Neural crest induction by the canonical Wnt pathway can be dissociated from anterior-posterior neural patterning in Xenopus

摘要

While Writ signaling is known to be involved in early steps of neural crest development, the mechanism remains unclear. Because Writ signaling is able to posteriorize anterior neural tissues, neural crest induction by Wins has been proposed to be an indirect consequence of posteriorization of neural tissues rather than a direct effect of Writ signaling. To address the relationship between posteriorization and neural crest induction by Writ signaling, we have used gain of function and loss of function approaches in Xenopus to modulate the level of Win signaling at multiple points in the pathway. We find that modulating the level of Writ signaling allows separation of neural crest induction from the effects of Writs on anterior-posterior neural patterning. We also find that activation of Writ signaling induces ectopic neural crest in the anterior region without posteriorizing anterior neural tissues. In addition, Win signaling induces neural crest when its posteriorizing activity is blocked by inhibition of FGF signaling in neuralized explants. Finally, depletion of beta-catenin confirms that the canonical Wnt pathway is required for initial neural crest induction. While these observations do not exclude a role for posteriorizing signals in neural crest induction, our data, together with previous observations, strongly suggest that canonical Wnt signaling plays an essential and direct role in neural crest induction. (C) 2004 Elsevier Inc. All rights reserved.