Regulation of cortical folding by niche progenitor cells that co-express cross-repressive transcription factors Neurog2 and Ascl1. Mus musculus

Humans exemplify gyrencephalic species with folded cerebral cortices, contrasting with lissencephalic mammals such as mice. Here we investigated how proneural genes Neurog2 and Ascl1 control cortical folding by regulating neurogenic patterns. Cortical neural progenitor cells (NPCs) stratify into four pools (proneural negative, Neurog2+, Ascl1+, double+) that are distributed evenly in mouse cortices and modular in gyrencephalic macaque cortices and pseudo-folded human cerebral organoids. Each pool has distinct developmental potentials, transcriptomes, epigenomes, and gene regulatory networks. Neurog2-Ascl1 form a bistable toggle switch double+ NPCs to prevent lineage commitment observed in single+ NPCs. Neurog2 and Ascl1 act redundantly to control neurogenic timing, with NPCs precociously depleted in Neurog2-/-;Ascl1-/- cortices. Finally, selective killing of Neurog2/Ascl1 double+ NPCs using Neurog2/Ascl1 split-Cre;Rosa-DTA transgenics breaks neurogenic symmetry in mice by locally disrupting Notch signaling, leading to cortical folding. Our findings suggest that Neurog2/Ascl1 double+ NPCs are Notch-ligand expressing ‘niche’ cells that regulate neurogenic continuity and cortical gyrification. Overall design: Atac-seq. CD15+ GFP/mCherry negative, single, double positive, double negative cortical progenitors were isolated from E12.5 Neurog2Flag-mcherryKI/+;Ascl1GFPKI/+ dorsal telencephalic tissue by FACS. ATAC-seq was performed on each cell type using 50,000 cells as input material for the transposase reaction (Buenrostro et al., 2015).