Megakaryocyte and platelet ontogeny

描述（由申请人提供）：血小板是来源于巨核细胞的无核细胞，是止血和血栓形成的关键成分，并介导炎症、免疫和血管生成。在成人中，所有的血小板都来源于造血干细胞（hsc）。我们以前在小鼠胚胎中发现，巨齿鲨谱系在HSC出现前几天被指定为胚胎（前HSC）巨核形成。我们还确定胚胎巨鼠具有有限的多倍体，并产生具有小a颗粒的极大的血小板。人类新生儿的血小板形成也具有有限的多倍体化和快速的细胞质成熟的特点。细胞周期抑制剂Cip/Kip家族在一定程度上调控细胞内复制。我们的初步研究表明，胚胎而非成人的血小板表达高水平的p57 （Kip2）。在Aim 1中，我们将进一步定义胚胎、胎儿和成人巨核形成的差异，并验证巨核内复制的差异部分受到Cip/Kip家族成员差异表达的调节这一假设。我们对初代胚胎血小板的初步研究表明，它们可以被凝血酶有效地激活，但是

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.