Embryonic endothelial evolution towards first hematopoietic stem cells revealed by single-cell transcriptomic and functional analyses

• Published in: Cell research Vol. 30; no. 5; pp. 376 - 392
• Main Authors: Hou, Siyuan, Li, Zongcheng, Zheng, Xiaona, Gao, Yun, Dong, Ji, Ni, Yanli, Wang, Xiaobo, Li, Yunqiao, Ding, Xiaochen, Chang, Zhilin, Li, Shuaili, Hu, Yuqiong, Fan, Xiaoying, Hou, Yu, Wen, Lu, Liu, Bing, Tang, Fuchou, Lan, Yu
• Format: Journal Article
• Language: English
• Published: Singapore Springer Singapore 01.05.2020; Nature Publishing Group
• Subjects: 13/1; 13/31; 13/51; 14/19; 631/136; 631/532/1542; 64/110; 64/60; Aorta; Biomedical and Life Sciences; CD44 antigen; Cell Biology; Computer applications; Coronary vessels; Developmental stages; Embryos; Endothelial cells; Hematopoietic stem cells; In vivo methods and tests; Life Sciences; Populations; Stem cell transplantation; Stem cells; Surface markers
• ISSN: 1001-0602; 1748-7838; 1748-7838
• DOI: 10.1038/s41422-020-0300-2

Hematopoietic stem cells (HSCs) in adults are believed to be born from hemogenic endothelial cells (HECs) in mid-gestational embryos. Due to the rare and transient nature, the HSC-competent HECs have never been stringently identified and accurately captured, let alone their genuine vascular precursors. Here, we first used high-precision single-cell transcriptomics to unbiasedly examine the relevant EC populations at continuous developmental stages with intervals of 0.5 days from embryonic day (E) 9.5 to E11.0. As a consequence, we transcriptomically identified two molecularly different arterial EC populations and putative HSC-primed HECs, whose number peaked at E10.0 and sharply decreased thereafter, in the dorsal aorta of the aorta-gonad-mesonephros (AGM) region. Combining computational prediction and in vivo functional validation, we precisely captured HSC-competent HECs by the newly constructed Neurl3-EGFP reporter mouse model, and realized the enrichment further by a combination of surface markers (Procr + Kit + CD44 + , PK44). Surprisingly, the endothelial-hematopoietic dual potential was rarely but reliably witnessed in the cultures of single HECs. Noteworthy, primitive vascular ECs from E8.0 experienced two-step fate choices to become HSC-primed HECs, namely an initial arterial fate choice followed by a hemogenic fate conversion. This finding resolves several previously observed contradictions. Taken together, comprehensive understanding of endothelial evolutions and molecular programs underlying HSC-primed HEC specification in vivo will facilitate future investigations directing HSC production in vitro.