Innovations in spinal cord cell type heterogeneity across vertebrate evolution

Area of Science:

• Comparative neurobiology
• Evolutionary developmental biology
• Spinal cord research

Background:

• Vertebrates exhibit diverse sensorimotor behaviors linked to ecological adaptations.
• Understanding the evolution of motor control requires knowledge of spinal cord circuitry across species.
• High-resolution spinal cord atlases are available for mammals, but lacking for non-mammalian vertebrates.

Purpose of the Study:

• To compare spinal cord cell types across diverse vertebrate species spanning ~450 million years of evolution.
• To identify conserved and divergent cell type specification programs.
• To investigate the evolutionary origins of mammalian-specific spinal cord adaptations.

Main Methods:

• Comparative analysis of spinal cord cell types in fish, frogs, mice, and humans.
• Spatial transcriptomics to map cell types within the spinal cord.
• Developmental and adult stage comparisons.

Main Results:

• Highly conserved cell type specification programs create similar cardinal neuron classes during development across species.
• Adult spinal cord cell-type composition diverges, particularly in excitatory neuron subpopulations.
• Species-specific divergence is localized to the superficial dorsal spinal cord.
• Variant neuropeptide expression distinguishes mammalian-specific cell types in the dorsal spinal cord.

Conclusions:

• Spinal neuron development follows conserved evolutionary pathways across vertebrates.
• The superficial dorsal spinal cord has evolved into a mammalian-specific sensory integration hub.
• This dorsal region represents a 'neospinal cord' analogous to the neocortex in function.