How an animal establishes its body axis is a fundamental question in developmental biology. The freshwater cnidarian Hydra is an attractive model for studying axis formation because it is radially symmetric, with a single oral-aboral axis. It was recently proposed that the orientation of the new body axis in a regenerating Hydra polyp is determined by the oral-aboral orientation of the actin-myosin contractile processes (myonemes) in the animal’s outer epithelial layer. However, it remained unclear how the oral-aboral polarity of the body axis would be defined. As Wnt signaling is known to control axis polarity in Hydra and bilaterians, we hypothesized that it plays a role in axis formation during regeneration of Hydra tissue pieces. We tested this hypothesis using pharmacological perturbations and novel grafting experiments to set Wnt signaling and myoneme orientation perpendicular to each other to determine which controls axis formation. Our results demonstrate that Wnt signaling is the dominant encoder of axis orientation and polarity, in line with its conserved role in axial patterning.

动物如何建立其体轴是发育生物学中的一个基本问题。淡水刺胞Hydra是研究轴形成的一种有吸引力的模型，因为它是径向对称的，具有一个单一的口腔-口腔轴。最近有人提出，在再生的九头蛇息肉中新的身体轴的方向是由动物外上皮层中肌动蛋白-肌球蛋白收缩过程（肌动蛋白）的口腔-口腔方向决定的。然而，仍不清楚如何定义体轴的口腔-胸腔极性。由于已知Wnt信号会控制九头蛇和双侧人的轴极性，因此我们假设它在九头蛇的再生过程中在轴形成中起作用组织碎片。我们使用药理学扰动和新颖的嫁接实验对这一假设进行了测试，以将Wnt信号传导和Myoneme方向设置为彼此垂直，以确定哪个控制轴的形成。我们的结果表明，Wnt信号是轴方向和极性的主要编码器，与其在轴向构图中的保守作用一致。