Figure 4. Expression of stem cell markers in UM. ABCG2 (middle panel) and OCT4 (right panel) protein expression was assessed by indirect immunofluorescence in a mixed UM primary tumor. Positive staining appears in red. Nuclei were counterstained using Hoechst (in blue). No positive staining was observed in the negative control section using mouse IgG (left panel). Scale bars, 50 μm.