Megakaryocytopenia in W/Wv mice is accompanied by an increase in size within ploidy groups and acceleration of maturation.

Megakaryocytopoiesis was evaluated in W/Wv mice and their normal +/+ littermates to analyze the mechanisms by which normal platelet production is maintained in W/Wv mice even though numbers of megakaryocytes are low. Relative sizes of megakaryocytes, and their nuclei and cytoplasm, were measured microscopically in bone marrow smears, and the ploidy of the same cells was measured by two-wavelength microspectrophotometry. Maturation rate of megakaryocytes was estimated after they were labeled with tritiated thymidine. W/Wv megakaryocytes were macrocytic: average cell size was increased in each ploidy group. The increase in cytoplasmic area exceeded that of the nucleus. Further analysis of the predominant 16N ploidy group revealed that the increase in average cell size was due to depletion of cells of small size. Megakaryocytes matured more rapidly than normal in W/Wv mice. These results showed that megakaryocyte size and ploidy can be regulated separately. They suggest that alterations in cell growth and maturation may be mechanisms by which the organism can compensate for a deficiency in numbers of megakaryocytes, but they do not define the mechanism by which the deficiency may be sensed or by which the compensatory changes may be mediated. This is a US government work. There are no restrictions on its use.