Ontogeny of the spinal cord dorsal horn.

The dorsal horn of the mammalian spinal cord is organized into laminae where each layer is populated by different neuron types, has distinctive circuit connections, and plays specialized roles in behavior. An outstanding question is how this organization emerges during development from an apparently homogeneous pool of neural progenitors. Here, we show that mouse dorsal neurons are diversified by time, with families of related cell types born as temporal cohorts, and by a spatial-molecular gradient that specifies individual cell types. Excitatory neurons settle into a chronotopic arrangement that transforms their progressive birthdates into anatomical order and is required to establish proper laminae. We identified essential ontogenetic principles that shape dorsal progenitors into the diverse cell types and structure that subserve sensorimotor function.