Hematopoietic stem cells (HSCs) develop from hemogenic endothelial cells (HECs) in vivo during mouse embryogenesis. When cultured in vitro, cells from the embryo phenotypically defined as pre-HSC-I and pre-HSC-II have the potential to differentiate into HSCs. However, minimal factors required for HSC induction from HECs have not yet been determined. In this study, we demonstrated that stem cell factor (SCF) and thrombopoietin (TPO) induced engrafting HSCs from embryonic day (E) 11.5 pre-HSC-I in a serum-free and feeder-free culture condition. In contrast, E10.5 pre-HSC-I and HECs required an endothelial cell layer in addition to SCF and TPO to differentiate into HSCs. A single-cell RNA sequencing analysis of E10.5 to 11.5 dorsal aortae with surrounding tissues and fetal livers detected TPO expression confined in hepatoblasts, while SCF was expressed in various tissues, including endothelial cells and hepatoblasts. Our results suggest a transition of signal requirement during HSC development from HECs. The differentiation of E10.5 HECs to E11.5 pre-HSC-I in the aorta–gonad–mesonephros region depends on SCF and endothelial cell-derived factors. Subsequently, SCF and TPO drive the differentiation of E11.5 pre-HSC-I to pre-HSC-II/HSCs in the fetal liver. The culture system established in this study provides a beneficial tool for exploring the molecular mechanisms underlying the development of HSCs from HECs.

中文翻译：

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造血干细胞从造血内皮细胞发育过程中信号需求的转变


造血干细胞 (HSC) 在小鼠胚胎发生过程中由体内造血内皮细胞 (HEC) 发育而来。在体外培养时，来自表型定义为前 HSC-I 和前 HSC-II 的胚胎细胞具有分化为 HSC 的潜力。然而，HEC 诱导 HSC 所需的最小因素尚未确定。在本研究中，我们证明干细胞因子 (SCF) 和血小板生成素 (TPO) 在无血清和无饲养层培养条件下诱导 HSC-I 前胚胎 (E) 11.5 日移植。相比之下，E10.5 pre-HSC-I 和 HEC 除了 SCF 和 TPO 之外还需要内皮细胞层才能分化为 HSC。对 E10.5 至 11.5 背主动脉及其周围组织和胎儿肝脏的单细胞 RNA 测序分析检测到 TPO 表达仅限于成肝细胞，而 SCF 表达于各种组织，包括内皮细胞和成肝细胞。我们的结果表明 HSC 发育过程中信号需求从 HEC 发生了转变。主动脉-性腺-中肾区域中 E10.5 HEC 向 E11.5 pre-HSC-I 的分化取决于 SCF 和内皮细胞衍生因子。随后，SCF 和 TPO 驱动胎儿肝脏中 E11.5 pre-HSC-I 分化为 pre-HSC-II/HSC。本研究建立的培养系统为探索 HEC 发育 HSC 的分子机制提供了有益的工具。