Initiation of Mammalian Embryonic Hematopoiesis

描述（由申请人提供）：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生的细胞和分子事件。虽然已知胎儿和成人中的确定性造血是多谱系的，但卵黄囊中的原始造血集中于对胚胎存活至关重要的红系细胞的合成。我们最近在精液中观察到，小鼠胚胎中的原始成红细胞最终会去核。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。在这个建议的第一个目标，我们将测试的假设，即原始成红细胞响应趋化刺激，包括SDF-1，促进造血干细胞和祖细胞迁移到胎儿肝脏。在第二个目标中，我们将测试的假设，原始红细胞可以和胎儿肝脏巨噬细胞相互作用，使用成红细胞岛重建和去核实验室建立。粘附分子emp和ICAM 4各自在确定的红细胞-巨噬细胞相互作用中发挥重要作用。我们已经获得了初步的数据，原始成红细胞表达EMP和ICAM 4，在第三个目标，我们将测试的假设，这些分子是功能上重要的终端成熟的原始成红细胞。最后，我们最近发现缺乏c-myb的小鼠中的原始红系细胞不能去核，在第四个目标中，我们将检验这种去核失败是红系细胞非自主的假设。初级原始红系细胞的同步分化和去核促进了这些终末红系成熟的研究。此外，这些研究将使我们能够比较和对比原始红系细胞与在成红细胞岛中血管外成熟的定形红系细胞的终末成熟。更好地理解负责终末红细胞成熟的机制将最终导致红细胞的有效和完整的离体合成，以满足不断扩大的红细胞临床需求。

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.