Hematopoietic phenotype of aged Gata1s mice. PB analysis of RBC count and Hb level from WT and Gata1s (G1s) 20-month-old male (A) and female (B) Gata1s mice. The values of animals #4248, #4249, and #2873 are highlighted in different colors. (C) Photos of PB smears showing the increased reticulocytes in aging Gata1s (G1s) mice highlighted in panels A and B. Arrows indicate RBCs with abnormal morphology. Scale bars represent 50 μm. (D) Percentage of reticulocytes in the PB in panel C was determined by enumerating total RBCs and reticulocytes in 3 different fields. (E) Photos of enlarged spleens from animal #4248, #4249, and #2873 and 2 WT controls. Bars represent 1 cm. (F) Photomicrographs of hematoxylin and eosin (HE)– or reticulin-stained BM and spleen sections from mice in panel E. Scale bars represent 100 μm (left) and 50 μm (right) in BM sections, and represent 500 μm (left) and 100 μm (right) in spleen sections. Mean ± SD are shown in graphs, age = 20 months. ∗P ≤ .05, ∗∗P ≤ .01 by unpaired Student t test.