Fig. 1. A population of basal Keratin 17+ cells at the anorectal junction contributes to the anal epithelium during normal homeostasis.

a Human and mouse anorectal TZ are histologically (HES) and molecularly similar. A population of keratin 17 (Krt17) expressing cells (white) shown by immunofluorescence is present at the anorectal TZ (n = 55 independent experiments from 58 mice and n = 3 independent experiments from two independent human samples). The rectum expresses keratin 8 (Krt8) (red). Scale bars for HES are 100 and 50 μm for immunofluorescence panels. b Schematic of the mouse model used and time point analyzed after one injection of 2 mg of tamoxifen to only label few cells at the TZ. c, d Unipotency of Krt17+ TZ cells (green) during short and long-term lineage tracing. Representative images of n = 3 biologically independent samples at each time point are shown. Dashed lines delineate the epithelium from the stroma. Scale bars are 50 μm. e Quantification of the % of GFP cells in stratified and glandular tissue (n = 3 mice per time point) (Source data are provided as a source data file). Two-tailed paired t-test; error bars, mean ± SD ***p < 0.0001. f Krt17+ TZ cells give rise to differentiated suprabasal layer cells of the anal canal (4 weeks post-tamoxifen injection) positive for Krt10 (red) and to cornified layer cells positive for Loricrin (red). α6 integrin (in white) marks the basal layer. Scale bars are 50 μm; Insets for Krt10 and Loricrin are zoom in 1.5-fold and 1.1-fold, respectively.