Evolutionary decoupling of somatosensory circuit architecture and sensory neuron identity

The extent to which circuit evolution relies on the diversification of neuronal identities versus rewiring of existing populations remains poorly defined. We addressed this problem by examining the somatosensory system of the skate Leucoraja erinacea, leveraging its 420-million-year separation from mammals.

We find that core somatosensory circuit features - including layering of the dorsal spinal cord and modality-specific targeting of sensory afferents - are deeply conserved, thus defining an ancestral vertebrate organization. Unexpectedly, the molecular programs specifying sensory subtypes diverge extensively from those in mammals. Although sensory neuron identity and spinal connectivity rely on target-derived cues, skates employ distinct and neurotrophin receptor and transcription factor identity codes.