Fig. 5. Fgf8 can induce ectopic Nkx2.5 and Mef2c expression lateral to the heart field. Heparin-acrylamide beads soaked in Fgf8 protein (f) or control beads (c) were placed in stage 4-6 embryos (A) and incubated until stage 8-9. Whole-mount in situ hybridization was then performed for Nkx2.5 (B,C,E,G), Mef2c (D,F) and Sox3 (H). As seen in B-D, the Fgf8-soaked bead induced a lateral expansion of both Nkx2.5 and Mef2c expression. While Nkx2.5 expansion was seen in all three germ layers (E), Mef2c lateral expansion was observed only in the mesoderm (F). Fgf8-soaked beads placed medial to the heart field did not induce ectopic Nkx2.5 expression (G). In addition to expanding the heart field, Fgf8 beads also induced the expression of a neural marker, Sox3, in the ectoderm (H). An asterisk (*) marks experimental beads in sections. aip, anterior intestinal portal; ecto, ectoderm; endo, endoderm; hn, Hensen’s node; hp, head process; meso, mesoderm; np, neural plate; ps, primitive streak.
