The Prrx1 limb enhancer marks an adult subpopulation of injury-responsive dermal fibroblasts

The heterogeneous properties of dermal cell populations have been posited to contribute toward fibrotic, imperfect wound healing in mammals. Here we characterize an adult population of dermal fibroblasts that maintain an active Prrx1 enhancer which originally marked mesenchymal limb progenitors. In contrast to their abundance in limb development, postnatal Prrx1 enhancer-positive cells (Prrx1^enh+) make up a small subset of adult dermal cells (∼0.2%) and reside mainly within dermal perivascular and hair follicle niches. Lineage tracing of adult Prrx1^enh+ cells shows that they remain in their niches and in small numbers over a long period of time. Upon injury however, Prrx1^enh+ cells readily migrate into the wound bed and amplify, on average, 16-fold beyond their uninjured numbers. Additionally, following wounding dermal Prrx1^enh+ cells are found out of their dermal niches and contribute to subcutaneous tissue. Postnatal Prrx1^enh+ cells are uniquely injury-responsive despite being a meager minority in the adult skin.