Fig. 2: Grem1-lineage marks a progenitor cell population in the AC.

a Experimental schema. b Representative images of AC from Grem1-TdT (top row) and Acan-TdT (middle row) mice and age paired Lepr-TdT (bottom row) mice. n = 5 animals per group per time point. c Distal femur from neonatal tamoxifen Grem1-TdT, Acan-TdT and Lepr-TdT pulse-chased for 20 weeks. Representative IF staining of Grem1 (top row), Acan (middle row) and Lepr (bottom row) cells expressing OCN, SOX9 and COLX (indicated by yellow arrows). Subchondral bone (SB), articular cartilage (AC) and meniscus (M). n = 3 mice per group. d Experimental schema. e Articular joints, outlined in yellow, were used to isolate red cells for in vitro assays. f Percentage of Grem1-lineage (white) clones able to undergo expansion compared to Acan-lineage (grey) clones. g Number of CFU-F formed per clone. h, Representative images of Grem1-lineage cells stained for CFU-F or differentiation markers Alizarin Red (osteo), Alcian blue (chondro) and Oil Red O (adipo). i Number of Grem1- (white) or Acan-lineage (grey) clones that had undergone differentiation quantified as % of the total number of clones. f–i cells pooled from n = 3 animals, 22 clones per lineage. j Experimental Schema (right). Quantification of the total number of Grem1-lineage cells within the superficial and calcified zones as a percentage of the total number of chondrocytes within the AC at 8 weeks (filled circle, n = 4 mice), 10 weeks (square, n = 3 mice), 18 weeks (triangle, n = 4 mice), 32 weeks (diamond, n = 4 mice) and 58 weeks (open circle, n = 4 mice) of age (left). Bars show s.e.m. k Representative images of adult articular joint showing H&E of zonal organisation of chondrocytes in the superficial zone (SZ), non-calcified zone (NCZ) and calcified zone (CZ) and Grem1-lineage AC cells moving towards the CZ from 8 weeks (middle) to 32 weeks (right) of age. Superficial chondrocytes indicated with yellow arrows. f, i Two-sided Fisher’s exact test. g Two-sided unpaired t test. jTwo-way Anova Tukey’s test. Bars denote s.e.m. Source data are provided as a Source Data file. Mouse image in figure schemas created with BioRender.com.