KEL is expressed on all RBC precursors in the fetal liver and bone marrow of transgenic animals, in an RBC-specific fashion. (A-C) Fetal liver cells from KEL transgenic fetuses, with anti-KEL staining (solid) or secondary only staining (shaded) of RBC precursor populations (I = primitive erythroid progenitor cells, II = proerythroblasts and early basophilic erythroblasts, III = later basophilic erythroblasts, IV = chromatophilic and orthochromatophilic erythroblasts, and V = late orthrochromatophlic erythroblasts and reticulocytes). (D) Bone marrow from KEL transgenic animals, with anti-KEL staining (solid) or secondary only staining (shaded) of RBC populations (I = proerythroblasts, II = basophilic erythroblasts, III = polychromatic erythroblasts, IV = orthochromatic erythroblasts, V = reticulocytes, VI = mature RBCs). (E) Anti-KEL staining of peripheral blood cells. (F) Bone marrow and organs of a KEL-positive animal were evaluated for KEL expression by PCR. Results are from 2 independent experiments, with 1 to 2 mice per group.