Fig. 4. FGF8 promotes facial regeneration. (A) In a normal chick, at embryonic day 2 (E2), Fgf8 is expressed in the branchial arches (BAs, arrows) and nasofrontal (arrowheads) ectoderm, as well as in the neuroectoderm of the isthmus (Is) and prosencephalon. (B,C) After ablation of the FSNC (facial skeletogenic neural crest) at the 5-somite stage (ss) (B), Fgf8 expression is dramatically reduced both in BA1 (arrow) and forehead territories (arrowheads) (C). (D) Implantation of FGF8-soaked beads at the presumptive level of BA1 ectoderm following ablation of FSNC (D) induces regeneration of facial and cephalic structures. (E-G) Role of the rhombomere (r) 3-derived neural crest (NC) in regenerating the jaws. (E) Replacement of the r3-NC by its quail counterpart in a 5 ss chick embryo and FGF8-soaked bead implantation. (F) Skeletogenic cells in Meckel's cartilage (Mc) are exclusively quail derived, as shown in G, which shows a higher magnification of quail cell-specific antibody against a perinuclear antigen (QCPN) staining. Mdp, mandibular process; T, tongue.