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

Area of Science:

• Developmental Biology
• Hematopoiesis
• Cell Biology

Background:

• Adult hematopoietic stem cells (HSCs) originate from hemogenic endothelial cells (HECs) in mid-gestational embryos.
• HSC-competent HECs and their vascular precursors are rare, transient, and have been difficult to identify and capture.
• Understanding the precise origin and developmental trajectory of HECs is crucial for HSC research.

Purpose of the Study:

• To identify and characterize HSC-competent hemogenic endothelial cells (HECs) and their vascular precursors.
• To elucidate the developmental pathways and molecular programs governing HEC specification in vivo.
• To develop methods for precise capture and enrichment of HSC-competent HECs.

Main Methods:

• High-precision single-cell transcriptomics of endothelial cell (EC) populations from embryonic day (E) 9.5 to E11.0.
• Computational prediction and in vivo functional validation.
• Development and utilization of a Neurl3-EGFP reporter mouse model for HEC capture.
• Enrichment of HECs using surface markers (Procr+Kit+CD44+, PK44).

Main Results:

• Identification of two distinct arterial EC populations and putative HSC-primed HECs in the dorsal aorta of the aorta-gonad-mesonephros (AGM) region, peaking at E10.0.
• Precise capture of HSC-competent HECs using the Neurl3-EGFP reporter mouse and PK44 surface markers.
• Demonstration of endothelial-hematopoietic dual potential in single HEC cultures.
• Elucidation of a two-step fate choice for primitive vascular ECs: initial arterial fate choice followed by hemogenic conversion.

Conclusions:

• This study precisely identifies and captures HSC-competent HECs, resolving previous contradictions in HSC origin research.
• Primitive vascular cells undergo a two-step process to become HSC-priming HECs, involving arterial and hemogenic fate choices.
• Understanding these endothelial evolutions and molecular programs will advance in vitro HSC production strategies.