Analysis of ES cell contributions to the red cells of chimeras. (a) Acid urea-Triton X-100 (Sigma, St Louis, MO) polyacrylamide gel electrophoretic analysis of globin chains from the blood of EKLF−/− and EKLF−/−, LCRγ chimeras. Blood from a mouse transgenic for the human LCRγ hybrid gene (TGγ), a C57BL/6J mouse of Hbb^s haplotype and a (C57BL/6J × CBA/J) F1 mouse of Hbb^s/Hbb^d haplotype were used as controls. The gel was deliberately overstained with Protostain silver stain to enable detection of the human γ-globin chain and, the β^maj and β^min -globin chains in the EKLF−/−, LCRγ chimeric mice. (b) GPI-1 analysis of red blood cells. Red cell extracts from chimeras produced with EKLF+/− clone #12, EKLF−/− clone 2 and 6 and, EKLF−/−, LCRγ clone 6-10 and 6-13 were separated by cellulose acetate electrophoresis and stained for GPI-1 enzymatic activity. Red cell extracts from 129/SvEv mice and C57BL/6J mice were used as controls for GPI-1A and GPI-1B isozymes, respectively. R1 ES cells produce GPI-1A and cells derived from the host blastocyst produce GPI-1B. To detect GPI-1A activity in the blood of EKLF−/−, LCRγ 6-10 and 6-13 chimeras, the stain was overdeveloped such that detection of GPI-1B from the host blastocysts was past saturation limits of the assay.