Deletion of megakaryocytic-specific regulatory sequences of GATA-1 (Gata1 tm2Sho or GATA-1 low mutation) results in severe thrombocytopenia, because of defective thrombocytopoiesis, and myelofibrosis. As documented here, the GATA-1 low mutation blocks megakaryocytic maturation between stage I and II, resulting in accumulation of defective megakaryocytes (MKs) in the tissues of GATA-1 low mice. The block in maturation includes failure to properly organize ␣ granules because von Willebrand factor is barely detectable in mutant MKs, and P-selectin, although normally expressed, is found frequently associated with the demarcation membrane system (DMS) instead of within granules. Conversely, both von Willebrand factor and P-selectin are barely detectable in GATA-1 low platelets. IntroductionMegakaryocytes (MKs) are specialized cells of the blood responsible for platelet production. 1 They originate from committed progenitor cells, usually localized in the marrow, through a complex maturation process, during which MK precursors progressively increase in size, while undergoing extensive synchronous morphologic changes in the cytoplasm and nucleus. 2 At the ultrastructural level, the major cytoplasmic modifications are represented by massive compartmentalization into discrete regions, delimited by intrusions of the plasma membranes, bound to give rise to the demarcation membrane system (DMS). 2 The DMS will, in turn, internalize platelet-specific ␣ granules, giving rise to proplatelets through a process defined thrombocytopoiesis. 3 In the meantime, chromosomes undergo several cycles of endo-duplications. As a result, the nucleus itself appears multilobed.Despite few differences, the morphologic changes associated with the maturation of MK precursors are similar between mice and humans. 4 On the basis of distinct ultrastructural characteristics, murine and human MK precursors are divided into 4 classes 2 : the promegakaryoblast, a small mononuclear cell expressing already platelet-specific proteins, such as von Willebrand Factor (VWF); the megakaryoblast (or stage I MK), a cell 15 to 50 m in diameter with a large, oval or kidney-shaped nucleus and several nucleoli, whose cytoplasm presents abundant ribosomes and a welldeveloped rough endoplasmic reticulum (RER); the promegakaryocyte (stage II MK), a cell 20 to 80 m in diameter with an irregularly shaped nucleus and a more abundant cytoplasm, containing a rudimental DMS; and, finally, mature megakaryocytes (stage III MKs) that contain a multilobed nucleus surrounded by abundant cytoplasm divided into a perinuclear (hosting the centrioles, few biosynthetically active organelles, and many ␣ granules), the intermediate (containing a well-developed DMS and platelet territories), and the peripheral (devoid of organelles and enriched of cytoskeletal proteins and microtubules) zone. 2 The complex process of MK maturation is controlled by lineagespecific extrinsic and intrinsic factors represented, respectively, by growth factors (such as thrombopoietin 5 [TPO]) and transcriptio...

Key Points Abnormal signatures in TGF-β1 signaling gene expression were identified in spleen and marrow from the Gata1low model of MF. These signatures include abnormalities in individual gene (Id2, Stat1, mTOR) in spleen and of gene pathways (Smads and BMPs) in marrow.

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The present study was aimed at investigating whether human Periodontal Ligament Stem Cells (hPDLSCs) were capable of sensing and reacting to lipopolysaccharide from Porphyromonas gingivalis (LPS-G) which is widely recognized as a major pathogen in the development and progression of periodontitis. At this purpose hPDLCs were stimulated with 5 μg/mL LPS-G at various times and the expression of toll-like receptor 4 (TLR4) was evaluated. Toll-like receptors (TLRs) play an essential role in innate immune signaling in response to microbial infections, and in particular TLR4, type-I transmembrane proteins, has been shown recognizing LPS-G. Our results put in evidence, in treated samples, an overexpression of TLR4 indicating that, hPDLSCs express a functional TLR4 receptor. In addition, LPS-G challenge induces a significant cell growth decrease starting from 24 h until 72 h of treatment. LPS-G leads the activation of the TLR4/MyD88 complex, triggering the secretion of proinflammatory cytokines cascade as: IL-1α, IL-8, TNF-α and β and EOTAXIN. Moreover, the upregulation of pERK/ERK signaling pathways and NFkB nuclear translocation was evident. On the basis of these observations, we conclude that hPDLSCs could represent an appropriate stem cells niche modeling leading to understand and evaluate the biological mechanisms of periodontal stem cells in response to LPS-G, mimicking in vitro an inflammatory process occurring in vivo in periodontal disease.