Total RNA was isolated using a miRNeasy Mini Kit (Qiagen, Venlo, Netherlands). CAGE libraries were prepared using a CAGE Library preparation kit (DNAform, Kanagawa, Japan). Briefly, cDNA was synthesized from total RNA using random primers. The ribose diols in the 5′ cap structures of RNA were oxidized and then biotinylated. The biotinylated RNA/cDNAs were selected by streptavidin beads (a process known as cap-trapping). RNA was digested with RNaseONE/H, adaptors were ligated to both ends of cDNA, and CAGE libraries of double-stranded cDNA were constructed.