Geo-seq (Chen et al. 2017). E12 and E14 mouse embryonic heads were fresh frozen embedded in OCT and cryosectioned at a thickness of 12 μm. Geo-seq (Chen et al. 2017). Total RNA pellets were dissolved in a lysis solution (4M GuSCN), followed by reverse transcription using SuperScript II reverse transcriptase (Invitrogen), and whole transcription amplification with KAPA HiFi HotStart ReadyMix (2×; KAPA Biosystems). cDNA library was constructed using the Nextera XT Library Prep Kit (Illumina).