Fig. 10. PDGFB acts on connective tissue cells before it acts on myogenic cells. PDGFB beads were implanted into the dorsal regions of E5/HH26 chick wings and the embryos were fixed at various times after grafting. Consecutive sections of the PDGFB-treated wings, 9.5 (A,B), 12 (C,D) and 24 (E,F) hours after grafting were hybridized with the MyoD (A,C,E) and collagen I (B,D,F) probes. As soon as 9.5 hours, an increase in collagen I expression was observed (B), whereas no obvious effect on MyoD expression was observed (A). An effect on MyoD expression (loss of MyoD expression around the bead) was observed 24 hours after grafting. (E). (G) Analysis of cell density, visualized with Hoechst-labeled nuclei, 24 hours after PDGFB bead implantation. (H) An adjacent section to G was hybridized with the MyoD probe.