopsis nevadensis (Isoptera: Archotermopsidae)

“…Keywords Social insects · Caste differentiation · Gene expression · CYP15 · JHAMT * Kiyoto Maekawa kmaekawa@sci.u-toyama.ac.jp 1 Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan changes were identified (e.g., Cornette et al 2008bCornette et al , 2013Koshikawa et al 2005;Masuoka et al 2013;Toga et al 2012Toga et al , 2013Watanabe and Maekawa 2012). However, it is still unknown when the genes involved in JH biosynthesis are activated and/or the JH titer increases during soldier differentiation under natural conditions.…”

Termite soldier mandibles are elongated by dachshund under hormonal and Hox gene controls

“…Among the Hox genes that determine the identity of body parts along the anterior-posterior axis, Dfd is known to provide the mandibular identity (Carroll, 1995;Hughes and Kaufman, 2002;Hughes and Kaufman, 2000). In addition, Dfd reportedly contributes to mandibular remodeling during the soldier differentiation (Toga et al, 2013). In H. sjostedti, Dfd expression was upregulated in JHA1w, although it was not significantly different from that in PE (Fig.…”

“…However, the mechanisms by which endocrine signals regulate mandible-specific allometric development are unclear, although several molecular studies on downstream factors have been reported (e.g. Ishikawa et al, 2010;Koshikawa et al, 2005Koshikawa et al, , 2010Miura et al, 1999;Toga et al, 2013). Thus, because the mandible grows allometrically during soldier differentiation, we hypothesized that patterning factors provide spatial information to the mandibular epithelia.…”