Fig. 2. Fate map of embryos at stages 4-6. (A-C) A composite template of embryos with all injections at ‘0’ hours represented by a circle and number for each embryo, at stages 4 (A), 5 (C) and 6 (F). The color of the circle denotes the region of the heart (yellow, sinus venosus; blue, ventricle; red, atria; black, bulbus cordis or vitelline artery; and white, those that did not enter the heart) to which the DiI-labeled cells became incorporated 20 hours post-injection. The HFR is bilaterally demarcated by a black rectangle (see Materials and Methods) in A,C,F. The HFR at respective stages was superimposed on embryos stained for mRNA expression of Bmp2 at stages 4 (B), 5 (D) and 6 (G), and Nkx2.5 at stages 5 (E) and 6 (H). aip, anterior intestinal portal; hn, Hensen’s node; hp, head plate; ps, primitive streak. (I) The pre-cardiac region from Rosenquist and DeHaan (1966), as shown in Schultheiss et al., 1997. B,G,H reproduced, with permission, from Schultheiss et al., 1997; D,E reproduced, with permission, from Ehrman and Yutzey, 1999.