Sphere formation assay after modulation of miR-30a expression. MCF7 and 4T1 breast cancer cells were transiently transfected with miR-30a knock-down (KD), Pre-miR-30a, and miR-159 KD control probes. Efficiency of transfection was verified by TaqMan qRT-PCR (A, D). 48 hours following transfection, cells were used in a mammosphere assay (B, E). MMO were counted after 4 days. Technical triplicates were used for statistical analyses, with one representative experiment shown (C, F). P values (for comparisons to control miR-159 KD) under 0.05 (two-tailed student t test) are represented with an asterisk (*).