library_construction_protocol: ESCs (~106) were counted and mixed with ¼ of the number of SG4 Drosophila cells in PBS. RNA was extracted from cells using TRIzol reagent, according to the manufacturer's protocol (Thermo Fisher Scientific). gDNA contamination was depleted using TURBO DNA-free Kit (Thermo Fisher Scientific) and quality of RNA was assessed using 2100 Bioanalyzer RNA 6000 Pico kit (Agilent). 900 ng RNA was depleted of rRNA using the NEBNext rRNA Depletion kit (NEB). RNA-seq libraries were prepared from an equal amount of ribo-depleted RNA using the NEBNext Ultra II Directional RNA Library Prep kit, including 2.5-4 min fragmentation at 94⁰C (NEB).