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Science 332 (6031): 852-855

Copyright © 2011 by the American Association for the Advancement of Science

Polarized notum Activation at Wounds Inhibits Wnt Function to Promote Planarian Head Regeneration

Christian P. Petersen1,*, and Peter W. Reddien1,2,3,{dagger}

Abstract: Regeneration requires initiation of programs tailored to the identity of missing parts. Head-versus-tail regeneration in planarians presents a paradigm for study of this phenomenon. After injury, Wnt signaling promotes tail regeneration. We report that wounding elicits expression of the Wnt inhibitor notum preferentially at anterior-facing wounds. This expression asymmetry occurs at essentially any wound, even if the anterior pole is intact. Inhibition of notum with RNA interference (RNAi) causes regeneration of an anterior-facing tail instead of a head, and double-RNAi experiments indicate that notum inhibits Wnt signaling to promote head regeneration. notum expression is itself controlled by Wnt signaling, suggesting that regulation of feedback inhibition controls the binary head-tail regeneration outcome. We conclude that local detection of wound orientation with respect to tissue axes results in distinct signaling environments that initiate appropriate regeneration responses.

1 Whitehead Institute for Biomedical Research, Cambridge, MA 02142, USA.
2 Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02138, USA.
3 Howard Hughes Medical Institute, 4000 Jones Bridge Road, Chevy Chase, MD 20815, USA.

* Present address: Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208, USA.

{dagger} To whom correspondence should be addressed. E-mail: reddien{at}

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