Ultrastructural Analysis of Organelles Produced in Megakaryocytes Cultured from Human Stem Cells

Electron microscopic (EM) studies have permitted the elucidation of platelet anatomy while EM cytochemistry has recently revealed four distinct classes of granules. In spite of several EM investigations, knowledge of the production of organelles in developing platelets with in marrow megakaryocytes (MK) is limited. The recent possibility of obtaining human MK colonies in culture which mature with synchrony and derived from a single progenitor present in blood and marrow permits analysis of MK maturation. We determined that platelet peroxidase, demarcation membrane system, microtubules glycogen and numerous granules develop in MK cultured in vitro; a complete maturation proceeding as far as platelet shedding could be observed in some MK derived from marrow stem cells. The origin of the dense granules which represent the amine-storing organelle in platelets is uncertain. We are currently investigating whether the dense granules in cultured MK represent a separate class and attempting to establish the period of their synthesis. We anticipate that the culture method used in conjunction with EM will permit study of pathological megakaryocytopoiesis.

 

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