Evolutionary decoupling of somatosensory circuit architecture and sensory neuron identity

Here, we address this problem in the vertebrate somatosensory system using the little skate (Leucoraja erinacea), an early-diverging vertebrate that retains ancestral features of both finned and limb-based body plans. Combining molecular profiling, spatial transcriptomics, and embryological manipulations, we show that core features of somatosensory circuit organization—including laminar organization of the dorsal spinal cord and modality-specific targeting of sensory afferents—are deeply conserved.

In contrast, the molecular programs that define sensory neuron subtypes are extensively reconfigured, including divergent neurotrophin receptor and transcription factor codes. We demonstrate that target-derived cues regulate molecular programs and are required for sensory neuron differentiation and circuit assembly. Together, these findings support a model in which conserved circuit architectures provide a stable scaffold that leverages flexible molecular programs to enable the evolutionary diversification of sensory systems.