Oguchi Kohei, Miura Toru
Misaki Marine Biological Station, Graduate School of Science, The University of Tokyo, Miura, Kanagawa, 238-0225, Japan.
Evodevo. 2023 Jul 27;14(1):12. doi: 10.1186/s13227-023-00216-w.
In social insects, interactions among colony members trigger caste differentiation with morphological modifications. In termite caste differentiation, caste-specific morphologies (such as mandibles in soldiers, genital organs in reproductives or wings in alates) are well developed during post-embryonic development under endocrine controls (e.g., juvenile hormone and ecdysone). Since body part-specific morphogenesis in caste differentiation is hormonally regulated by global factors circulated throughout the body, positional information should be required for the caste-specific and also body part-specific morphogenesis. To identify factors providing the positional information, expression and functional analyses of eight Hox genes were carried out during the three types of caste differentiation (i.e., soldier, neotenic and alate differentiation) in a termite, Hodotermopsis sjostedti.
Spatio-temporal patterns of Hox gene expression during caste differentiation were elucidated by real-time qPCR, showing the caste-specific upregulations of Hox genes during the differentiation processes. Among eight Hox genes, Deformed (Dfd) was upregulated specifically in mandibles in soldier differentiation, abdominal-A (abd-A) and Abdominal-B (Abd-B) were upregulated in the abdomen in neotenic differentiation, while Sex-comb reduced (Scr) and Antennapedia (Antp) were upregulated during alate differentiation. Furthermore, RNAi knockdown of Dfd in soldier differentiation and of abd-A and Abd-B in neotenic differentiation distorted the modifications of caste-specific morphologies.
Gene expression and functional analyses in this study revealed that, in the caste differentiation in termites, upregulation of Hox genes provide positional identities of body segments, resulting in the caste-specific morphogenesis. The acquisition of such developmental modifications would have enabled the evolution of sophisticated caste systems in termites.
在社会性昆虫中，群体成员之间的相互作用会引发具有形态变化的种姓分化。在白蚁的种姓分化过程中，特定种姓的形态（如兵蚁的颚、生殖蚁的生殖器官或有翅成虫的翅膀）在胚胎后发育过程中，在内分泌控制（如保幼激素和蜕皮激素）下充分发育。由于种姓分化中特定身体部位的形态发生受到全身循环的全局因子的激素调节，因此种姓特异性以及身体部位特异性的形态发生都需要位置信息。为了识别提供位置信息的因子，对白蚁（Hodotermopsis sjostedti）三种类型的种姓分化（即兵蚁、若蚁和有翅成虫分化）过程中的八个Hox基因进行了表达和功能分析。
通过实时定量PCR阐明了种姓分化过程中Hox基因表达的时空模式，显示在分化过程中Hox基因存在种姓特异性上调。在八个Hox基因中，变形基因（Dfd）在兵蚁分化的颚中特异性上调，腹部-A（abd-A）和腹部-B（Abd-B）在若蚁分化的腹部上调，而性梳减少基因（Scr）和触角足基因（Antp）在有翅成虫分化过程中上调。此外，在兵蚁分化中敲低Dfd基因以及在若蚁分化中敲低abd-A和Abd-B基因会扭曲种姓特异性形态的变化。
本研究中的基因表达和功能分析表明，在白蚁的种姓分化中，Hox基因的上调提供了身体节段的位置特征，从而导致种姓特异性的形态发生。这种发育变化的获得可能促成了白蚁复杂种姓系统的进化。
