Fig. 4. Early Cre-induced recombination from Cre drivers Mesp1^Cre (A,A'), Foxg1^Cre (B,B'), TgFgf15Cre (C,C') and Hoxa3^Cre (D-E'). A',B' and D' are transverse sections through the pharynx, D, dorsal; V, ventral. C' and E' are coronal sections. (A,A') Mesp1^Cre induces recombination in all mesoderm-derived tissues, including vascular endothelia (arrowheads in A'). da, dorsal aorta; pe, pharyngeal endoderm; se, surface ectoderm; spm, splanchnic mesoderm; h, heart; oft, outflow tract. (B,B') Foxg1^Cre induces patchy recombination in pharyngeal ectoderm, endoderm and mesoderm from E8.5. oft, outflow tract. (C,C') TgFgf15Cre recombination begins in pharyngeal endoderm (pe) at E9. Hoxa3^Cre recombination in the pharyngeal region begins at E8.25 in surface ectoderm (D,D', arrows), and extends into pharyngeal endoderm and mesoderm by E8.5 (E,E'). Scale bars: 100 µm.