In the December 4th online edition of PNAS, V. Agrawal et al. from the Univ. of Pittsburgh reported their study results on delineating the mechanism of epimorphic regeneration in adult mammals. With infusion of extracellular matrix (ECM) degradation products, the investigators were able to recruit progenitor and multipotent stem cells to the site ot tissue injury. Adult 6-8 week-old mice had their third digit to the right hind foot amputated and they were left untreated or treated with chemotactic ECM degradation products. The animals receiving the degradation product had accumulated a population of heterogeneous cells expressing multipotency markers such as Sox2, Sca1, and Rex1 at the injury site. Additionally, these cells had the ability to differentiate in vitro into neuroectodermald and mesodermal lineages. Cells isolated from the amputated site of untreated animals were found to only differentiate into mesodermal lineages. The authors concluded that their experimental results demonstrate the recruitment of endogenous stem cells to a site of tissue injury in response to ECM degradation products. They further speculated that the ECM degradation products contained bioactive matricyptic peptides that recruit the stem cells to the injury site via an unknown chemotactic pathway(s).