Quantitation of Gene Expression Levels

Gene expression level is generally measured by the amount of mRNA transcribed by the gene. HTSeq-count tool v0.6.0 was used to count the presence of each gene in each sequenced sample (Anders et al., 2015). Reads per kilobase of transcript per million mapped reads (RPKM) is an effective tool for quantitatively estimating gene expression values using RNA-Seq technology and to eliminate the effect of sequencing depth and gene length on gene expression levels (Mortazavi et al., 2008). Therefore, RPKM was calculated to estimate the expression level of genes in each sample.