Figure 1.

Antagonistic activities of Shh and Wnt/BMP pattern the developing spinal cord. Counteracting gradients of Shh, secreted from the floorplate (FP), and Wnt/BMP, derived from the roof plate (RP) induce the concentration-dependent differentiation of precursor cells along the dorso-ventral (D-V) axis. During morphogenesis, Shh and Wnts have antagonistic functions. Shh promotes the formation of Gli activator forms, while Wnts directly induce the expression of Gli3, which acts as a transcriptional repressor in the absence of Shh (see Dessaud et al., 2008, for details). In turn, the specific combinations of transcription factors induced by Shh and Wnts generate a cell identity code that specifies the neural progenitor subtypes. As these cells exit the cell cycle, they distribute laterally in a specific order along the dorso-ventral axis (dI1-v3).