Toga Kouhei, Yoda Shinichi, Maekawa Kiyoto
Graduate School of Science and Engineering, University of Toyama, Toyama, Japan.
Naturwissenschaften. 2011 Sep;98(9):801-6. doi: 10.1007/s00114-011-0825-9. Epub 2011 Aug 2.
Termite soldiers are the most specialized caste of social insects in terms of their morphology and function. Soldier development requires increased juvenile hormone (JH) titer and the two molts via a presoldier stage. These molts are accompanied by dramatic morphological changes, including the exaggeration and regression of certain organs. Soldiers of the most apical termitid subfamily Nasutitermitinae possess not only a horn-like frontal tube, called the nasus, for the projection of defensive chemicals from the frontal gland reservoir but also regressed mandibles. Although candidate genes regulating soldier mandibular growth were reported in a relatively basal termite species, the regulatory mechanisms of mandibular regression remain unknown. To clarify these mechanisms, we performed morphological and histological examinations of the mandibles during soldier differentiation in Nasutitermes takasagoensis. Mandibular size reduced dramatically during soldier differentiation, and mandibular regression occurred just prior to the presoldier molt. Spotted TUNEL signals were observed in regressing mandibles of presoldiers, suggesting that the regression involved programmed cell death. Because soldiers of N. takasagoensis possess exaggerated organs (nasus and frontal gland), the present results suggest that JH-dependent regressive mechanisms exist in the mandibles without interfering with the formation of the exaggerated organs.
从形态和功能方面来看，白蚁兵蚁是社会性昆虫中最特化的品级。兵蚁的发育需要增加保幼激素（JH）滴度，并经过一个前兵蚁阶段进行两次蜕皮。这些蜕皮伴随着显著的形态变化，包括某些器官的增大和退化。最进化的白蚁亚科鼻白蚁亚科的兵蚁不仅拥有一个角状的额管，称为鼻，用于从额腺储库中喷射防御性化学物质，而且其下颚也退化了。尽管在一个相对原始的白蚁物种中报道了调控兵蚁下颚生长的候选基因，但下颚退化的调控机制仍然未知。为了阐明这些机制，我们对高砂鼻白蚁兵蚁分化过程中的下颚进行了形态学和组织学检查。在兵蚁分化过程中，下颚大小急剧减小，下颚退化发生在前兵蚁蜕皮之前。在前兵蚁退化的下颚中观察到点状TUNEL信号，表明这种退化涉及程序性细胞死亡。由于高砂鼻白蚁的兵蚁拥有增大的器官（鼻和额腺），目前的结果表明，下颚中存在依赖保幼激素的退化机制，而不会干扰增大器官的形成。
