DORSALIZATION OF THE NEURAL-TUBE BY THE NONNEURAL ECTODERM

The patterning of cell types along the dorsoventral axis of the spinal cord requires a complex set of inductive signals, While the chordames oderm is a well-known source of ventralizing signals, relatively littl e is known about the cues that induce dorsal cell types, including neu ral crest, Here, we demonstrate that juxtaposition of the non-neural a nd neural ectoderm is sufficient to induce the expression of dorsal ma rkers, Wnt-1, Wnt-3a and Slug, as well as the formation of neural cres t cells, In addition, the competence of neural plate to express Wnt-1 and Wnt-3a appears to be stage dependent, occurring only when neural t issue is taken from stage 8-10 embryos but not from stage 4 embryos, r egardless of the age of the non-neural ectoderm. In contrast to the in duction of Wnt gene expression, neural crest cell formation and Slug e xpression can be induced when either stage 4 or stage 8-10 neural plat es are placed in contact with the non-neural ectoderm. These data sugg est that the non-neural ectoderm provides a signal (or signals) that s pecifies dorsal cell types within the neural tube, and that the respon se is dependent on the competence of the neural tissue.