RNA was extracted using TRIzol reagent following the manufacturer's instructions. Remaining DNA was removed by treatment with Qiagen-RNase free DNase and -RNAeasy MinElute Cleanup Kit 50. Total RNA from tissues were shipped to be processed by Zoetis Inc. (Kalamazoo, MI, USA) for  construction of cDNA libraries using Illumina's TruSeq Stranded mRNA Library Prep Kit. For experiment 1, there were 100 bp paired-end reads. For experiment 2, there were 75 bp single-end reads.