Cyclin-dependent kinase inhibitors sequentially determine the neural-glial lineage boundaries in the developing cortex

Neural stem cells (NSCs) can generate neurons and glia, but the regulatory mechanisms to invoke different lineages are largely unclear. Here, we addressed the role of cyclin-dependent kinase inhibitors (CDKIs) in the later stage of embryonic brain development. We found upregulations of p18 and p27 among CDKIs at the onset of astrocyte generation. Acute manipulation of p18 and p27 expressions in vivo revealed that the level of CDKIs at the transitional stage regulates the lineage switching between neurons and astrocytes. We generated a conditional knock-in mouse to induce p18 in NSCs. The transcriptome of micro-dissected tissue showed the enhanced activities of glial cell development and delta-notch signaling by the increased p18. Furthermore, Dlx2 induced olfactory bulb interneuron from multipotent intermediate cells with reduction of astrocyte in the late embryonic stage. Together, our results demonstrated the function of CDKIs in sequentially determining the boundary among different cellular lineages in the brain. To identify functional link between the CDKIs and the neural to astrocytic differentiation switching, we generated a conditional knock-in mouse containing a loxP-flanked stop sequence and p18-P2A-mKO2 in the ROSA26 locus.