Polycomb repressive complexes (PRCs) are known for repressing transcription through histone modifications and chromatin compaction. The PRCs consist of two central protein complexes, PRC1 and PRC2, which are important for normal gene regulation and development. This study found that PRC1 is essential for the specification of segmentally restricted spinal motor neuron subtypes, while PRC2 activity is unnecessary for maintaining motor neuron positional identities during terminal differentiation. They examined mice in which core subunit-encoding genes were selectively removed from motor neuron progenitors to determine the relative contributions of PRC1 and PRC2 to neuronal specification. The dataset includes RNA sequencing and ATAC sequencing data. These results indicate that PRC1 function is essential during terminal differentiation to specify the transcriptional identities of motor neurons.