Caste differentiation in termites is one of the most conspicuous examples of facultative polyphenism in animals. It is clear that specific cuticular formation occurs in hard exocuticles during caste differentiation. However, the developmental pattern of the soft endocuticle in the differentiation pathways of castes is unknown. To reveal whether the endocuticle is involved in caste differentiation, we compared the exocuticle and endocuticle thickness of individuals in 2 pathways (nymph line and worker line) of caste differentiation in the termite Reticulitermes aculabialis. The endocuticle protein genes were identified by transcriptome analysis and the expression patterns of these genes were confirmed in caste differentiation. We found that the endocuticle structure showed dynamic changes in 2 pathways, and the first difference in endocuticle structure occurred after larvae differentiation bifurcated into workers and nymphs. The thinning of the endocuticle was a significant event from nymphs developing into alates with the thickest exocuticle and thinnest endocuticle. The thickest endocuticle layers were found in the heads of the workers and the ultrastructure of the endocuticle in the heads was more complex than that in the thorax–abdomens. Six endocuticle protein genes were identified and annotated as endocuticle structural glycoproteins SgAbd-2, SgAbd-9, and Abd-5. The expression levels of endocuticle protein genes changed dramatically during caste development and the expression levels in neotenic reproductives (secondary reproductives) were significantly higher than those in alates (primary reproductives). These results reveal the roles of endocuticles in caste differentiation and adaptation to the environment.

中文翻译：

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内表皮参与低等白蚁的种姓分化


白蚁的种姓分化是动物兼性多型现象最明显的例子之一。很明显，在种姓分化过程中，硬外角质层中发生了特定的角质层形成。然而，软内表皮在种姓分化途径中的发育模式尚不清楚。为了揭示内表皮是否参与种姓分化，我们比较了白蚁散白蚁种姓分化的 2 个途径（若虫系和工蜂系）中个体的外表皮和内表皮厚度。通过转录组分析鉴定了内表皮蛋白基因，并在种姓分化中证实了这些基因的表达模式。我们发现内表皮结构在2个途径中表现出动态变化，并且内表皮结构的第一个差异发生在幼虫分化为工蚁和若虫之后。内表皮变薄是若虫发育成具有最厚的外表皮和最薄的内表皮的有翼的一个重要事件。工蚁头部的内表皮层最厚，且头部内表皮的超微结构比胸腹部更为复杂。六个内表皮蛋白基因被鉴定并注释为内表皮结构糖蛋白 SgAbd-2、SgAbd-9 和 Abd-5。在种姓发育过程中，内表皮蛋白基因的表达水平发生了显着变化，幼态生殖动物（二次生殖动物）的表达水平显着高于有翼动物（初级生殖动物）。这些结果揭示了内表皮在种姓分化和适应环境中的作用。