Immunofluorescent labeling of cytospin preparations from 12.5-dpc liver and blood stained with the anti-runt box antiserum. (A) Anti-runt box staining of liver cells; two primitive erythrocytes labeled at the nucleus-cytoplasmic border are indicated (arrows). (B) Staining with preimmune serum. Competition experiments were performed on 12.5-dpc liver (C and D) and blood (E and F ) as for bone marrow (Fig 2). In both tissues, the staining persisted after preincubation with GST (C and E), but was abolished after preincubation with GST/runt (D and F ).