TpH and SERT expression during amphioxus development. Whole mounts with anterior to the left. The cross-section in C is viewed from the caudal end of the animal. Whole mount and section scale bars are 50 μm and 25 μm, respectively. A: Side view of a 22-hour embryo. B: Magnification of the anterior end of the embryo in A showing SERT-positive cells in the most anterior tip of the neural tube (arrow). C: Cross-section through the most anterior labeled cells in B (arrow). D: Anterior portion of a 72-hour larva. Transcripts are detectable in cells of the frontal eye complex (black arrow), in the center and posterior end of the cerebral vesicle (red arrow) and in cells in the hindbrain region (green arrow). E: Anterior end of a 22-hr embryo showing TpH expression in the precursor region of the frontal eye complex (arrow). F,G: TpH expression in the anterior end of 24-hr and 72-hr larvae, respectively. TpH is expressed in cells of the frontal eye (arrow) and in ventrolateral cells of the cerebral vesicle (arrowhead). N, notochord.