The Touch Dome Defines an Epidermal Niche Specialized for Mechanosensory Signaling

In mammalian skin, Merkel cells are mechanoreceptor cells that are required for the perception of gentle touch. Recent evidence indicates that mature Merkel cells descend from the proliferative layer of skin epidermis; however, the stem cell niche for Merkel cell homeostasis has not been reported. Here, we provide genetic evidence for maintenance of mature Merkel cells during homeostasis by Krt17(+) stem cells located in epidermal touch domes of hairy skin and in the tips of the rete ridges of glabrous skin. Lineage tracing analysis indicated that the entire pool of mature Merkel cells is turned over every 7-8 weeks in the adult epidermis and that Krt17(+) stem cells also maintain squamous differentiation in the touch dome and in glabrous skin. Finally, selective genetic ablation of Krt17(+) touch-dome keratinocytes indicates that these cells, and not mature Merkel cells, are primarily responsible for maintaining innervation of the Merkel cell-neurite complex.