Neural crest (NC) cells arise in the neural tube (NT), undergo an epithelial-mesenchymal transition, and migrate away along defined routes, differentiating into multiple lineages. Precisely how NC cells exit the NT, and whether their fate is predetermined by their initial position within the NT, has been controversial. To address these issues, the Kulesa and Bronner laboratories performed a collaborative study (). Using a combination of photoactivation and two-photon time-lapse microscopy, they precisely marked individual or small groups of NC precursors in vivo in the chick embryonic NT and followed their fate. They found that most NC cells exit the NT at the dorsal midline, and that some precursors remain resident in the dorsal midline, producing an unordered emigration of cells. Moreover, they showed that differentiation potential is not defined by initial position within the NT, as has previously been suggested, although time of NT exit did influence fate. Together, these results suggest a more plastic and dynamic behaviour for NC cell emigration than previously appreciated.
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