Department of Molecular Evolution and Genomics, Heidelberg Institute of Zoology, University of Heidelberg, D-69120 Heidelberg, Germany.
Proc Natl Acad Sci U S A. 2011 May 31;108(22):9137-42. doi: 10.1073/pnas.1018109108. Epub 2011 May 16.
Polarized Wnt signaling along the primary body axis is a conserved property of axial patterning in bilaterians and prebilaterians, and depends on localized sources of Wnt ligands. However, the mechanisms governing the localized Wnt expression that emerged early in evolution are poorly understood. Here we find in the cnidarian Hydra that two functionally distinct cis-regulatory elements control the head organizer-associated Hydra Wnt3 (HyWnt3). An autoregulatory element, which mediates direct inputs of Wnt/β-catenin signaling, highly activates HyWnt3 transcription in the head region. In contrast, a repressor element is necessary and sufficient to restrict the activity of the autoregulatory element, thereby allowing the organizer-specific expression. Our results reveal that a combination of autoregulation and repression is crucial for establishing a Wnt-expressing organizing center in a basal metazoan. We suggest that this transcriptional control is an evolutionarily old strategy in the formation of Wnt signaling centers and metazoan axial patterning.
极性化的 Wnt 信号沿着初级体轴是两侧对称动物和原两侧对称动物轴向模式形成的一个保守特征，并且依赖于 Wnt 配体的局部来源。然而，在进化早期出现的局部 Wnt 表达的控制机制还了解甚少。在这里，我们在刺胞动物水螅中发现，两个功能不同的顺式调控元件控制与头部组织者相关的水螅 Wnt3（HyWnt3）。一个自调节元件，介导 Wnt/β-catenin 信号的直接输入，高度激活头部区域的 HyWnt3 转录。相比之下，一个抑制元件是必要的，也是充分的，以限制自调节元件的活性，从而允许组织者特异性表达。我们的结果表明，自调节和抑制的组合对于在基础后生动物中建立一个表达 Wnt 的组织中心是至关重要的。我们认为，这种转录控制是 Wnt 信号中心形成和后生动物轴向模式形成的一种古老的进化策略。
