Fig. 3: Prx1⁺ MPCs in mouse knee joints at 1 WPI.

The top panel illustrates the experimental design and time-points. Safranin O stained sections shown the injury site in both C57BL/6 (A) and p21^−/− mice (F). Fluorescent images depict the localization of Prx1 progenitors (non-lineage traced/promoter driven GFP expression in green; lineage traced in red) and Ki67/proliferating cells (blue) within the cartilage defect area (B, C, G, H), adjacent synovium (D, I), and fat pad (E, J) in both C57BL/6 (A–E) and p21^−/− mice (F–J), with arrows in H’ indicating GFP⁺ cells lining the articular cartilage at the surface of the FTCD. Images C’ and H’ have the Nuc channel removed. Cell quantification was performed within three regions: FTCD, SYN, and FP using tissue cytometry (K). A T-test was used to determine significance (p < 0.05) between strains at each timepoint for each marker. An n = 5 mice per strain per timepoint was used in this experiment. All values are expressed as mean ± standard deviation (SD). Scale bars are equal to 50 µm. The white dotted lines outline the cartilage injury site, the yellow dotted lines mark the boundary between the articular cartilage and subchondral bone.