Megakaryocytes exit from mitotic cell cycle and enter a phase of repeated DNA replication without undergoing cell division, in a process termed as endomitosis of which little is known. We studied the expression of a DNA replication licensing factor mini chromosome maintenance protein 7 (MCM7) and its intronic miR-106b-25 cluster during mitotic and endo-mitotic cycles in megakaryocytic cell lines and in vitro cultured megakaryocytes obtained from human cord blood derived CD34C cells. Our results show that contrary to mitotic cell cycle, endomitosis proceeds with an uncoupling of the expression of MCM7 and miR-106b-25. This was attributed to the presence of a transcript variant of MCM7 which undergoes nonsense mediated decay (NMD). Additionally, miR-25 which was up regulated during endomitosis was found to promote megakaryopoiesis by inhibiting the expression of PTEN. Our study thus highlights the importance of a transcript variant of MCM7 destined for NMD in the modulation of megakaryopoiesis.

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Megakaryopoiesis is the process of formation of mature megakaryocytes that takes place in the bone marrow niche resulting in the release of platelets into the peripheral blood. It has been suggested that cell to cell communication in this dense bone marrow niche may influence the fate of the cells. Numerous studies point to the role of exosomes and microvesicles not only as a messenger of the cellular crosstalk but also in growth and developmental process of various cell types. In the current study, we explored the effects of megakaryocyte-derived microvesicles in hematopoietic cell lines in the context of differentiation. Our study demonstrated that microvesicles isolated from the induced megakaryocytic cell lines have the ability to stimulate noninduced cells specifically into that particular lineage. We showed that this lineage commencement comes from the change in the methylation status of Notch1 promoter, which is regulated by DNA methyltransferases. K E Y W O R D S differentiation, DNA methyltransferase, megakaryopoiesis, microvesicles, Notch