design: Illumina TruseqTM RNA sample prep Kit was used to construct the library. The mRNA with polyA tail was enriched by magnetic beads with Oligo(dT), and the mRNA was interrupted by ultrasound. Using fragmented mRNA as template and random oligonucleotides as primer, the first cDNA strand was synthesized in M-MuLV reverse transcriptase system, then the RNA strand was degraded by RNaseH, and the second cDNA strand was synthesized in DNA polymerase I system using dNTPs as raw material. The purified double-stranded cDNA was end-repaired, A-tail was added, and sequencing joints were connected. cDNA of about 200bp was screened by AMPure XP beads for PCR amplification, and PCR products were purified by AMPure XP beads again.