Figure.

A model for the sequential generation of distinct cell types in the vertebrate CNS. Neural stem cells (NSCs) from the rat embryonic brain give rise to progenitors that are restricted to neuronal or glial fates. In vitro treatment of glial-derived precursors (GRPs) with members of the bone morphogenetic protein (BMP) family of secreted signaling molecules drives their differentiation into a distinct subtype of astrocyte (type 1 astrocyte, AstI) that promotes repair when transplanted to the injured adult spinal cord. In contrast, treatment of GRPs with the secreted protein Sonic hedgehog (Shh), a member of a different family of signaling molecules, causes their differentiation into type II astrocytes (AstII) and oligodendrocytes.