Effects of Caste on the Expression of Genes Associated with Septic Injury and Xenobiotic Exposure in the Formosan Subterranean Termite

As social insects, termites live in densely populated colonies with specialized castes under conditions conducive to microbial growth and transmission. Furthermore, termites are exposed to xenobiotics in soil and their lignocellulose diet. Therefore, termites are valuable models for studying gene expression involved in response to septic injury, immunity and detoxification in relation to caste membership. In this study, workers and soldiers of the Formosan subterranean termite, Coptotermes formosanus, were challenged by bacterial injection or by no-choice feeding with a sublethal concentration (0.5%) of phenobarbital. Constitutive and induced expression of six putative immune response genes (two encoding for lectin-like proteins, one for a ficolin-precursor, one for the Down syndrome cell adhesion molecule, one for a chitin binding protein, and one for the gram-negative binding protein 2) and four putative detoxification genes (two encoding for cytochrome P450s, one for glutathione S-transferase, and one for the multi antimicrobial extrusion protein), were measured via quantitative real time polymerase chain reaction and compared within and among 1) colonies, 2) treatment types and 3) castes via ANOVA. Eight genes were inducible by septic injury, feeding with phenobarbital or both. Colony origin had no effect on inducibility or differential gene expression. However, treatment type showed significant effects on the expression of the eight inducible genes. Caste effects on expression levels were significant in five of the eight inducible genes with constitutive and induced expression of most target genes being higher in workers than in soldiers.作为社会性昆虫，白蚁栖息于种群密度极高的社群中，拥有特化的品级，其生存环境适宜微生物的增殖与传播。此外，白蚁还会接触到土壤及其木质纤维素（lignocellulose）膳食中的外源性化合物（xenobiotics）。因此，白蚁是研究与品级相关的脓毒症损伤应答、免疫及解毒过程相关基因表达的理想模型。本研究以台湾乳白蚁（Coptotermes formosanus）的工蚁与兵蚁为实验材料，分别通过细菌注射法，以及以0.5%亚致死浓度苯巴比妥（phenobarbital）进行无选择饲喂的方式开展胁迫处理。本研究通过实时荧光定量聚合酶链式反应（quantitative real time polymerase chain reaction），检测了6个推定免疫应答基因（分别编码2个凝集素样蛋白（lectin-like proteins）、1个纤维胶凝蛋白前体（ficolin-precursor）、1个唐氏综合征细胞黏附分子（Down syndrome cell adhesion molecule）、1个几丁质结合蛋白（chitin binding protein）以及1个革兰氏阴性菌结合蛋白2（gram-negative binding protein 2））和4个推定解毒基因（分别编码2个细胞色素P450（cytochrome P450s）、1个谷胱甘肽S-转移酶（glutathione S-transferase）以及1个多抗菌外排蛋白（multi antimicrobial extrusion protein））的组成型表达与诱导型表达水平，并通过方差分析（ANOVA）从1）蚁群来源、2）处理类型、3）品级三个维度，对基因表达在组内及组间的差异进行了比较。共有8个基因可被脓毒症损伤、苯巴比妥饲喂或两者联合处理诱导表达。蚁群来源对基因的诱导性及差异表达均无显著影响。但处理类型对这8个诱导型基因的表达水平具有显著影响。在8个诱导型基因中，有5个基因的表达水平存在显著的品级差异；多数靶基因的组成型与诱导型表达水平均在工蚁中高于兵蚁。