The specification of dorsal cell fates in the vertebrate central nervous system

The generation of distinct classes of neurons at defined positions within t he developing vertebrate nervous system depends on inductive signals provid ed by local cell groups that act as organizing centers. Genetic and embryol ogical studies have begun to elucidate the processes that control the patte rn and identity of neuronal cell types. Here we discuss the cellular intera ctions and molecular mechanisms that direct neuronal cell fates in the dors al half of the vertebrate central nervous system. The specification of dors al neuronal cell fates appears to depend on a cascade of inductive signals initiated by cells of the epidermal ectoderm that Rank the neural plate and propagated by roof plate cells within the neural tube. Members of the tran sforming growth factor(-beta) (TGF beta) family of secreted proteins have a prominent role in mediating these dorsalizing signals. Additional signals involving members of the Wnt and fibroblast growth factor (FGF) families ma y also contribute to the proliferation and differentiation of dorsal neuron al cell types.