The Fine Structure of the Megakaryocyte in the Mouse Spleen

Megakaryocyte and Platelet Formation: A Scanning Electron Microscope Study in Mouse Spleen

“…4) The megakaryocytes project small ectoplasmic blebs (type I microprocesses) into the sinus lumen and then detach them. By this process, as well as by the fragmentation of the ectoplasm above mentioned, megakaryocytes may produce platelets lacking in organelles.Since WRIGHT (1914) described that the megakaryocyte is the mother cell of blood platelets, many investigations have been made on this cell by means of light microscopy, phase contrast cinematography, transmission electron microscopy (TEM) and recently by means of scanning electron microscopy (SEM).In these studies, the areas of inquiry have been how and where the megakaryocyte releases the platelets and, since YAMADA (1957) found the platelet demarcation membrane system (DMS), how the system is formed in the cell. Various observations on the origin of the DMS have been made: YAMADA (1957) reported that the system was formed by the coalescence of special vesicles which were distinctly different from the elements of smooth endoplasmic reticulum.…”

“…In these studies, the areas of inquiry have been how and where the megakaryocyte releases the platelets and, since YAMADA (1957) found the platelet demarcation membrane system (DMS), how the system is formed in the cell. Various observations on the origin of the DMS have been made: YAMADA (1957) reported that the system was formed by the coalescence of special vesicles which were distinctly different from the elements of smooth endoplasmic reticulum.…”

“…Various observations on the origin of the DMS have been made: YAMADA (1957) reported that the system was formed by the coalescence of special vesicles which were distinctly different from the elements of smooth endoplasmic reticulum.…”

New roads to a megakaryocyte inner territory

“…A convoluted internal system of membranes within the megakaryocyte, termed demarcation membranes, was observed decades ago, using electron microscopy. 2 An early study, 3 as well as subsequent ones, proposed that this system forms the plasma membrane of newly generated platelets 2,3 and that thrombopoietin promotes the development of these membranes. 4 Live cell imaging of mature megakaryocytes showed that the intracellular demarcation membranes extend from peripheral plasma membranes.…”

“…Released in the circulation via neutrophil extracellular traps, leaking from necrotic cells, or secreted in response to lipopolysaccharide, these nuclear proteins, or nuclear cytokines, are generally proinflammatory and often cytotoxic to cells as they are recognized by pattern-recognition receptors (PRRs) such as the various Toll-like receptors (TLRs) and the receptor for advanced glycation end products (RAGE). 2,3 In a striking example, histones cause profound platelet activation mediated at least in part by platelet TLRs, resulting in the release of platelet-derived polyP with prohemostatic, prothrombotic, and proinflammatory effects. [4][5][6] Previously, the pathophysiologically achievable concentrations of nuclear proteins in the circulation and the concentrations required for cytotoxicity in experimental models seemed to overlap narrowly at best.…”