Figure 3.

Increased bone morphogenetic protein (BMP) signaling in Prg4^-/- discs. Histograms depicting the relative expression of Bmp2, Bmpr1b, and Bmpr2 in Prg4^-/- and control discs at age of 2 mo (A) and 6 mo (B) and presented as average ± SD (n = 3 for mouse/each group, *P < 0.05, **P < 0.01). Semiquantitative reverse transcription polymerase chain reaction showing that increased expression of Bmp2, Bmp type I and type II receptors, and Id-1 in discs from Prg4^-/- mice as compared with wild type (WT) at age of 6 mo (C). TMJ discs from 4-mo-old control (D, F, I) and Prg4^-/- (E, G, H, J, K) mice were analyzed by in situ hybridization with isotope-labeled riboprobes for Bmp2 (D, E) or by immunohistochemistry with phosphorylated Smad 1/5/8 (pSmad1/5/8) antibodies. Sections not treated with primary antibodies served as control (H, K). Note increased Bmp2 expression (E; arrowheads) and pSmad1/5/8-nulear translocation (G, J; arrowheads) are detected in chondrocyte-like cells in the anterior band (Ant. Band) and the intermediate zone (Int. Zone) in Prg4^-/- discs. Scale bars: 90 µm in D, also for E; 55 µm in F, also for G–K.