Figure 5. CD34+ bulge SCs and HG are the only cells used in normal HF homeostasis.
(A) Representative example and quantifications of HFs in early anagen (AnaII-AnaIII) with 2d BrdU pulse. Note BrdU in some CD34+ HF-SCs (arrowheads) but not inner K6+ bulge cells. White dots denote autofluorescent club hair (n=2 mice, 61 HFs for AnaII; n=3 mice, 133 HFs for AnaIII). (B) A 2d BrdU pulse given at anagen’s end is followed through 2 hair cycles. While not proliferative, K6+ bulge cells retain label from late anagen predecessors. K6+/BrdU+ cells persist through the next hair cycle and become the K6 layer of old bulge. (C) Lineage tracing using Tet-Off H2BGFP mice shows that the new HF comes from bulge LRCs. Chase was begun at 1st telogen; analysis began at end of 2nd telogen when H2BGFP selectively label old, new bulge and HG. Developing HFs are composed solely of H2BGFP+ cells. IF, infundibulum; JZ, junctional zone; SG, sebaceous gland. Scale bars, 30μm. Box-and-whisker plots measure H2BGFP epifluorescence intensity within different HF populations. Note paucity of GFP intensity in IF, JZ and K6+ bulge, revealing their lack of contribution to (GFP+) newly forming HF. **: P<0.01. Data are mean ± SD.