Fig. 3. Expression of Fgf8 during cardiac specification. At stage 6, Fgf8 expression is found in cells of the primitive streak and in a crescent pattern in the anterior half of the embryo (A). The anterior crescent roughly overlaps the anterior expression patterns of Bmp2 (B) and Nkx2.5 (C). Sections reveal that the anterior Fgf8 expression is localized to the endoderm underlying the heart field (E). Fgf8 expression persists in the lateral endoderm of Stage 9 embryos (D), and is expanded medially in the posterior-most part of this domain (arrow in D). endo, endoderm; np, neural plate; ps, primitive streak.