Fig. 1. Tbx2 expression during cardiogenesis, 8.5-9.5 dpc. (A) Right view of an 8.5 dpc embryo showing Tbx2 expression in the allantois (al) and cardiac crescent (cc). The line indicates the plane of the section shown in B. (B) Vibratome section of an 8.5 dpc embryo stained in whole-mount, showing expression in cardiac mesoderm (cm). (C) Ventral view of the head and heart of an 8.5 dpc embryo, showing Tbx2 expression in the otic placode (op), inflow tract (ift) and septum transversum (st). (D) Right view of a 9.5 dpc embryo showing previously unreported Tbx2 expression in somites (s) and nephrogenic mesoderm (nm). The line in the trunk indicates the plane of section in G. (E) Left view of the embryo shown in D. Labeled are the dorsal retina (dr), otic vesicle (ov), forelimb bud (fl) and previously unreported expression in the body wall of the caudal trunk and tail (bw). The line in the tail region indicates the plane of the section in F. (F) Vibratome section of a 9.5 dpc embryo showing specific expression in the nephrogenic mesoderm (nm). (G) Vibratome section of a 9.5 dpc embryo showing expression in pharyngeal arch mesenchyme (arrow), also the site of cardiac neural crest cells migrating into the outflow tract (oft). Note the absence of expression in the aorticopulmonary septum (arrowhead). (H) Right whole-mount view of a 9.5 dpc heart showing Tbx2 expression in the outflow tract (oft). (I) Left view of the heart shown in G, demonstrating Tbx2 expression in the atrioventricular canal (AVC) and septum transversum. (J) Ventral view of a dissected 9.5 dpc heart stained in whole-mount, showing Tbx2 expression in the outflow tract (oft). (K) Ventral view of the heart in J with the outflow tract removed, showing Tbx2 expression on the outer curvature of the AVC (arrowhead). (L) Dorsal view showing Tbx2 expression in the AVC and ventricular inner curvature (arrow). nf, neural fold; c, coelom; fg, foregut; nt, neural tube; da, dorsal aorta; hg, hindgut; rv, right ventricle; v, ventricle; a, atrium.