library_construction_protocol: Embryos and cells were used directly for library preparation without RNA extraction. SMART-Seq v4 Ultra Low Input RNA kit (Takara, Mountain View, CA) was used for cDNA synthesis and amplification, followed by Tn5 tagmentation and library preparation with Nextera XT DNA Library Prep Kit (Illumina, San Diego, CA). The final libraries were subject to size selection with 0.6x AMPure XP bead wash (Beckman Coulter, Indianapolis, IN).