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.