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. 2016 Jun 21;5(1):787. doi: 10.1186/s40064-016-2384-1

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© The Author(s) 2016

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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Fig. 1 — The process of megakaryocyte differentiation and platelet production from HSCs within the niches. There are at least two niches in the bone marrow (BM) identified for HSC hematopoiesis, including the osteoblastic niche and the vascular niche. The HSCs live next to the endosteal bone surface, lined mainly by osteoblasts, which constitute the physiological microenvironment called the osteoblastic niche, providing a quiescent environment for HSC maintenance. The vascular niche consists of HSCs and endothelial cells, offers an alternative niche for mobilized stem cells, and promotes proliferation and further differentiation or maturation into the circulation system. There may be four primarily sequential biological stages for thrombopoiesis and megakaryopoiesis. The self-renewal of HSCs living in the BM osteoblastic niches is the first step. Stem cells then proliferate and differentiate to increase the number of MK progenitors. In the third step of maturation events, MK progenitors undergo a process known as endomitosis. The fourth stage is characterized by platelet assembly and release. The current model of platelet formation recognizes that mature megakaryocytes extend long, branching processes, called proplatelets, which are composed of platelet-sized swellings in tandem arrays that are connected by thin cytoplasmic bridges. Platelet production begins with the erosion of one pole of the megakaryocyte to generate large pseudopodial-like structures that elongate, thin, and branch to yield slender tubular projections of uniform diameter (2–4 μm). The product released by megakaryocytes may be proplatelets, and the product released by proplatelets may be preplatelets and/or platelets of various sizes. The red dotted line showed HSC circulation, which contains HSCs leaving the BM, entering the vascular system (termed mobilization), and returning to the BM (known as homing). However, the underlying physiological function of these events remains elusive. SNO cell spindle-shaped N-cadheri⁺CD45⁻ osteoblastic cell, MEP megakaryocyte-erythroid progenitor, HSCs hematopoietic stem cells, MK megakaryocyte