Deletion of Jak2 beginning at postnatal day 4 results in profound anemia.

<p>(A) Representative PN17 control (n = 7) and PN17 Jak2 cKO (n = 6) mice and body weights plotted as a function of genotype. Size bar = 5 mm. (B) Pallor due to poor peripheral perfusion secondary to severe anemia was seen in the tail, forelimb, and mesenteric vasculature of the Jak2 cKO mice, but not the controls. Size bar = 5 mm. (C) Representative peripheral blood films for both genotypes. Jak2 cKO blood films revealed marked anemia, hypochromasia, and microcytosis. Hematocrits plotted as a function of genotype indicating severe anemia in the Jak2 cKO mice. Size bars = 10 µm. (D) Representative bone marrow sections from both genotypes and quantification of marrow cellularity plotted as a function of genotype. Size bars = 500 µm for 4X images and 50 µm for 40X images. (E) Representative spleens from both genotypes and spleen weight to body weight ratios plotted as a function of genotype. Size bar = 5 mm. (F) Histologic sections through the spleen are shown which indicate a hypoplasia phenotype in the Jak2 cKO mice. Size bars = 500 µm for 4X images and 50 µm for 40X images. (G) Representative liver sections from both genotypes showing hepatocellular atrophy in the Jak2 cKO tissue, but not in the control tissue. Size bars = 50 µm for 40X images and 10 µm for 100X images. (H) Determination of Jak2 mRNA levels in the liver from both genotypes. **, p<0.01.