Fig. 7. Muscle progenitors inhibited by S-FR4-Fc retain their ability to respond to FGF stimulation. S-FR4-Fc cells are injected in the segmental plate of two-day-old embryos. Two or 4 days later, heparin beads coated with FGF2 or FGF8 were implanted into the developing limb of embryos. In a first set of experiments (A,B), the beads were grafted in E4 embryos and re-incubated for an additional 2 days. (B) The contralateral, non-infected, non-implanted forelimb of the embryo shown in A. In a second set of experiments (C,D), the beads were implanted in E6 embryos and re-incubated for only 8 hours. We observed 2 days (A) or 8 hours (C) after implantation of the beads a rescue of MyoD expression immediately around implanted beads. No rescue was observed with control heparin beads (D).