In the developing spinal cord, morphogenetic signals secreted from dorsal and ventral signalling centres control dorsoventral (DV) patterning. The Shh/Gli pathway plays a major role in patterning the ventral neural tube but what restricts its activity to specific domains? On , Alvarez-Medina and colleagues propose that the Wnt canonical pathway fulfils this role. Wnt1 and Wnt3a, which signal through the canonical β-catenin pathway, are expressed in the dorsal midline region of chick embryos. Their misexpression along the DV axis by in ovo electroporation, the authors report, expands dorsal marker gene expression in the developing neural tube, whereas their inhibition suppresses the dorsal programme and expands ventral gene expression. These phenotypes, the authors show, depend on the Wnt-controlled expression of Gli3, which in its repressor form (Gli3R) acts as the main transcriptional repressor of the Shh/Gli pathway. Together, these observations suggest that the Wnt canonical pathway indirectly restricts graded Shh/Gli ventral patterning activity by regulating the dorsal expression of Gli3 to ensure proper spinal cord patterning.
