Increased incidence and analysis of emperipolesis in megakaryocytes of the mouse mutant gunmetal.

Mutant gunmetal (gm/gm) mice exhibit prolonged bleeding, platelet granule defects, abnormal megakaryocyte demarcation membranes, and thrombocytopenia. The number of megakaryocytes in gm/gm mice is increased substantially. Also, the percentage of gm/gm megakaryocytes exhibiting emperipolesis is increased. However, the number of emperipolesed cells per megakaryocyte is not. EC are of several hematopoietic lineages, with a slight skew to granulocytes, and include mature, primitive, and degenerating cells. No significant differences in the types of emperipolesed cells were observed between mutant mice and their normal gm/+ or +/+ counterparts. The increased incidence of emperipolesis in gm/gm megakaryocytes is controlled by the megakaryocyte genotype, not systemic factors. A significant practical finding of these studies was the demonstration that increased emperipolesis results in a significant "right shift" in megakaryocyte ploidy determined by flow cytometry.