Beta-catenin and axis formation in planarians

In three recent articles it was shown that P-catenin is crucial for the establishment and the maintenance of the overall polarity and especially for the character 'posterior' in planarians. If the transcription of the P-catenin gene was silenced by RNA interference, the overall polarity is lost, and in regenerating fragments a posterior blastema displays anterior characters by forming eyes and anterior ganglia. An attempt is made to integrate these new data, well-known older observations, and observations from other regenerating systems into an outline of a model that will clarify our current understanding as well as highlight areas still to be developed.