Abnormal hematopoiesis in VavP-MYC mice. (A) An abnormally large megakaryocyte in the bone marrow of a 4-week-old MYC17 mouse (right panel) containing internalized granulocytes (some indicated by arrowheads) and for comparison, a normal megakaryocyte (left panel; indicated by arrow) in the bone marrow of a wild-type littermate. H&E-stained sections; scale bar equals 20 μm. (B) Abnormally large macrophage colonies developed in M-CSF–stimulated cultures of MYC17 (right panel) and MYC10 (not shown) bone marrow cells when compared with cultures of wild-type cells (left panel); scale bar equals 125 μm. (C) Primary M-CSF–stimulated macrophage colonies from 8-week-old MYC17 (red) and wild-type (B6) mice were recultured in M-CSF (Round 1) and the colonies that developed were counted. Recloning was performed for 2 more successive rounds using colonies from the first and second rounds. Bars indicate the mean.