Effects of bone morphogenetic protein signaling on the mRNA expression of GREM1 , FRZB and DKK1 . Chondrocytes were stimulated for 48 hours with different concentrations of BMP2 ranging from 0 to 200 ng/μl. Effects on gene expression of GREM1, FRZB, DKK1, AXIN2 and DKK1 were analyzed using quantitative PCR. Data expressed as fold-change relative to control and represents the mean of three donors ± standard deviation. *P <0.05 compared with 0 ng/ml BMP2. BMP2, bone morphogenetic protein 2; DKK1, dickkopf 1 homolog (Xenopus laevis); FRZB, frizzled-related protein; GADPH, glyceraldehyde 3-phosphate dehydrogenase; GREM1, Gremlin 1.