The extracellular signals and transcription factors involved in motor neuron (MN) development have been identified, but it remains to be seen if these developmental insights can be employed to direct stem cells to a motor neuron fate. In August 9 Cell, Hynek Wichterle and colleagues at Columbia University, New York, show that inductive signals involved in normal neurogenesis pathways are enough to direct embryonic stem (ES) cells to form specific classes of CNS neurons (Cell 2002, 110:385-397).

Wichterle et al. examined the influence on murine ES of different factors that operate along the rostrocaudal and dorsoventral axes of the neural tube to specify MN fate in vivo. They observed that these developmentally relevant signaling molecules induced the cells to differentiate into spinal progenitor cells — and subsequently into motor neurons — through a pathway similar to that used in vivo. In addition, they showed...

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