Temporal transition of NPC developmental competence during mouse cortical development. (A) Six cortical layers are formed in an inside-out manner during mouse cortical development. Glial cells are omitted for simplification. SVZ, subventricular zone; VZ, ventricular zone. (B) During cortical development, multipotent NPCs generate neurons populating the six cortical layers and glial cells such as astrocytes and oligodendrocytes sequentially in a time-dependent manner. During early cortical development, neuroepithelial cells divide symmetrically to increase NPC pools. Neuroepithelial cells transform into RGCs and then typically divide asymmetrically to self-renew and produce either neurons or IPCs. RGCs first produce Cajal-Retzius (CR) neurons (layer I) and deep-layer (DL) neurons (layers VI/V) and subsequently superficial-layer (SL) neurons (layers IV/III/II) mostly though IPCs. In later stages, RGCs transition from neurogenesis to gliogenesis and give rise to astrocytes and oligodendrocytes. Eventually, RGCs are depleted by transforming into astrocyte progenitors in postnatal stages.