Endogenous miRNAs that target up-regulated genes are expressed at relatively higher levels in pre-transfected cells. Frequency distribution of log2 signal values for all 281 miRNAs expressed in HEY cells (grey) compared with signal value distribution for 45 miRNAs expressed among those targeting up-regulated genes after miR-128 transfection (black). The bar chart shows that the 45 miRNAs targeting up-regulated genes have a greater frequency of being expressed at log2 signal value >10, while most miRNAs frequently have log2 (signal value) ≤10 (Mann–Whitney p-value <0.0001). Only miRNAs with at least one “TRUE” detection (Additional file 1 Table S5) call across all samples and with a ‘hsa’- prefix in probeset names were used for plotting the distribution of signal values. Frequency of miRNAs having signal values between log2 4–14 was calculated and plotted using the ‘data analysis’ package in Microsoft Excel.