a, Representative IF images of COL17A1, Survivin and KRT10 in the bulge area at 3 days after hair with or without topical H2O2 treatments (H2O2). H2O2 triggered the stress responsive (SR) type of ACDs. b, Representative IF images of KRT15, COL17A1 and ITGA6 in the bulge area of control, Col17a1 cKO and Itga6 cKO mice at 11 weeks old. A deficiency of Col17a1 or Itga6 affected the stability of the expression of each protein in the bulge area. c, Quantification of percent cells with polarized localization in the Bg and sBg areas of Control (n = 9 mice, n = 43 cells), Col17a1 cKO (n = 7 mice, n = 25 cells), Itga6 cKO (n = 3 mice, n = 23 cells) and Col17a1:Itga6 dcKO (n = 3 mice, n = 26 cells) mice. Col17a1 and/or Itga6 deficiency significantly abolished the polarized expression. d, IF images of KRT75 and KRT10 in control, Col17a1 cKO and Itga6 cKO mice at 3d. Col17a1 or Itga6 deficient HFSCs differentiated into KRT10+ cells, but not KRT75+ cells through the SR type of ACDs. e, Heat map showing the log fold change of HFSC signature genes between RU486-treated control (Cont) and Col17a1 cKO telogen stage HFSCs (tHFSCs) from microarray data. Col17a1 cKO tHFSCs decreased the expression of HFSC signature genes. f, Quantification of LacZ+ HFSCs contribution in the Bg, SG, JZ and EPI after nonHC, 3xHC and 5xHCs (Cont, nonHC, n = 3 mice, n = 37 HFs; Cont, 3xHC, n = 3 mice, n = 27 HFs; Cont, 5xHC, n = 46 HFs; Col17a1 cKO, nonHC, n = 3 mice, n = 33 HFs; Col17a1 cKO, 3xHC, n = 2 mice, n = 27 HFs; Col17a1 cKO, 5xHC, n = 3 mice, n = 68 HFs). LacZ-labeled control HFSCs retained the Bg, whereas Col17a1 and/or Itga6 deficient HFSCs dose-dependently retained SG, JZ and EPI. g, Representative TEM images of the basement membrane structure of control, Col17a1 and Itga6 cKO mice. Right panels show schematics for rete ridge-like structures in the basement membrane. h, Quantification of the depth of rete ridge-like structures (n = 3 mice, 27–34 images in each group). A deficiency of Col17a1 or Itga6 significantly decreased the depth of rete ridge-like structures. White dashed line, basement membrane; white line and fan-shaped line and upper number, spindle angle against basal cell layer (o); green(control)/red(IR or cKOs) dashed line, dividing cells. Error bars, means ± SEM; Chi-square test (c), one-way ANOVA with Tukey’s post-hoc test (f) or Dunnett’s post-hoc test (h).