Study
Smed-βcatenin-1 is required for anteroposterior blastema polarity in planarian regeneration
Petersen, Christian P.; Reddien, Peter W.
Science, 2008
RNA interference was used to knock down β-catenin, a component of the Wnt signalling pathway, in planarians which were then cut in half. Regeneration of head and tail ends was scored against controls, and the pathway manipulated in the opposite direction as well.
- Studied in
- Schmidtea mediterranea
- Sample size
- planarians across RNA interference and control treatments
Planarians with β-catenin knocked down regenerated a head at both ends of the fragment, producing two-headed animals with no tail. Increasing Wnt signalling produced the opposite outcome: tails where heads should be. The polarity of the regenerate is set by the level of this one signalling pathway.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
A Wnt/β-catenin gradient specifies anteroposterior polarity during regeneration, determining whether a wound builds a head or a tail.
How NatureHQ reads it
A two-headed worm produced on purpose is a striking image and the substance is better than the image. The question a regenerating fragment has to answer first is not "how do I grow" but "which end am I" — a piece cut from the middle must build a head at one wound and a tail at the other. This shows that decision resting on the level of a single signalling pathway, and shows it by getting the answer wrong in both directions on demand. It is also a good corrective to "planarians are immortal": what regenerates is a body plan, and the animal will happily rebuild an unviable one if you tell it to.
- RNA interference reduces rather than eliminates gene function, and residual activity varies.
- Polarity involves more than one pathway; this identifies a necessary component rather than the whole system.
- One species, in a laboratory strain maintained asexually.
Making a worm build a head at both ends
How does a fragment of a worm know which of its two wounds should become a head and which a tail?
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Published by: American Association for the Advancement of SciencePublished in Science or Science Advances (AAAS).
doi.org/10.1126/science.1149943
This reference was resolved automatically against Crossref on 2026-08-11.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-08-11.