Studies of hematopoietic stem cell (HSC) development from pre-HSC-producing hemogenic endothelial cells (HECs) are hampered by the rarity of these cells and the presence of other cell types with overlapping marker expression profiles. We generated a Tg(Runx1-mKO2; Ly6a-GFP) dual reporter mouse to visualize hematopoietic commitment and study pre-HSC emergence and maturation. Runx1-mKO2 marked all intra-arterial HECs and hematopoietic cluster cells (HCCs), including pre-HSCs, myeloid- and lymphoid progenitors, and HSCs themselves. However, HSC and lymphoid potential were almost exclusively found in reporter double-positive (DP) cells. Robust HSC activity was first detected in DP cells of the placenta, reflecting the importance of this niche for (pre-)HSC maturation and expansion before the fetal liver stage. A time course analysis by single-cell RNA sequencing revealed that as pre-HSCs mature into fetal liver stage HSCs, they show signs of interferon exposure, exhibit signatures of multi-lineage differentiation gene expression, and develop a prolonged cell cycle reminiscent of quiescent adult HSCs.

从前 HSC 产生的造血内皮细胞 (HEC) 发育造血干细胞 (HSC) 的研究因这些细胞的稀有性以及具有重叠标记表达谱的其他细胞类型的存在而受到阻碍。我们生成了 Tg（Runx1-mKO2；Ly6a-GFP）双报告小鼠，以可视化造血承诺并研究 HSC 出现和成熟前的情况。 Runx1-mKO2 标记所有动脉内 HEC 和造血簇细胞 (HCC)，包括前 HSC、骨髓和淋巴祖细胞以及 HSC 本身。然而，HSC 和淋巴潜能几乎只在报告双阳性 (DP) 细胞中发现。首先在胎盘的 DP 细胞中检测到强大的 HSC 活性，反映了该生态位对于胎儿肝脏阶段之前的（前）HSC 成熟和扩张的重要性。单细胞 RNA 测序的时间过程分析表明，当前 HSC 成熟为胎肝期 HSC 时，它们表现出干扰素暴露的迹象，表现出多谱系分化基因表达的特征，并形成让人想起静止成体的延长的细胞周期HSC。