Total RNA was extracted from tissues using TRIzol (Invitrogen, Carlsbad, California, USA) according to manual instruction Library preparation is performed using Optimal Dual-mode mRNA Library Prep Kit (BGI-Shenzhen, China). A certain amount of RNA are denatured at suitable temperature to open the secondary structure, and mRNA is enriched by oligo (dT) attached magnetic beads. After reacting at a suitable temperature for a fixed time period, RNAs are fragmented with fragmentation reagents