Fig. 6. Interaction of BMP and Ihh signaling in chick embryos. Wings of HH32 chick embryos were cultured for 2 days in control medium (A,B) or medium supplemented with Noggin (C,D), Shh and Noggin (E,F), Shh (G,H), BMP2 (I,J), BMP2 and cyclopamine (K,L) or cyclopamine (M,N). Parallel sections were hybridized with riboprobes for chick Ihh (A,C,E,G,I,K,M) or chick PTHrP (B,D,F,H,J,L,N). Noggin treatment results in small cartilage elements that show a reduced level of Ihh (C) and PTHrP (D) expression compared with untreated cultures (A,B). Treatment with Shh leads to a delay in hypertrophic differentiation as seen by the smaller domain of Ihh expression and the increased distance between the Ihh expression domain and the joint region (G) if compared with untreated explants (A). Shh-treated limbs show high expression of PTHrP in periarticular chondrocytes (H). Co-treatment of limbs with Shh and Noggin leads to a further reduction of Ihh expression (E) and does not block the expression of PTHrP (F). BMP2-treated limbs show high expression of Ihh (I) and PTHrP (J). Treatment with cyclopamine results in an advanced onset of hypertrophic differentiation, as seen by the expanded domain of Ihh expression and reduced distance between the Ihh expression domain and the joint region (M) compared with control limbs (A). Furthermore, PTHrP expression is blocked by cyclopamine treatment (N). Both effects cannot be rescued by BMP2 in explants co-treated with BMP2 and cyclopamine (K,L). Arrows point to the PTHrP expression domain. All panels display sections through metatarsals. cycl, cyclopamine; Nog, Noggin.
