Histopathology of transgenic mice and controls. Mice were euthanized 25 weeks after starting tamoxifen. Hematoxylin-eosin and Gömöri staining of bone marrow and spleen are shown (magnification, ×400). Frequency of mice displaying grade 0, grade 1, or grade 2 myelofibrosis is shown in the lower panel for each genotype.