Fig. 2. HNK-1 expression in the splanchnic mesoderm underlying the pharynx at stages 12 (A), 14 (B), 16 (C) and 18 (D). Over time, HNK-1 expression increases in the cranial splanchnic mesoderm and distal outflow tract and decreases in the dorsal mesocardium. (A) Section through the outflow tract (oft) showing its attachment to the ventral pharyngeal wall (p, pharynx). The splanchnic mesoderm (sm) flanking the outflow myocardium is not HNK-1 positive. (B) At stage 14, the cells in the splanchnic mesoderm flanking the primary myocardium of the outflow tract are HNK-1 positive (arrow). (C) HNK-1 expression (arrow) in the distal outflow tract myocardium is continuous with the splanchnic mesoderm caudal to the attachment of the outflow tract to the pharynx (arrowhead). (D) HNK-1 expression in an extended length of caudal outflow myocardium is continuous with that in the splanchnic mesoderm (arrowhead). (E) The myocardium of the outflow tract is positive for Slug antibody but the splanchnic mesoderm is devoid of Slug expression. Scale bars: 100 µm; A and B are the same magnification.