Heads or Tails

Planarians--tubular flatworms--can regenerate all of their body parts and entire organ systems after amputation. However, the mechanism by which the animal "knows" how to generate a head after head removal or a tail after tail removal, a property called regeneration polarity, is unknown. Gurley et al. and Petersen and Reddien now find that a conserved factor within the Wnt signaling pathway is used to distinguish head from tail. Decreased Wnt signaling through β-catenin causes the regeneration of heads, whereas activation of Wnt signaling induces tails. β-catenin also maintains the anteroposterior body axis in uncut animals. K. A. Gurley, J. C. Rink, A. Sánchez Alvarado, β-catenin defines head versus tail identity during planarian regeneration and homeostasis. Science 319 , 323-327 (2008). [Abstract] [Full Text] C. P. Petersen, P. W. Reddien, Smed -β catenin -1 is required for anteroposterior blastema polarity in planarian regeneration. Science 319 , 327-330 (2008). [Abstract] [Full Text]