Staining of various transforming growth factor (TGF)-beta signaling molecules in cartilage. Paraffin sections of knee joints of young and old mice were stained with antibodies against (a,c) Smad2, (b,d) Smad-2P, (e,g) TGF-beta receptor II (TGF-betaRII) and (f,h) TGF-beta2. The medial tibia of the young mice clearly show a high number of cells staining positive for (b) Smad-2P, (e) TGF-betaRII and (f) TGF-beta2, whereas the (d,g,h) old mice had only a very low number of cells staining positive for these factors. (a,c) Smad2 staining remained unchanged with age. F, femur; T, tibia.