Fig. 7. Forced Runx2 expression rescues an Nkx3.2-induced but not a PTHrP-induced blockade of chondrocyte maturation. (A) Forced Runx2 expression rescues an Nkx3.2-induced blockade of chondrocyte maturation in vivo. The right wing buds of E3 chick embryos were co-infected with RCAS(A)-Nkx3.2 plus RCAS(B)-Alkaline Phosphatase (AP) viruses (b,e,h,k,n), or RCAS(A)-Nkx3.2 plus RCAS(B)-Runx2 viruses (c,f,i,l,o), and reincubated until E10. The control contralateral uninfected wing (a,d,g,j,m) and the co-infected wings were analyzed either by Alcian Blue/Alizarin Red staining (AB/AR, a-c), or by section ISH with the indicated probes (d-o). (B) Nkx3.2 does not block chondrocyte hypertrophy induced by ectopic Runx2 in vitro. Explants of presomitic mesoderm were co-infected with the indicated viruses and cultured sequentially in Shh for 2 days and Bmp4 for 3 days. Gene expression was assayed by RT-PCR. (C) PTHrP and forskolin can block chondrocyte hypertrophy induced by ectopic Runx2 in vitro. Explants of presomitic mesoderm were infected with RCAS(A)-Runx2 and cultured as described in part B, in either the absence (lanes 1 and 5) or in the presence of increasing amounts of either PTHrP (lanes 2-4) or forskolin (lanes 6 and 7), as indicated. Gene expression was assayed by RT-PCR.