FIG. 5.

Endogenously produced WNT antagonists DKK1 and FRZB determine chondrogenesis and chondrocyte terminal differentiation. Chondrogenesis is defined by a series of processes. In the first step of chondrogenesis, DKK1 and FRZB promote chondrogenesis and prevent chondrocyte dedifferentiation through inhibiting WNT/β-catenin signaling. In the second step, DKK1 and FRZB inhibit chondrocyte terminal differentiation by blocking WNT/β-catenin signaling. The expression of typical markers of the various stages of chondrogenesis is indicated at the bottom. Color images available online at www.liebertpub.com/scd