Cis-regulatory elements driving motor neuron-restricted viral payload expression within the mammalian spinal cord

Spinal motor neuron (MN) dysfunction is the cause of a number of clinically significant movement disorders. Despite the recent approval of gene therapeutics targeting these MN-related disorders, there are no viral delivery mechanisms that achieve MN-restricted transgene expression. In this study, chromatin accessibility profiling of genetically defined mouse MNs was used to identify candidate cis-regulatory elements (CREs) capable of driving MN-selective gene expression. Subsequent testing of these candidates identified two CREs that confer MN-selective gene expression in the spinal cord as well as reduced off-target expression in dorsal root ganglia. Within one of these candidate elements, we identified a compact core transcription factor (TF)-binding region that drives MN-selective gene expression. Finally, we demonstrate that selective spinal cord expression of this mouse CRE is preserved in non-human primates. These findings suggest that the generation of cell-type-selective viral reagents, in which cell-type-selective CREs drive restricted gene expression, will be valuable research tools in mice and other mammalian species, with potentially significant therapeutic value in humans. SIGNIFICANCE STATEMENTMotor neurons transduce the motor outputs of nervous system activity to muscle and are the vulnerable neurons in a number of clinically significant degenerative conditions, including spinal muscular atrophy and amyotrophic lateral sclerosis. A recent strategy for treating motor neuron degenerative diseases has been to use viruses to introduce genes into motor neurons to inhibit the degenerative process. However, we still lack viral reagents that promote gene expression in motor neurons without potentially toxic off-target expression in other cell types. Our study identifies cis-regulatory elements capable of conferring motor neuron-selective transgene expression in a viral context. These findings have important implications for future gene therapeutics for motor neuron-related disorders.