Ectopic centriolar protein complexes become the structures more related to procentrioles by incorporating HsSAS-6 and other centriolar proteins.Figure 6A U2OS cells treated with RBM14 siRNA and stained with antibodies against centrin-2 (green) as well as HsSAS-6 (magenta). DNA is shown in blue. Insets show approximately twofold magnified views of fluorescent foci around the centrosome. Scale bar, 5 μm. Histograms represent the frequency of mitotic cells with the indicated phenotype. Values are mean percentages ± SEM from three independent experiments (n = 60 for each condition). B Control U2OS cells or U2OS cells treated with siRNA targeting RBM14 were stained with antibodies against HsSAS-6 as well as centrin-2. Immunofluorescence micrographs are shown in Supplementary Fig S6D. When we counted HsSAS-6 foci in this paper, we only counted cells before metaphase/anaphase transition considering the disappearance of HsSAS-6 from anaphase in mitosis. Histograms represent frequency of mitotic cells with excess foci of the indicated proteins at spindle poles. Values are mean percentages ± SEM from three independent experiments (n = 30 for each condition). *P < 0.05 (one-tailed t-test). C U2OS cells treated with the indicated siRNAs were stained with anti-α-tubulin antibodies and Hoechst 33258. Histograms represent frequency of mitotic cells with the multipolar spindle in the indicated conditions. Values are mean percentages ± SEM from three independent experiments (n = 30 for each condition). *P < 0.05 (one-tailed t-test). D RBM14-depleted HeLa cells expressing GFP-centrin (green) were stained with antibodies against CP110 (magenta) and HsSAS-6 (blue). Scale bar, 1 μm. A representative stained procentriole-like structure as well as endogenous centrioles is shown together with a schematic. Histograms represent length between the centers of the foci of the indicated proteins. Values are mean percentages ± SEM from seven individual cells. E, F Ectopic DsRed-centrin-2 foci in RBM14-depleted cells recruit HsSAS-6-GFP. (E) Live imaging of RBM14-depleted U2OS cells expressing HsSAS-6-GFP (green) and DsRed-centrin-2 (magenta). Time is denoted in hh:min, and scale bar is 10 μm. Time zero corresponds to the onset of recording. Pre-existing HsSAS-6-GFP foci (white arrowheads) and ectopic HsSAS-6-GFP focus (red arrowhead) were traced throughout the time-lapse recording. White broken lines represent cell shapes, and blue broken lines represent nuclear shapes. (F) Histograms represent the percentages of ectopic DsRed-centrin-2 foci with HsSAS-6-GFP recruitment (n = 69 foci for control, and n = 67 foci for RBM14 siRNA). G Histograms represent frequency of mitotic cells with excess foci of HsSAS-6 in the indicated conditions. In this experiment, cells were treated with double amount of RBM14 siRNA (20 pmol) compared to that in the other experiments. Values are mean percentages ± SEM from three independent experiments (n = 30 for each condition). *P < 0.05 (one-tailed t-test). H HeLa cells expressing GFP-centrin (green) and RFP-H2B (magenta) and treated with RBM14 siRNA were analyzed using Live CLEM. Pre-existing GFP-centrin foci (white arrowheads) and ectopic GFP-centrin foci (red arrowheads) were traced throughout the time-lapse recording. Z-stacked confocal images spanning the entire height of the cells (< 30 μm) are shown (upper panels). Time is denoted in hh:min. Time zero corresponds to the onset of ectopic formation of GFP-centrin foci. The cells fixed after live imaging were also analyzed for confirming the local correlation between LM and EM images (lower panels). Red square (ectopically formed GFP-centrin foci) represents the region corresponding to that of the EM images acquired from serial sections. Note that ectopic GFP-centrin foci that form a spindle pole include not only electron-dense structures (1, 3) but also a morphologically recognizable centriole-like structure (2). Scale bars, 10 μm (live imaging) and 500 nm (EM).