Fig. 2. Med1 null mice develop and regenerate hair on incisors.

a Left, diagram depicting hair generation via pocket-like structures (red) in Med1 cKO incisor in adult mice. Right and lower picture set, HE staining to evidence hair in pocket formation and eosin-positive aberrant cell clusters surrounding hair shafts (yellow triangles) in dental tissues. b Top, immuno-staining for hair marker KRT71 (green) and dental SI marker NOTCH1 (red) in the hair-generating tissues in Med1 cKO incisors or for KRT71 only (green) in normal skin. Bottom, epidermal marker LOR (green) and NOTCH1 (red) in dental tissues compared to LOR (green) and KRT14 (red) localization in the skin. The location of hair shafts is marked by dotted lines. c HE staining on sections of skin (orange) and dental (blue) tissues before (day 0) and after hair depilation (3 and 7 days). Large orange arrows show hair follicles in the skin. Large blue arrows show hair roots in dental tissues. Small pale blue arrows show eosin positive cell clusters. Bars = 50 μm. d Full hair regeneration 12 days after hair depilation from Med1 cKO mice (blue arrow). e Schematic representation of cellular processes and anatomical location of dental SI/SR derived dental epithelia (yellow) that are gradually transformed into epidermal (dotted circle) and various hair gene expressing cells (solid circles). Multiple hair keratins are expressed, equivalent to skin hair follicle layers including companion layer (Cl), inner root sheath (IRS), outer root sheath (ORS), and hair cortex, but in disorganized manner in aberrant cell aggregates that lack hair follicle structures in Med1 cKO incisors. Presence of mesenchymal cells and melanocytes are also shown in blue and brown, respectively. For a-d, all of the Med1 cKO mice have the same phenotypes, and representative images are shown, and reproducibility was confirmed at least in two different litters of Med1 cKO and control mice (n = 3).