Initiation of Mammalian Embryonic Hematopoiesis

描述(申请人提供)：我们的长期目标是阐明哺乳动物胚胎中造血系统早期个体发育的细胞和分子事件。虽然已知胎儿和成人的明确造血是多血统的，但卵黄囊的原始造血集中在红系细胞的合成上，红系细胞对胚胎的存活至关重要。我们最近做了一项开创性的观察，即小鼠胚胎中的原始红细胞最终去核。然而，调节原始红系细胞去核的过程和机制仍然未知，是这次更新的主题。在这项提议的第一个目标中，我们将测试原始红细胞对趋化刺激(包括SDF-1)的反应，该刺激促进造血干和祖细胞向胎肝的迁移。在第二个目标中，我们将使用实验室建立的红细胞岛重建和去核实验来验证原始红系细胞可以并确实与胎肝巨噬细胞相互作用的假设。黏附分子emp和ICAM4各自在确定的红系-巨噬细胞相互作用中发挥重要作用。我们已经获得了原始红细胞同时表达EMP和ICAM4的初步数据，在第三个目的中，我们将检验这两个分子对原始红细胞终末成熟具有重要功能的假设。最后，我们最近发现，在缺乏c-myb的小鼠中，原始红系细胞无法去核，在第四个目的中，我们将检验这种去核失败是红系细胞非自治的假设。原代原始红系细胞的同步分化和去核促进了红系终末成熟的研究。此外，这些研究将使我们能够比较和对比原始红系细胞和最终的红系细胞在红细胞岛血管外成熟的情况。更好地理解红细胞终末成熟的机制将最终导致红细胞的高效和完整的体外合成，以满足不断扩大的临床对红细胞的需求。

DESCRIPTION (provided by applicant): Our long-term aim is to elucidate the cellular and molecular events underlying the early ontogeny of the hematopoietic system in the mammalian embryo. While definitive hematopoiesis in the fetus and adult is known to be multilineage, primitive hematopoiesis in the yolk sac is centered on the synthesis of erythroid cells that are critical for survival of the embryo. We recently made the seminal observation that primitive erythroblasts in the mouse embryo ultimately enucleate. However, the process and mechanisms regulating enucleation of primitive erythroid cells remain unknown and are the subject of this renewal. In the first aim of this proposal, we will test the hypothesis that primitive erythroblasts respond to chemotactic stimuli, including SDF-1, that facilitate the migration of hematopoietic stem and progenitor cells to the fetal liver. In the second aim, we will test the hypothesis that primitive erythroid cells can and do interact with fetal liver macrophage cells, using erythroblast island reconstitution and enucleation assays established in the laboratory. The adhesion molecules emp and ICAM4 each play important roles in definitive erythroid-macrophage interactions. We have obtained preliminary data that primitive erythroblasts express both emp and ICAM4 and in the third aim we will test the hypothesis that these molecules are functionally important for terminal maturation of primitive erythroblasts. Finally, we have recently discovered that primitive erythroid cells in mice lacking c-myb fail to enucleate and in the fourth aim we will test the hypothesis that this enucleation failure is erythroid cell non-autonomous. These studies of terminal erythroid maturation are facilitated by the synchronous differentiation and enucleation of primary primitive erythroid cells. Furthermore, these studies will allow us to compare and contrast the terminal maturation of primitive erythroid cells with definitive erythroid cells that mature extravascularly in erythroblast islands. A better understanding of the mechanisms responsible for terminal erythroid maturation will ultimately lead to the efficient and complete ex vivo synthesis of erythrocytes to serve an ever-expanding clinical need for red blood cells.