These laminar expression patterns mirror cellular composition and developmental processes, shown by enrichment analysis (Fig. 2d; Suppl. Table 4; Methods). SZo-enriched categories primarily related to cell division and contained many astrocytic markers likely expressed in outer radial glia (ORG)7. Functional ontology of postmitotic layers reflected developmental maturity. SP, which contains the earliest-generated neurons, showed enrichment for mature neuronal markers and synaptic transmission, reflecting early thalamic afferent input by midgestation35. The next oldest neurons in CPi are additionally enriched for genes involved in forming connections, whereas the youngest neurons in CPo are primarily enriched for terms related to metabolism rather than mature neuronal function.
