Department of Integrative Biology, University of Wisconsin-Madison, Madison, WI 53706.
Department of Integrative Biology, University of Wisconsin-Madison, Madison, WI 53706
Proc Natl Acad Sci U S A. 2018 Apr 10;115(15):E3491-E3500. doi: 10.1073/pnas.1720193115. Epub 2018 Mar 26.
The jointed appendages of arthropods have facilitated the spectacular diversity and success of this phylum. Key to the regulation of appendage outgrowth is the Krüppel-like factor (KLF)/specificity protein (Sp) family of zinc finger transcription factors. In the fruit fly, , the homolog is activated by () and establishes ventral appendage (leg) fate. Subsequently, maintains expression of the axial patterning gene (), which promotes limb outgrowth. Intriguingly, in spiders, has been reported to have a derived role as a segmentation gap gene, but the evolutionary origin and regulation of this function are not understood because functional investigations of the appendage-patterning regulatory network are restricted to insects. We tested the evolutionary conservation of the ancestral appendage-patterning network of arthropods with a functional approach in the spider. RNAi-mediated knockdown of the spider ortholog resulted in diminution or loss of expression and truncation of appendages, as well as loss of the two body segments specified by the early function. In reciprocal experiments, is shown not to be required for expression. Knockdown of (Wnt-1 coreceptor) disrupted segmentation and appendage development but did not affect the early expression domain. Ectopic appendages generated in the spider "abdomen" by knockdown of the Hox gene () expressed comparably to wild-type walking legs. Our results support () the evolutionary conservation of an appendage-patterning regulatory network that includes canonical Wnt signaling, , and and () the cooption of the regulatory cassette in arachnid head segmentation.
节肢动物的关节附肢促进了这一门类的惊人多样性和成功。调节附肢生长的关键是 Krüppel 样因子（KLF）/特异性蛋白（Sp）家族的锌指转录因子。在果蝇中，同源物被 ()激活，并建立腹侧附肢（腿）命运。随后，维持轴向模式基因 ()的表达，促进肢体生长。有趣的是，在蜘蛛中，已经报道 ()具有衍生的体节间隙基因的作用，但这种功能的进化起源和调节尚不清楚，因为对附肢模式形成调控网络的功能研究仅限于昆虫。我们通过在蜘蛛中进行功能测试，检验了节肢动物祖先附肢模式网络的进化保守性。蜘蛛 同源物的 RNAi 介导敲低导致 ()表达减少或丧失，附肢缩短，以及早期 ()功能指定的两个体节丧失。在相互实验中，表明 ()不需要用于 ()表达。()（Wnt-1 核心受体）的敲低破坏了体节和附肢发育，但不影响早期 ()表达域。通过敲低 Hox 基因 ()在蜘蛛“腹部”产生的额外附肢表达与野生型步行腿相当。我们的结果支持 ()包括经典 Wnt 信号、()、和 ()的附肢模式形成调控网络的进化保守性，以及 ()蛛形纲头部体节中 ()调控盒的共适应。
