A U2OS cells were transfected with indicated siRNAs, cultivated for 3 days, treated with 1 mM EU for 30 min and stained for EU incorporated to nascent RNAs by click chemistry. Bar, 10 μM. B Quantification of EU signal in nucleoli of cells from A. Nucleolar EU intensities are shown as box plot. Quantified nuclei: 334 and 425 for siCON and siWDR75, respectively. Data shown are representative of two independent experiments. C U2OS cells were transfected with indicated siRNAs, cultivated for 3 days and cell lysates analyzed by immunoblotting with indicated antibodies. D U2OS cells were transfected with control and WDR75-targeting siRNAs, cultivated for 3 days and RT-qPCR analysis performed. Data are expressed as relative quantity of siWDR75 treated cells compared to control cells. Data shown as mean of three independent experiments (n = 3).