Megakaryocyte and platelet ontogeny

描述（由申请方提供）：血小板是来源于巨核细胞（megs）的无核细胞，作为止血和血栓形成的关键组分，并介导炎症、免疫和血管生成。在成人中，所有血小板均来源于造血干细胞（HSC）。我们先前在小鼠胚胎中发现，在HSC出现前几天，meg谱系被指定为胚胎（前HSC）巨核细胞生成。我们还确定胚胎megs有有限的多倍化，并产生非常大的血小板与小的α-颗粒。人类新生儿中的血小板生成也以有限的多倍化和快速的细胞质成熟为特征。胞内复制部分受细胞周期抑制剂Cip/Kip家族调节。我们的初步研究表明，胚胎，但不是成人，血小板表达高水平的p57（Kip 2）。在目标1中，我们将进一步定义胚胎，胎儿和成人巨核细胞生成之间的差异，并测试的假设，在梅格endoreficit的差异调节，部分，由Cip/Kip家族成员的差异表达。我们对原代胚胎血小板的初步研究表明，它们能被凝血酶有效激活， ADP的情况明显较低。这些功能研究与原代胚胎血小板与成人血小板中PAR 1的差异上调和P2 Y12的下调相关。在目标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 在激活和凝块形成方面的作用。对造血个体发生的理解与从胚胎干（ES）细胞和诱导多能干（iPS）细胞产生血细胞特别相关，其具有作为基于细胞的疗法的重要来源的潜力。我们假设ES细胞来源的MEG和血小板将主要具有胚胎特征。将通过比较ES细胞来源的meg成熟和血小板功能与原代胚胎细胞的功能来检验这一假设。这项拟议的研究建立在我们对小鼠胚胎中巨细胞个体发育和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.