Wnt in the Hydra

The cells of a hydra are in a constant state of flux. It is therefore not surprising that Wnt, the molecule that defines the body axis, is continuously active near the head of the animal, always informing the cells of the body axis direction.

Wnt activity is shown by dark staining in this picture. Two buds are also expressing Wnt to define the body axis within the buds. When a head is removed, the Wnt gene is turned on at the regenerating tip very quickly. This defines the location of the new head.