Single cell hematopoietic fate acquisition during embryonic development: To be a stem cell or not?

成人骨髓中的稀有干细胞负责所有循环血细胞的健康终生生产。这些干细胞被用于血液相关疾病的根治性临床移植和癌症治疗。尽管英国和世界各地都有这类干细胞的血库，但用于移植的干细胞(高质量和大量细胞)供应不足，重要的是，捐赠者的干细胞需要与患者的细胞紧密匹配，以避免移植排斥反应。多年来，研究人员一直试图增加培养系统中的血液干细胞数量。然而，从成人骨髓或脐带血中获得的血液干细胞在培养时不能保留其干细胞特性。取而代之的是，它们成熟为红细胞、巨噬细胞和免疫细胞类型，而这些细胞类型是短暂的。不是进一步的培养方法来扩大血液干细胞，而是采用了一种新的重新编程方法来从皮肤细胞和胚胎细胞中产生新的干细胞。到目前为止，这些重新编程的方法取得的成功非常有限。在我的实验室里，在老鼠身上的发现表明，所有的血液干细胞都是在胚胎早期由血管内壁的特殊(内皮)细胞制造的。重要的是，血液干细胞在发育过程中只产生一次。我们对血液干细胞发育和引导细胞成为血液干细胞的分子程序的了解，对于旨在产生患者特有的干细胞和缓解移植所需干细胞供应不足的方法是基本的。这项研究的目的是证明血液干细胞在小鼠胚胎主动脉中产生时的完整遗传程序。挑战是识别真正的血液干细胞，在大约700种其他类型的血细胞中，胚胎中只有1-2种。这些其他血细胞与血液干细胞非常相似，但在移植后不能重新填充血液系统，因此无法治愈。由于目前还没有从其他血细胞类型中分离纯血干细胞的技术，我们将使用独特的荧光报告程序从小鼠胚胎主动脉中分离出单个细胞，并通过移植测试它们的功能。我们将进行最先进的单细胞RNA测序实验，并使用一种新的高度创新的DNA标记技术来首次识别编码这些独特功能强大的血液干细胞的完整遗传程序。这一重要信息将进一步加深我们对血液干细胞是如何制造的理解，并推进产生强大的患者特异性干细胞用于治疗白血病和血液病的策略。

Rare stem cells in the adult bone marrow are responsible for the healthy life-long production of all circulating blood cells. These stem cells are used in curative clinical transplantations for blood-related diseases and for cancer therapies. Although blood banks for such stem cells exist in the UK and worldwide, there are insufficient supplies of stem cells (high quality and large numbers of cells) for transplantations and importantly, the donor stem cells need to closely match the patient's cells to avoid graft rejection. For years, researchers have attempted to increase the number of blood stem cells in culture systems. However, blood stem cells obtained from adult bone marrow or umbilical cord blood do not retain their stem cell properties when cultured. Instead they mature into red blood cells, macrophages and immune cell types which are short-lived. Rather than furthering culture approaches to expand blood stem cells, a new reprogramming approach has been taken to generate new stem cells from skin cells and embryonic cells. To date, these reprogramming approaches have had very limited success. In my lab, discoveries in the mouse revealed that all blood stem cells are made early in the embryo from specialized (endothelial) cells lining the blood vessels. Importantly, blood stem cells are made only once during development. Our knowledge of blood stem cell development and the molecular program directing cells to become blood stem cells is fundamental to approaches aiming to generate patient-specific stem cells and for alleviating insufficient supplies of these cells for transplantation. This study aims to demonstrate the complete genetic program of blood stem cells as they are generated within the mouse embryonic aorta. The challenge is to identify the true blood stem cells, of which there are only 1-2 in the embryo amongst about 700 other types of blood cells. These other blood cells are very similar to blood stem cells but cannot repopulate the blood system following transplantation and thus are not curative. Because there is no current technology that allows the isolation of pure blood stem cells from the other blood cell types, we will isolate single cells from the mouse embryonic aorta using unique fluorescent reporters and test their function through transplantation. We will perform state-of-the-art single cell RNA sequencing experiments and use a new and highly innovative DNA marking technique to identify for the first time the complete genetic program that codes these unique functionally potent blood stem cells. This important information will further our understanding of how blood stem cells are made and advance strategies for generating robust patient specific stem cells for treatment of leukemia and hematologic disorders.