Fig. 2. Requirement of TGFß for the in vitro chondrogenesis of the ES-cell-derived mesodermal cells. The sorted flk-1^–PDGFR⁺ cells (A,B), flk-1⁺PDGFR^– cells (C,D), DP cells (E,F), and DN cells (G) were subjected to the pellet culture with (B,D,F,G) or without (A,C,E) TGFß3. Particles formed in 15 days of culture were formalin-fixed, paraffin-embedded, sectioned and stained with Toluidine blue. These results are representative of three independent experiments.