RNA was prepared using Qiagen RNEasy Micro kit and sent to LC Biosciences for low input RNA sequencing. Briefly, a Poly (A) RNA sequencing library was prepared using Illumina's TruSeq-stranded-mRNA preparation protocol. RNA integrity was determined using Agilent Technologies 2100 bioanalyzer. Poly (A) tail-containing mRNAs were purified using oligo-(dT) magnetic beads with two rounds of purification, followed by fragmentation using divalent cation buffer in elevated temperature. After DNA library construction, quality control analysis was performed using Agilent Technologies 2100 Bioanalyzer High Sensitivity DNA chip.