Neural crest lineage in the protovertebrate model Ciona.

Neural crest cells are multipotent progenitors that produce defining features of vertebrates such as the 'new head'. Here we use the tunicate, Ciona, to explore the evolutionary origins of neural crest since this invertebrate chordate is among the closest living relatives of vertebrates. Previous studies identified two potential neural crest cell types in Ciona, sensory pigment cells and bipolar tail neurons. Recent findings suggest that  bipolar tail neurons are homologous to cranial sensory ganglia rather than derivatives of neural crest. Here we show that the pigment cell lineage also produces neural progenitor cells that form regions of the juvenile nervous system following metamorphosis. Neural progenitors are also a major derivative of neural crest in vertebrates, suggesting that the last common ancestor of tunicates and vertebrates contained a multipotent progenitor population at the neural plate border. It would therefore appear that a key property of neural crest, multipotentiality, preceded the emergence of vertebrates.