Graduate School of Science and Engineering, University of Toyama, Toyama, Japan.
J Exp Zool B Mol Dev Evol. 2013 Sep;320(6):385-92. doi: 10.1002/jez.b.22512. Epub 2013 May 15.
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.
分工是真社会性昆虫的一个显著特征。为了理解决定级型的近因，阐明每个级型分化过程中的发育机制是至关重要的。白蚁兵蚁具有特定物种、多样的形态，专门用于蚁群防御。在最衍生的白蚁类群之一的鼻白蚁亚科（白蚁科）中，兵蚁具有长而角状的额前突起（鼻）、头部内陷的腺状结构（额腺）和退化的下颚。这些形态变化发生在预兵蚁蜕皮之前（兵蚁的前一个阶段）。在果蝇和其他昆虫中，Hox 基因决定体节的身份；因此，它们可能参与兵蚁分化过程中这种特定于身体部位的修饰。变形（Dfd）不仅在下颚和上颚的形成中起作用，而且在其他昆虫的其他头部部分（例如，眼触角盘）中也起作用。在这项研究中，我们研究了 Dfd 在鼻白蚁（Nasutitermes takasagoensis）的鼻/额腺形成和下颚退化中的作用。相对表达分析表明，在预兵蚁蜕皮之前，Dfd 在口器中的表达水平明显高于任何其他体节的表达水平。Dfd RNA 干扰导致预兵蚁分化过程中下颚退化的抑制，但鼻和额腺的形成不受影响。这些结果表明，Dfd 参与了 Nasutitermes takasagoensis 中下颚位置信息的决定和预兵蚁分化过程中的特定修饰。这是首次证明 Hox 基因对社会性昆虫特定级型形态发生的影响的工作。
