Figure 2. Clonal analysis of epidermal SC during stretch-mediated skin expansion.

a, K14CREER-RosaConfetti clones (n=4 independent experiments). Second Harmonic Generation (SHG) visualizes the collagen fibers (white). 7AAD for nuclei (blue). Scale bars, 50 μm. b-k, Clonal analysis in control (CTRL) and expansion (EXP) conditions. (b,g), Distribution of clone sizes at D14 based on basal and total cell number, (c,h), average clone size based on basal (black) and total (blue) cell content, (d,i), clone persistence, (e,j), average labelled cell fraction, and (f,k), cumulative clone size distribution at D14 showing an approximate exponential size dependence (lines). b-f, D0: 115 clones from n=7 mice; D2: 175 clones from n=7 mice; D4: 136 clones from n=5 mice; D8: 159 clones from n=3 mice; D10: 146 clones from n=3 mice; D14: 195 clones from n=4 mice. g-k, D2: 231 clones from n=4 mice; D4: 197 clones from n=4 mice; D8: 199 clones from n=4 mice; D10: 157 clones from n=4 mice; D14: 199 clones from n=4 mice. l, Schematic showing the cellular organization in a one-progenitor model and the proposed two-progenitor model of back skin interfollicular epidermis. In the two-progenitor model, the epidermis contains renewing stem cells (SC), committed cells (CC), and suprabasal cells. In homeostasis, stem cells divide at an average rate λ. With probability 1—r, this division results in asymmetric fate outcome, leading to the replacement of the partner committed cell, which in turn is lost through terminal division and stratification from the basal layer. The remaining divisions lead to the correlated loss and replacement of renewing cells through symmetric cell divisions. c-f, h-k, Mean + s.d. c, d, e, h, i, j, Points show data and lines the results of a two-progenitor model (Supplementary Note).