Fig. 6. Possible roles of RECK and MMPs during chondrogenic differentiation. (A) Schematic representation of the temporal changes in the amounts of mRNA encoding MMP (representing MMP2, MMP9 and MT1-MMP; red line), RECK (green line), and type II collagen (blue line) during ATDC5 differentiation. (B) A working hypothesis: elevated MMP activity is required for cellular condensation in the early phase and nodule expansion in the later phase in ATDC5 differentiation. Elevated RECK expression is required for ECM accumulation inside the nodules in the later phase. Constitutive RECK expression suppresses cellular condensation. RECK knockdown suppresses ECM accumulation and hence nodule maturation.