NOTCH, ERK and SHH signaling respectively control the fate determination of cortical astrocytes, oligodendrocytes, and olfactory bulb interneurons

During cortical development, radial glial cells, known as neural stem cells, initially generate a large number of cortical glutamatergic pyramidal neurons through a process called neurogenesis. This is followed by the generation of a diversity of cortical astrocytes, oligodendrocytes, and olfactory bulb interneurons, known as gliogenesis. However, the molecular mechanisms underlying the switch from cortical neurogenesis to gliogenesis, and the subsequent fate determination of cortical astrocytes, oligodendrocytes, and olfactory bulb interneurons, remain unclear. Here, we report that extracellular signal-regulated kinase (ERK) signaling plays a fundamental role in promoting cortical gliogenesis and the generation of cortical glial progenitors. Additionally, SHH-SMO-GLI activator signaling has an auxiliary function to ERK during these processes. We further demonstrate that NOTCH signaling is absolutely required for the fate determination of astrocytes, while ERK signaling plays a prominent role in oligodendrocyte fate specification, and SHH signaling is crucial for the fate determination of olfactory bulb interneurons from cortical progenitors. We provide evidence suggesting that this mechanism is conserved in both mice and humans. Finally, we propose a unifying principle of mammalian cortical gliogenesis. Overall design: FlashTag (CellTrace Yellow, Life Technologies, #C34567, 0.5 µl of 10 mM) was injected into the cortical lateral ventricle of control mice (Map2k1 and Map2k2 flox), Emx1-Cre; MAP2k1/2-dcko and hGFAP-Cre; MAP2k1/2-dcko mice at E18.0. P2 pups were sacrificed, and the brains were immediately removed and submerged in fresh ice-cold Hanks' balanced salt solution (Gibco 14175-095). The dorsal cortices were cut into small pieces and dissociated into a single-cell suspension using a Papain Cell Dissociation Kit by following the manufacturer's instruction. The tdTomato+ (tdT+) cells were captured and harvested through fluorescence-activated cell sorting (FACS). The Chromium droplet-based sequencing platform (10X Genomics) was used to generate scRNA-Seq libraries, following the manufacturer's instructions (manual document part number: CG00052 Rev C). The cDNA libraries were purified, quantified using an Agilent 2100 Bioanalyzer, and sequenced on an Illumina Novaseq 6000.