Figuring out the heads or tails decision in regeneration

Wounding a planarian flatworm (red dotted line, left) causes rapid expression of the wntP-1 gene at both tail-facing wounds (above, right) and head-facing wounds (below, right). wntP-1 controls the head-versus-tail regeneration polarity decision in planarians.

Image: PNAS (Petersen and Reddien) Published online before print on September 14th, 2009.