Researchers at the Salk Institute for Biological Studies have published the results of a study in which they activated the Wnt signaling system in the embryo of a chicken, which allowed it to grow back a wing that had been removed. Blocking the pathway appears to stop animals like salamanders and zebrafish from regrowing limbs. Their work suggests that humans have the genetic ability to regenerate lost limbs.
"In this simple experiment, we removed part of the chick embryo's wing, activated Wnt signaling, and got the whole limb back--a beautiful and perfect wing," said the lead author, Juan Carlos Izpisúa Belmonte, Ph.D., a professor in the Gene Expression Laboratory. "By changing the expression of a few genes, you can change the ability of a vertebrate to regenerate their limbs, rebuilding blood vessels, bone, muscles, and skin--everything that is needed."
- here's the report from ScienceAGoGo