Nucleospin RNA II kits were used for total RNA extraction. Subsequent denaturation by magnetic oligo (dT) beads was performed before RNA sample purification. After the first-strand cDNA was obtained by reverse transcription of purified mRNA and a second cDNA was synthesized, fragmented DNA samples were blunt ended and adenylated at the 3' ends. Adaptors were ligated to construct a library. DNA sample quantification was performed by Qubit (Invitrogen), and the samples were then sequenced by an Illumina Nova-seq 6000 instrument from Genergy Bio (Shanghai) after cBot cluster generation. Then, the raw DNA sequencing data were converted into Fastq format.