Xldax, an inhibitor of the canonical Wnt pathway, is required for anterior neural structure formation in Xenopus

Wnt signaling pathways are involved during various stages in the development of many species. In Xenopus, the accumulation of beta-catenin on the dorsal side of embryo is required for induction of the organizer, while the head structure formation requires inhibition of Wnt signaling. Here, we report a role for xldax, a negative regulator of Wnt signaling. Xldax is expressed in neural tissues at the neurula stage, and in the restricted region of the tadpole brain. Ectopic expression of xldax inhibits the target gene expression, suggesting that xldax can inhibit canonical Wnt signaling. To examine the function of xldax, a morpholino oligo for xldax (xldaxMO) was designed. An injection into an animal pole cell caused a loss of forebrain. The anterior neural marker expression is decreased in xldaxMO-injected embryo, suggesting that xldax is required for anterior neural development. Moreover, a negative regulator that acts downstream of xldax rescued this defect. We propose that Idax functions are dependent on the canonical Wnt pathway and are crucial for the anterior neural development. (C) 2004 Wiley-Liss, Inc.