Sequencing libraries was constructed using the NEBNext Ultra RNA Library Prep Kit for Illumina (NEB, Ipswich, Massachusetts, U.S.A.) following the manufacturers recommendations, and index codes were added to attribute sequences to sample. mRNA was purified and fragmented into short sequences. cDNA was synthesized for each RNA fragment, and NEBNext Adaptor with hairpin loop structure was ligated to cDNA fragments. PCR was performed and PCR products were purified (AMPure XP system), and library quality was assessed on the Agilent Bioanalyzer 2100 system.