Fig. 6. Wnt promotes proliferation of limb mesenchyme via Nmyc and inhibits chondrogenesis independently via Sox9. (A,B) BrdU staining on longitudinal sections through the midregion of E11.5 forelimb bud of wild-type (A) and Nmyc^-/- littermate (B). (C) Proliferation in E11.5 limb bud cells infected with adenovirus expressing the indicated genes (n=6). (D,E) Vehicle (D) or Wnt3a (E) beads implanted in E11.5 Nmyc^-/- limb buds do not affect BrdU labeling (n=8). (F) BrdU density around vehicle or Wnt3a beads implanted in E11.5 Nmyc^+/- and Nmyc^-/- limbs (n=4). Wnt3a promotes proliferation 5-fold in Nmyc^+/- limb buds (P=0.0001, n=4), but fails to promote proliferation in Nmyc^-/- limb buds (P=0.38, n=4). (G,H) Wnt3a beads repress Sox9 in Nmyc^-/- limb buds (H); vehicle beads (G) have no effect (n=4). (I,J) Wnt3a inhibits cartilage formation around the bead in Nmyc^-/- limb buds (J); vehicle beads have no effect (I). Cartilage stained red with Safranin O (n=4). (K,L) Wnt3a beads (L), but not vehicle beads (K), induce collagen 1 in Nmyc^-/- limb buds (n=4). Dorsal is upwards, distal rightwards (A,B). Scale bars: 100 µm. B, bead; car, cartilage.