<p>(A–D) Whole-mount <i>in situ</i> hybridization (ISH) for <i>phox2b</i> expression in wild-type embryos at the indicated time points. <i>phox2b</i> expression is seen in cells of the prospective superior cervical ganglion (SCG; white arrows, boxed) at 36 hpf (A), which start to extend caudally to form the sympathetic chain. These cells are identified as sympathetic neuronal cells by their expression of <i>dbh</i> and <i>th</i> (E, F). Expression is also seen in the brachial arches (black asterisk) and hindbrain (white asterisk). By 50 hpf, <i>phox2b</i> expression is seen in the enteric precursors (B–D, black arrow). Expression continues in two parallel rows caudally, encompassing the sympathetic chain until 4 dpf. (E) Lateral view (cranial to the left) of a 4-dpf zebrafish embryo analyzed by whole-mount ISH for <i>dbh</i> expression, which is seen in the SCG (black square), the arch associated complex (AAC) also derived from the neural crest, and the hindbrain (HB). Inset shows enlarged dorsal view of the SCG. (F) Whole-mount ISH of 4-dpf embryo analyzed for <i>th</i> expression. Aggregates of cells expressing <i>th</i> are seen in the SCG (arrow) as well as in the midbrain (MB), HB and retina (R).</p
