Hematopoietic Stem Cell-Independent Differentiation of Mast Cells From Mouse Intraembryonic VE-Cadherin(+) Cells
STEM CELLS(2022)
Abstract
Hematopoietic stem cell (HSC)-independent hematopoiesis from hemogenic endothelial cells (HECs) in the mouse embryo has been recognized as a source of tissue-resident hematopoietic cells in adult mice. Connective tissue mast cells (MCs) have been reported to originate from VE-cadherin (VE-cad)-expressing HECs in the yolk sac and embryo proper (EP) by a VE-cad-Cre-mediated lineage-tracing analysis. However, it remains unclear whether MCs are generated via a conventional HSC-dependent hematopoietic differentiation pathway, or whether through a fast-track pathway bypassing the emergence of HSCs. Here, we investigated whether EP-derived VE-cad(+) cells differentiate into MCs independently of HSCs. VE-cad(+) cells isolated from the embryonic day (E) 9.5-10.5 EP robustly formed connective tissue-type MCs in a newly established co-culture system using PA6 stromal cells. In contrast, bone marrow (BM) reconstitution assays of cultured cells indicated that E9.5 VE-cad(+) cells did not differentiate into transplantable HSCs in this culture condition. Lymphoid-biased HSCs with a limited self-renewal capacity were occasionally detected in some cultures of E10.5 VE-cad(+) cells, while MC growth was constantly observed in all cultures examined. HSCs purified from adult BM required a more extended culture period to form MCs in the PA6 co-culture than the embryonic VE-cad(+) cells. Furthermore, E9.5-E10.5 VE-cad(+) cells contributed to tissue-resident MCs in postnatal mice when transplanted into the peritoneal cavity of newborn mice. These results suggest that EP-derived VE-cad(+) cells generate MCs independently of HSC development in vitro and possess the potential of generating connective tissue MCs in vivo, although the exact differentiation program remains unsolved.
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Key words
hematopoietic stem cells, hemogenic endothelial cells, mast cells, stromal cells, VE-cadherin, mouse
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