Kinetics of Megacaryocyte Proliferation.

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Abstract
The kinetics of the megakaryocytic cell line of the rat bone marrow were studied autoradiographically using H3-thymidine. The transit time for the most immature recognizable stage of megakarcyocytic development to megakaryocytic disintegration was found to be approximately 40 hours. Evidence was obtained that the recognizable megakaryocytic elements originate from urecognized precursors which nearly continuously synthesize DNA for a period of at least 1 to 3 days prior to maturation into recognizable immature megakaryocytic cells. Approximately 35% of the immature megakaryocytic cells were able to synthesize DNA, and to incorporate more H3-thymidine than the rest of the bone marrow cells, consistent with polyploidy. The later phase of maturation without DNA synthesis lasted approximately 25-30 hours. Chromosome arrangements comparable to multicentric metaphase were occasionally seen within the immature megakaryocytic cells. A sequence of mitotic events from prophase to telophase was not observed.