Setton Emily V W, Sharma Prashant P
Department of Integrative Biology, University of Wisconsin-Madison, Madison, WI, USA 53706.
Dev Biol. 2021 Jul;475:91-105. doi: 10.1016/j.ydbio.2021.02.006. Epub 2021 Feb 16.
Segmentation is a key characteristic of Arthropoda that is linked to the evolutionary success of this lineage. It has previously been shown in both vertebrates and short germ insects that posterior segmentation requires canonical Wnt (cWnt) signaling, which maintains the expression of Caudal and the posterior growth zone; disruption of cWnt signaling incurs posterior truncations in these lineages due to the loss of the tail bud. However, comparable datasets for Wnt signaling are limited outside of holometabolous insects, due to incomparable phenotypic spectra and inefficacy of gene misexpression methods in certain model species. We applied RNA interference (RNAi) against the Wnt co-receptor arrow (arr), a key member of the cWnt signaling pathway in holometabolous insects and vertebrates, to examine posterior axis elongation of the cobweb spider Parasteatoda tepidariorum (short germ embryogenesis; one Wnt8 homolog), the cricket Gryllus bimaculatus (intermediate germ; one Wnt8 homolog), and the milkweed bug Oncopeltus fasciatus (short germ; two Wnt8 homologs). Knockdown of arr in insects resulted in posterior truncations affecting the gnathos through the abdomen in O. fasciatus, whereas posterior truncations only affected the T3 segment through the abdomen in G. bimaculatus. Spider embryos with disrupted arr expression exhibited defects along the entire axis, including segmentation defects throughout the germband. RNA-Seq-based differential gene expression analysis of severe Ptep-arr loss-of-function phenotypes at two developmental stages was used to confirm that knockdown of Ptep-arr results in systemic disruption of the Wnt pathway. Intriguingly, we found that knockdown of arr did not abrogate Wnt8 expression in any of the three species, with cad expression additionally retained in severe loss-of-function phenotypes in the cricket and the spider. Together with data from a holometabolous insect, our results suggest that cWnt signaling is not required for maintenance of Wnt8 expression across Arthropoda. These outcomes underscore the diagnostic power of differential gene expression analyses in characterizing catastrophic phenotypes in emerging model species.
分节是节肢动物的一个关键特征，与该谱系的进化成功相关。此前在脊椎动物和短胚昆虫中均已表明，后部体节形成需要经典Wnt（cWnt）信号传导，该信号传导维持尾型基因（Caudal）的表达以及后部生长区；cWnt信号传导的破坏会导致这些谱系中由于尾芽缺失而出现后部截断。然而，由于表型谱不可比以及某些模式物种中基因错误表达方法的无效性，全变态昆虫之外的Wnt信号传导的可比数据集有限。我们针对Wnt共受体箭蛋白（arrow，arr）应用RNA干扰（RNAi），arr是全变态昆虫和脊椎动物中cWnt信号通路的关键成员，以研究蛛形纲动物温氏蛛（Parasteatoda tepidariorum，短胚发育；一个Wnt8同源物）、双斑蟋（Gryllus bimaculatus，中胚发育；一个Wnt8同源物）和乳草蝽（Oncopeltus fasciatus，短胚发育；两个Wnt8同源物）的后部轴伸长情况。在昆虫中敲低arr会导致后部截断，在乳草蝽中影响从颚节到腹部的部分，而在双斑蟋中后部截断仅影响从第三胸节到腹部的部分。箭蛋白表达被破坏的蜘蛛胚胎在整个轴上都表现出缺陷，包括胚带各处的分节缺陷。基于RNA测序的两个发育阶段严重温氏蛛arr功能丧失表型的差异基因表达分析用于确认敲低温氏蛛arr会导致Wnt通路的系统性破坏。有趣的是，我们发现敲低arr在这三个物种中均未消除Wnt8的表达，在蟋和蜘蛛严重功能丧失表型中尾型基因表达也得以保留。结合来自全变态昆虫的数据，我们的结果表明，在整个节肢动物中维持Wnt8表达不需要cWnt信号传导。这些结果强调了差异基因表达分析在表征新兴模式物种灾难性表型方面的诊断能力。
