library_construction_protocol: cells were sorted directly into extraction buffer of PicoPure RNA Isolation Kit (Applied Biosystems) and RNA was extracted according to manufacturer's protocol with on-column DNase I treatment (Qiagen 79254). Total RNA (5 ng) was then reverse transcribed and amplified into cDNA using Ovation RNA-Seq System V2 (Nugen). Amplified cDNA was sonicated into 250 bp by Covaris E220 Focused-ultrasonicators. Subsequently, RNA-seq library was generated with 500 ng of fragmented cDNA using Ovation Rapid DR Multiplex System (Nugen). Libraries were subjected to single-end 50 bp sequencing on HiSeq 4000 sequencing system (Illumina)