IMMATURE MEGAKARYOCYTES IN THE MOUSE - PHYSICAL CHARACTERISTICS, CELL-CYCLE STATUS, AND INVITRO RESPONSIVENESS TO THROMBOPOIETIC STIMULATORY FACTOR

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  • 1 January 1982
    • journal article
    • research article
    • Vol. 59  (3) , 569-575
Abstract
The heterogeneity among immature megakaryocytes was examined by physical properties, cell cycle status and responsiveness to thrombopoietic stimulatory factor. Three types of immature megakaryocytes exist that can be recognized by acetylcholinesterase staining, nuclear shape, high nucleus/cytoplasm ratio and small size (8-18 .mu.m) with respect to mature megaka ryocytes (> 18 .mu.m). These 3 acetylcholinesterase-containing cell types are distinguished by their nuclear configuration: a round, indented and lobed nucleus. The lobed cell type overlaps with and enhances detection of megakaryoblasts (stage I megakaryocytes). These cells had a sedimentation velocity range of 3.5-19.0 mm/h and a density range of 1.072-1.095 g .cntdot. cm-3. Separation of these 3 classes of immature megakaryocytes was achieved by equilibrium density centrifugation with modal buoyant densities of 1.079 g .cntdot. cm-3 (round), 1.084 g .cntdot. cm-3 (indented) and 1.089 g .cntdot. cm-3 (lobed). In the presence of thrombopoietic stimulatory factor, the round nucleated cells, but not the indented or lobed nuclei morphology, develop into large mature megakaryocytes in 60-h semisolid cell cultures. Development of 2 cell groups, or colonies of megakaryocytes, was not observed during this in vitro incubation period. In vivo treatment with hydroxyurea indicated that 57.5% .+-. 19% of the round nucleus form were actively synthesizing DNA. No reduction in the numbers of indented or lobed nucleus forms were observed following hydroxyurea treatment. These 3 types of immature megakaryocytes apparently reflect the early maturation stages occurring in megakaryocyte differentiation.