Massive increase in the ratio of early to late erythroblasts in spleens of anemic Stat5a^−/−5b^−/− mice.

(A) Flow cytometry density plots of spleen cells from 3 representative wild-type mice (numbers 1-3, mean hematocrit = 48.5%) and 3 anemic Stat5a^−/−5b^−/− mice (numbers 4-6, mean heamtocrit = 23%) from the same mouse colony. Cells were labeled for Ter119 and CD71 as described in Figure 4. The relative number of cells in each of regions I to IV as a percent of all viable, nucleated erythroid cells is indicated on each plot. Erythroid cells (defined as all cells in regions I to IV) in each spleen constituted 61.7%, 53%, and 37.4% of all spleen cells for the wild-type mice (numbers 1-3, respectively); and 87.7%, 93.2% and 91.1% of all spleen cells for Stat5a^−/− 5b^−/− mice (numbers 4-6, respectively). (B) Flow cytometry forward-scatter distribution histograms of wild-type and Stat5a^−/−5b^−/−mice (corresponding to mice numbers 1 and 4, respectively, in panel A). Left-hand panel shows data for all Ter119^high cells. Middle and right-hand panels show data for Ter119^highCD71^high (region II) cells and Ter119^highCD71^low (region IV) cells, respectively. (C) Flow cytometry density plots of spleen cells from a representative wild-type mouse (right-hand panel, hematocrit = 42%) and a representative mouse with a tissue-specific deletion of VHL (VHL^−/−, left-hand panel; see “Materials and methods”). The VHL^−/− mouse shown had an enlarged spleen and a hematocrit of 84%.