Fli-1 protein is expressed in human megakaryocytes. A and B show immunohistochemical analysis for Fli-1 expression in 293T cells that were transiently transfected with either nonspecific plasmid (A) or the Fli-1 expression construct CMVFli-1 (B). Hoechst DNA staining is cyan and Fli-1 staining is red. Regions that colocalize for DNA and Fli-1 staining appear as magenta. Panels C and D show CD34⁺ cells that were treated with 10 ng/mL of thrombopoietin for 7 days before triple staining. Panel C shows Hoechst DNA stain (blue) and Fli-1 (red). Areas of colocalization appear as magenta. Panel D displays the same cells as panel C showing GPIIb antigen (green) and Fli-1 (orange). In panel D Fli-1 appears as orange. Original magnification of panels A and B was 40× and panels C and D was 200×.