Megakaryocyte and platelet ontogeny

描述(申请人提供)：血小板是来源于巨核细胞(Megs)的无核细胞，它是止血和血栓形成的关键成分，并在炎症、免疫和血管生成方面起中介作用。在成人，所有的血小板都来自造血干细胞(HSCs)。我们之前在小鼠胚胎中发现，MEG谱系在HSC出现前几天被指定为胚胎(HSC前)巨核生成。我们还确定胚胎MEG具有有限的多倍化，并产生带有小α颗粒的极大的血小板。人类新生儿的血栓生成也以有限的多倍化和快速的胞浆成熟为特征。细胞周期抑制因子Cip/Kip家族在一定程度上调节细胞内复制。我们的初步研究表明，胚胎而不是成人的血小板表达高水平的p57(Kip2)。在目标1中，我们将进一步定义胚胎、胎儿和成人巨核生成之间的差异，并检验MEG内复制的差异部分受Cip/Kip家族成员差异表达调控的假说。我们对原始胚胎血小板的初步研究表明，凝血酶能有效地激活它们，但 而ADP的情况则明显不同。这些功能研究与初级胚胎和成人血小板中PAR1的差异上调和P2Y12的下调有关。在Aim 2研究中，我们将检验胚胎血小板具有内在功能差异的假设。 与成年同龄人相比，在激活和凝块形成方面。对造血个体发育的理解与从胚胎干细胞(ES)和诱导多能干细胞(IPS)生成血细胞特别相关，这些细胞具有作为基于细胞的治疗的重要来源的潜力。我们假设ES细胞来源的MEG和血小板将具有主要的胚胎特征。这一假设将通过比较ES细胞来源的MEG成熟和血小板功能与原始胚胎细胞的功能来检验。这项拟议的研究建立在我们对MEG个体发育和小鼠胚胎中血小板出现的研究基础上，并为从ES/iPS细胞来源开发临床有用的基于细胞的疗法奠定了基础。

DESCRIPTION (provided by applicant): Platelets are anucleate cells derived from megakaryocytes (megs) that serve as critical components of hemostasis and thrombus formation, and mediate aspects of inflammation, immunity, and angiogenesis. In the adult, all platelets are derived from hematopoietic stem cells (HSCs). We previously discovered in the mouse embryo that the meg lineage is specified several days before HSC emergence as embryonic (pre- HSC) megakaryopoiesis. We have also determined that embryonic megs have limited polyploidization and generate extremely large platelets with small a-granules. Thrombopoiesis in human neonates is also characterized by limited polyploidization and rapid cytoplasmic maturation. Endoreplication is regulated in part by the Cip/Kip family of cell cycle inhibitors. Our preliminary studies indicate that embryonic, but not adult, platelets express high levels of p57 (Kip2). In Aim 1, we will further define the differences between embryonic, fetal and adult megakaryopoiesis and test the hypothesis that differences in meg endoreplication are regulated, in part, by the differential expression of Cip/Kip family members. Our preliminary studies of primary embryonic platelets indicate that they are effectively activated by thrombin but markedly less so by ADP. These functional studies correlate with the differential upregulation of PAR1 and down-regulation of P2Y12 in primary embryonic versus adult platelets. In Aim 2 studies, we will test the hypothesis that embryonic platelets have intrinsic functional differences in activation and clot formation when compared to their adult counterparts. An understanding of hematopoietic ontogeny is particularly relevant to the generation of blood cells from embryonic stem (ES) cells and induced pluripotent stem (iPS) cells, which carry the potential to serve as an important source of cell-based therapies. We hypothesize that ES cell-derived megs and platelets will have predominantly embryonic characteristics. This hypothesis will be tested by comparing ES cell-derived meg maturation and platelet function with that of primary embryonic cells. This proposed research builds upon our studies of meg ontogeny and platelet emergence in the murine embryo and establishes a foundation for the development of clinically useful cell-based therapies from ES/iPS cell sources.