Single Cell Analysis Reveals Unexpected Transcriptional Heterogeneity of Neural Progenitors in the Developing Human Cortex

The human cerebral cortex depends for its normal development and size on a precisely controlled balance between self-renewal and differentiation of diverse neural progenitor cells. Specialized progenitors that are common in humans, but virtually absent in rodents, called ‘outer radial glia’ (ORG), have been suggested to be crucial to the evolutionary expansion of the human cortex. We combined cell type-specific sorting with transcriptome-wide RNA-sequencing to identify genes enriched in human ORG, including targets of the transcription factor Neurogenin, and previously uncharacterized, evolutionarily dynamic, long noncoding RNAs. Single-cell transcriptional profiling of human, ferret, and mouse progenitors showed that more human RGC co-express proneural Neurogenin targets than in ferret or mouse, suggesting greater self-renewal of neuronal lineage-committed progenitors in humans. Finally, we show that activating the Neurogenin pathway in ferret RGC promotes delamination and outward migration. Thus, we find that the abundance of human ORG is paralleled by increased transcriptional heterogeneity of cortical progenitors. Three biological replicates of human late mid-fetal cortex (18 to 19 weeks of gestation) were dissociated and immunolabeled. Apical and outer radial glial cells were purified by FACS and compared to an immunonegative population, predominantly neurons.