Fig. 5. Maximum intensity projections of deconvolved serial sections through heterokaryons of cells from line YFPSmBE1 and primary human fibroblasts (DFSF1), stained with antibodies to p80-coilin and SMN. Cells co-cultured without fusion show prominent Cajal bodies in nuclei from line YFPSmBE1 (arrows in A-C), containing p80-coilin (A), YFPSmB (B) and SMN (C). By contrast, DFSF1 nuclei show fine punctate staining with p80-coilin (A) and SMN (C), with no co-localization of the two into obvious Cajal bodies (overlay in D). In cells fixed 2 hours after PEG fusion (E-H), Cajal bodies are seen in nuclei from both cell types. YFPSmB is seen in nuclear bodies in DFSF1 nuclei (arrows in F). These bodies also contain both p80-coilin (arrows in E) and SMN (arrows in G). In cells fixed 16 hours after fusion, YFPSmB is seen in speckles in DFSF1 nuclei fused to YFPSmBE1 nuclei (arrowheads in J). Cajal bodies (arrows in I-K) containing YFPSmB (J), p80-coilin (I) and SMN (K) are also present in DFSF1 nuclei at this time point (overlay in L). Labeling of heterokaryons fixed 2 hours after PEG fusion with antibodies to the trimethyl cap of snRNAs (M) confirms that the nuclear bodies seen in DFSF1 cell nuclei at this time point contain snRNA (arrow in M) in addition to YFPSmB (arrow in N) and p80-coilin (arrow in O). Bar, 10 µm. (ii) Western blot analysis of total cell lysates from DFSF1 cells and HeLa cells. The intensity of signals seen for -tubulin confirms that proteins from similar numbers of cells have been loaded in each lane. The core snRNP, Sm proteins, the U2 snRNP-specific protein U2B'', the U1 snRNP-specific proteinU1A, and the SMN protein are both much more abundant in HeLa cells than in DFSF1 cells.