Oct4 staining on USSC-derived spheres. Representative microscopy images of seven day spheres fixed and stained with an Oct4 antibody (Alexa488; green) and counter stained with 4, 6-diamidino-2-phenylindole (DAPI; blue). As a positive control, the nuclear localisation of the Oct4 antibody was confirmed in hES cells. USSCs were also probed to confirm the Oct4 status of the starting cell population. The respective negative isotype control images are also shown. USSCs and seven day spheres do not express Oct4 at the protein level. (Magnification, ×200; scale bar is 100 μm).