Fig. 3. Residual CBs containing fibrillarin do not associate with PML bodies. Wild-type (WT, panel A) and coilin knockout MEF cells (KO, panel B) were stained with antibodies to PML to mark PML bodies (green) and fibrillarin to detect CBs and residual CBs (red). Fibrillarin normally localizes to nucleoli and CBs, but is also enriched in one kind of rCB (Tucker et al., 2001). An arrow marks an association between a CB and a PML body (panel A), while arrowheads mark residual CBs in KO cells that fail to associate with PML bodies (double arrowhead, panel B). DAPI staining (blue) was used to define the nucleus. Wild-type (WT, panel C) and coilin knockout MEF cells (KO, panel D) were also transfected with YFP-Sp100 (green) to mark PML bodies and stained with anti-fibrillarin (red) to detect CBs and residual CBs (rCBs). Arrows mark some of the associations between CBs and PML bodies in wild-type cells (panel C). Double arrowheads mark PML bodies that fail to associate with rCBs (arrowheads) in knockout cells (panel D). Scale bar, 2 µm.