Genes, lineages and the neural crest: a speculative review

Sensory and sympathetic neurons are generated from the trunk neural crest. The prevailing view has been that these two classes of neurons ar derived f rom a common neural crest-derived progenitor that chooses between neuronal fates only after migrating to sites of peripheral ganglion formation. Here I reconsider this view in the light of new molecular and genetic data on th e differentiation of sensory and autonomic neurons. These data raise severa l paradoxes when taken in the context of classical studies of the timing an d spatial patterning of sensory and autonomic ganglion formation. These par adoxes can be most easily resolved by assuming that the restriction of neur al crest cells to either sensory or autonomic lineages occurs at a very ear ly stage, either before and/or shortly after they exist the neural tube.