miRNA heterogeneity in EGF-treated HeLa cells. Distribution of the different types of sequences mapping to the indicated miRNA loci. The percentage of sequences annotated as the reference-miRNA (Ref), and as the different types of isomiRs is shown in control cells (dark gray) and EGF treated cells (light gray). IsomiRs consist in trimming variants at the 3’ end of the reference miRNA (3’-trim), trimming variants at the 5’-end of the reference miRNA (5’-trim), variants showing changes in the nucleotide composition with respect the reference miRNA (subst) and variants consisting in nucleotide additions to the 3’ end of the reference miRNA (3’-add). Data are presented as the mean and the standard deviation of three independent experiments per condition.