Reduction of a nymphal instar in a dampwood termite: heterochronic shift in the caste differentiation pathways
Reduction of a nymphal instar in a dampwood termite: heterochronic shift in the caste differentiation pathways
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DOI：
10.1186/s13227-019-0123-8
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发表时间：
2019-05-16
期刊：
影响因子：
4.1
通讯作者：
Miura, Toru
中科院分区：
文献类型：
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作者：
Nii, Ryotaro;Oguchi, Kohei;Miura, Toru
背景：一般来说，在白蚁中，有翼虫通过多个若虫龄进行分化，并逐渐发育出翼芽。然而，在湿木白蚁（Hodotermopsis sjostedti）中，直接从具有短翅芽的单个若虫龄中蜕皮。本研究为了探讨H. sjostedti有翅分化过程中翅形成的机制，对若虫龄期间翅形成的发育过程进行了组织学和形态学观察，并与具有两个若虫期的Zootermopsis nevadensis进行了比较。此外，在有翼分化过程中对被认为负责翅膀形成的基因（即翅膀图案基因和编码激素相关因子的基因）的表达模式进行了定量，并在两个物种之间进行了比较。 结果：结果表明，在H. sjostedti中，翅膀形成为复杂的折叠形状，不仅像内华达州的翅芽内部，而且在背胸角质层下，翼尖向胸中部移动。因此，翅膀的展开模式也与 Z. nevadensis 不同。此外，对翅膀图案基因和激素相关基因整体表达谱的实时 qRT-PCR 结果表明，H. sjostedti 中的单个若虫龄与 Z. nevadensis 中的第二若虫龄非常相似。特别是，在 Z. nevadensis 的第二若虫龄中观察到的 Vestitial (vg) 的显着上调和 Kruppel 同源物 1 (Kr-h1) 的显着下调，显然发生在 H. sjostedti 的单若虫龄期间。被认为可以补偿小翅芽内部的空间限制，从而完成功能性翅膀。
Background: Generally in termites, alates differentiate through multiple nymphal instars which gradually develop wing buds. However, in a dampwood termite, Hodotermopsis sjostedti, alates molt directly from a single nymphal instar with short wing buds. In this study, to examine the mechanism underlying the wing formation during the alate differentiation in H. sjostedti, histological and morphological observations were carried out on the developmental process of wing formation during the nymphal instar, in comparison with those in Zootermopsis nevadensis, which has two nymphal instars. Furthermore, the expression patterns of genes that are thought to be responsible for wing formation, i.e., wing-patterning genes and genes encoding hormone-related factors, were quantified during alate differentiation and compared between the two species.Results: The results showed that, in H. sjostedti, wings were formed in a complicatedly folded shape, not only inside the wing buds as seen in Z. nevadensis, but also under the dorsal thoracic cuticle, where the wing tips shifted toward the median thoracic part. Accordingly, the wing expansion pattern also differed from that in Z. nevadensis. Furthermore, the results of real-time qRT-PCR on overall expression profiles of wing-patterning genes and hormone-related genes suggest that the single nymphal instar in H. sjostedti well resembles to the second nymphal instar in Z. nevadensis. In particular, significant upregulation of vestigial (vg) and downregulation of Kruppel homolog 1 (Kr-h1) that were observed at the second nymphal instar in Z. nevadensis apparently occurred during the single nymphal instar in H. sjostedti.Conclusion: The developmental events for wing formation are compacted into a single nymphal instar in H. sjostedti, and as a result, the unique wing formation is seen to compensate for the spatial restriction inside small wing buds, leading to the completion of functional wings.