Schematic views of Merkel cell innervation in wild type, <i>TrkA^−/−</i> and <i>Ret^−/−</i> neonatal touch domes and the wild type glabrous skin.

<p>A, In the trunk hairy skin of wild type mouse, touch dome Merkel cells are innervated by two types of fibers: NFH⁺/TrkC⁺ and Ret⁺/TrkA⁺ fibers. Most Merkel cells receive dual innervation from both types. B, In <i>TrkA^−/−</i> mice, most Ret⁺/TrkA⁺ fibers are lost, while NFH⁺/TrkC⁺ fibers are not affected in the touch dome innervation. C, In the back hairy skin of <i>Ret^−/−</i> mice, Ret⁺ and NFH⁺ fibers are not significantly changed. D, In the glabrous skin of wild type mouse, Merkel cells are mainly innervated by NFH⁺/TrkC⁺ fibers.