Total RNA was quantified with Qubit RNA HS Assay Kit (Thermo Fisher Scientific, Q32852), and quality was assessed using RNA ScreenTape on 4200 TapeStation (Agilent Technologies, 5067-5576). cDNA library was generated from 2ng RNA using Smart-Seq V4 Ultra Low Input RNA Kit (Takara, 634894). 150pg cDNA was used to make sequencing libraries by Nextera XT DNA Sample Preparation Kit (Illumina, FC-131-1024). Libraries were quantified with Qubit dsDNA HS Assay Kit (Thermo Fisher Scientific, Q32851) and the average library size was determined using D1000 ScreenTape on 4200 TapeStation (Agilent Technologies, 5067-5582). Libraries were pooled and sequenced on NovaSeq 6000 (Illumina, San Diego, CA) to generate an average of 30 million single-end 50-base pair reads for each sample.