Figure 1.

Treatment of a “non‐regenerative” anterior wound with retinoic acid (RA) induces the formation of ectopic limbs. (A) Diagram of an axolotl forelimb indicating the positions at which wounds were made around the limb circumference. (B) Diagram illustrating the experimental procedures performed on anterior wound sites. An anterior wound site with a deviated nerve forms an ectopic blastema within 5−10 days. Without a posterior skin graft, the ectopic blastema integrates into the limb and the wound heals over without forming an ectopic limb (Endo et al. 2004). If a skin graft from the posterior side of the limb is grafted into the wound site, an ectopic limb is generated (Endo et al. 2004). Ectopic blastemas without a graft (non‐regenerating) were treated with RA to determine whether RA can replicate the positional confrontation normally induced by the posterior tissue graft. (C) Images of the same ectopic limb induced by RA treatment of an anterior ectopic blastema taken over a period of 7 weeks. The first image is the blastema on the day of RA treatment. The blastema forms an amorphous mass that eventually forms two well patterned ectopic limbs. These images are representative of what was observed in 10 of 20 ectopic structures that eventually formed paired ectopic limbs from an RA‐treated anterior wound (see Table 1). Blue scale bars are 1 mm in length.