Shortened survival and defective hematopoiesis in gp130^flox/flox/TCre mice. (A) Shortened survival of gp130^flox/flox/TCre mice. (B) Peripheral-blood smear of a 16-week-old gp130^flox/flox/TCre mouse exhibits polychromasia and anisopoikilocytosis of erythrocytes. Scale bar represents 20 μm. Objective, × 63/1.4 NA. (C) Splenomegaly in a 12-week-old gp130^flox/flox/TCre mouse. Scale bar represents 1 cm. (D) Spleen of a 12-week-old gp130^flox/flox/TCre mouse exhibits extramedullary hematopoiesis with abundant megakaryocytes. Bone marrow of a 16-week-old gp130^flox/flox/TCre mouse exhibits normal cellularity in the endosteal niche (EN) adjacent to bone. In contrast, the vascular niche (VN) is markedly hypocellular, except for retention of normal numbers of megakaryocytes. Scale bar represents 50 μm. Objective, × 20/0.5 NA. (E) Quantification of blood cells of B-cell, T-cell, myeloid, and erythroid lineage expressing the indicated markers in bone marrow (BM), spleen, and thymus of gp130^+/+/TCre and gp130^flox/flox/TCre mice. Data represent the mean ± SD of 5 mice (age 12 weeks) in each genotype. ^*P < .05 and ^**P < .01 compared with gp130^+/ +/TCre.