Graded arrays of spinal and supraspinal V2a interneuron subtypes underlie forelimb and hindlimb motor control [scRNA-seq]

The spinal cord contains neural networks that enable regionally-distinct motor outputs along the body axis. Nevertheless, it remains unclear how segment-specific motor computations are processed because the cardinal interneuron classes that control motor neurons appear uniform at each level of the spinal cord. V2a interneurons are essential to both fore and hindlimb movements and here we identified two major types that emerge during development: Type-I neurons marked by high Chx10 form recurrent networks with neighboring spinal neurons, and Type-II that downregulate Chx10 and project to supraspinal structures. Type-I and -II V2a interneurons are arrayed in counter-gradients and this network activates different patterns of motor output at cervical and lumbar levels. Single cell RNA-seq revealed Type-I and -II V2a neurons are each comprised of multiple subtypes. Our findings uncover a molecular and anatomical organization of V2a interneurons reminiscent of the orderly way motor neurons are divided into columns and pools. Single-cell RNA-Seq (scRNA-Seq) conducted on cervical and lumbar spinal V2a interneurons from 2 P0 neonates. Cells were sorted via FACS and pooled as a single sample on the 10x Chromium Controller.