Gufler S, Artes B, Bielen H, Krainer I, Eder M-K, Falschlunger J, Bollmann A, Ostermann T, Valovka T, Hartl M, Bister K, Technau U, Hobmayer B
Institute of Zoology and Center for Molecular Biosciences, University of Innsbruck, Austria.
Department of Molecular Evolution and Development, University of Vienna, Austria.
Dev Biol. 2018 Jan 15;433(2):310-323. doi: 10.1016/j.ydbio.2017.09.005. Epub 2017 Nov 3.
Wnt/β-Catenin signaling plays crucial roles in regenerative processes in eumetazoans. It also acts in regeneration and axial patterning in the simple freshwater polyp Hydra, whose morphallactic regenerative capacity is unparalleled in the animal kingdom. Previous studies have identified β-catenin as an early response gene activated within the first 30min in Hydra head regeneration. Here, we have studied the role of β-Catenin in more detail. First, we show that nuclear β-Catenin signaling is required for head and foot regeneration. Loss of nuclear β-Catenin function blocks head and foot regeneration. Transgenic Hydra tissue, in which β-Catenin is over-expressed, regenerates more heads and feet. In addition, we have identified a set of putative β-Catenin target genes by transcriptional profiling, and these genes exhibit distinct expression patterns in the hypostome, in the tentacles, or in an apical gradient in the body column. All of them are transcriptionally up-regulated in the tips of early head and foot regenerates. In foot regenerates, this is a transient response, and expression starts to disappear after 12-36h. ChIP experiments using an anti-HydraTcf antibody show Tcf binding at promoters of these targets. We propose that gene regulatory β-Catenin activity in the pre-patterning phase is generally required as an early regeneration response. When regenerates are blocked with iCRT14, initial local transcriptional activation of β-catenin and the target genes occurs, and all these genes remain upregulated at the site of both head and foot regeneration for the following 2-3 days. This indicates that the initial regulatory network is followed by position-specific programs that inactivate fractions of this network in order to proceed to differentiation of head or foot structures. brachyury1 (hybra1) has previously been described as early response gene in head and foot regeneration. The HyBra1 protein, however, appears in head regenerating tips not earlier than about twelve hours after decapitation, and HyBra1 translation does not occur in iCRT14-treated regenerates. Foot regenerates never show detectable levels of HyBra1 protein at all. These results suggest that translational control mechanisms may play a decisive role in the head- and foot-specific differentiation phase, and HyBra1 is an excellent candidate for such a key regulator of head specification.
Wnt/β-连环蛋白信号通路在真后生动物的再生过程中起着关键作用。它也在简单的淡水水螅的再生和轴向模式形成中发挥作用，其形态再生能力在动物界中无与伦比。先前的研究已将β-连环蛋白鉴定为水螅头部再生最初30分钟内被激活的早期反应基因。在此，我们更详细地研究了β-连环蛋白的作用。首先，我们表明核β-连环蛋白信号传导是头部和足部再生所必需的。核β-连环蛋白功能的丧失会阻碍头部和足部再生。β-连环蛋白过度表达的转基因水螅组织能再生出更多的头部和足部。此外，我们通过转录谱分析鉴定出一组假定的β-连环蛋白靶基因，这些基因在口部、触手或体柱的顶端梯度中表现出不同的表达模式。它们在早期头部和足部再生的顶端均转录上调。在足部再生中，这是一种短暂反应，12 - 36小时后表达开始消失。使用抗水螅Tcf抗体进行的染色质免疫沉淀实验表明Tcf与这些靶标的启动子结合。我们提出，在预模式形成阶段，基因调控性β-连环蛋白活性通常作为早期再生反应是必需的。当再生被iCRT14阻断时，β-连环蛋白和靶基因会发生初始局部转录激活，并且在接下来的2 - 3天里，所有这些基因在头部和足部再生部位均保持上调。这表明初始调控网络之后是位置特异性程序，该程序会使该网络的部分失活，以便进行头部或足部结构的分化。短尾相关蛋白1（hybra1）先前已被描述为头部和足部再生中的早期反应基因。然而，HyBra1蛋白在断头后不早于约12小时出现在头部再生顶端，并且在iCRT14处理的再生体中不发生HyBra1翻译。足部再生体根本从未显示出可检测到的HyBra1蛋白水平。这些结果表明，翻译控制机制可能在头部和足部特异性分化阶段起决定性作用，并且HyBra1是这种头部特化关键调节因子的极佳候选者。
