Total RNA was extracted from fresh frozen cell pellets using Qiagen RNeasy Plus Universal mini  kit following manufacturer's instructions (Qiagen, Hilden, Germany). Extracted RNA samples were quantified using Qubit 2.0 Fluorometer (Life Technologies,  Carlsbad, CA, USA) and RNA integrity was checked using Agilent TapeStation 4200 (Agilent  Technologies, Palo Alto, CA, USA). RNA sequencing libraries were prepared using the NEBNext Ultra II RNA Library Prep Kit for  Illumina following manufacturer's instructions (NEB, Ipswich, MA, USA). Briefly, mRNAs were first  enriched with Oligo(dT) beads. Enriched mRNAs were fragmented for 15 minutes at 94 °C. First  strand and second strand cDNAs were subsequently synthesized. cDNA fragments were end  repaired and adenylated at 3'ends, and universal adapters were ligated to cDNA fragments,  followed by index addition and library enrichment by limited-cycle PCR. The sequencing libraries  were validated on the Agilent TapeStation (Agilent Technologies, Palo Alto, CA, USA), and  quantified by using Qubit 2.0 Fluorometer (Invitrogen, Carlsbad, CA) as well as by quantitative  PCR (KAPA Biosystems, Wilmington, MA, USA).