[Affiliation between endothelial and intra-embryonic hematopoietic stem cells]

Area of Science:

• Developmental biology
• Hematology
• Vascular biology

Background:

• The developmental origins of hemopoietic (blood-forming) and endothelial (blood vessel-lining) lineages are crucial for understanding embryonic development.
• The floor of the embryonic chicken aorta is a known site for the emergence of hemopoietic progenitor cells.

Purpose of the Study:

• To investigate the developmental relationship between hemopoietic and endothelial lineages in the embryonic chicken aorta.
• To determine if hemopoietic progenitor cells originate from the aortic endothelium.

Main Methods:

• Utilized the endothelium-specific membrane receptor VEGF-R2 and the common leukocyte antigen CD45 to distinguish between endothelial and hemopoietic cells.
• Employed a non-replicative retroviral vector and low-density lipoproteins to tag the endothelial tree in embryonic chickens.
• Tracked labeled cells in the vascular tree and dorsal mesentery over time.

Main Results:

• Prior to hemopoiesis, aortic endothelium uniformly expresses VEGF-R2.
• Hemopoietic clusters express CD45 and downregulate VEGF-R2 (CD45+/VEGF-R2-), while the surrounding endothelium remains CD45-/VEGF-R2+.
• Labeled endothelial cells were found to differentiate into hemopoietic cells, appearing in paraaortic foci.

Conclusions:

• Hemopoietic progenitor cells and clusters in the embryonic chicken aorta originate from precursors with an endothelial phenotype.
• This study provides evidence for endothelial-to-hemopoietic transition in vivo.
• The findings elucidate a key developmental pathway for blood cell formation.