Fig. 1. Lmo2 and Scl/Tal1 induce early blood and endothelial cells throughout the lateral mesoderm. (Aa-i,Ba-b,Ca-b) Flat mounts; anterior top. (Cc-h) Transverse sections; dorsal top. (D) Schematic of results. (A) In uninjected embryos (a-c), lmo2^end. (a), scl/tal1^end. (b) and fli1 (c) expression overlap in bilateral stripes in the ALM and the PLM. fli1 is also expressed in anterior neural crest cells (c, asterisk). [The nkx2.5⁺ (see Fig. 2A) cardiogenic mesoderm is located in the gap between the ALM and the PLM.] (A) In scl/tal1-injected embryos (d-f), lmo2^end. (d), scl/tal1^end. (e) and fli1 (f) are ectopically expressed in the SPM (arrows). (A) In scl/tal1-lmo2-injected embryos (g-i), lmo2^end. (g), scl/tal1^end. (h) and fli1 (i) are, in addition, ectopically expressed in a broader domain in the head (arrowheads) and in the cardiogenic mesoderm (brackets). (B) Lineage tracing reveals that ectopic scl/tal1^end. (b) is induced on the injected, ß-galactosidase-positive side of the embryo (a). (C) Sections (taken at the levels indicated by c-h, shown below) confirm that scl/tal1-lmo2 injection induced scl/tal1^end. expression in the head mesoderm (c,d), in the cardiogenic mesoderm (e,f), as well as in the SPM (g,h). (D) Whereas scl/tal1 injection (s-inj.) induces ectopic haemangioblasts (purple) in the somitic mesoderm, scl/tal1-lmo2 injection (sl-inj.) expands haemangioblasts into the head, heart (H) and somitic mesoderm. Not, notochord.