library_construction_protocol: Total RNA was extracted using PAXgene Blood miRNA Kit. Library construction: Using total RNA as starting material, polyA-tailed mRNA was enriched by Oligo(dT) magnetic beads. The enriched mRNA was randomly fragmented by divalent cations in Fragmentation Buffer. In the M-MuLV reverse transcriptase system, random oligonucleotides were used as primers to synthesize the first-strand cDNA with fragmented mRNA as template, and the RNA strand was degraded using RNaseH. Subsequently, the second cDNA strand was synthesized using dNTPs as raw materials in DNA polymerase I system. About 370~420 bp of purified double-stranded cDNA was screened by using AMPure XP beads after end repair, A-tail addition and sequencing junction ligation steps, and further amplified by PCR, and then the PCR product was purified again by using AMPure XP beads, and the library was finally obtained.