Overexpressed pri-miRNAs accumulate in nuclear foci containing splicing factor SC35 and Microprocessor components. (A) Pri-miRNA–containing nuclear foci colocalize with SC35. ISH was performed on transfected cells, followed by IF for SC35. (B and C) IF for Drosha (B) or DGCR8 (C) was performed on transfected cells, followed by ISH for the pri-miRNA. Arrowheads indicate untransfected cells. (D) IF for Drosha followed by ISH was performed on cells transfected with a β-globin cDNA construct. Bars, 10 μm.