AUTHOR=Tang Wanbo , He Jian , Huang Tao , Bai Zhijie , Wang Chaojie , Wang Haizhen , Yang Ruichuang , Ni Yanli , Hou Jun , Wang Junliang , Zhou Jie , Yao Yingpeng , Gong Yandong , Hou Siyuan , Liu Bing , Lan Yu 

TITLE=Hlf Expression Marks Early Emergence of Hematopoietic Stem Cell Precursors With Adult Repopulating Potential and Fate

JOURNAL=Frontiers in Cell and Developmental Biology

VOLUME=Volume 9 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/cell-and-developmental-biology/articles/10.3389/fcell.2021.728057

DOI=10.3389/fcell.2021.728057

ISSN=2296-634X

ABSTRACT=In mouse aorta-gonad-mesonephros (AGM) region, pre-hematopoietic stem cells (pre-HSCs) are generated from rare and specialized hemogenic endothelial cells (HECs) via endothelial-to-hematopoietic transition (EHT), followed by maturing into bona fide hematopoietic stem cells (HSCs). As HECs also generate a lot of hematopoietic progenitors not fated to HSCs, powerful tools that are pre-HSC/HSC-specific become urgently critical. Here using gene knockin strategy, we firstly developed a Hlf-tdTomato reporter mouse model, and detected Hlf-tdTomato expression only in part of the immunophenotypic CD45- and CD45+ pre-HSCs in E10.5 AGM region. By in vitro co-culture together with long-term transplantation assay stringent for HSC precursor identification, we further revealed that unlike the CD45- counterpart in which both Hlf-tdTomato-positive and negative sub-populations harbored HSC competence, the CD45+ E10.5 pre-HSCs existed exclusively in Hlf-tdTomato-positive cells. The result indicates that cells must obtain Hlf expression prior to or together with CD45, otherwise they cannot further proceed into the HSC stage. Furthermore, we constructed a novel Hlf-CrexER mouse model and performed time-restricted genetic lineage tracing by a single dose induction at E9.5. We observed the labeling in E11.5 AGM precursors and their contribution to the immunophenotypic HSCs in fetal liver. Importantly, these Hlf-labeled early cells contributed to and retained the size of the HSC pool in the bone marrow, which continuously differentiated to maintain a balanced and long-term multi-lineage hematopoiesis in the adult. Therefore, we provided another valuable mouse model to specifically trace the fate of emerging HSCs in the mid-gestation embryo.