The route to spinal cord cell types: a tale of signals and switches

• The anterior nervous system and spinal cord have distinct developmental origins
• The spinal cord shares a common lineage with paraxial mesoderm
• En route to the spinal cord, extrinsic signals guide cells through a set of intermediate transcriptional states
• The intermediate states represent decision points between alternative developmental fates that are controlled by extrinsic signals.

Understanding the mechanisms that control induction and elaboration of the vertebrate central nervous system (CNS) requires an analysis of the extrinsic signals and downstream transcriptional networks that assign cell fates in the correct space and time. We focus on the generation and patterning of the spinal cord. We summarize evidence that the origin of the spinal cord is distinct from the anterior regions of the CNS. We discuss how this affects the gene regulatory networks and cell state transitions that specify spinal cord cell subtypes, and we highlight how the timing of extracellular signals and dynamic control of transcriptional networks contribute to the correct spatiotemporal generation of different neural cell types.