Expression of surface proteins and colony forming ability of the cultured CD34⁺ cells during early erythropoiesis. (A) Immunoblot analysis. Blots of sodium dodecyl sulfate-polyacrylamide gel electrophoresis of total cellular protein prepared from cells cultured from day 1 to day 7 were probed with antibodies against the indicated proteins. Note the decreased expression of CD34 and IL-3R, and the increased expression of CD36 and CD71. CD45 remained constant throughout and GPA was negative until day 6. Glyceraldehyde-3-phosphate dehydrogenase was used as loading control. (B) Flow cytometric analysis. The surface expression of indicated proteins was measured by flow cytometry. The representative profiles are shown. Gray line: autofluorescence control from unstained cells; black line: fluorescence from cells stained with indicated antibody. (C) Quantitation of colony forming ability. BFU-E colonies peak at day 4 then gradually decrease, whereas CFU-E colonies peak at day 5 and then decrease. The data are from 7 independent experiments.