Molecular and functional dissection of the zebrafish hematopoietic stem cell niche

 描述（由申请人提供）：在发育过程中指定了四种独立的造血前体细胞类型，最终指定了造血干细胞（HSC），其自我更新并在成年生物体的一生中提供所有主要的血液谱系。前三种前体细胞类型是暂时的祖细胞，被认为可以暂时为胚胎提供血液和免疫细胞，直到HSC最终出现。直到最近，HSC的确切位置和时间一直存在很大争议，但最近的研究已经最终证明它们来自生血内皮细胞，原始背主动脉腹壁内的一群特殊的内皮细胞转分化为HSC。在我们以前的研究中，我们首次直接成像腹主动脉内皮细胞的HSC的诞生。这些HSC创始者的互补谱系追踪表明，它们提供所有成体造血细胞，因此是所有HSC的唯一来源。生血内皮细胞发育特化的信号传导机制仍知之甚少。在我们最近的研究中，我们利用斑马鱼胚胎提供的独特实验优势，发现了一种新的HSC诱导模型，其中腹侧体节中的Wnt16功能是HSC特异性所必需的。Wnt16 morphants中的HSC缺陷可以通过强制Notch信号传导来挽救，但仅在发育的早期窗口内，远早于HSC前体经历Notch信号传导。这种环境Notch需求是由Notch配体DeltaC和DeltaD介导的，但这些配体如何连接到HSC前体内的Notch信号传导尚不清楚。我们目前的研究表明，四种Notch受体中的三种是建立HSC命运所必需的。我们持续努力的重点是确定何时何地需要这些要求中的每一个，以确定是否以细胞自主的方式需要每一个，以确定哪些Notch配体用于调节每个信号传导事件，并确定何时通过谱系追踪和细胞移植测定在功能上建立HSC命运。随着对该信号传导轴及其控制的细胞行为的阐明，我们的工作最终将使离体方法能够将患者特异性iPS细胞导向细胞替代疗法的HSC命运。

 DESCRIPTION (provided by applicant): Four independent hematopoietic precursor cell types are specified during development, culminating in specification of hematopoietic stem cells (HSCs), which self-renew and provide all of the major blood lineages over the lifetime of an adult organism. The first three precursor cell types are transient progenitors believed to temporarily provide blood and immune cells to the embryo until HSCs finally emerge. Precisely where and when HSCs are specified has until recently been highly controversial, but recent studies have conclusively demonstrated that they arise from hemogenic endothelium, a special population of endothelial cells within the ventral wall of the primitive dorsal aorta that transdifferentiate into HSCs. In our previous studies, we imaged directly the birth of HSCs from ventral aortic endothelium for the first time. Complementary lineage tracing of these HSC founders indicated that they provide all adult hematopoietic cells, and are thus the unique source of all HSCs. The signaling events underlying the developmental specification of hemogenic endothelium remain poorly understood. In our recent studies, we utilized the unique experimental advantages afforded by the zebrafish embryo to uncover a novel model of HSC induction, where Wnt16 function in the ventral somite is required for HSC specification. The HSC defect in Wnt16 morphants could be rescued by enforced Notch signaling, but only within an early window of development, well before HSC precursors experience Notch signaling. This environmental Notch requirement is mediated by the Notch ligands DeltaC and DeltaD, but how these connect to Notch signaling within the precursors of HSCs is unknown. Our current studies demonstrate that three of the four Notch receptors are required to establish HSC fate. The focus of our continuing efforts is to determine where and when each of these requirements are needed, to determine whether or not each is required in a cell-autonomous manner, to determine which Notch ligands are utilized to regulate each signaling event, and to determine functionally when HSC fate is established through lineage tracing and cell transplantation assays. With the elucidation of this signaling axis, and the cellular behaviors it controls, our wok will ultimately enable ex vivo approaches to direct patient-specific iPS cells towards the HSC fate for cellular replacement therapies.