Figure 2.

Some suggestions made by different authors regarding the evolutionary origin of the neural crest. Proto-neural crest cells are filled with red color, and their hypothesized origins are represented by the cells with red contours. (A) Evolution of the neural crest started with the exit of pigmented cells from the CNS to give rise to pigmentation of the body in lower chordates [20]. (B) The neural crest originated from the rare peripheral glial cells from the Amphioxus dorsal roots. (C) Precursors of Rohon-Beard sensory neurons migrated out of the neural tube and gave rise to the peripheral progeny consisting of sensory neurons and glia, and thus proto-neural crest [13,50]. (D) Neural crest cells originated from the overlaying non-neural ectodermal sheets appearing during Amphioxus development [42]. (E) Neural crest cells originated from several independent cell types with diverse differentiation potentials that have collectively assembled into a presumptive proto-neural crest at the neural plate border [19].