A conserved molecular logic for neurogenesis to gliogenesis switch in the cerebral cortex [ChIP-seq]

During development neural stem cells (NSCs) in the cerebral cortex, also known as radial glial cells (RGCs), generate excitatory neurons, followed by production of cortical macroglia and inhibitory neurons that migrate to the olfactory bulb (OB). Understanding the mechanisms for this lineage switch is fundamental for unraveling how proper numbers of diverse neuronal and glial cell types are controlled. We and others recently showed that Shh signaling promotes cortical RGCs to switch lineage to generate cortical oligodendrocytes and OB interneurons. During this lineage switch, cortical RGCs generate intermediate progenitor cells (IPCs) that express Ascl1, Egfr and Olig2, genes critically regulating gliogenesis. The timing of increased Ascl1 expression and the appearance of Egfr+ and Olig2+ cortical progenitors is concurrent with the switch from excitatory neurogenesis to gliogenesis and OB interneuron neurogenesis in the cortex. While Shh signaling promotes Olig2 expression in the developing spinal cord, the exact mechanism for this transcriptional regulation is not known. Further, the transcriptional regulation of Olig2 and Egfr has not been explored. Here we show that in cortical progenitor cells, multiple genetic programs, including Pax6 and Gli3, prevent precocious expression of Olig2, a gene essential for production of cortical oligodendrocytes and astrocytes. We identify multiple distal enhancers that control Olig2 expression in cortical progenitors and show that the mechanisms for regulating Olig2 expression are conserved between mouse and human. Our study reveals evolutionarily conserved regulatory logic controlling the lineage switch of cortical neural stem cells.