Figure 2. Tracing the SG during homeostasis and after wounding.

(A) Schematic for tracing PPARγ+ cells. Left, in the absence of doxycycline (doxy), Pparg promoter-driven tTA induces Cre expression, causing genomic recombination that activates YFP expression. Right, doxy suppresses tTA activity.

(B) Immunohistochemical localization of YFP (green) and PPARγ (red, top) or K14 (red, bottom) in label-on PPARγ;YFP mice. Basal SG cells, sebocytes, and sebaceous ducts express YFP, but other hair follicle epithelia do not, in either telogen (top, bottom) or anagen (middle). Right panels are magnified views of the left panels, with DAPI omitted.

C) Top panels, 8-week-old skin from label-off (left) or label-on (right) PPARγ;YFP mice. Bottom panels, skin from mice treated for the first time with doxy starting at 8 weeks of age, for 10–30 continuous weeks (label-on → label-off). Arrow, unlabeled SG.

(D) Quantitation of labeled SGs, following 0–30 weeks of continuous doxy treatment.

(E) Wounded skin from a label-on → label-off PPARγ;YFP mouse, examined 1 week (top) or 8 weeks (bottom) after injury. Top right panel is a magnified view of the boxed area showing labeled cells that have departed the SG and entered the epidermis. Asterisk, SG-derived YFP+ cells maintained long-term in the healed epithelium. K14 staining was omitted from the bottom panel for clarity.

(F) Wounded skin from a label-on → label-off PPARγ;YFP mouse, examined 3 weeks after injury. Bottom panel is a magnified view of the boxed area showing unlabeled, wound-proximal SGs.

(G) Quantitation of SG labeling as a function of distance from the wound site. The closest SG cluster to the wound site is designated “closest 1,” and the closest 3 SG clusters are designated “closest 3.” W, wound site. w, weeks. **p < 0.01 by one-way ANOVA and Tukey post hoc test, comparing closest 3 or closest 1 with “intact” or “wound away.” n ≥ 4 mice per time point for (D). Four mice were wounded for (G). Data are represented as mean ± SEM. Scale bar, 50 μm.