How Hydras get their heads

In the 14 September Nature Hobmayer et al. find that Wnt signaling proteins are expressed in the head organizer of Hydra, a freshwater polyp, suggesting that Wnt was central in the evolution of axial differentiation in early multicellular animals (Nature 2000, 407:186-189). Hobmayer et al. isolate a number of Wnt pathway proteins from Hydra and find that their protein-interacting domains are well conserved when compared with Wnt pathway proteins from metazoans. Expression of Hydra β-catenin in frog embryos duplicates the embryos' head structures, and Wnt signaling proteins are turned on in newly budded or regenerating Hydra heads. The previous candidates for ancient anterior patterners were the Hox genes; determining how Hox function and Wnt function relate to each other will require further study.