Fig 1: ITGA4+ defines molecularly distinct subsets of articular cartilage that are enriched for osteochondral proteins. a BMPR1B (red) identifies many cells of the superficial layer of adult human articular cartilage. b ITGA4 (green) labels rare cells in the most superficial region of adult human articular cartilage. c DAPI (blue) labels nuclei. d Merge channels. Arrow labels a BMPR1B+ITGA4+ cell, arrowhead labels a BMPR1B+ITGA4−cell and asterisk labels a BMPR1B−ITGA4−cell. Dotted line indicates articular surface. e Flow cytometry of adult pig chondrocytes identified four populations of cells based on expression of BMPR1B and ITGA4. f–i Western Blot analysis and quantification of protein expression in adult pig chondrocytes sorted on expression of BMPR1B (B1B) and ITGA4 (A4). SOX9 (f), GLI1 (g), pSTAT3 (h), and RUNX2 (i) are all significantly enriched in BMPR1B+ITGA4+ cells compared to other sorted populations as calculated by one-way ANOVA followed by Tukey’s multiple comparison test. j The four populations of sorted pig chondrocytes were sequenced and differential expression analysis was performed in pairwise fashion. 38 genes are uniquely enriched in BMPR1B+ITGA4+ cells compared to all other population. k GO analysis of these 38 genes. N = 3; scale bars = 50 μm