Identification of unique mesenchymal subpopulations for regenerating follicular and interfollicular epithelia after devastating necrosis in the skin graft
We investigated chronological changes of the skin graft in mice for 15 days at  single cell-transcriptomic levels. We found devastating necrotic changes in the dermal and epidermal tissues at post-operated day 3, (POD3), followed by significant regeneration processes of the follicular and interfollicular tissues after POD 6. Dermal papilla cells in the necrotic milieu exserted significant activation of Wnt signaling pathway and Sox2 and Fgf7 expressions, all of those are critical for follicular development in the fetal skin. We further identified a unique mesenchymal subpopulation, which expressed keratinocyte-specific genes, such as Krt5 and Epcam, as well as Irf6, a transcriptional factor to induce mesenchymal to epithelial transition (MET). Our data revealed significant contribution of the unique mesenchymal cell populations for the follicular and interfollicular epithelial regeneration after severe necrosis in the skin graft. Overall design: Skin from C57BL6/J neonatal mice were transplanted on the back of beta-actin-EGFP adult mice. Mice were devided into three groups, which were the drug administrated group, saline administrated group and non-treated group. The transplanted skins were hervested at post-operative day (POD) 3,6,9,12,15. As the non-treated control, dorsal skins from postnatal day0 and 15 mice were also obtained. Each specimens were dissociated enzymatically, and then the cell suspensions were isolated by fluorescence-activated cell sorting (FACS) according to absence of dead cell stain. The sorted cells were analyzed using single cell RNA sequencing.