Total RNA was extracted from approximately 10^6 cells using the miRNeasy Mini Kit (QIAGEN, 217004). mRNA were purified using poly-T oligo-attached magnetic beads. Then, the mRNA is fragmented into small pieces using divalent cations under elevated temperature. The first strand cDNA were produced from cleaved RNA fragments using reverse transcriptase and random primers and then second strand cDNA synthesis using DNA Polymerase I and RNase H. cDNA fragments were purified and enriched with PCR amplification. Finally, we quantified the PCR yield by Qubit and pooled samples together to make a single strand DNA circle (ssDNA circle), which gave the final library..