Fig. 6

Representative immunohistochemistry demonstrates that cartilage pellets cultured in hyperoxia (20 % oxygen) and physioxia (2 % oxygen) exhibit oxygen-dependent expression of extracellular collagen protein, including type II collagen (a–d) of the articular cartilage phenotype, type I collagen (e–h) of the fibrocartilaginous phenotype, and type X collagen (i–n) of the hypertrophic phenotype. Type X collagen expression was variable among ACP clones differentiated in hyperoxia (k, m). Nuclei were counterstained with DAPI, and composite images of collagen staining and nuclei were digitally merged using ImageJ software (National Institutes of Health, Bethesda, MD, USA). Negative controls with isotype-matched antibodies were used for background correction (images not shown). Scale bars = 100 μm. ACP articular cartilage progenitor, MSC mesenchymal stem cell