Xenopus Wnt-5a induces an ectopic larval tail at injured site, suggesting a crucial role for noncanonical Wnt signal in tail regeneration

Amputation of the larval tail of Xenopus injures the notochord, spinal cord, muscle masses, mesenchyme, and epidermis, induces the growth and differentiation of cells in those tissues, and results in tail regeneration. A dorsal incision in the larval tail injures the same tissues and induces cell growth and differentiation, but never results in the formation of any extra appendages. The first sign of tail regeneration is the multilayered wound epidermis and Xwnt-5a expression in the distal region, neither of which is observed in the recovering region after a dorsal incision. To evaluate the role of Xwnt-5a in tail regeneration, Xwnt-5a was overexpressed in the recovering region. When an animal cap injected with Xwnt-5a mRNA was grafted into the dorsal incision, an ectopic protrusion was formed. Morphological and molecular analyses revealed that the protrusion was an ectopic larval tail, which was equivalent to the regenerating tail but different from the tail that develops from the embryonic tail bud. Lineage labeling revealed that the major differentiated structures of the ectopic tail were formed from host cells, suggesting that Xwnt-5a induced host cells to make a complete tail. The ectopic tail was not induced by Xwnt-8 or Xwnt-11, demonstrating the specificity of Xwnt-5a in this process. A pharmacological study showed that JNK signaling is required in tail regeneration. These results support the proposition that Xwnt-5a plays an instructive role in larval tail regeneration via Wnt/JNK signaling.