The RBM6-CSF1R–induced megakaryocyte phenotype is mouse-strain specific. (A) Immunohistochemistry on spleen section using von Willebrand factor antibody. Note that both megakaryocyte and platelet numbers are increased in the C57/Bl6 background, whereas only megakaryocytes numbers are increased in the Balb/C background. (B) Splenocytes were plated in collagen-based media containing TPO, IL-11, IL-3, and IL-6. Slides were stained for acetylcholinesterase and colonies were enumerated. Experiment was performed at least in triplicate and mean ± SD is represented. CFU-MK indicates colony-forming unit–megakaryocyte. Bone marrow cells from C57/Bl6 (C) or Balb/C (D) recipients were cultured for 4 days in presence of TPO and SCF. Cells were then stained with propidium iodide (PI) and CD41⁺ cells were analyzed for ploidy content.