To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.cell.2009.11.035 Byline: Christian P. Petersen (1), Peter W. Reddien (1)(2)(3) Abstract: How animals establish and pattern the primary body axis is one of the most fundamental problems in biology. Data from diverse deuterostomes (frog, fish, mouse, and amphioxus) and from planarians (protostomes) suggest that Wnt signaling through [beta]-catenin controls posterior identity during body plan formation in most bilaterally symmetric animals. Wnt signaling also influences primary axis polarity of pre-bilaterian animals, indicating that an axial patterning role for Wnt signaling predates the evolution of bilaterally symmetric animals. The use of posterior Wnt signaling and anterior Wnt inhibition might be a unifying principle of body plan development in most animals. Author Affiliation: (1) Whitehead Institute for Biomedical Research, 9 Cambridge Center, Cambridge, MA 02142, USA (2) Department of Biology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02142, USA (3) Howard Hughes Medical Institute