Current dogma asserts that mammalian lifelong blood production is established by a small number of blood progenitors. However, this model is based on assays that require the disruption, transplantation and/or culture of embryonic tissues. Here, we used the sample-to-sample variance of a multicoloured lineage trace reporter to assess the frequency of emerging lifelong blood progenitors while avoiding the disruption, culture or transplantation of embryos. We find that approximately 719 Flk1⁺ mesodermal precursors, 633 VE-cadherin⁺ endothelial precursors and 545 Vav1⁺ nascent blood stem and progenitor cells emerge to establish the haematopoietic system at embryonic days (E)7-E8.5, E8.5-E11.5 and E11.5-E14.5, respectively. We also determined that the spatio-temporal recruitment of endothelial blood precursors begins at E8.5 and ends by E10.5, and that many c-Kit⁺ clusters of newly specified blood progenitors in the aorta are polyclonal in origin. Our work illuminates the dynamics of the developing mammalian blood system during homeostasis.

中文翻译：

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终生造血是由哺乳动物个体发育过程中数百个前体细胞建立的。


目前的教条认为，哺乳动物的终生血液生产是由少数血液祖细胞建立的。然而，该模型基于需要破坏、移植和/或培养胚胎组织的测定。在这里，我们使用多色谱系追踪报告器的样本间方差来评估终生血液祖细胞的出现频率，同时避免胚胎的破坏、培养或移植。我们发现大约 719 个 Flk1 ⁺中胚层前体细胞、633 个 VE-钙粘蛋白⁺内皮前体细胞和 545 个 Vav1 ⁺新生血液干细胞和祖细胞在胚胎 (E)7-E8.5、E8.5-E11 日出现建立造血系统分别为.5和E11.5-E14.5。我们还确定内皮血液前体细胞的时空募集开始于E8.5并结束于E10.5，并且主动脉中新指定的血液祖细胞的许多c-Kit ⁺簇是多克隆起源的。我们的工作阐明了哺乳动物血液系统在稳态过程中发育的动态。