Alternative activation of the Gata1 locus in stem/progenitor cells and erythroid and MK precursors from the spleen of Gata1^low mice. (A) Levels of GFP expressed by marrow and spleen stem/progenitor cells divided into stem/common erythroid-megakaryocytic progenitors (pink) and granulomonocytic and common myeloid progenitors (blue) by CD34 staining (CD34^neg and CD34^pos, respectively). (B) Levels of GFP expressed by marrow and spleen erythroid cells (Ter119^pos) divided into immature (CD71^high, gray) and mature (CD71^med, blue) erythroblasts.²⁸  (C) Levels of GFP expressed by marrow and spleen MKs identified by CD41/CD61 staining. Irrelevant controls for GFP-specific signal are presented as light gray histograms in all of the panels. The pictures (40 × original magnification) of representative MKs double stained for cKit and GFP are included in panel C. The frequency and average GFP fluorescence intensity (AFI) of the different populations is summarized in Table 1. Similar results were obtained in 4 separate experiments.