Abnormalities of megakaryocytes in S1-S1d mice.

Megakaryocytopoiesis was evaluated in size. Numbers of megakaryocytes in bone SI/SId mice and their heterozygous and marrow and spleen were reduced, but homozygous normal ( +1+) littermates. individual megakaryocytes were larger SI/SId mice had a normal concentration than normal. of blood platelets which were of normal T HE MICROENVIRONMENT has been shown to influence hematopoietic cell differentiation into erythropoietic or granulocytopoietic cell systems.1 Megakaryocytes are thought to originate from the same pluripotential stem cell as red cells and granulocytes, but nothing is known about microenvironmental influences on megakaryocytopoiesis except that it may be influenced by body age.2 The Sl/Sl ’ mouse has a genetically determined macrocytic anemia that appears to be due to a defect in the cellular environment rather than to defective hematopoietic cells.3 The anemia of Sl/Sl ’ mice is not corrected when normal hematopoietic stem cells are transplanted into them,4 but it is improved by transplantation of intact spleens from normal donors.5’6 SI/SId spleens have, further, been shown to be incapable of supporting colony formation by transplanted hematopoietic stem cells in irradiated hosts.7 The W/WV mouse also has hereditary macrocytic anemia associated with a defect in transplantable stem The dependence of the anemia on the stem-cell defect in W/W V and on the tissue-environmental defect in SI/SId is shown by the facts that transplantation of stem cells from SI/SId to W/WV will cure the anemia in the W/Wv,4s but splenic tissue transplantation, rather than just stem-cell transplantation, from W/WV to SI/SIC’ is necessary to improve the anemia of the Sl/Sld.S Sutherland et al.9 found that granulocytopoiesis was not totally normal in SI/SId mice. However, the effect of the SI defect on megakaryocytopoiesis has not been reported; hence, the present studies were undertaken.