A role for the roof plate and its resident TGF beta-related proteins in neuronal patterning in the dorsal spinal cord

Distinct neuronal cell types are generated at characteristic times and positions in the dorsal horn of the spinal cord. We provide evidence that the identity and pattern of generation of dorsal neurons depend initially on BMP-mediated signals that derive from the epidermal ectoderm and induce dorsal midline cells of the roof plate. Roof plate cells provide a secondary source of TGF beta-related signals that are required for the generation of distinct classes of dorsal interneurons. These inductive interactions involve both qualitative and quantitative differences in signaling by TGF beta-related factors and temporal changes in the response of neural progenitor cells.