The experiment used the TruSeq Stranded Total RNA Library Prep Kit to construct the library. During the synthesis of the second strand of cDNA, dUTP was used instead of dTTP in the dNTP mix, so the bases in the second strand of cDNA contained A/U/C/G. Before PCR amplification, the second strand of cDNA was digested with UNG enzyme, so that the library contained only the first strand of cDNA.