Figure 2: Isolation of articular cartilage-derived stem cells. [A] Surface zone chondrocytes were subjected to differential adhesion to fibronectin and colonies consisting of more than 32 cells were counted at 6 and 10 days and the results expressed as colony forming efficiency (CFE). Colonies initially appeared at 6 days in samples derived from the surface zone and the CFE of this cohort had increased by 10 days. [B] Chondroprogenitors cultured for 21 days in chondrogenic medium demonstrate Notch1 labelling (arrowed). [C] Seven-day bovine articular cartilage labelled with antibody to Notch1 (green) and counterstained with propidium iodide (red). Chondrocytes within the uppermost 2-3 cell layers of the surface zone (arrows) label strongly for Notch1. [D] Chondrocytes were labelled with anti-Notch1 antibody and subjected to single channel FACS analysis immediately after isolation; 86% of surface zone cells label positively for Notch1 compared with 10% and 34% from middle and deep zone, respectively. (*P < 0.001; compared with middle and deep.).