Planarian Regeneration: Wnt/β-catenin Polarity Switch

Amputation

Cut position (head → tail) 50%

Signaling

Wnt / β-catenin signaling 100%

Regeneration speed 0.6 days/s

Live Readouts

Days post-amputation

0.0

Blastema cells

Intact worm — no wound. Move the cut slider and press Cut worm.

How it works

A cut planarian regenerates because pluripotent adult stem cells (neoblasts) near the wound proliferate into a mass of undifferentiated tissue, the blastema. What the blastema turns into — a new head or a new tail — is set by a graded Wnt/β-catenin signal that runs along the body's anterior–posterior axis: posterior identity requires active β-catenin signaling, anterior (head) identity requires it to be locally suppressed (by antagonists such as notum).

This simulator scores each wound with a simple linear model of that decision:

effective(wound) = m + bias(wound) × 0.5
fate(wound) = TAIL   if effective ≥ 1.0
              HEAD   otherwise

m = Wnt/β-catenin signaling level (slider, 1.0 = normal)
bias = +1 for the posterior-facing wound (anterior fragment)
       −1 for the anterior-facing wound (posterior fragment)

At normal signaling (m = 1) each fragment regenerates the missing part correctly. Knocking β-catenin down (low m) — as in the classic RNAi experiments of Gurley et al. (2008) and Petersen & Reddien (2008) — removes the posteriorizing signal everywhere, and both wounds default to head fate: a two-headed worm. Pushing signaling up (high m, mimicking GSK-3 RNAi, which keeps β-catenin active) does the opposite: both wounds become tails.

Cut position — where along the body the transection happens; also sets how much tissue each fragment has to work with.
Wnt/β-catenin signaling — the master polarity dial described above.
Regeneration speed — how fast simulated days pass; blastema growth follows a logistic curve, matching the roughly two-week regeneration timeline seen in real Schmidtea planarians.
Freshly grown blastema tissue is drawn pale/unpigmented, exactly as real blastemas are, and darkens toward its final head or tail color as it differentiates.

Blastema (undifferentiated) Head tissue Tail tissue

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