Expression of amphioxus homologs of neural crest effector genes and summary for putative neural border gene network in amphioxus. (A) Expression of Mitf, tyrosinase, Tyrp-a, and Tyrp-b in late neurula stage embryos. Side views are shown here; anterior is at left and dorsal is up. Scale bar, 50 μm. All four of these genes are coexpressed in the neural tube at the level where the first primary pigment spot will form. (B) In amphioxus, gene expression and BMP signaling perturbation suggest that the processes of dorsal ectoderm patterning and neural border specification are conserved between vertebrates and amphioxus. In addition, the differentiation gene battery for pigment cell development appears conserved in both vertebrates and amphioxus. However, at intermediate levels of their respective neural border networks, the two groups diverge. Amphioxus lacks neural border expression of most neural crest specifiers, as well as the effector subcircuit controlling neural crest delamination and migration, consistent with a lack of bona fide neural crest cells in this lineage.
