Total mRNA was extracted with oligo(dT) beads and then randomly fragmented in fragmentation buffer.First-strand cDNA was synthesized with fragmented mRNA as template and random hexamers as primers, followed by second-strand synthesis with addition of PCR buffer, dNTPs, RNase H and DNA polymerase I. Purification of cDNA was processed. Double-strand cDNA was subjected to end repair. Adenosine was added to the end and ligated to adapters. Select cDNA fragments within size range of 300-600 bp.cDNA library was obtained by certain rounds of PCR on cDNA fragments.