The transcription factor Sox9, which is required to establish the chondrocyte lineage, has essential functions at several steps throughout the chondrocyte differentiation pathway. Sox9 is nee-ded at an early step that of mesenchymal condensation. It is then needed for the overt differentiation of chondrocytes in part because Sox9 is required during chondrogenesis for expression of Sox5 and Sox6, which in turn have an essential role at this step. Sox9 also inhibits the maturation of chondrocytes into hyper-trophic chondrocytes. .
